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CPFG Version 3.4 User`s Manual

1. ifdef BBOX defines only the bounding box is predefined surfaces a set of triangles for each name 1 grid 20 20 20 surface triangles end instantiated objects name plant ray grid 20 20 20 objects defining the plant end ndif rescale the object using specified values ifndef NOHEADERS define an instance of the object 53 ndif This structure allows the user to either use the rayshade file on its own or include it in a scene comprising several plants In the second case the surfaces and the view may be set by the main rayshade file that includes all plant s files and the local definitions can be ignored by defining the macro NOSURFACES or NOHEADERS Also only bounding box can be defined for a fast preview of the scene using the macro BBOX The following sections describe each feature of the rayshade file 7 1 1 Materials The rayshade file includes definitions of all materials specified in the material file used by cpfg In the case a colormap is defined only colors actually used by cpfg objects are output to the file In rayshade the material definition uses keyword surface that is why the macro mentioned above is called NOSURFACES followed by the assigned name The name consists of the letter s and the index of the material or color corresponding to the index used by cpfg increased by the index
2. 1 next N p values initialize array items name 0 1 0 name 0 1 N p 1 and so on Several arrays can be de fined with each specification separated by a comma and the last one terminated by a semicolon The specification can extend over several lines In the following example three one dimensional arrays are defined and the first two are immediately initialized define array GrowthRate 5 1 0 8 0 7 0 6 0 5 BranchingAngle 4 60 55 55 50 ReceivedNutrients 5 6 1 5 Predefined functions The following predefined functions can be included in L system expressions sin a cos a tan a standard trigonometric functions Argument a is in degrees asin x acos x atan r atan2 x y standard inverse trigonometric func tions Functions asin and atan return value of an angle between 90 and 90 Function acos returns a value between 0 and 90 Function atan2 returns arctangent of y x in the range 90 to 90 19 exp x log x sart r fabs r y other standard functions floor x ceil x trunc x rounding functions sign x returns 0 for x 0 1 for positive x and 1 for negative values of x srand seed initializes a random number generator used in all four following func tions ran x generates floating point values uniformly distributed in interval 0 x nran mean o generates random numbers with normal distribution with mean mean hofs cpfg3 0 features and
3. ficient The shorter dimensions then can be reduced accordingly this has to be done by the user If the object dimension are not known values 20 x 20 x 20 would work If a module starting with a letter is not one of the recognized interpreted mod ules a warning message is issued during the interpretation of the string An exception are modules OZ and Y which are used for controlling the tropism elasticities in a program for interactive editing of L system generated strings currently in develop ment 33 hofs environment hofs cpfg3 0 fea tures labels 6 2 View file A view file contains drawing viewing and rendering parameters as well as the names of surface specification files for any surfaces to be included in the image The format of the view file is given below All text in typewriter font special symbols and all spaces should be entered as shown Unless stated otherwise the symbols zx y and z represent floating point numbers 7 represents an integer id represents a single char acter and other text in italics represent character strings Comments can be included using standard C notation Many of the parameters in this file have default values and can be omitted but it is good practice to have everything in the file This makes it easier to change default values because the appropriate keywords are already in the file also it makes it easier to change parameters with control panels Note that t
4. AR 7 Di RES BL B BR 7 0 00 20 64 0 00 0 00 25 00 0 00 0 00 16 41 0 00 0 00 81 29 21 85 4 31 5 00 5 00 10 00 22 17 5 00 10 00 40 00 2 50 1 20 70 24 2 50 8 59 7 50 7 50 15 74 10 00 7 50 20 00 25 00 5 00 12 08 68 89 0 00 14 80 4 23 5 00 25 68 28 94 5 00 21 80 45 19 5 00 19 08 51 62 2 50 21 4 petal s This section specifies the surface of a leaf such as the one shown in Figure 25 114 5 93 34 60 8 43 50 90 1 47 7 91 CONTACT POINT X 23 63 Y 8 49 Z 0 13 END POINT X 23 63 Y 8 70 Z 0 37 HEADING X 0 00 Y 1 00 Z 0 00 UP X 0 01 Y 0 00 Z 1 00 STEAKS 3959 Petal 1 TOP COLOR 0 DIFFUSE 0 00 BOTTOM COLOR 0 DIFFUSE 0 00 Abs At PARES he k Bb Bao BRE 22 64 8 49 0 00 20 53 15 22 4 03 13 10 30 26 5 80 15 07 40 29 4 35 22 60 8 49 0 00 19 67 15 00 1 97 19 67 30 00 2 14 16 65 49 99 4 83 23 42 8 49 0 00 26 53 15 00 1 80 26 19 30 00 1 97 28 94 50 90 1 47 22 96 8 43 0 00 26 03 15 00 3 69 34 60 30 75 7 91 32 18 41 26 1 28 22 More predefined surfaces Figure 26 shows a lilac inflorescence incorporating predefined surfaces The specifi cation files can be found in SVLABHOME oofs ext examples ext lilac 23 Use of sub L systems Figure 27 shows a model of the sedge Carex laevigata In this model sub L systems are used to generate the male and female spikes The main L system shown in Sec tion 23 1 uses the symbol to incorporate the productions from the sub L systems inclu
5. It is also possible to specify a surface not as a bicubic patch but by a set of triangles These triangles are input from a text file which follows a syntax of a rayshade input 47 hofs cpfg3 0 features interpretation gen_cylinders contours hofs cpfg3 0 features interpretation tsurfaces file except that the only lines that are processed are those with the keyword triangle at the beginning of the line Following this keyword there are 3 lines each containing 6 numbers specifying the zx y and z coordinates of triangle vertices and the normal in each vertex Optionally additional two numbers defining u and v coordinates of a texture at the vertex can be included on each line Example without texture coordinates triangle 0 01 08 0000 T 0 20 001 0 5 1 50 070 1 triangle 0 510 001 0 00 001 205140 00 00 1 and with texture coordinates triangle 50 58 10 001 050 0 2 0 0 0 1 1 0 5 0 510 001 0 5 1 triangle OS 101 C007 Ae D5 1 0 0707107901005 051 0 00 039 0 6 4 4 Texture image file Each texture specification in the view file includes a file name of an image used for the texturing Any of the following format can be used e RGB SGI RGB format e RAS SGI colormap RAS format e TGA Truevision Targa format e RLE Utah raster toolkit rle format produced for example by rayshade The specific format is recognized automatically by the extension rgb ras tga and rl
6. T Ef Symbols for Sub L systems id scale Causes the generator to save a reference to the current L system on a stack and to use the list of productions from the sub L system identified by id during subsequent production matching and application During interpretation the current scale is saved on a stack and the structure resulting from interpretation of the generated substring is scaled by scale End the sub L system and return to the previous set of productions and scale Query and communication symbols P zx y 2 queries the current turtle position If the module is present in any L system production an interpretation step is performed after each generate step when productions are applied The string is thus interpreted even if cpfg does not draw to the window During the interpretation the two or three parameters of the module are set to the x y or x y and z coordinates of the current turtle position respectively These parameters then can be accessed in the follow ing generate step and affect the selection of productions see the definition of environmentally sensitive L systems in 6 2H z yl z queries the current turtle heading vector similarly as P L x y z queries the current turtle left vector similarly as P 2U z yl z queries the current turtle up vector similarly as P 32 hofs cpfg3 0 features interpretation tropisms hofs cpfg3 0 fea tures subL systems hofs cpfg3 0
7. The background color is then either the colormap color with index 0 in the given set of 256 colors controlled by the command line parameter c or the emission color of the material with index 0 6 2 6 Material mode Lights and textures light subcommand subcommanda sets a light source The subcommands are O x y z origin of a point light source the default light source is a point source located at 0 0 1 V x y z vector specifying a directional source 40 A r g b ambient default 1 1 1 D r g b diffuse default 1 1 1 S r g b specular default 1 1 1 P x y z e c specified a spotlight with the direction x y z expo nent e and cutoff angle c default 0 0 1 0 180 T c 1 q attenuation factors constant linear and quadratic default 100 More than one light can be specified by including several commands light into the view file texture subcommand subcommanda defines a texture mapped on surfaces hofs cpfg3 0 features cylinders conses and generalized cylinders not disks and spheres The interpretation subcommands are textures F image specifies the image file name a necessary subcommand The image width and height is clamped in such a way that the image size is 27 x 2 Currently it is possible to specify rgb rle and tga images with the proper extension H filter for textures with texels bigger than image pixels The pa rameter filter is either linear
8. modulate cpfg multiplies the surface color with the texel color decal only the texel color is taken and the surface is not shaded blend interpolates between surface and texture color using the color index value of the surface only in colormap mode The default is modulate only m d or b can be specified S when present the surface texture is mapped per surface not per patch The default is mapping per patch i e texture coordinates are derived from s and coordinates of the B zier patch representing the surface both s and vary from 0 to 1 In case of mapping per surface first the surface boundaries are found and then the texture is mapped into z 0 plane with respect to the computed boundaries R ratio defines the aspect ratio of a texture mapped on cylinders and generalized cylinders The default is 1 A value greater than 1 will cause the texture to be more stretched along the cylinder mode controls the way the texture is combined with the surface colors More than one texture can be specified by including several commands texture into the view file 6 2 7 Tropisms tropism direction x y z y and z coordinates of the vector indicating the direction toward which branches tend to bend This command is kept only for backward compatibility Use the command t ropi sm instead initial elasticity x a value specifying the susceptibility of a branch to bending This command is kept only for backward compati
9. ples homomorphism rayshade instancing created by the same modules with the same number parameters For exam ple if the format is set to 2f the precision of two decimal points is used in comparisons f or g results in the full precision comparisons The parameter flag is equal either to considered or ignored and it controls whether even the turtle is considered when comparing two objects created by the same module with the same parameters if the objects are different the second one is not an instantiation of the first one rayshade scale scale specifies a scale factor which is applied to the rayshade objects output by cpfg This command can be used for scaling up and down specific plants generated by different L systems in different scales Note it is usually better to use the parameter turtle scale see command initial scale 6 2 4 Lines surfaces and generalized cylinders line style style specifies how the lines represented by modules F or G are drawn Parameter style is one of the following pixel flat shaded lines are drawn with their width in pixels polygon lines are drawn as flat shaded polygons with a width in world units cylinder lines are drawn as cylinders with the width specified in world units tapered lines flag controls whether lines or cylinders are drawn tapered or not flag is equal to on or of f the default is on polygonization level n determines the level of detail used in generati
10. t lt 2 gt F t RATE t lt 2 gt F t 117 RAT E 2 F t RATI h won t be increased 1 3 F 30 a 5 EF 30 a 5 _ 0 F_SPIK EAF E 2 endlsystem include female 1 include male 1 include leaf 1 23 2 female l This L system contains the line lsystem 2 and generates the image shown in Figure 28 It is included into the main L system with the turtle symbols 2 1 25 specifying that L system 2 is to be included and scaled by a factor of 1 25 define I_RATE 1 01 internode growth rate define S_RATE 1 05 seed growth rate lsystem 2 derivation length 76 axiom F 5 axiom lt A t gt t lt 75 gt F 2 B 137 5 A t4 1 lt B gt gt 35 1 180 7 1 7c 1 1 F 5 KoL TEGE gt A t lt 1 gt F t I RATE Ka a lt 50 gt 4 a S RATE KUE EE E t lt 2 gt t S RATE Ree Tet gt 8 t lt 2 gt e t S RATE lt axiom gt gt 30 180 2 25 1 F 5 F 1 180 amp 30 180 2 25 1 F 5 137 5 A 0 endlsystem 24 L System defined surfaces Figure 29 shows several stages in the development of a Lychnis coronaria flower The specification files can be found in SVLABHOME oofs ext examples ext lychnis This model uses Bezier surfaces specified by the L system using the PD i s
11. v See Section 6 2 for details Contains parameters controlling frame by frame production of im ages for animation purposes By convention this file name has suffix a See Section 6 3 for details 4 2 Graphics and windowing cmap nr The value of the integer map_nr defines the 256 entry portion of the color or material table to be used by cpfg A value of 0 indi cates the first 256 entries 1 the second 256 and so on up to 15 The backgroundis colored using the first entry of the selected color table or using the emissive color of the first entry of the selected material table The colors or materials used by the turtle are in dexed relative to this entry The default value of map_nr is 1 Note that there is no space between c and map_nr on the command line m map_nr mapfile Instead of the index mode which uses hardware colormap an RGBA drawing mode is switched on In this case color indices are read from a file containing 256 triplets of bytes defining red green and blue The integer map_nr specifies the 256 entry portion of the color table as for option c m corresponds to m1 Note that there is no space between m and map_nr on the command line M map nr matfile Instead of the the index mode which uses hardware colormap w xsize ysize an RGBA drawing mode with OpenGL lighting computations is used In this case the turtle parameter color index specifies an index to a material defined in a material file
12. which can be created by program medit The integer map_nr specifies the 256 entry portion of the material table as for option c M corresponds to M1 Note that there is no space between M and map nr on the command line This option tells cpf g what should be the size of the opened draw ing window For example w 1024 683 will open a window WP xpos ypos wt window_title sb suitable for saving image files with an aspect ratio of 3 2 appro priate for film recorders Specifies the initial position of the window of its top left corner The automatic positioning of windows has to be switched on see the IRIX window manager menu Desktop Customize Windows This option changes the title of the window the icon name is still cpf8 In addition to popup menus a menu bar is created at the top of the cpfg window cpfg uses an X pixmap as a back buffer The drawing is slower but handling of expose events is very fast plus the full 24 bit per pixel resolution can be used even in double buffered mode Single buffer mode is set this option takes precedence over the command single buffer in Animation file In the double buffered RGBA mode a single buffer mode may be necessary to avoid dithering This switch overrides switch pm and a pixmap is not used Menus do not use SGI overlay planes which results in producing an expose event and redrawing the generated structure every time they overlap the drawing window 4 3 S
13. Defines the number of polygons around a cylinder w xsize ysize Specifies the size of the window Since the program is drawing the models into an pixmap which is then copied into the window when necessary and it does not store the information coming from plant models it is not possible to resize the window Switches r and c are considered only if the interpretation of OpenGL like commands is performed Although the program draw_server is designed to communicate with the plant sim ulator cpfg it is possible to use a simple process draw_client that sends all the data from its standard input to the drawing process specified by a socket Let us consider an example in which first the drawing programs is executed with following switches draw server C m specs e 1244 w 640 480 setting the window size and a socket for the communication The communication is specified by file specs e strings only on 86 hofs cpfg3 4 exam ples Distr environ with_start which allows strings being sent between the processes not communication modules 7 E After its execution the drawing process is waiting for the first transfer of data through the specified socket If the draw_server is running on machine shere for ex ample the data can be sent by calling draw_client C m specs e 1244 shere and typing in following commands clear 1 1 1 background color material 0 5 0 5 0 1 ambient color r g b alpha 1101
14. In the next derivation step the four edges of the generator can be associated with four triangles that are similar to ABC 20 Global variables in parametric L systems Figure 22 shows a fractal generated with a parametric L system 20 1 flake l define STEPS 5 define af 1 08 define hf 0 41 lsystem 0 Start h 20 a 66 EndEach h h hf a a af derivation length STEPS axiom 90 F 60 110 A B P D g Figure 21 Construction of the generator for the row of trees The edges are associ ated with triangles indicated by ticks Figure 22 Snowflake generated using a parametric L system F x gt F x 2 h tan a a F h sin a 2 a F h sin a a F x 2 h tan a endlsystem This L system makes use of two global variables h and a The line Start h 20 a 66 111 Figure 23 A stylized apple blossom sets the initial values at the begining of the derivation and EndEach h h hf a a af updates the values at the end of each step 21 Incorporation of predefined surfaces Figure 23 shows a model which uses predefined surfaces 21 1 blossom l define SIZE 100 lsystem 0 derivation length 3 axiom 154 B B gt amp 72 F 5 SIZE K K gt S 72 S 72 S 72 S 72 8 S gt 103 c 7 72 pl 34 F SIZE F SIZE F SIZE endlsystem 2
15. a Instead of keeping potentially big rayshade files it is possible to output only the L system string and then pipe it through cp g directly to rayshade cat plant015 strb cpfg g pipestrb ray stdout M plant mat plant l plant v rayshade O plant015 rle In the next example the program monitors a specified socket and if a text command representing a menu item comes through the socket it performs it as if the item was interactively chosen in the menu cpfg S 1000 M plant mat plant l plant v plant a The following call runs an interactive simulations with the environment defined by an external process as specified in the file plant e cpfg M plant mat e plant e plant l plant v plant e The plant can be also executed as a part of a distributed simulation although it will be very likely done by another program and not by the user In this case there are two connections to two environmental processes whose executables are specified in files plantl e and plant2 e cp g C m plantl e 200 m plant2 e 300 M plant mat plant l plant v plant e 12 5 User interaction The left mouse button is used to rotate the model in the cpfg window Holding down the left button and moving the mouse will cause the model to rotate in the direction of mouse movement Moving mouse up and down while holding down the middle mouse button rescales the model in the cpfg window A menu activated using the right mouse button is provide
16. animation menu becomes available The menu contains all items as the main menu except the item Animate mode In addition the fol lowing items become available allowing the user to control the animation process Step Run Forever Stop Rewind Clear Displays the frame resulting from the next step derivation steps If this goes past the last frame the first frame will be displayed Displays consecutive animation frames after each step derivation steps until the last frame is reached or passed The same as Run except that when the last frame is reached the anima tion returns automatically to the first frame and continues Pauses the animation at the current frame Redisplays the animation from the first frame Removes the current image from the window New animate Rereads the animation parameter file Begin Recording Gives access to a sub menu allowing the user to initiate record ing in a selected file format The sub menu is similar to the Output sub menu After picking Run from the animate menu all subsequent frames are recorded until Stop Recording is selected For an L system foobar 1 and selecting the rgb output for example the frames are recorded by default as foobarl rgb foobar2 rgb etc unless the default file is set using a corresponding command line option in this case rgb filename Note that the filename can be specified as a format string e g plant 03d rgb Recording formats and default
17. bounding box is incorrect if the rayshade file is output in the off screen mode during which the bounding box is not computed It is possible though to force computing of 54 the bounding box by outputting also the view volume file e g directly to dev null if you do not want to keep it using command line parameters vv dev null 7 1 4 Predefined surfaces All predefined surfaces specified in the cpfg s view file are included in the rayshade file Each surface is named using the single letter name defined in the view file The surface definition consists of a grid of fixed size 20 x 20 x 20 containg a set of triangles The triangles are defined by their vertices and possible also normals and texture parameters at each vertex The normals are included if the smooth shading is used by cpfg Since there are two ways of mapping a texture on a surface it may happen that there are two surface definitions in the file with index and 2 as the second letter of the name each with different texture coordinates associated with vertices 7 1 5 Instantiated objects It is possible to take advantage of instantiation not only for surfaces but also for parts of the plant such as complex leaves or flowers If the user specifies a homomorphism production with delimiter o gt instead of gt during the rayshade output the prede cessor will be instantiated if it appears again if it has the same parameters and possibly also the sam
18. but before the predecessor is replaced by the successor If a production does not have a condition the empty condition x has to be used Icontext lt predecessor gt rcontext B y successor Compared to the C syntax the syntax of L system programming statements has to follow these specific rules e Each assignment statement or a function call has to be terminated with a semi colon even if it is a last statement in a block of statements just before Y e Even if there is a single statement following the keyword if else while and do it has to be enclosed in curly brackets e Operators like etc are not supported 6 1 3 Global programming statements Similarly to programming statements associated with productions operating on local variables global statements executed at specific points of the simulation can be used to define global variables accessible in all productions In the cpfg language it is possible to define four blocks of statements which are defined before the list of L system productions using the commands Start statements processed at the beginning of the simulation End statements processed at the end of the simulation StartEach statements processed at the beginning of each step EndEach statements processed at the end of each step 18 The statements are of the same type as production statements introduced in the previous section Variables use
19. communication module 4 and to set the parameters of query modules P H L and U see Section 6 1 9 Consequently if you use a homo morphism production that is applied to one of the module E the module will not be sent to the environment Similarly a homomorphism production with P H L or U in the predecessor will cause that the values of the parameters of this module will not be set For example if there was an additional production ha P y gt 00 in the example above the parameters of P would stay O and all branches would be drawn 6 1 8 Decomposition Decomposition productions make it possible to decompose a module in the string into several components Thus the L system productions can focus only on the develop ment of main building blocks of a plant such as an apex meristem or leaf After each simulation step before the string is interpreted and a possible homomorphism is applied modules representing these organs can be replaced by several other modules representing parts of the organs Unlike for homomorphism productions the result of decomposition stays in the string Decomposition productions have to be specified after L system productions and 24 hofs cpfg3 4 exam ples homomorphism rayshade instancing hofs cpfg3 4 exam ples decomposition before homomorphism productions or at the end of an L system if no homomorphism productions are included lsystem label derivation length d
20. data have to be transferred between these machines to create the image of the plant Thus if it is not possible to connect to the display on the same machine as the one of the plant simulator either the plant simulator should generate only a list of primitives or L system strings or it should be compiled using a public domain graphics library equivalent to OpenGL which does not need the connection to an X server Note that command setenv used for modifying the variable DISPLAY may not work in every operating system In that case it is possible to add a corresponding variant of the command setenv to the command line of the process Each command can be replaced by one or more letters because only the first character of a command is considered A line starting with symbol is ignored An empty line separates definitions of different processes Every process specified in the list has to be compiled with the same version of the communication library and has to start with call to function CIntialize or CSInitial ize and finish with a call to CTerminate see the previous section All communicating processes have to be specified before defining connections The specification of connections follows the command connections Each line defines a set of connections For example the line masterl masterN gt slavel slaveM spec file common parameters initiates M N connections between each of the N masters and all M slaves usi
21. empty and not using them in other places If a contour includes some singularity e g a sharp edge created by having three control points at the same location the normals are not correct Cpfg should start with a reasonable colormap in the index mode to avoid a black window if the user forgets to run loadmap Spheres are not textured What mapping to use Cpfg generated Inventor files have sometimes too big memory requirements possibly related to too many items in a group Directional lights do not convert properly to Inventor output they are defined as a very distant point source If a predefined surface is not included in the view file the created input file can not be viewed the viewer does not read such a file Either remove the references to such surfaces or at least print a warning message Currently cpfg sends only recognized blackbox modules to the environment e g AC is not passed to the environment but O is This is a bigger problem related to multiple symbol modules I would suggest to send only a single mod ule after E because a homomorphism production can be used to replace this module with a multiple symbol module Cpfg displays the final image without showing the drawing process a depar ture from cp g2 7 visible in particular in lilacs 94 11 2 11 3 Maybe input string should not reread the view A good question what should and what should not be reread The materials with textu
22. fea tures query module E x1 Z m module E communication module is used both to send and receive environmental information represented by the values of parameters 21 m Specifically parameters 71 2 act as an interface between the plant and the environment simulated by an external process They can be set by the plant model and transferred to the environment or set by the environment and transferred to the plant model see the definition of Open L systems in 2 4 Miscellaneous commands L Label Prints the label in the drawing window at the current turtle loca tion using the font specified in the view file It is also possible to specify a printf like format string and print out values of subsequent parameters e g L a gq a S any system call Will make the system call when interpreted I rayshade object scale Includes a rayshade objects with a given name lo cated at the current turtle location and scaled by a given value only for a rayshade output The second parameter is optional J size1 sizez size3 As a default all objects output into a rayshade file are en closed in one grid To be able to create more grids tightly enclosing each plant for example the module J closes the current grid and starts a new grid of a given size in number of voxels This module is interpreted only during the rayshade output Usually a value of 20 for the longest object dimension is suf
23. file extensions are the same as for Output files Stop Recording Stops the recording of animation frames Don t Animate leaves the animate mode and switches back to the main menu 15 6 Input files 6 1 L system file The essential theoretical notions of L systems are described in The Algorithmic Beauty of Plants 7 The syntax is defined formally in Appendix A Every L system file spec ifies a derivation length a list of symbols to be ignored or considered when context matching an axiom and a set of productions which may be either deterministic or stochastic A production consists of a predecessor and a successor with optional left and or right contexts The L system can be defined over an arbitrary alphabet which does not contain the asterisk or any separators space tab etc Section 6 1 9 lists the symbols which have a graphical interpretation The typical file has the following format in the deterministic case lsystem label derivation length d ignore symbols axiom axiom Icontext lt predecessor gt rcontext a C B gt successor Icontext lt predecessor gt rcontext a C B gt successor Icontext lt predecessor gt rcontext a y C B gt successor endlsystem The text in typewriter font all spaces and all special symbols must be entered as shown The derivation length d must be a positive integer or zero The symbols list should include all symbols to be ignored while
24. file see Section 6 4 1 and a surface scaling factor The parameters s t and tex are optional If parameters s and are included they specify the level of detail used when drawing patches Patches are drawn using s polygons along the rows and t along the columns If s and t are not specified they default to 5 Several surfaces may be specified in this manner The last parameter tex 1f present specifies a texture associated with the surface This value takes precedence over the texture index associated with the turtle during the interpretation and all instances of this surfaces will have the same texture It is better not to include this parameter and set the texture inside the L system Note that the parameter tex can be present even if the couple of parameters s and t is omitted line idname sx the character used to identify the line to be drawn a string con taining the name of the surface specification file and a surface scaling factor tsurface id name rays the character used to identify the surface a string con taining the name of a file using rayshade like file format and a surface scal ing factor s The file should contain a set of triangles with 6 or 8 values per vertex specifying vertex point vertex normal and optionally texture coordi nates see Section 6 4 3 twist of cylinders flag As a default generalized cylinders are drawn in such a way that their twist is minimalized If the twist is desired set flag to
25. file is a text file with commands specifying the name of the environmental program with possible options and input files the format of data the plant model sends to the environment and the type of communication between the programs For example the communication in the example from the previous section L system 3 has been defined using the following specification file executable ulam turtle position 5g 5g communication type pipes The environmental program is called ulam because it was originally used for gener ating Ulam s patterns see 2 the data between the two processes are transferred using a pair of Unix pipes and only the turtle position is sent together with each com munication module in addition to the module s address The specification of the environmental program is included mainly for the plant simulator which controls the communication and executes the environment at the be ginning of the simulation 63 To reduce the amount of transferred data as a default only the minimum infor mation is transferred from the plant simulator to the environment namely the address of the communication module and parameters of the module All additional informa tion such as the module following the communication module and its parameters the turtle position orientation current line width etc has to be specified in the com munication file see Section 8 4 1 for the list of all commands On the other h
26. finishing at the next specified control point and for the following segment starting at the same point The angle is defined with respect to the axis of a straight segment of a unit length thus the real slope of the radius may not correspond to the set value for curved segment or segment of a different length the second problem can be avoided by using module Gr 1 In addition if you increase the length of the tangents of the axis too much by module Gt the strips close to the control points will be wider that the strip in the middle and the angle of radius tangents will be skewed as well As a default or when both lengths are equal to 0 the radius at the control points is set so that it is linearly interpolated along the segment if only one length is set to O the tangent at the point is set as if the radius was interpolated linearly Gr flag Switches on flag 1 or off flag 0 an automatic adjustment of radius tangents for segments of a non unit length If the flag is 1 the tangents are defined for a segment of a unit length and then stretched onto the segment of a non unit length thus the specified tangent angles do not correspond to the real angles of the tangents As a default tangents are not adjusted after the stretching contourid Sets the contour specified by contour_id as the current contour for hofs cpfg3 0 features generalized cylinders Contours are specified in the view file see the command interpretation c
27. fractal ps The user must choose the Output postscript item from the main menu to write to this file Section 5 1 cpfg ps fractal ps fractal l fractal v fractal a For large models model generation can be made faster by specifying a larger initial string size on the command line The default initial string size is large enough for most models If a model is too large for the given string size cp fg will reallocate the string and output the message String is too long reallocating cpfg s1000000 complexplant 1 complexplant v In the next example cpfg uses color map number 3 and enters verbose mode Output file names are specified for both rayshade and Postscript formats Note that the options can be listed in any order but that the L system view and animation files must be specified last cpfg ray plant ray c3 v ps plant ps plant l plant v plant a In all previous examples a hardware colormap was used for coloring the surfaces A colormap can be specified on the command line cp g m plantl map m2 plant2 map plant 1l plant v Instead of a colormap a material file can be included improving the results of the shading calculations cpfg M plant mat plant l plant v 11 It is possible to generate output files without the drawing window in an off screen mode In the example below for all steps specified in the animate file a rayshade file will be output cpfg g a ray plant 03d ray M plant mat plant 1 plant v plant
28. gt include comm_lib h define EPSILON 0 001 precision of comparisons define MAXQUERIES 1000 maximum number of queries struct item_type 74 float position 2 float query unsigned long id int master queries MAXQUERIES queries int num_queries actual number of stored queries BOK KKK kok k KK I I S void StoreQuery int master unsigned long module_id Cmodule_type comm_symbol CTURTLE tu if tu gt positionc lt 2 do not write to stdout because it is used for pipes fprintf stderr environment turtle position missing n return if num gueries gt MAXQUERIES fprintf stderr environment too many queries n return queries num_queries position 0 tu gt position 0 queries num gueries position 1 tu gt position 1 queries num gueries guery comm symbol gt num params gt 1 answer only if E has one or more parameters queries num gueries master master queries num gueries id module id num_queries JARA KKK KKK KK k kok k kok k Koko k kok k kok k K kk kk X kk k X k X k X k kk kk void DetermineResponse void int i j Cmodule_type comm symbol comm symbol num params 1 comm symbol params 0 set Hle comm symbol params 0 value 0 report only collisions for i 0 i lt num queries i for all queri
29. ignore symbols axiom axiom Icontext lt predecessor gt rcontext a CY B gt successor Icontext lt predecessor gt rcontext a C B gt successor Icontext lt predecessor gt rcontext a y C B gt successor decomposition maximum depth d Icontext lt predecessor gt rcontext a C B gt successor Icontext lt predecessor gt rcontext a C B gt successor homomorphism seed s maximum depth d Icontext lt predecessor gt rcontext a C B gt successor Icontext lt predecessor gt rcontext a y C B gt successor endlsystem The syntax of decomposition productions is similar to homomorphism productions in that there are decomposition productions specific for each sub L system and the user can specify the maximum depth or whether warnings about reaching the maximum depth are printed the only difference is that the productions with delimiter o gt have no special effect on the rayshade output The command seed cannot be included at the beginning of decomposition decomposition productions use the same random number generator as the L system productions 6 1 9 Interpreted symbols During the visualization the string of symbols is parsed from left to right and every time a special symbol controlling the turtle is encountered the function associated with the symbol is performed Symbols with predefined interpretations are listed below Symbols
30. memory files Specifies the type of communica tion between the plant simulator and the environmental process The default 1s pipes because pipes provide the most efficient means of communication on a single machine Important note The standard input stream stdin and the standard output stream stdout must not be used in an environmental process because during the com munication the input and output pipes are connected to these streams In the case of the file communication the plant simulator creates two files to_fieldXXXX 0 and from fieldXXXX 0 where XXXX is equal to cpfg s process id as returned by the system The communication through memory or files is synchronized by a pair of Unix semaphores which are set automatically by the plant simulator The size of the shared memory in bytes and communication files in number of communication modules as well as the name of communication files are fixed These values do not limit the amount of transferred data since the communication is done piecewise For debugging purposes it is possible to specify the maximum size of communication files as a parameter following the keyword files executable binary field params Specifies the executable of the environmental pro cess and its optional command line parameters following module yes no Defines whether the module following the communication 9 module is sent to the environmental process The default is no turtle position f
31. more polygons are on the stack turn the polygon flag off See also module type in the section on generalized cylinders below Place the current state of the turtle on the polygon stack if the polygon flag is on Drawing circles and spheres o d Draw acircle of diameter d in the plane of the screen If no parameter is given the current line width will be used c d Draw a circle of diameter d in the AL plane If no parameter is given the current line width will be used O d Draw a sphere of diameter d If no parameter is given the current line width will be used The spheres produced can be shaded even in the colormap mode since a set of polygons approximating a sphere is generated using code from the widely available sphere c file by Jon Leech leech cs unc edu Drawing parametric bicubic surfaces N Draw the predefined surface identified by the symbol immediately following the at the turtle s current location and orientation The control points geometry and neighborhood information for surfaces are read from surface specification files at the beginning of the simulation 29 hofs cpfg3 0 features interpretation polygons hofs cpfg3 0 features PS i basis Initializes the four rows and columns of control points for an L system hofs cpfg3 0 features defined surface i to 0 0 0 The optional parameter basis specifies the type of interpretation Lsys patch as defined surf textured 1 B
32. o gt is applied to a module this module with its parameters is searched in a hash table If the hash table does not contain the same module with the same set of parameters the module is added to the table together with selected turtle parameters the line width the scale factor the color index the color index for the back side of a surface and the texture index Otherwise the encountered module is an instance of the already stored module and it is not necessary to add it to the hash table It is possible to control the precision with which the parameters of the encountered module are compared with parameters of stored modules To this end a view file command rayshade objects format defines the printf style format string e g 3f used for specifying the precision of the compared parameters The default value is g the full precision is used but the number of instances of a single module can be increased and consequently the size of the rayshade file reduced if the precision 1s decreased to a few decimal points In this case a module can be represented by a module with slightly different parameters but the resulting structure may be still acceptably close to the original In some instances the same modules with the same parameters can result in dif ferent structures because some turtle parameters such as the current line width or color index are different when the second instance of the module is interpreted It is possible to in
33. of the cpfg window when the snap shot is taken will be included in the image hoofs cpfg3 4 exam ples socket commands ras ras file Specify name for the color index SGI image file Note that any window that appears on top of the cpfg window when the snap shot is taken will be included in the image tga tga file Specify name for the Truevision Targa image file Note that any window that appears on top of the cpfg window when the snap shot is taken will be included in the image Available also in sun version unlike rgb and ras formats rle rle file Specify name for the URT Utah Raster Toolkit run length en coded image file Note that any window that appears on top of the cpfg window when the snapshot is taken will be included in the image Available also in sun version unlike rgb and ras formats ray rayfile Specify name for the rayshade output file ps ps file Specify name for the Postscript output file see Section 7 2 iv iv file Specify name for the Inventor output file str text string file Specify the name of the file to which the string generated by cpfg will be output in text format see Section 7 3 strb binary_string file Specify the name of the file to which the string generated by cpfg will be output in binary format see Section 7 3 homo strings are output after applying homomorphism gls gls file Specify the name of the file to which the structure generated by cpfg will be output in gls format a
34. of the module is added to the object name The index differentiate between the same modules with the same parameters At the beginning of interpretation of each module the turtle position and orienta tion is set to the default values positioned at 0 and pointing upwards Other turtle parameters such as the current color or material index or the current line width are set to the values stored with the module in the hash table Thus if the turtle is ignored during the stage 1 all instances will use the same turtle parameters as the ones at the first occurrence of the module during the stage 1 If the turtle is considered for the module comparisons each instance will have correct turtle parameters If during the interpretation of a module another module that can be found in the hash table is encountered the encountered module is not interpreted Instead a refer ence to its object name is included in the rayshade file followed by a transformation matrix capturing the current turtle position and orientation Processing of the mod ules in the opposite order than the order in which they appear during the interpretation guarantees that the object is already defined in the file Stage 3 After all instantiated modules are output to the file the L system string is interpreted again If a module is not found in the hash table its geometry is output to the rayshade file In the case that the turtle is considered for the comparisons even if the tu
35. on background scene list listis a list of file names separated by a space comma or semicolon Each file contains a set of OpenGL like graphics commands see Section 6 4 5 which specify additional objects drawn after the L system generated string is interpreted 6 2 5 Color map mode Colors and lights light direction x y z x y and z coordinates of the vector indicating the di rection of light for shading purposes This command should be used only if the program is running in the colormap mode In the material mode use command light ambient light red green blue the ambient light specified as red green and blue components This command is effective only in version 2 7 and lower 39 hofs cpfg3 0 features interpretation tsurfaces hofs cpfg3 0 features interpretation gen_cylinders twist hofs cpfg3 0 features interpretation gen_cylinders background_scene diffuse reflection i an integer number indicating the range of colors cho sen for lighting a shaded surface effective only in colormap mode The surface color col is varied within the interval col i col i to achieve a color variation due to the different orientation of polygons representing the surface with respect to the direction of the light source only of the first light source if more then one source is specified The color of a polygon repre senting a cylinder or generalized cylinder is chosen in the following way If col is the c
36. seed 2454 derivation length 3 axiom F F gt F F F F F 1 3 F gt F F F 23 F gt F F F 143 endlsystem This is a stochastic L system There are three possible successors for the F symbol For each F symbol in the string cpfg randomly picks one of the three available pro ductions The probabilities for each production are given as 1 3 so they are equally likely to be applied Note that expressions can be used for the probability The seed keyword specifies a seed for the random number generator 18 Context sensitive L systems Figure 19 shows a plant generated with a context sensitive L system 11Note that the New Model and New L system menu options do not reset the seed value so a different structure will be generated each time one of these items is selected 107 Figure 19 A plant generated with a context sensitive L system 18 1 context l lsystem 0 derivation length 30 ignore F axiom F1F1F1 A es ty F1F1 OOOOFHF HF MAA BR DN ODN AAA OOFEFOCO VVvVvVvVvvvvovoyv RXAOPORPORO VV t OoOrRrRPRrRPORrRFO V I 108 y IU 4 TT V mene Lh f A l Figure 20 Row of Trees generated using a parametric L system endlsystem The productions of this L system have the following structure 1 lt dl gt 1 gt 0 Left Context Predecessor Right Context Successor This production will replace a
37. set of OpenGL like com mands see Section 7 4 for detailed description So far only triangles of generalized cylinders and predefined surfaces are out put vv vy file Specify the name of the file to which the bounding volume infor mation will be output See the box entry in Section 6 2 f anim path format Specify the directory and the format of file names for saving consecutive animation frames when selecting Begin Animate from the animation menu see Section 5 2 This switch is obsolete with the possibility to specify file names as format strings e g plant 03d rgb 2Rayshade is a public domain ray tracer developed by Craig Kolb Cpfg currently supports rayshade version 4 0 which is available at ftp graphics stanford edu pub rayshade rayshade4 0 tar Z 10 A filename may be specified as a format string e g plant 03d rgb and the number of the generation step is automatically inserted This can be used for saving animations A filename may be specified also as stdout and the files are sent to a standard output Often used in pipe mode pipestrb In the case of string output both in the text or binary format the specified filename is also used as the default name for the input of the string 4 5 Usage examples The most basic call to cpfg contains only an L system and a view file cpfg fractal l fractal v The next call includes an animation file and specifies that Postscript output is to be written to the file
38. standard deviation o random bran a returns random values with beta distribution biran n p generates random values with binomial distribution how many out of n numbers are below p stop n stops animation When the parameter n is equal to 1 and Run or Forever hofs environment is selected from the menu cp g only draws the current string and continues the chiba two_competing simulation Otherwise the simulation is stopped print format string var varz prints variables to standard output All variables are of type float thus the format string should contain only f or g fopen file name type opens a file specified by its name for input type r or output type w The function returns an index of the file used in the functions below fclose file closes the file file fscanf file format string amp var amp vare allows to input data from an hofs cpfg3 0 features external file specified by file index file file input Rootmap fprint file format string vari var2 outputs specified variables into the file file using the format string As in the case of function printf the hofs environment string should contain only f or g MonteCarlo test runs fflush file flushes the buffers associated with the file file 6 1 6 Sub L systems It is often convenient to apply concepts of structural programming to L system models and to divide bigger structures into
39. surface the end point is where the turtle is positioned after drawing the surface and the heading and up vectors are matched to the corresponding vectors of the turtle to determine the surface s orientation Size is a scaling parameter giving the size in surface units to be considered as equivalent to the default unit length associated with the F symbol in cpfg The above section is followed by groups of ten lines each describing one compo nent patch As many ten line groups as there are patches making up the surface are specified The first line gives the patch name The next two lines contain patch specific rendering information giving colors and diffuse lighting coefficients for either side of the surface If the values are zero the current turtle parameters are used The next three lines contain patch neighborhood information This information is used when render ing to determine if smooth shading is required across a patch boundary The adjoining patches are specified by their patchname in the appropriate position above left AL above A above right AR left L right R below left BL below B and below right BR The lack of a neighboring patch in a given direction is indicated by a 46 hofs cpfg3 0 features symbol The corresponding entries must match in the neighboring patch specification The last four lines contain patch control points each line representing one row of four points each with an x y and z coordina
40. t symbols The file Lychnis 1 contains many parameters controlling both the timing of the development and the angles and sizes of various components 118 Figure 28 Female spike Figure 29 Lychnis 25 Other examples Other examples imllustrating homomorphism decomposition the use of generalized cylinders and various other features can be found either on the system see the objects 119 noted at the margins in places where various features are described or in 2 3 120 References 1 HANAN J S Parametric L systems PhD thesis University of Regina Regina Saskatchewan Canada 1992 2 MECH R Modeling and Simulation of the Interaction of Plants with the Environ ment using L systems and their Extensions PhD thesis The University of Calgary Calgary Canada November 1997 3 M CH R PRUSINKIEWICS P AND HANAN J Extensions to the graphical interpretation of L systems based on turtle geometry Tech Rep 97 599 01 Dept of Computer Science The University of Calgary Calgary Canada 1997 4 MECH R AND PRUSINKIEWICZ P Visual models of plants interacting with their environment Computer Graphics SIGGRAPH 96 Conference Proceedings August 1996 397 410 PRUSINKIEWICZ P AND HANAN J L systems From formalism to program ming languages In Lindenmayer systems Impact on theoretical computer science computer graphics and developmental biology G Rozenberg and A Sa
41. the command line as strb file strb Graphics Library statements Output the generated geometry in a local text format see Section 7 4 The file name may be specified on the command line as gls file gls View Volume Output the computed bounding box into a text file The file format is as follows The file consists of a single line box x Emin zmax y ymin ymax 2 zmin zmax The file name may be specified on the command line as vv file vv 52 e Inventor Output in SGI Inventor format The file name may be specified on the command line as iv file iv This option requires the inventor shared libraries and for some executables may not be available The following sections describe some of the supported output formats in more detail 7 1 Rayshade output The program cp f g allows the user to output the geometry into a rayshade format mak ing it possible to render the generated objects with a high degree of realism Rayshade is a public domain ray tracer developed by Craig Kolb Cpfg currently supports rayshade version 4 0 which is available at ftp graphics stanford edu pub rayshade rayshade4 0 The manual is also available for download from the same site The general structure of a file output by cpfg is as follows ifndef NOSURFACES material definitions ndif ifndef NOHEADERS view settings screen resolution background colors lights ndif
42. the incorporation of open L systems and the specified communication interface to the plant simulator cpfg are discussed in the following section 8 2 Implementation of the modeling framework In order to implement the designed modeling framework the L system based plant modeling program cpfg has been extended by incorporating open L systems into it 62 Interface plant c c o environment o M M M M N N Plant a Environ moge E A mental data L system a T I I o N Model of the environment Plant simulator Communication specification Figure 6 Organization of the software for modeling plants interacting with their en vironment Shaded rectangles indicate components of the modeling framework clear rectangles indicate programs and data that must be created by a user specifying a new model of a plant or environment Shaded arrows indicate information exchanged in a standardized format and by including a special purpose communication library The library facilitates the exchange of information between the plant model and the environmental process Con sequently the library also has to be included in a program simulating the environment The parameters of the communication are defined in a communication specification file shared between the programs modeling the plant and the environment Figure 6 The communication specification
43. there is no universal model of the environment Various phenomena can be modeled by different environ mental programs that use a specific representation of the environment suitable for par ticular problems To be able to communicate with the plant simulator an environmental program has to be compiled with the communication library The library provides a programmer with a set of functions which have to be called in a given order Section 8 4 2 provides a list of functions of the communication library and explains how to use them in an en vironmental program The section also includes the source code for the environmental program used as an example in Section 8 1 8 3 Visualization of the environment Visualization is an essential part of every simulation It is often useful to visualize not only the plant model but also the environment creating one composite scene in order to better understand the interaction between them The plant simulator cp f g provides the user with many useful graphical features 3 making it possible to visualize both the plant and the environment The environment can be visualized in two ways 1 As the background image for the visualized structure For this purpose the envi ronmental process outputs an image file which is used by the plant simulator to define a texture on a rectangle representing the background 2 As a set of primitives forming a background scene which is displayed together with the ge
44. with no parameters use default values specified at the beginning of the simulation If a symbol has more parameters than those specified below the additional parameters are ignored Changing position and drawing 25 AP H A n A Figure 2 Controlling the turtle in three dimensions F d Move forward a step of length d and draw a line segment from the original po sition to the new position of the turtle If the polygon flag is on see the symbols and the final position is recorded as a vertex of the current polygon If no parameter is given the default step size 1 is used f d Move forward a step of length d without drawing a line If the polygon flag 1s on the final position is recorded as a vertex of the current polygon If no parameter is given the default step size 1 is used G d Move forward a step of length d and draw a line If no parameter is given the default step size 1 is used g d Move forward a step of length d without drawing a line If no parameter is given the default step size 1 is used OM x y z sets the turtle position to x y z The global parameter line style specifies whether the line is drawn as a line poly gon or a cylinder Turtle rotations The turtle can be rotated only around its heading left or up vector Figure 2 0 Turn left by angle 9 around the U axis 9 Turn right by angle 9 around the U axis amp 0 Pitch down by angle 8 around t
45. zier 2 B spline 3 Cardinal spline If no basis is given the default B zier is used PC i rc Assigns the current position of the turtle to the control point of the L system defined surface in row r and column c PD is t Draws the surface defined by the control points of surface 2 using s lines along the rows and lines along the columns Drawing generalized cylinders Gs Start a generalized cylinder in the current turtle position Equivalent to 1 hofs cpfg3 0 features followed by see below interpretation gen cylinders type Start a generalized cylinder The parameter type is one of the following 1 an open curve consisting of Hermite spline segments as in the case of Gs 2 a closed curve consisting of Hermite spline segments 3 an open curve consisting of B spline segments 4 a closed curve consisting of B spline segments If the parameter type is O or is not specified the points between a pair of curly brackets and specify a polygon see above The module does not specify the first control point Gc strips Specifies a control point on the central line of the generalized cylinder The value of straps specifies how many mesh strips are drawn between the control point and the previous one The more strips are drawn the smoother the generalized cylinder looks If no parameter is given one strip is drawn Equivalent to strips see below strips Equivalent to Gc strips o
46. 1 2 blossom v angle factor 21 initial color 120 color increment 32 112 Figure 24 Apple Leaf initial line width 20 0 line width increment 3 0 projection parallel front distance 26000 0 back distance 26000 0 scale factor 0 7 z buffer on cue range 0 shade mode 3 light direction 1 0 0 0 0 0 diffuse reflection 25 tropism direction 0 0 2 0 0 0 initial elasticity 0 02 elasticity increment 0 02 surface ambient 15 surface diffuse 85 line line s 1 0 surface c leaf s 350 surface p petal s 500 21 3 leaf s This section specifies the surface of a leaf such as the one shown in Figure 24 It consists of two patches but there is no interpolation of shading between them 28 72 25 68 20 64 81 29 7 50 21 85 CONTACT POINT X 0 00 Y 20 00 Z 0 00 113 Figure 25 Apple Petal END POINT X 0 00 Y 19 61 Z 0 00 HEADING X 0 00 Y 0 99 Z 0 14 UP X 0 02 Y 0 14 Z 0 99 SIZE 101 93 Patch_1 TOP COLOR 298 DIFFUSE 0 75 BOTTOM COLOR 298 DIFFUSE 0 75 AL A AR 7 Li Re BL B BR 7 15 51 0 84 5 00 22 12 13 03 5 00 28 72 42 48 5 00 17 84 60 08 2 50 7 35 10 67 5 00 20 00 10 00 7 50 20 00 36 05 5 00 8 90 75 60 0 00 10 00 5 00 5 00 10 00 15 00 5 00 10 00 40 00 2 50 1 52 71 71 2 50 0 00 20 64 0 00 0 00 16 75 0 00 0 00 16 75 0 00 0 00 81 29 21 85 Patch_2 TOP COLOR 298 DIFFUSE 0 75 BOTTOM COLOR 298 DIFFUSE 0 75 AL A
47. 5 Open Lsys Sierpinski The L system model is as follows L system 3 w E 0 pi 2E c c 0 gt F 180 2E 0 F E 0 The end point of a segment is represented by a communication module with one parameter This parameter is initialized to 0 and if the point collides with another point the environment sets it to 1 If the point does not collide the parameter stays 0 Production p then creates two new branch segments only for points with parameter 0 The communication is set up in such a way that with each communication module the environment obtains its identification the address in the string and its position The first few steps of the simulation are described below Initialization The simulation begins with a single point E Before the first derivation step the environmental step is performed and the environment receives the following information address 0 E 0 position 0 0 0 It is convenient to think of the address as the number of modules before the communi cation module The position is equivalent to the initial position of the turtle The point obviously does not collide with another point thus the environment does not reply i e sends an empty message and the parameter of the module F stays 0 Step 1 The environmental step is followed by a derivation step in which production p is applied replacing module E with the string F 180 E 0 F E 0 which is interpreted for visualization purp
48. 5 Dragon curve Figure 15 shows several generations of the dragon curve The L system used to gener ate this image is shown below 15 1 dragon lsystem 0 derivation length 12 axiom FL 103 n 8 n 12 Figure 15 Dragon Curves L gt L RF R gt FL R endlsystem The dragon curve consists of two types of edges left and right The L system which generates the dragon curve is based on an L system with two symbols for edges Fy and F axiom F pm ROF F 4 P2 Fy gt h F Figure 16 shows the replacements made by this L system We can convert this L system to one which uses only one type of edge symbol as follows 104 Figure 16 The productions F gt F F and F gt Fi F Assume temporarily that a production predecessor can contain more than one let ter thus an entire subword can be replaced by the successor of a single production a formalization of this concept is termed a pseudo L system and is discussed in The Algorithmic Beauty of Plants 7 The dragon generating L system can be rewritten as axiom Fl p Fl gt Fl rF p2 rF gt Fl rF where the symbols and r are not interpreted by the turtle Production p replaces the letter by the string l rF while the leading letter F is left intact In a similar way pr
49. BlankLines ArrayDef ArrayDef lt identifier gt ArrayDims lt identifier gt ArrayDims ArrayInit Block ArrayDim Expression external ExrternalDefs BlankLines ExternalDef 4 ExternalDef ExternalDef lt identifier gt lt identifier gt ArrayDims 124 Axiom Productions Production Predecessor Lcontext Strictpred Rcontext Conditional Precondition Postcondition Condition Successor StrictSuce AN i axiom Modules lt newline gt Production BlankLine Predecessor Conditional gt Successor lt newline gt Predecessor Conditional o gt Successor lt newline gt Strictpred Lcontext lt Strictpred Strictpred gt Rcontext Lcontext lt Strictpred gt Rcontext FormalModules FormalModules FormalModules Condition Precondition Condition Condition Postcondition Precondition Condition Postcondition Block Block Expression StrictSucc StrictSucc Probability Modules 125 Probability FormalModules FormalModule Modules Module Symbol FormalParameters FormalParameter Parameters Expression ale eh ah bok E ob du ok Expression FormalModule Symbol Symbol FormalParameters Module Symbol Symbol Parameters lt character gt FormalParameters FormalParameter lt identifier gt Expression Expression Expression Expression Expression amp amp Express
50. CPFG Version 3 4 User s Manual Radom r M ch May 7 1998 based on the CPFG Version 2 7 User s Manual by Mark James Mark Hammel Jim Hanan Radom r M ch Przemyslaw Prusinkiewicz Contents 1 Introduction 2 Machine requirements 3 Distribution I Reference 4 Command line parameters AT General 3 a A A ee de 4 2 Graphics and windowing lt lt 4 3 Special working modes o a AAs Output A o a a Gene ib avert Es 45 Usage examples a a ad dee 5 User interaction JL E ee a eee 0 dk n a eS ee Eas 332 Animation MENU 5 5 es P Roe hes a se Pt aaa 6 Input files 6 1 6 2 6 3 6 4 Lsystem file gt z AOS eo cok ee oR ee lk ER ey GAL Variables 43 85 ee ee aie Bee Ane i a 6 12 Programming statements o 6 1 3 Global programming statements 614 Arrays caba Soy A Sal td A ied a 6 1 5 Predefined functions lt lt lt 6 1 6 Sub L s stems ocu si asics dua op 3 kosa 6 1 7 Homomorphism lt lt 6 1 8 Decomposition lt e 6 1 9 Interpreted symbols lt lt oo View le ita vaa a ads ES 6 2 1 Setting turtle s parameters o a 6 2 2 Settings the VIEW 4 e 6 2 3 General drawing parameters 6 2 4 Lines surfaces and generalized cylinders 6 2 5 Color map mode Colors and lights 6 2 6 Material mode Lights and textures 6 27 I
51. General drawing parameters shade mode i an integer defining the type of rendering to be applied ON SON E FOU Ba 7 simple fill interpolated fill Gouraud shade B spline closed B spline two sided wireframe This command is kept only for backward compatibility Use render mode instead render mode mode where mode defines one of the following render modes fast similar to mode filled see below only spheres and disks are drawn in wireframe wireframe the wireframe of all objects is visualized If the image is output filled to a postscript pairs of neighboring triangles are visualized as a single polygon to reduce the number of lines all polygons representing a surface have the same color associated with the surface If materials are specified the diffuse color is used interpolated similar to mode filled If the color or material at the beginning flat of a straight line or cylinder using modules F s and Gs is different from the color at the end the two colors are interpolated along the line Similarly the color of L system defined polygons is interpolated if the colors at different vertices are different in this mode the color of each polygon representing surfaces lines or generalized cylinders is determined according to the position of the polygon with respect to the light If materials are specified the color is determined according to the material specification using a single nor mal fo
52. LE struct CTURTLE float position 3 int positionC number of values sent for position float heading 3 int headingC number of values sent for heading float left 3 69 int leftC number of values sent for left float upl3 int upC number of values sent for up float line width int line widthC number of values sent for width float scale factor int scale factorC number of values sent for scale y typedef struct CTURTLE CTURTLE It contains selected turtle parameters together with a parameter specifying how many values have been sent for a given parameter Thus if a particular turtle parameter is not received by the environment i e it is not listed in the communication specification file the corresponding count parameter is set to 0 This allows the environmental process to check whether a required turtle parameter is available see the examples below Structure Cmodule type is used to store parameters of the communication module and the module immediately following it define CMAXPARAMS 20 max number of module parameters define CMAXSYMBOLLEN 4 max length of a module name struct module_type char symbol CMAXSYMBOLLEN 1 int num params struct param type float value char set if set 1 the value is sent back params CMAXPARAMS y typedef struct module_type Cmodule_type The structure
53. ULT COLORMAP and cpfg uses this colormap the id if the colormap is again accessible from the X root Sometimes though the colormap does not exists or is not big enough and an external program install map is called This program creates and installs a colormap of the size 4096 if possible creates a new X root variable called OPENGL INDEX COLORMAP and stores the colormap 90 index there Unfortunately to properly install the colormap the program has to be terminated Thus this cannot be done by cpfg The program install map is located together with other utilities in the same direc tory as cpfg This directory should be included in your PATH variable otherwise the program will not be executed and the colormap allocation fails 10 2 Using cpfg on less than 24 bit screens If your hardware does not support true color visuals i e it has less than 24 bits per pixel the index mode may not work properly To determine the number of bits per pixel of the screen buffer run command ginv on SGIs only and sum the number of bitplanes for a single buffered alpha red green and blue channels For example on 8 bit screen you will be able to use only a colormap of size 256 not 16 x 256 as is usual on on 24 bit screen and in the index mode cpfg will au tomatically switch to this 256 entries even if the default colormap uses the second 256 entries in the hardware colormap of a bigger size Unfortunately the current versions of utility prog
54. and the environment responds by sending selected communication modules with their address and parameters The communication between the two programs is implemented using mechanisms provided by the underlying operating system Unix Thus the data can be exchanged using a pair of Unix pipes a pair of sockets a pair of files or shared memory There are always two data streams one for data going from the plant model to the environment and the other one for data coming back The variety of communication mechanisms make it possible to choose one that provides an efficient data transfer between the pro cesses using pipes sockets or shared memory or to choose a slower communication using files allowing the user to access the exchanged data Section 8 4 6 In the case of pipes or sockets the synchronization of communication is straight forward one of the processes waits for the input from the other process on a designated pipe or a socket and the system suspends its operation during that time In the case of files or shared memory the communication is synchronized using a pair of semaphores which inform the processes about the availability of data in a shared memory or a des ignated file The communication follows these steps Figure 7 1 Plant simulator cp f g is executed It reads the communication specification file establishes data structures necessary for the communication starts the environ mental process and waits for the confir
55. application of productions module id switches the control to an L system with index id i e all following modules are replaced by productions from this L system An optional second parameter can specify the scale applied to all geometry produced by the L system with index d Module without parameters returns the control to the original parent L system see Figure 1 In the following example productions for development of the main axis and devel opment of lateral branches are separated L system 1 Lsystem 1 Main L system simulating growth of the main axis W A 2 1 pia A l o F D amp 86 2 2 Ro B 1 95 8 86 2 Ro B 0 95 8e 86 2 2 Ry B 1 95 amp 86 2 2 Ry B 1 95 A l Ri 0 1 6 0 pia Allo o gt 1 gt F U amp 86 2 2 Ry B 0 129 amp 86 2 2 Ry B 0 129 amp 86 2 Ro B 0 2 129 A L Ri o 1 0 endL system 21 hofs cpfg3 0 features subLsystems Lsystem 2 Sub L system simulating growth of branches W B 1 poi BM gt F B lx Ro B l R 0 7 p22 BM 10 F 0 180 B Ix Ro 0 3 endL system Each branch apex B introduced in the main L system by productions pi 1 or p1 2 is enclosed by modules and presented in bold to make them more visible In the next simulation step the module 2 R inserted just before the apex B switches the control to the sub L system and sets the scaling to Ry Thus the module B is replaced
56. as degenerate triangles and cylinders or cones with length below 0 00001 as degenerate cones The problem 1s that 1f these primitives are degenerate they are ignored and it may happen that there will be an object containing no primitives which will cause rayshade to core dump To avoid this make sure for example that you are not using generalized cylinders which starts or finish with width 0 7 2 Postscript output Similarly as for the rayshade output an attempt was made to produce a PostScript file which is essentially a snapshot of the window Therefore the file consists of the L system object in a box of the background color positioned the same way as on the screen even in the case the user interactively rotates and scales the object before the output regardless the used projection Care must be taken if standard black and white output is desired for inclusion in text documents such as in AT EX For this purpose the background is generally made white and the foreground black or shades of grey The following caveats apply e Textures are not supported e Primitives are not drawn with interpolating colours as cpfg draws them An attempt is made to guess the best colour e PostScript has no Z buffer and no additional depth testing is performed during the output thus an object located later in the string will overlap another object 56 located earlier in the string even if on the screen it appears behind the earlier specifie
57. aster specified on the command line int CSSendString int master char item Sends a string to the specified master with index master int CSSendBinaryData int master char item int item_size int nitems Sends a binary data to the specified master This function is used for example for sending images with a depth information to a drawing program see Sec tion 8 5 3 The function returns O if the data have not been sent To communicate with its slaves a process can call functions int CMBeginTransmission void Initializes connections to all slave processes for a single data exchange Cur rently the function always returns 1 int CMEndTransmission int current_step Terminates the data sent by the master in a single data exchange The parameter current_step is used by cpfg to send the number of the current simulation step to the environment This number is returned as the module_id parameter of the function CSGetData see above Currently the function always returns 1 int CMTerminate void Terminates all slave processes The function returns 1 if all processes are suc cessfully terminated int CMGetNumberOfSlaves void Returns the number of slaves communicating with the process int CMSendString int slave char item Sends a string to the specified slave int CMGetString int slave char str int length Receives a string from the specified slave Returns 0 1f there is no string coming int CMSendBinaryData int slav
58. ated by an L system The default value is 150 000 Note that there is no space between s and string_size V This option puts cpfg in verbose mode in which a trace of input data and execution details are printed to stdout v This option puts cpfg in warning mode A trace of input data and execution details significantly reduced compared to the verbose mode are printed to stdout d This option puts cpfg in debugging mode Selected information pertinent to the cpfg operation is printed to stdout This mode is intended only for code development P preprocessor Changes the C macro preprocessor applied to the L system file and view file The default preprocessor is invoked by cpfg us ing the cc E call For example P acpp invokes the ANSI C preprocessor a The program starts in animate mode with animate menu This op tion is necessary in off screen rendering modes g pipestrb to create an animation according to the animate file e communication_specification file specifies parameters of plant field communi L system file View file Animation file cation and switches on environmental mode in which cpfg com municates with an external program simulating the environment The L system definition By convention this file name has suffix I See Section 6 1 for details Contains viewing rendering and drawing parameters including the names of surface specification files By convention this file name has suffix
59. ation type 1s also ignored it is always set to sockets e two new commands have been added strings only on off the data exchanged between the processes contain only text strings No L system modules are transferred This switch is used for ex ample for transferring a list of primitives from plant models to the drawing program binary data on off binary data can be exchanged between processes The re ceiving process must be aware of the coming binary data thus often the data are preceded by a special command string The following section lists the functions provided by the communication library 78 hofs cpfg3 4 exam ples Distr environ 8 5 1 Communication library functions This sections lists all functions of the communication library which can be used by processes communicating with each other in a distributed system First there are three functions used by all processes regardless their role in the communication i e slave master or both void CInitialize char program name char command_string Initializes the communication The first parameter specifies the name of the pro cess which is used to distinguish messages from different processes displayed on the same terminal The second parameter contains the string following the switch C containing the specification of all connections The format of the string is described above void CSInitialize int argc char argv An optional function to the previous on
60. ault is the number of derivation steps specified in the L system file step i number of derivation steps between drawing and recording of frames It defaults to 1 5The memory allocated by cpfg s the resident size increases with each New View This increase may be significant in animations in which the new view is invoked after each animation step See Section 11 44 hofs environment soil 2d no avoiding animation frame intervals frame frames from toi from toz step step Allows the user to select frames or change the step during an animation The command is followed by e alist of specific frames and or e by ranges of frames without specifying the step thus step of 1 is used and or e by ranges of frames with given step all divided by commas Example frame intervals 1 3 5 8 12 step 2 25 In addition every time a range is specified it is possible to change the scal hofs cpfg3 0 features ing or rotate the given object by a certain amount after each frame using interpretation commands animate rotate rz ry rz rotates by angle rx in degrees around axis x an gle ry around axis y and angle rz around axis z scale sr sy 82 scales by values sz sy and sz There can be only one command rotate or scale present for a single range Examples frame intervals 1 99 100 150 rotate 1 500 frame intervals 1 99 100 150 scale 0 9 0 9 0 9 If the command frame intervalsis specified in t
61. background to a given color Usually included at the beginning of the file light posz posy posz posw specifies a light source by four homogeneous coordi nates of light position If posw is equal to O the light is directional The color of the light source is always white 57 222 Projection ortho ming maxx miny mazxy front dist back dist specifies an orthographic pro jection the same way as OpenGL library does perspective viewing_angle front_dist back_dist specifies a perspective pro jection the same way as OpenGL library does lookat posg posy posz refx refy refz upz upy upz defines the view by speci fying the camera position the view reference point and optionally also the up vector Matrices and transformations matrixmode 0 1 sets the current matrix 0 for modelview matrix 1 for projection matrix 7 5 Inventor output Cpfg can output the generated objects into Inventor format if the executable was com piled on the system which has Inventor libraries installed on it The output consists of a main file containing the definition of all objects except predefined surfaces which are stored in separate files one file per surface Note that sometimes there may be two files per surface with two different sets of texture coordinates see also Section 7 1 4 The inventor output has the following features e The camera is not defined in the file thus the initial view in the inventor viewer e g ivview will no
62. be running on different machines they exchange data using Unix sockets The connection to other processes is specified in the command line of a process following the switch C C c confirm socket start machine m spec filel socketl s spec fileK socketK master machineK The single string of switches specifies c the number of a socket and a machine name to which the confirmation about a successful execution should be sent After the confirmation the process monitors the socket for a possible reguest to terminate m a master connection The process operates as a master it sends data specified in the communication specification file spec file to the defined socket socket and expects the reply on a socket with number socket1 1 There can be several master connections s a slave connection The process acts as a slave it expects data defined in the communication specification file spec_fileK from a given socket on a specified machine processes the incoming data and responds back through a socket with number socketK 1 If there are more slave connections the data from the sockets are processed in the order given in the command line gt The delimiters in the command string can be characters or The communication specification file contains the same commands as in the case of two process communication with following modifications e command executable is ignored e the type of communication communic
63. bility Use the command t ropism instead elasticity increment x the value used to increment or decrement the elas ticity associated with the _ symbol This command is kept only for backward compatibility Use the command t ropi sm instead 4See The OpenGL Programming Guide Chapter 9 Section Modulating and Blending 42 hofs cpfg3 0 features interpretation tropisms tropism subcommand subcommanda sets tropism parameters The sub commands are T x y z tropism vector must be present ang angle in degrees with respect to the tropism vector that seg ments are trying to reach for example the angle of 90 corre sponds to diatropism The default is 0 I int intensity global intensity of the tropism default is 1 E ela initial elasticity default is 0 S step elasticity step default is 0 torque subcommand subcommandy sets parameters of a movement that ad just rotates segments around their heading without modifying the heading orientation The subcommands are the same as for command tropism except that subcommand A is ignored 43 6 3 Animation file An animation file contains parameters controlling frame by frame display of images for animation purposes Line Contents Comments double buffer flag specifies whether double buffering is on or off during animation The default is on In cpfg version 3 0 and higher the command line setting of single or double buffe
64. block Endblock Starteach Endeach Block Statements Statement Assignment LHS ArrayRef s ArrayRef Ae dE ls a d as te k de al Seed Dlength Ignore Consider BlankLine Defines Startblock Endblock Starteach Endeach seed Characters lt newline gt derivation length Expression lt newline gt consider Characters lt newline gt ignore Characters lt newline gt lt character gt start Block lt newline gt end Block lt newline gt start each Block lt newline gt end each Block lt newline gt Statements Statement Assignment Procedure If Statement W hileStatement DoStatement LHS Expression BlankLines lt identifier gt lt identifier gt ArrayRef ArrayRef Expression 123 Procedure If Statement W mleStatement DoStatement Defines DefineBlock Def Statements Def Statement Array Def Statement ArrayDefs Array Def ArrayDims ArrayDim ExternalDef Statement ExternalDefs ExternalDef dl le e des ta ro de es ade de S book L y Expression BlankLines if Expression BlankLines Block Blank Lines if Expression BlankLines Block else Blank Lines Block BlankLines while Expression BlankLines Block BlankLines do BlankLines Block while Expression BlankLines define DefineBlock lt newline gt BlankLines Def Statements Def Statement Array Def Statement ExternalDef Statement array ArrayDefs
65. bol par turtle index where turtle index points to a special array of turtles This array stores the turtle parameters as they were when the module par was encountered After the substring is moved to the end of the L system string every time a module par turtle index is encountered in the following interpretation steps the turtle parameters are set to the values stored in the array of turtles under index turtle index The context searches are not passing over this module if the parameter is present Be careful when defining sub L systems because if the module par appears within a set of d and see below the result after the cut is unde fined A production with par as a predecessor will prevent the moving of the substring The value of parameter par can be arbitrary mce flag Conditional cut Operates as the module with no parameter only if the value of flag is equal to 1 Otherwise it has no effect 28 hofs cpfg3 0 features cut module hoofs cpfg3 0fea tures fragmentation hofs cpfg3 0 features cutmodule condition al_cut F F F F F F F F Figure 3 Turtle interpretation of a bracketed string Symbols used to create polygons along with F and f Start a new polygon by pushing the current turtle position onto the polygon stack and set the polygon flag on See also module type in the section on generalized cylinders below Pop a polygon from the stack and render it If no
66. by applying either production pz 1 or p2 2 The symbol behind module B returns the control to the main L system In the subsequent steps all modules of the lateral branch enclosed between modules are processed using productions of the sub L system The axiom w of the sub L system does not affect the simulation but it is useful when the sub L system is being developed and tested without the main L system 6 1 7 Homomorphism An L system homomorphism is defined as a set of productions applied only for inter pretation purposes This allows the modeler to change the details of the appearance without modifying the underlying logic of the model captured by L system produc tions In cpfg an L system homomorphism is specified by productions that are placed at the end of an L system between keywords homomorphism and endlsystem During the interpretation of the L system generated string a matching homomorphism production is selected for each module in the string The homomorphism image of a module is then defined by the successor of the matching homomorphism production If there is no matching production the homomorphism image of this module is the module itself Productions with parameters or local programming statements operate similarly as L system productions i e the values of formal parameters in expressions are replaced by the real values of the module s parameters The resulting overall structure of an L system with homomorphism is
67. caling work only in parallel mode viewing angle x the viewing angle of perspective projection the default is 45 It is ignored in parallel projection front distance x the distance from the viewer to the front clipping plane in perspective projection or the position of the clipping plane with respect to the viewpoint in parallel projection thus a negative value has to be used Note that modifying scale factor see below in perspective projection moves the viewer closer or farther from the view point and the front distance has to be adjusted back distance x the distance from the viewer to the back clipping plane in perspective projection or the the position of the clipping plane with respect to the viewpoint in parallel projection Note that modifying scale factor see below in perspective projection moves the viewer closer or farther from the view point and the back distance has to be adjusted 3 As described in the SGI Graphics Library Programming Guide 35 scale factor x aparameterindicating the size of the final image on the screen A value of 1 0 corresponds to full size In perspective projection the scaling amounts to moving the viewer closer or farther from the view points which may require adjustments in front and back distance box x xmin xmax y ymin ymax z zmin zmax sets a bounding box for the model The view is adjusted so the whole bounding box is visible effective only in parallel projection 6 2 3
68. chine cpfg is running on thus the command can be send also from a remote machine and the number of the corresponding socket The first parameter can be omitted in which case the program command client is trying to access a socket on the local machine The commands sent to cpfg contain the text of the desired menu items in case of submenus also the text of the upper menu is included separated by The program command client reads the commands from the standard input one command per line but it is often more convenient to pipe the commands to the program For example echo New view command_client machine 3000 or echo Output Image REB Save as command_client 3000 The command can be all in lower case because the matching is not case sensitive If the menu item with a predefined filename is to be selected the file has to be replaced by a dot Thus echo Input String binary Input from command_client 3000 inputs a binary string to cpfg from the default file name unless another file name is specified on the command line cpf yg M plant mat strb my string strb S 3000 plant l plant v 10 Limitations This section addresses some limitations of the current version of the plant simulator cpf8 10 1 Using the hardware colormap When using a hardware colormap the program cpfg checks whether a colormap of size 4096 already exists Usually it does as indicated by an X root variable SGI DEFA
69. clude also turtle parameters namely the line width the scale factor the color index the color index for the back side of a surface and the texture index to the comparison between two modules with the same parameters To do so words turtle considered have to be added after the format string to the view file command rayshade object At the end of this stage the hash table contains all the modules whose geometry has to be specified at the beginning of the rayshade file since rayshade format does not allow backward referencing Each module is also linked to the module that previously 88 hofs cpfg3 4 exam ples homomorphism rayshade instancing occurred during the interpretation to be able to process the modules in the opposite order than the order in which they appeared used in the following stage Stage 2 The modules stored in the hash table are interpreted in the order given by the linked list from right to left in the string For each module M or M a1 a2 an a rayshade object with the name M or M a1 a2 an is created and all the geome try resulting from the interpretation of the module is stored within this object If the module is not a letter the name starts with symbol c followed by the ascii code of the character for example module would be represented as c073 In the case that also the turtle parameters are used for the differentiating between the same instances a symbol i followed by a unique index
70. consists of the module name possibly a multisymbol module such as AGs AGc AT xz etc see Section 6 1 9 the number parameters and an array of parameter values Since the same structure is also used to inform the plant model about modified parameters of the communication module the flag set associated with each parameter value specifies whether the parameter has been modified by the environment or not Both structures Cmodule_type and CTURTLE are defined in the library header file comm lib h 8 4 4 Library functions To facilitate the writing of an environmental process the following functions are spec ified in the communication library comm The first two functions are used in both modes of operation Section 8 4 2 70 void CSInitialize int argc char argv Initializes the communication and parses necessary options This call should be made as the very first operation in the function main The parameters of the function C STnitialize are pointers to the standard parameters of the function main specifying the number of command line options of the program and an array storing these options Since the communication library may add some addi tional internally used options to the command line the function C S Initialize parses these options and updates the values of parameters argc and argv so that the user can process the options listed after the command executable in the com munication specification file see Secti
71. context for a homomorphism production is defined as the context of the module in the L system string to which the homomorphism is applied i e the homomorphism image of the modules on the left and right will not affect the context search In the following example the context of production h is used to draw only branches whose end point has y coordinate less than 3 L system 2 w A p Alopo lt 6 gt 20 F P 0 0 A o 1 20 F P 0 0 A o 1 homomorphism hy F gt P z y y gt 3 gt f Even if the homomorphism productions in the previous example were homomorphism maximum depth 2 h F G P 0 0 ha G gt P z y y gt 3 gt f The context for the production hz would be the module P in the L system string with the properly set parameters and not the module P introduced by the homomorphism production h The use of random values in a homomorphism is not recommended during an an imation of the plant development because the values used in one simulation step are 23 hofs cpfg3 4 exam ples homomorphism recursive hofs cpfg3 4 exam ples homomorphism recursive hofs cpfg3 4 exam ples homomorphism context different from values used in another step and visible discontinuities may result The resulting structure may change after each redraw for example during rotations or win dow expose events To prevent this from happening it is possible to use a separate random number generator used only by the homomopr
72. context matching Alter natively symbols to be considered when context matching can be specified following a consider keyword The axiom and the predecessor string in each production must be nonempty The successor strings in each production may be empty in which case it must be represented by an asterisk The context and rcontext strings may be empty in which case they can be represented by an asterisk or left out completely along with the respective lt and gt symbols A production may optionally include a con dition C which is a boolean expression using C like syntax The production will be used only if this expression evaluates to true If a production has a condition either a or 8 or both may also be included They represent lists of semicolon terminated statements expressed using C like syntax If a is given it specifies statements to be executed before evaluating the condition C If 3 is given it specifies statements to be executed after if the result of evaluating the condition is true For example the following is a valid production A x y z xty z gt 10 fn cos x y gt A n z Note that all parameters are assumed to have real floating point values The end of an L system specification is signaled by the endlsystem keyword 16 For a stochastic L system a seed for the random number generator is also required and the typical file has the following slightly modified format lsystem label
73. d for interaction with cpfg The available menu items depend on command line options and the current state of the program The menu controls re reading of input files regeneration of the image output in a variety of formats and the switch to and from animate mode Once animate mode is selected animation items are added to the menu These items control the animation process With the menu bar present in the cp fg window program option mb the program starts in animate mode and all menu items are accessible also from the two pulldown menus on the menu bar 5 1 Main menu The main menu is composed of the following items New Model Rereads the L system and view files generates a new string and inter prets it to create a new image The model is automatically centered in the window or placed according to user specified viewing parameters as described in Section 6 2 New L system Rereads the L system file generates a new string and interprets it to create a new image without modifying the view New homomorphism Rereads the L system file containing homomorphism and re interprets the current string using the new homomorphism for more details see Section 6 1 7 New View Rereads the view file and re interprets the existing string to create a new image The model is automatically centered in the window or placed ac cording to user specified viewing parameters as described in Section 6 2 New environment Restarts the process simulating
74. d object Note that if your version of cp fg supports Inventor output it may be preferable to out put your models as Inventor objects and then print them to PostScript using a facility such as ivprint or SceneViewer 7 3 L system string L system generated string can be output as a text or binary file An example of a text file is A 3 0 25 F 3 FA 1 0 5 F 4 0 0 333333 A 2 0 75 The numbers are output using maximum possible number of digits after the decimal point e g 1 3 is output as 0 333333 unless it is possible to output less digits e g for 3 0 25 etc The binary file starts with a text header L system string length_in_bytes generation_step_no followed by length_in_bytes bytes of the string in internal representation in which mod ule parameters are stored as 4 byte floats Example L system string 47 1 A 2222 2222 F 222 FA F 80 A 7 4 Graphics Library Statements format The program cpfg can output the geometry in a format similar to the format of a background scene Section 6 4 5 Thus the geometry produced in one simulation can be included as a background scene in another model In addition the GLS format is used by some environmental programs e g soil or arvo to define obstacles The output file can include all commands specified in Section 6 4 5 plus the fol lowing commands Lighting clear red green blue this command clears the window and sets the
75. d on the right side of an assignment statement in one of these four statement blocks are considered as global variables and can be accessed in any other block or production A conflict of two productions accessing the same global variable at the same time is avoided because in the modeling program cpfg the parallel rewriting process is captured by applying the productions sequentially from left to right 5 6 1 4 Arrays The values of parameters of a plant model depend frequently on the order of an apex or a branch or on another value such as the apex age or vigor It is possible for example to have a separate production for each order with a successor using different values of growth parameters But it is more effective to define an array of values and use only one production To define arrays the cpfg language was extended by the command de fine followed hofs cpfg3 0 features by a specification of all arrays used in the model arrays define array name1 N 1 Ni p V 0 0 0 gt U o 1 gt UIN 1 1 N1 p 1 J gt namen Nn 1 Nn Dn The command can be placed anywhere before the list of productions A single ar ray is specified by its name name and sizes N i Ni p for each of D array di mensions The array can be initialized by including a list of all array values be tween a single pair of curly brackets The first N p values initialize array items name 0 0 0 rame 0 0 Ni p
76. ded from the files female 1 male landleaf 1 23 1 sedge l internode growth rate define RATE 1 02 For a doubling in branch length we want 1 26 times the width The exponent is equivalent to log 1 26 log 2 approximately for 1 1 we use an exponent of 1375 for 1 2 we use an exponent of 2630 for 1 26 we use an exponent of 3334 for 1 3 we use an exponent of 3785 define STEMRATE 1 06 width of stem at start of internode define STEMWIDTH 0075 Sub L systems for female spike male spike and leaf 115 Figure 26 A lilac inflorescence define F_SPIKE 2 1 25 axiom define M_SPIKE 3 1 25 axiom leaf L system parameters starting delay time to turn and new elasticity define LEAF 4 1 axiom a 10 a a 13 100 lsystem 1 nice derivation length 90 95 derivation length 95 axiom 30 10 STEMWIDTH A 4 4 lt A a t gt a 30 gt F 1 137 5 M_SPIKE lt A a t gt t lt 10 gt F 1 A a 1 t 1 116 d gt gt NA A A gt gt gt Sok is used here so x Xx Figure 27 Carex laevigata t 10 gt F 1 137 5 L a S a STEMWIDTH A at1 0 d lt 200 gt gt gt d S that widt 7 25 0 7 60 TEM RATE zal 1 L
77. diffuse color 0001 specular color 0001 emissive color 0 transparency polygon 0 0 0 010 10 0 When the last line is typed in and the input is terminated by pressing keys Control and D the data are transferred to the drawing process that draws a yellow triangle on a white background Thus it is possible to add the drawing client into the distributed system and interac tively add primitives to the visualized scene 87 9 Miscellaneous features 9 1 Rayshade instantiation Homomorphism productions generally produce the same geometry for a given mod ule with a given set of parameters It is then convenient to take advantage of this information during the output into a rayshade file format since this format supports instantiation It is possible to mark selected homomorphism productions using a delimiter 0 gt instead of the standard gt During the rayshade output an object with a name given by the predecessor of the productions and the values of its parameters is created Each time such a module is encountered during the interpretation of the string while creating the rayshade file only a reference to the given object is included in the file not the geometry representing the module The output consists of three stages Stage 1 The string is parsed left to right with the full update of the turtle parameters but no output file is created yet Each time a homomorphism production with the delimiter
78. e Both the image height and width has to be a power of two If it is not the case the texture image is clamped and only a part of the texture appears on the textured surfaces If your texture size does not meet this condition scale up or down your texture using command imscale infile outfile xres x y res y 48 hofs cpfg3 0 features interpretation textures 6 4 5 Background scene specification file The background scene can be effectively used for defining additional objects around the simulated plant such as obstacles It can be also used during the simulation of plant environment interactions for visualizing the environmental field together with the plant The name of the background scene file is specified in the view file Often the scene is read only at the beginning of the simulation but it is also possible to update it automatically before each interpretation step animate file command new view between frames or manually from a menu for selected steps of the simulation Primitives of the background scene are defined in a text file using simple OpenGL like statements 8 The commands can be divided into several groups discussed below Primitives The following statements specify basic geometric primitives similarly as in the OpenGL graphics library 8 The coordinates of the vertices or the size of primitives are defined with respect to a local coordinate system It is possible to translate the ob jects or scale
79. e This function retrieves all the necessary information from the process command line In this case the switch C has to be the first one on the command line void CTerminate void Ends the communication this should be the last function called int CShouldTerminate void This function returns 1 if the process is requested to terminate when a special character is sent to the process confirmation socket by a control process see Section 8 5 2 A process can operate as a slave master or both The latter means that the process waits for an input from its masters and then can require some data from its slaves Communicating with its masters the process can use functions as in the case of a two process communication void CSMainLoop int AnswerQuery Cmodule type CTURTLE int CSBeginTransmission void int CSEndTransmission void int CSGetString int master char str int length int CSGetData int master unsigned long module_id Cmodule type two modules CTURTLE turtle This function is generally used only by environmental processes directly com municating with the plant simulator cp g void CSSendData int master unsigned long module id Cmodule type comm module This function is generally used only by environmental processes directly com municating with the lant simulator cpfg 79 In addition there are few new functions int CSGetNumberOfMasters void Returns the number of connections to a m
80. e char item int item_size int nitems Transfers a binary data to a given slave int CMGetBinaryData int slave char data int item_size int nitems Receives a binary data from a given slave Returns 0 if there is no data coming int CMSendCommSymbol int slave unsigned long module id Cmodule_type two_modules CTURTLE turtle Sends two modules a communication module with the following module with 80 their identification number to a given slave The function returns 1 if the second module should be graphically interpreted and the resulting set of triangles trans ferred to the slave This function is used mainly by the plant simulator cp g int CMGetCommunicationModule int slave unsigned long moduleid Cmodule_type comm_module Receives a communication module with its identification number from a speci fied slave The function returns 0 if there are no more modules coming from the slave Unless specified the functions return a value of 1 if they finish successfully Note that unlike for a slave in the case of a master the incoming data are fetched from a specified slave This allows the program to process the response from the same slave as the one to which the data from the master has been transferred Example Following example illustrates a program hub that acts as a common interface between several plant simulators masters of the hub and models of the environment slaves of the hub The program establishes al
81. e can also be modified interactively through the menu The supported output formats are RGB Saves the current window in SGI RGB format The file name may be specified on the command line as rgb file rgb RAS Saves the current window in SGI colormap RAS format The file name may be specified on the command line as ras file ras TGA Saves the current window in Truevision Targa format The file name may be specified on the command line as tga file tga RLE Saves the current window in Utah raster toolkit rle format The file name may be specified on the command line as rle file rle Rayshade Outputs a complete file in rayshade 4 0 format The viewing param eters produce the same view as cpfg provided that the perspective view is used Surface color is chosen according to the current color map using the basic color modified by the ambient light parameter but not by the diffuse light component The file name may be given on the command line as ray file ray Postscript Output the generated string in PostScript see Section 7 2 The file name may be specified on the command line as ps file ps String Output the generated string in a text format see Section 7 3 Two decimal digits of parameter values are output The file name may be specified on the command line as str file str String binary Output the generated string in a binary format see Section 7 3 The file name may be specified on
82. e of the current color index or material by the color in crement or set to n if a parameter is given Increase the value of the current color index or material index of the back side of a surface by the second parameter of command color increment in the view file or set to n if a parameter is given Surfaces can have different colors or materials specified for each side only if the view file command initial color has two parameters Decrease the value of the current color index or material of the back side of a surface by the color increment or set to n if a parameter is given Increase the value of the current line width by the global parameter line width increment or set to n if a parameter is given Decrease the value of the current line width by the global parameter line width increment or set to n if a parameter is given Tx index Sets texture with index index the order of the texture specification in the view file Index O switches off texturing If a predefined bicubic surface has associated a texture index in the view file its texture is fixed and cannot be changed by module AT z 27 hofs environment soil 2d no avoiding animation hofs cpfg3 0 features interpretation double_sides surfaces hofs cpfg3 0 features interpretation textures D scale Sets the current turtle scale to scale All subsequent geometry will be scaled by the specified value The default value is set by the view file command
83. e turtle parameters The precision of object parameters used for differ entiating between two objects created by the same modules with the same number parameters can be controlled by specifying a format string in the view file using the command rayshade objects see Section 6 2 It can be specified whether even the turtle is considered when comparing two objects created by the same module with the same parameters if the objects are different the second one is not an instantiation of the first one Sometimes it may happen that an empty object is defined and rayshade would core dump on the file Currently a tiny transparent sphere is defined in such cases This could be better solved by noting which instances are empty and not using them in other places ADD It would be nice to include an example of rayshade instancing o gt productions where turtle s parameters are considered 7 1 6 The main object The name od the main object is generally equal to the name of the rayshade output file without the path The whole object is enclosed in a grid of resolution 20 x 20 x 20 to speed up the rendering Sometimes though cpfg may define several plants positioned further away from each other and it is more efficient to use a separate grid for each plant For this purpose the user can use module J in the L system string see Section 6 1 9 The module 55 J size1 sizes sizez closes the current grid and starts a new grid of a given
84. ed by assignment statements of the form varname expression where variable names are specified as in C and expression is an arithmetic expression In this case the expression can also include local variables which have been assigned a value in previous assignment statements within the same production as in the following production A y x y 2 s x x s lt 5 z sqrt y B z C z 1 All variables have floating point values In case of function printf it is possible to omit the assignment part and ignore the value returned by the function 17 a a 1 printf a f n a e The second type of statement includes conditional statements if condition statmt statmtn and if condition statmt statmty else statmt statmtm where condition is a logical expression and statmt are statements e The third type of statement is represented by loop statements while condition statmt statMtn and do statmt statmt while condition The meaning of condition and statmt is the same as for conditional statements Statements a are performed every time the predecessor and left and right contexts match before the condition is evaluated even if it results in not applying the produc tion and before the matching production is found Thus statements a can be applied to precompute expressions used in the condition The 8 statements are performed after a condition is evaluated as true
85. ed to the environment or set by the environment and transferred to the plant model This interface is sufficient for receiving the information from the environment but the environment also has to obtain information about the position and orientation of plant organs affecting the environment or being affected by it Thus in addition to parameters of a communication module the environment receives the position and orientation of the communication module retrieved from the current turtle parameters and a module following the communication module with its parameters To accommodate the exchange of information between the plant and its environ ment each derivation step after which the interpretation step can be possibly performed is followed by an environmental step In the environmental step the string resulting from a derivation step is scanned from left to right to determine the state of the turtle associated with each symbol This phase is similar to the graphical interpretation of the string except that the results need not be visualized Upon encountering a com munication symbol the plant process creates and sends a message to the environment including all or a part of the following information e the address position in the string of the communication module mandatory field needed to identify this module when a reply comes from the environment e values of parameters z e the state of the turtle coordinates of the position a
86. end the first communication module The function always returns a value of 1 int CSGetData int master unsigned long module_id Cmodule type two modules CTURTLE turtle Obtains a communication module and possibly the following module from the plant simulator 1f the second module is not present its name is an empty string i e two modules 1 symbol 0 is equal to 0 The parameter module_id spec ifies a unique identification number of the communication module the pointer 71 two_modules points to a two dimensional array containing the communication module and the next module and the pointer turtle points to the turtle structure note that only some turtle parameters are sent according to the specification file The parameter master is set to the index of the calling master This value is used only in a multiprocess environment Section 8 5 and in the case of a two process communication it is always equal to 0 The function returns 0 when there is no other module at the end of the en vironmental pass In this case module_id is set to the number of the current simulation step int CSGetString int master char str int length Reads a string str with maximum length length sent by the plant simulator Ac cording to the communication specification file selected modules can be inter preted during an environmental step and the polygons representing the modules or their homomorphic image are sent as a set of strings followin
87. error message is printed if such a variable or array is defined but it should be fixed so that the programs allows both There s an error message that is given in the new subLsystem code when a re cursive call is attempted to a sub Lsystem ERROR Recursive call to Sub L system Right now it exits the program but it should do like other errors do and leave the process running for future rereads One thing Jim have noticed is that when running the binary on an O2 there are strange things happening with the buffers There seems to be a one pixel margin around the edge of the window that gets cleared ok but when the image is finally drawn apparently random colours appear in that margin giving a pulsing effect Very disconcerting He does not have the O2 any more but he should be getting his Octane early in 1998 and he will check it again and try compiling to see if it fixes the problem The memory allocated by cpfg s the resident size increases with each New View This increase may be significant in animations in which the new view is invoked after each animation step This problem has not been traced yet it may be something related to OpenGL or X It is not anything directly caused by cpfg calling malloc strdump or realloc because these calls can be moni tored if cpfg is compiled after running make heapcheck Maybe related to textures Maybe cpfg does not call some cleaning functions of X or OpenGL The Jim s c
88. es if queries i query don t answer if no parameter for j 0 j lt num_queries j if i j 75 if fabs queries i position 0 queries j position 0 lt EPSILON amp amp fabs queries i position 1 queries j position 1 lt EPSILON CSSendData queries i master queries i id amp comm_symbol break BOK KKK KKK KK KR kok k kok k kok k k kk S void MainLoop void controls the loop of data exchange Cmodule type two modules 2 unsigned long module id int master CTURTLE turtle infinite loop until message exit comes for 1 CSBeginTransmission num gueries 0 while CSGetData master module_id two_modules amp turtle StoreQuery master module id two modules turtle DetermineResponse EndTransmission returns 1 when the process is requested to exit if CSEndTransmission break BORK KKK KKK KK I RR RRA X k kk k int main int argc char argv initialize the communication as the very first thing CSInitialize amp argc amp argv MainLoop CTerminate should be the last function called return 1 76 Each incoming query is stored in a one dimensional array of a fixed size To determine the response for queries with more than one parameter the coordinates of the query point are compared with the coordinates of all other points If there is another point with the same co
89. es but many of the example models will not show up in the correct colors The described distribution has been compiled and tested using IRIX 5 3 release of the operating system A C macro preprocessor is also required the default preprocessor is invoked by cpfg using the cc E call 3 Distribution The simplest way to use cpfg is within the Virtual Laboratory Environment v lab The complete cpfg and vlab software distribution binaries only with sample mod els and documentation is available at http www cpsc ucalgary ca projects bmv vlab index html Part I Reference 4 Command line parameters A call to cpfg takes the following form cpfg sstring size v V d P preprocessor a e environmentfile g pipestrb C communication setup string S socket num c mapnr w xsize ysize wp xpos ypos wt window title m n colormap file M n material file mb pm sb o homo rgb rgbfile ras rasfile t ga tgafile x le rlefile ray rayfile ps psfile st r textstringfile st rb binarystringfile 91s glsfile vv vvfile iv ivfile L system file View file Animation file The L system_file and View file arguments are mandatory the arguments in square brackets are optional A call to cpfg without any arguments prints a message with a list of options 4 1 General sstring_size The value of the integer string_size defines the initial space allot ment for a string gener
90. f the specification file and an optional switch v to run the program in a verbose mode with detailed report displayed in the terminal window The specification file contains the definition of processes and connections between couples of processes The specification of a process starts with command processes followed by a group of lines not separated by an empty line with commands name process_ name Defines a unique process name host machine name Defines the name of the machine on which the process is exe cuted If the command is omitted the local machine is used files list of filenames Specifies files which have to be copied to the remote machine This command can be repeated several times to specify more files command binary with parameters Defines the executable of the process The full path does not have to be specified if the process path is set in the system variable PATH display machine Specifies the machine to which the display is redirected If not spec ified the system variable DISPLAY is set to the local machine Since plant simulator cpfg needs the connection to an X server it is necessary to spec ify a valid display variable especially if the program is executed on a remote machine The X server connection is required in order to use calls to graphics 83 hofs cpfg3 4 exam ples Distr environ with_start library OpenGL If the plant simulator is connected to the X server on a different machine a lot of
91. g the communi cation module Thus the function CSGetString is used in a loop after each call to CSGetData to retrieve these strings It is recommended to always include a loop of calls to CSGetString to receive possible strings from the incoming data see examples below because if the plant simulator sends some strings which are not read by the environmental process the communication would be interrupted The function returns 0 when there is no string coming void CSSendData int master unsigned long module id Cmodule_type comm_module Sends the modified communication module back to the plant simulator The original module_id must be specified In the case of two process communication the value of master should be 0 int CSEndTransmission void Ends a transmission after all modified communication modules are sent back to the plant simulator The function returns 1 when the process is requested to terminate In this case the communication loop should be exited the process should free its data structures and call CTerminate Instead of calling the library function CSMainLoop the user has to define a func tion MainLoop which should have the following general form void MainLoop void Cmodule_type two_modules 2 int master current_step unsigned long module_id CTURTLE turtle char str 2048 72 for 1 CSBeginTransmission while CSGetData smaster amp module_id two modules turtle StoreQ
92. ged Switch off environmental step on a flag as in the previous point modules E can be introduced just before they are needed using global variables e g a step counter although this solution would not eliminate the environmental pass only no data would be transferred between cpfg and the environment enable different homomorphisms one for the environment one for the screen actually there could be one for each type of output as well string rayshade postscript etc Switching from one to another could be controlled by some variable Add a smooth interpolation of colors e g along the stems even in the shaded mode Would it be possible to use shared libraries to add mathematical and blackbox functions without recompiling 96 How about the ability to put the labels in screen space maybe in a separate A L parameter 0 1 for each dimension and scaled to fit Might be nice if fonts could be specified per label Allow the user to change format for parameters in string output currently scien tific notation Should there be a window opened when a warning message is sent rather than just to the console The console is not necessarily open Allow for different timing within sub L systems In perspective viewing can the image be automatically scaled to properly fit the window and if this is the case how should the parameters be passed to rayshade How about having the light stay fixed when the object is r
93. given 1 with 0 only if it is preceded by 1 and followed by 1 The command ignore F tells cpfg not to consider the and F symbols when matching contexts Other examples of context sensitive L systems are given in Section 1 8 of The Algorithmic Beauty of Plants 7 The production x lt gt gt lists for both the left and right context and consequently will match a symbol with any context The is not required The following productions are equivalent x lt gt gt gt gt lt gt gt 19 Parametric L systems Figure 20 shows a fractal generated with a parametric L system 109 19 1 rowoftrees l define STEPS 7 define a 86 define p 0 3 define dl 2 define d2 1 define d3 0 define q 1 p define h p q 70 5 lsystem 0 derivation length STEPS axiom 90 F 1 F x x gt 0 05 gt F x p a F x h a a F x h a F x q endlsystem This L system makes use of parameters to control the distance moved by the turtle The initiator production predecessor is the hypotenuse AB of a right triangle ABC Figure 21 The first and the fourth edge of the generator subdivide AB into segments AD and DB while the remaining two edges traverse the altitude C D in opposite directions From elementary geometry it follows that the lengths of these segments satisfy the equations g c p and h pa
94. hanges related to variables local to each sub L system do not take account of cut strings appended at the end of the L system string Sometimes the buffers are not switched properly if you resize the window The size of the rgb image output by cpfg is wrong but ras output is fine on IRIX 6 2 93 The normals seem to be wrong when Gr is set to 90 The bounding box is wrong for all off screen generated rayshade outputs used when defined the optional object consisting of only the bounding box see Section7 1 unless the user includes also the view volume using vv dev null Since determining the view volume takes some time and the bounding object is often not used it would not be a good idea to compute the bounding box as a default but maybe some switch would be nice when mapping textures on generalized cylinders the aspect ratio of the texture image is preserved To do this the length of the contour has to be computed Right now it is done approximately by computing the distances between 10 n points lying on the contour n is the number of control points specifying the contour It would be better to compute the real length of the contour During instancing of homomorphism productions in rayshade output Section 7 1 it may happen that an empty object is defined and rayshade would core dump on the file Currently a tiny transparent sphere is defined in such cases This could be better solved by noting which instances are
95. he L axis A Pitch up by angle 9 around the L axis Roll left by angle 6 around the H axis 9 Roll right by angle 6 around the H axis 26 Turn around 180 around the U axis This is equivalentto 180 or 180 It does not roll or pitch the turtle Roll the turtle around the H axis so that H and U lie in a common vertical plane with U closest to up OR hzx hy hz ux ux uz Set the turtle heading to ha hy hz if the vector is not normalized the program will automatically do it If only the first three parameters are specified the turtle up and left vectors are adjusted minimizing their rotation with respect to their previous orientation Otherwise the next three parameters specify the turtle up vector also this vector does not have to be normalized In this case the left vector is computed directly from the specified heading and up vectors Modules v and R adjust the turtle orientation with respect to absolute coordinates as compared to other rotations performed with respect to the current turtle orienta tion If no parameter is given for the symbols A and the value of the view file parameter angle increment see Section 6 2 is used Changing turtle parameters The following symbols change turtle parameters n n n Increase the value of the current color index or material index by the color increment or set to n if a parameter is given Decrease the valu
96. he animation file re gardless the order it takes precedence over the commands first frame last frame and step The command in the file can be in an arbitrary order The file is not preprocessed thus comments may cause problems at least a warning will be issued 45 6 4 Other input files 6 4 1 Surface specification file A surface specification file details a bicubic surface in B zier form composed of an arbitrary number of patches The file has the following format where x y and z are real values 7 is an integer value and the remaining strings in italics represent text strings Tmin Tmax Ymin Ymaz min maz CONTACT POINT X Y y2Z z ND POINT X 2Y y2Z z HEADING X 3 Y Y4Z zZz UP X 2Y yZ Zz SIZE amp patchname TOP COLOR i DIFFUSE zx BOTTOM COLOR DIFF g AL patchl A patch2 AR patch3 L patch4 R patch5 BL patch6 B patch7 BR patch8 T11 Y11 711 T12 Y12 212 T13 Y13 213 Tia Y14 214 T21 Y21 221 T22 Y22 222 T23 Y23 223 T24 Y2 224 T31 Y31 231 T32 Y32 232 T33 Y33 233 134 Y34 234 Tar YAl 241 T42 Ya2 242 T43 Y43 243 T44 Yaa 244 zal The first six lines of the file contain information about the surface as a whole The first line lists the minimum and maximum values of x y and z for the surface The next four lines detail geometry parameters required for integrating the surface with the remainder of the structure generated by cpfg The contact point specifies where the turtle connects to the
97. he following commands are processed in the order they are specified in the view file Thus if there are two commands controlling the same parameter the second command takes precedence This does not apply to commands such as light texture and others that specify a new set of parameters every time the command occurs 6 2 1 Setting turtle s parameters Line Contents Comments angle factor x 360 a is the angle increment associated with the and symbols angle increment x Set the angle increment associated with the 8 and symbols to x The commands angle increment and angle factor are alternatives and the last one appearing in the file will be used initial color 22 number between 0 and 255 specifying the initial value of the index to the color map or a set of materials The second number if present specifies the index of the color or material of the back side of the surface The program cpfg then considers two different colors materials for each surface color increment 21 22 number specifying the color or material index incre ment associated with the and for the front index and and for the back index initial line width x pixels shaded the number z represents initial line width in the specified line style If no string is listed after the number then Fs and Gs are drawn as flat shaded polygons with a width in world units The width of line in this case is re
98. he opaque objects then to sort all transparent or semitransparent objects according to their position with respect to the viewer and draw them in that order with the depth 91 buffer switched off This is a very time consuming process Consequently all objects resulting from the interpretation of the L system string are drawn opaque even if the material has transparency set to a value above 0 Nevertheless it is possible to define transparent object in the background scene used for example to visualize the concentration contour in the three dimensional model of roots The only limitation is that the objects are not sorted for the second drawing pass and the resulting image may be incorrect Note that the transparent objects are output to rayshade or inventor even if they are not transparent on the screen 92 hofs cpfg3 0 features interpretation gen_cylinders background_scene 11 Things to do 11 1 Problems On April 21 1998 Jim discovered a problem when using new homomorphisms and the instance stuff it causes a crash He wanted to look at it I am not sure what is the current status When using stochastic productions cpfg requires stochastic values for ALL productions whether they are stochastic or deterministic This should not be necessary Also the seed is not set This should be looked at soon you cannot have a variable with the same name as an array It used to be possible but now it does not work An
99. hims productions This option is switched on by specifying the seed for this generator using a keyword seed fol lowing either the keyword homomorphi sm or the keyword maximum depth If sub L systems are also used each sub L system has its own homomorphism which has to be specified at the end of the sub L system ADD It would be nice to have a global homomorphism that would be shared by the main L systems and all sub L systems not implemented yet If a homomorphism production is specified with the delimiter o gt an object pro duction instead of gt the operation of such a production is similar to the operation of a production with delimiter gt During outputting the geometry to a rayshade file the object productions specify objects which should be instantiated It is possible to specify using the view file command rayshade objects a format string for module s parameters that controls the precision used for differentiating between two objects created by the same modules with the same number of parameters It is also possible to control whether even the turtle is considered when comparing two objects created by the same module with the same parameters if the objects are different the second one is not an instantiation of the first one Note that the homomorphism productions are applied also during the environmen tal step to be able to properly determine the turtle parameters to be sent to the environ mental program with
100. hooting lt 44 8 5 Distributed system lt lt lt lt lt 8 5 1 Communication library functions 8 5 2 Initialization program 4 8 5 3 Drawing program lt lt e 9 Miscellaneous features 9 1 Rayshade instantiation 9 2 Sending commands to cpfg through sockets 10 Limitations 10 1 Using the hardware colormap lt lt lt 10 2 Using cpfg on less than 24 bit screens lt lt 10 3 Use of symbol in the L system file 10 4 Transparent objects o 4 e e 1 This section is incorporated from 2 j Things to do 93 Ti Problems 3 8835 ects Et nd os EA Soi i d vd An ete te tnt at hs 93 11 2 Fixes to the manual 00000500 G 95 11 3 Suggestions for future extensions or improvements 95 Examples 98 Quadratic Koch island 98 A A E tat l dyz 98 122 7KOCKV e nd a A a es ar 99 Koch snowflake curve 100 13 1 MowWilakKed ica dad ts ie Be Bee A 100 13 2 snowflakes 33 5 rr a ad WK he ee Eek BO 102 Combination of islands and lakes 102 TA Takes ana o Kia ote a a 6 By tn Aara e 102 Dragon curve 103 A O Bae ea Eke Gas rere 26630 es 103 Branching structures 105 TO plantitas ise bed bined da dad 105 Stochastic L systems 106 TE plants Laia as a e as 107 Context sensitive L systems 107 VS CONntEXtel ae n e a da a ed ern A Se t 108 Parametric L systems 109 19 Trowottreesili
101. ii a EA ee os rs ee z 110 Global variables in parametric L systems 110 D2ON flakes Ea Ea nets heed al esa me els da A je 110 Incorporation of predefined surfaces 112 21 1 cblossomel 3774 2 85 4 a a ee SS Be eS e s 112 21 2 blossom V oe Zb P a eS a Se es 112 VIAS a Bae ache Oo Sth ee v Lod kg we Beye eed 18 113 DACA PA Sia ad ee na Bee eit A GR ee ee A 114 More predefined surfaces 115 23 Use of sub L systems 115 23d sedge lns iaa a 115 23 2 Temale sd A A Ge Be A l BAe A 118 24 L System defined surfaces 118 25 Other examples 119 References 121 A L system Input Grammar 122 Index 128 1 Introduction The plant and fractal generator with continuous parameters cp g is a program for modeling plants and visualizing their development It can also be used to generate images of 2D and 3D fractals Models are expressed using the formalism of L systems This manual assumes that the reader is familiar with the concepts of L systems and turtle interpretation presented in The Algorithmic Beauty of Plants 7 as well as the elements of the C programming language Part I contains reference materials It describes cpfg usage user interaction and input and output file formats Part II contains examples from an L system for a simple fractal to realistic models of plants 2 Machine requirements The cpfg program runs on SGI workstations and works best on machines with 24 bit planes The program will run on machines with only 8 bit plan
102. independent parts This allows the modeler to first describe the development of some parts of the plant and then combine the pieces together in the complete model Thus the design of a model is more efficient and it is possible to reuse productions simulating the growth of certain plant organs in other models 20 axiom applying main L ac main L sys Sub L id main L system id 1 idp 0 5 main sub main sub main L sys L sys id L system L sys id L sys Figure 1 Example of a developmental sequence generated by an L system with two sub L systems applying applying applying applying applying main L system SUb L system dy To this purpose Hanan in his thesis 1 extended parametric L systems to include multiple sets of productions The framework consists of a main L system controlling the development of the overall structure and additional sets of productions sub L systems which are invoked from the main L system or from each other in a manner similar to calling subroutines in a program Unlike subroutines no values are returned to the main L system upon a completion of a sub L system In the cpfg language the main L system is the first set of productions in the L system file Each set of productions has assigned to it a unique index using command Lsystem on the first line of the specification of the main L system index 1 or a sub L system During the
103. ing response sending responses V end of transmission a V simulation step S suspended Figure 7 Flow of control during the simulation message It then waits again for the plant simulator returning to the beginning of step 4 5 The plant simulator receives the data coming from the environment and sets the parameters of communication modules accordingly After encountering the end of transmission message it performs a simulation step and returns to step 3 The simulation is terminated by the plant simulator which sends a special terminate message to the environment If you are using shared memory or files for the data exchange between cpfg and the environmental program and one of the program crashes the other one will not be terminated and you have to do so manually You can list all your processes using ps u your_login_name and kill the process by kill process_id The process 1d PID is listed by ps Also the semaphores and the shared memory stays allocated and after a while you may not be able to receive more semaphores from the system In this case use ipcs to list all your semaphores and shared memory and ipcrm m idoripcrm s idtoremove them 8The organization of communication with different channels used to send information to and from the environment makes it also possible to send the response immediately this situation is not captured in Figure 7 65 Because of the great variety of environmental phenomena
104. initial scale Di factor Multiplies the current turtle scale by factor If no parameter is speci fied the default value set by the view file command scale multiplier is used Dd factor Divides the current turtle scale by factor If no parameter is speci fied the default value set by the view file command scale multiplier is used Modeling of structures with branches Figure 3 Push the current state of the turtle all its parameters onto a pushdown stack Pop a state from the stack and make it the current state of the turtle The symbol cuts the remainder of a branch Whenever it is detected in the string during the generation process it and all following symbols up to the closest unmatched right bracket are ignored for derivation purposes and will therefore disappear from the generated string If an unmatched right bracket is not found symbols are ignored until the end of the string The symbols is ignored if it is introduced by a homomorphism production par Supports fragmentation If the symbol is found on the right side of any L system production a special interpretation step is performed after each generate step if also the environmental pass is performed these two passes are done together When the module is encountered during this pass the following substring up to the closing at the same level or up to the next par is moved to the end of the L system string and it is preceded by a sym
105. interpretation past flag flag equal to on default allows the turtle to interpret past symbol which in subsequent step cuts a substring When the flag is set to off the symbols after are not interpreted interpretation step i an integer value i specifies number of interpreted symbols between an X event is checked The interpretation during rotation or after selecting New model New L system New view or New Homomorphism from the menu can be interrupted by an X server event This allows one for example to quit the program before the drawing is finished to rotate much quicker just a part of the string is drawn depending on the machine speed and value of i or to reduce the number of redraw events when the window is resized or exposed several times in a row Setting i to 1 switches off this feature i e all modules are interpreted without checking for the next event rayshade objects format turtle flag controls the output of instantiated objects into rayshade file If you specify a homomorphism production with delimiter o gt instead of gt during the rayshade output the predecessor will be instantiated if it appears again if it has the same parameters and possibly also the same turtle parameters The format string controls the precision of object parameters used for differentiating between two objects 37 hofs cpfg3 0 fea tures labels hofs cpfg3 0 features interpretation interpr step hofs cpfg3 4 exam
106. ion Expression Expression Expression Expression Expression lt gt Expression Expression lt Expression Expression lt Expression Expression gt Expression Expression gt Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Expression Function Name Value LValue String 126 Function FunctionName Value Name LV alue String gt gt de a A i FunctionName Expression tan sin cos atan asin acos ran nran bran biran srand exp log floor ceil trunc fabs sign stop sqrt printf fprintf fopen fclose fflush fscanf lt number gt lt identifier gt amp lt identifier gt amp lt identifier gt ArrayRefs lt string gt 127 Index animate mode 7 animation file 7 46 array 20 background scene 41 51 buffering 8 46 color 42 colormap 7 command define 20 end 20 endeach 20 Isystem 22 start 20 starteach 20 command line parameters 6 communication library 66 74 module 34 62 multiple processes 9 specification file 66 70 type 70 contour 41 49 debugging mode 6 decomposition 26 drawing parameters 38 environmental process 72 debugging 80 example 77 environmental step 62 functions 21 generalized cylinder specification 32 twist 41 homomorphism 10 23 in
107. is forced to terminate 85 After all processes are successfully started the program waits for a signal from processes about their termination After all signals are received the program removes all files and directories created in tmp on all used hosts 8 5 3 Drawing program In the example from the previous section two processes simulating two trees are com municating with a drawing program draw_server that displays both trees in a single window The program draw_server communicates with plant simulators by sending text commands such as new view or step and receiving the graphical information about the simulated structure Currently the program recognizes two forms of graphical data First itis an array of values representing the color and depth for each pixel The depth value is necessary in case images from several programs are combined into one window The second format consists of a list of primitives a sequence of OpenGL like commands see Section 7 4 describing the geometry of the modeled structure The program draw_server is linked with the communication library comm thus connections between the program and plant models are defined using command line switch C This switch is set automatically if the distributing program start is used see the previous section Other command line parameters include r mode Sets the rendering mode Currently shaded flat and wireframe mode is supported The default is shaded c num
108. ith themselves In other words cpfg treats this L system as if it contained these productions gt jj gt 98 n 2 n 3 Figure 9 Koch Islands generated in n 0 1 2 and 3 derivation steps 12 2 koch v angle factor 4 initial color 1 color increment 0 initial line width 2 line width increment 0 viewpoint 0 0 1 view reference point 0 0 0 twist 0 99 Figure 10 The production F gt F F F FF F F F projection parallel front distance 100000 0 back distance 100000 0 scale factor 0 9 z buffer off cue range 0 shade mode 7 light direction 1 0 1 0 1 0 diffuse reflection 0 tropism direction 0 0 1 0 0 0 initial elasticity 0 0 elasticity increment 0 0 This is a fairly typical viewing file The most important value for this fractal is angle increment 90 This tells cpfg that the angle increment used with the and commands is equal to 90 13 Koch snowflake curve Figure 11 shows several derivations of the Koch snowflake They were generated with the command cpfg snowflake l snowflake v The files contents are detailed in the following sec
109. l connections to its masters and slaves Then for each communication module it receives from a given master it sends the module to a slave with an index specified as the first parameter of the communication module The index of the master is stored as the first parameter of the symbol sent to the slave After each module is transferred to a specific slave the response from a slave is checked and if there is one the communication modules sent by the slave are trans ferred to the proper master Just in case the slave processes are not responding imme diately the input from all of them is again checked at the end of a single transmission The full listing of the program follows include comm_lib h void MainLoop void Cmodule_type two_modules 2 comm_module unsigned long module_id CTURTLE turtle char string 2048 int slave master infinite loop until signal exit comes for CSBeginTransmission begin transmission to all slaves for 1 0 1 lt CMGetNumberOfSlaves i CMBeginTransmission i 81 process the data while CSGetData amp master amp module_id two modules amp turtle if two_modules CM 0 num_params gt 0 amp amp two_modules 0 params 0 value gt 0 amp amp two_modules 0 params 0 value lt CMGetNumberOfSlaves slave two_modules 0 params 0 value 1 store the index of the master two_modules 0 params 0 value ma
110. lomaa Eds Springer Verlag Berlin 1992 pp 193 211 PRUSINKIEWICZ P JAMES M AND MECH R Synthetic topiary Computer Graphics SIGGRAPH 94 Conference Proceedings 38 July 1994 351 358 PRUSINKIEWICZ P AND LINDENMAYER A The algorithmic beauty of plants Springer Verlag New York 1990 second printing 1996 With J S Hanan F D Fracchia D R Fowler M J M de Boer and L Mercer 8 Woo M NEIDER J AND DAVIS T The OpenGL Programming Guide Second Edition Addison Wesley 121 A L system Input Grammar Lfile Lsystems Lsystem Homomorphism Homoltems Homoltem HomoW arning HomoSeed Decomposition DecompW arning Decompltems ProdDepth Header BlankLines BlankLine Label Items gt if de Sade a de kA Lsystems BlankLines Lsystems Lsystem empty Header Productions Decomposition Homomorphism endlsystem lt newline gt homomorphism HomoW arning lt newline gt Homoltems Productions empty Homoltems Homoltem empty HomoSeed ProdDepth warnings no warnings seed Expression lt newline gt decomposition DecompWarning lt newline gt Decompltems Productions empty warnings no warnings ProdDepth empty depth Expression lt newline gt BlankLines Label Items Axiom BlankLine lt newline gt lsystem Characters lt newline gt Item 122 Item Seed Dlength Consider Ignore Characters Start
111. mand rcp After all connection are read all processes are started one by one using system command rsh rsh host cd tmp cpfg tmp XXXXXX setenv DISPLAY host 0 0 path binary connection params common params specified params amp amp The process path path is either specified or obtained using system command which The connection is specified by connection parameters connection params described at the beginning of this section C c confirm socket host of start m spec filel socketl s spec fileK socketK master hostK Each process obtains a socket confirm_socket to which it should confirm execution and send a character I upon termination Each master connection is defined by a socket and a specification file Each slave connection in addition needs the machine name of the master that sets up the socket Parameters common params are parameters shared by both processes communicating with each other specified with each connection in the example above g w 640 480 and specified params are these defined with the process The program start waits up to 20 seconds for the confirmation of a successful ex ecution of a process If it is confirmed the next process is spawned Otherwise all previously started processes are terminated by sending character K on their confirm socket This sockets is automatically monitored during calls to functions of the commu nication library Any ongoing communication is terminated and the process
112. mation from the environment 2 The environmental process reads the communication specification file connects itself to data streams confirms its initialization and waits for the first transmis sion from the plant simulator 3 The plant simulator starts the simulation and performs an environmental step to process the communication modules specified in the axiom The communi cation modules are transferred to the environment using the specified streams The last communication module in the string is followed by a reserved end of transmission message The plant simulator then waits for data from the environ ment 4 The environment recognizes the beginning of transmission by being able to read from a pipe or a socket or by checking a given semaphore and starts receiving the data After encountering the end of transmission message the environment processes the queries and starts sending the response back to the plant simulator The environment terminates the transmission by a similar end of transmission 64 Plant simulator Environmental process executed gt executed suspended sending confirmation start env step lt anne ees begin transmission suspended i V 7 V sending data receiving data V end of transmission y gt process data _ i suspended begin transmission V s V receiv
113. nd orientation vector as well as some other attributes such as the current line width e the type and parameters of the module following the communication module in the string module B in Figure 4 It is also possible to include the graphical represen tation of this module Specifically a set of triangles resulting from the interpretation of the module or of its homomorphic image Section 6 1 7 is transferred to the environment The environment processes the received information and returns the results to the plant model using messages in the following format e the address of the target communication module SThis section is incorporated from 2 It would be nice to have an option for having interpretation step both before and after the environmental step only before it or only after it 59 hofs environment MonteCarlo test runs interpret derive env step vee A ay 2 2E X 45 29 B Dy Dp turtle environment vee Ag 500058 E Y 4s Vm BlD4 4Bn Figure 4 Information flow during the simulation of a plant interacting with the envi ronment implemented using an open L system e values of parameters y carrying the output from the environment The plant process uses the received information to set parameter values in the commu nication modules Figure 4 Note that by preceding every symbol in the string with a communication module it is possible to pass complete info
114. ned func tions or typed variables It would be really good if the extent of labels was included in the bounding box computed by cpfg It would be helpful to be able to define a command that would be run for files before input and after output e g gzip 95 In case of textures do not limit the size to power of two e g some new machines can handle a size of a multiple of 2 Include a switch or create a bigger texture image with black boundaries and scale the texel coordinates Adding of depth test to postscript output Textures in the background scene It would be better if it was possible to avoid menus by pressing keys Especially when the menu causes expose event after it is closed At least to have a stop animation button Create an HTML version of this manual Enable user defined functions in cpfg Is there a way how to allow the user to specify a blackbox functions Add antialiasing For a more efficient visualization of environments add the possibility to send the visualization information images or GLS files through additional data stream or using the current communication process at the end after all Es are sent back to cpfg Use the OpenGL shared display lists for a more efficient displaying of predefined surfaces Switch between sub L systems or tables on a flag this could be done even now by using a global variable and having a production which would switch the sub L system if this variable is chan
115. nerated plant The primitives are read from a text file containing a list of OpenGL like statements Section 7 4 In the case where the environment is static it is sufficient to read the texture image or the background scene file once at the beginning of the simulation In the examples in this chapter though the environment is changing over time thus it is necessary to update the image or the background scene every time the environment changes Consequently the background file is periodically updated by the environmental process and read by the plant simulator after each simulation step before the visual ization To limit the amount of transferred data the environmental process can create the background files only at specific simulation steps The number of the current sim ulation step is sent by the plant simulator together with the message about the end of transmission after all communication modules from the string are sent to the environ ment see Section 8 4 4 8 4 Two process communication 8 4 1 Specification of the communication The communication between the plant simulator cpfg and an environmental pro gram is initiated when the simulator is executed with a command line parameter e 66 hofs environment density Cohen hofs environment soil 3d no avoiding tapered comm spec file The communication specification file comm_spec file is a text file with the following commands communication type pipes sockets
116. ng the polygons for spheres and cylinders For stems for example there is 27 polygons around the circumference A high value such as 4 will generate very smooth surfaces but take longer to display A lower value such as 1 the lowest produces very rough approximations to these surfaces If this line is not specified the default value is 2 This command is kept only for backward ompatibility Use contour sides instead contour i file defines a contour with integer id i specified by a set of 2d or 3d control points read from the file file For more details see Section 6 4 2 contour sides n determines the level of detail used in generating the poly gons for spheres and cylinders this initial value can be modified by module In the case of cylinders n n gt 3 polygons around circumference is drawn For spheres the closest upper power of two is used If you want to have smooth connections between cylinders and spheres for small values of n use a power of 2 If this command or command polygonization 38 hofs cpfg3 0 features interpretation gen_cylinders contours level is not specified the default value is 8 Make sure this command 1s not followed by command polygonization level later in the view file because then the parameter could be changed by the second command surface id name s x s t tex the character used to identify the surface a string containing the file name of the surface specification
117. ng the same output format In the case of string output both in the text or binary format the stored filename is also used as the default name for the input of the string Inputs data from the following formats String current string is read from a file of type text simple text format binary internal representation Both entries invoke a sub menu allowing the user to input from a file with the default name the name of the L system file with an appropriate extension or the file specified on the command line using str or strb or from a selected file In the second case a special window is opened allowing the user to browse through the current directory and select the input file The modified name is then stored and it appears as the default input name next time user want to input a string using the same format The stored filename is also used as the default name for the output of the string 14 Animate mode selects an animation mode which has its own menu see Section 5 2 Exit Exits cpfg 5 2 Animation menu The animation process begins with input of parameters including first frame last frame and step from the animation file see Section 6 3 If the animation file is not specified on the command line the animation parameters are set to its defaults i e the first frame is 1 the last frame is equal to the derivation steps specified in the L system file and the step is equal to 1 In the animation mode an
118. ng the same type of communication specified in the communication specification file In addition common command line parameters added to process executables com mon_parameters can be defined Processes are referred to by their name In the following example a drawing process draw_server named draw commu nicates with two modeling programs cpfg named tree and tree2 Both modeling programs are masters to an environmental process chiba named light simulating the local light environment shared by the two trees The specification file is listed below processes name draw files specs e command draw server r shaded name treel host ik files specs e tree e tree mat treel l tree v tree a leaf s command cpfg a M tree mat treel l tree v tree a display shere 101 ibrary MESA by Brian Paul available at http www ssec wisc edu brianp Mesa html 84 name tree2 host shere files specs e tree e tree mat tree2 1 tree v tree a leaf s command cpfg a M tree mat tree2 1 tree v tree a name light host ip files tree e light spec command chiba2 light spec connections draw gt treel tree2 specs g w 640 480 treel tree2 gt light tree e The program start operates as follows First it processes the specification file For each process run on a remote machine a unique directory tmp cpfg tmp XXXXXX is created on the specified host and all required files are copied into it using system com
119. nly it can be used also for specifying vertices of a polygon see the Section Symbols used to create polygons above If the generalized cylinder is started using symbol a control point is also defined after each f or F the same way as in the case of polygons the number of strips is then set to the default value of 4 Ge strips End a generalized cylinder The parameter strips controls the number of strips as for symbol Gc 30 type Finishes a generalized cylinder started by a module types The parameter type has to match the value of types If a new generalized cylinder is started be fore an old one is finished the result is undefined unless it is defined in a branch delimited by square brackets e g 4 1 1 4 3 1 3 1 1 EGt start end Multiplicative parameter for the length of tangents of a Hermite hofs cpfg3 0 features curve that specify the axis of the generalized cylinder between two consecu interpretation tive control points The tangent lengths are equal to the distance between the gen_cylinders two control points multiplied by the tangent coefficients the default value is tangents 1 2 Gr angle1 length angles length2 Specifies the slope and length of two tan hofs cpfg3 0 features gents of a Hermite curve which describes the change of radius of a generalized interpretation cylinder The command defines the angle of the tangent and its length for a seg gen_cylinders radii ment
120. oduction pa replaces the letter r by the string F l r and leaves the trailing F intact Thus the L system can be transformed as follows axiom Fl p lol rFt Pa r gt Fl r 16 Branching structures Branches in structures such as those shown in Figure 17 are delimited by the turtle symbols and The turtle saves its state at the start of a branch and restores it when the turtle reaches the end See page 24 of The Algorithmic Beauty of Plants 7 for more details The following section shows the L system file for the first plant Productions for the remaining structures are indicated in Figure 17 16 1 plant l lsystem 0 derivation length 5 axiom F F gt F F F F F endlsystem 105 F gt F F F F F F gt F F F F F F FF F F F F F F X F X F X X X gt E X X FX X F X X F FX X F FF F FF F FF Figure 17 Examples of plant like branching structures 17 Stochastic L systems All plants generated by the same deterministic L system are identical An attempt to combine them in the same picture would produce a striking artificial regularity Stochastic L systems provide for random variations that preserve the general aspects of a type of plant but modify the details Figure 18 shows several plants generated with the same stochastic L system except 106 Figure 18 Stochastic branching structures for different seed values 17 1 plants l lsystem
121. odules CTURTLE turtle static float zero 3 0 0 0 73 if turtle gt positionC lt 3 fprintf stderr Turtle position not set n return 0 if two_modules 0 num_params gt 1 two_modules 0 params 0 set 1 parameter modified two_modules 0 params 0 value Distance turtle position zero gt two_modules 0 params 0 value 1 0 return 1 void main int argc char argv CSInitialize amp argc amp argv CSMainLoop Answer CTerminate The function Answer determines the distance of the turtle position from the point 0 0 0 and if it is greater than the first parameter of the communication module the parameter is set to 1 Otherwise it is set to 0 The following example illustrates the second mode of operation when the incom ing communication modules queries have to be stored before their parameters can be modified The environmental program detects whether a communication module col lides with another one The program has been used in the model of Sierpinski s gasket from Section 8 1 The communication is defined by the following communication specification file executable point_collision communication type pipes o turtle position 5g 5g The environmental program is given below Environmental process testing point overlapping include lt stdio h gt include lt stdlib h gt include lt string h gt include lt math h
122. of the main material set or colormap multiplied by 256 usually the colormap index is equal to 1 and all surface indexes are increased by 256 If cpfg uses materials all material components except emissive color are included in the surface definition The transparency parameter only one per surface not like in OpenGL where each color can have its own alpha channel is determined from the alpha value of the emissive color If cpfg uses a colormap only ambient and diffuse colors are specified both equal to the r g b color values specified by the colormap 7 1 2 View parameters and lights The view and lights set in the rayshade file correspond to the view and lights set by the cpfg s view file The object is rotated and scaled so it is oriented the same way as on the screen using a transformation matrix specified together with the instance of the object at the end of the rayshade file Only perspective projection can be defined in the rayshade file Consequently the parallel projection used by cpfg has to be converted to perspective projection This process often produces views which are inconsistent with the view on the scene For the best results it is advisable to use perspective projection in cpfg if the plant is to be output to rayshade 7 1 3 Bounding box To be able to preview a scene that consists of a vast number of plants it is very con venient to use only a box representing the bounding box of the plant Note that the
123. olor index associated with the cylinder is the diffuse refection coefficient V is the normal of the polygon and L is the direction towards the light source the resulting index is index col i L surface ambient x a number between 0 and 1 indicating the amount of am bient light present for shading bicubic surfaces and tsurfaces This command is effective only if the program is running in the colormap mode In the ma terial mode materials specify ambient light for surfaces See the following command for the description of computing the resulting color surface diffuse x a number between 0 and 1 indicating the amount of dif fuse light present for shading bicubic surfaces and tsurfaces This command is effective only if the program is running in the colormap mode In the material mode materials specify diffuse light for surfaces The color of a polygon representing a surface is chosen in the following way If col is the color index associated with the surface int is the intensity of the color int col 64 floor col 64 amb is the predefined ambient intensity di f f is the predefined diffuse intensity di f f x N is the normal of the polygon and L is the direction towards the light source the resulting index is index 64 int amb dif f abs N L background color red green blue the background color specified as red green and blue components In cpfg version 3 0 and above this command is ig nored
124. on 8 4 1 void CTerminate void Ends the communication this should be the last call in the function main If the parameters of a communication module can be modified immediately the following function can be used void CSMainLoop int Answer Cmodule_type CTURTLE The parameter of the function C S Main Loop is a mapping function Answer The mapping function modifies the parameters of the communication module stored in a two dimensional array pointed to by the first function parameter which also includes the module following the communication module The sec ond parameter of the function contains the received turtle parameters If the environmental program calls the function CSMainLoop with a mapping func tion as the parameter the communication is fully controlled by the communication part of the modeling system The function CSMainLoop returns when the plant simulator sends a message to terminate the environmental program The environmental program can then clear its local data structures and call CTerminate see the first example in Section 8 4 5 If the incoming query cannot be answered immediately the following functions have to be called in a specific order see Figure 8 and the code listing below int CSBeginTransmission void Starts transmission of all communication modules in the string generated by the plant simulator The process waits for the plant simulator to perform a simulation step and to s
125. ontour in Section 6 2 A contour with id 0 is the default circle Unlike gen_cylinders in case of textures or tropisms contour id is specified in the view file foreach contours contour separately and it does not depend on the order of commands contour polygons Sets the number of polygons around a generalized cylinder or a cylin der that is represented by F or G Changing tropisms parameters 31 OTs index value Set elasticity parameter of tropism with index index to value Index is given by the order of the tropism specification in the view file starting with 1 Td index value Decrease the elasticity parameter by the default elasticity incre ment specified in the view file or by the given value value Ti index value Increase the elasticity parameter by the default elasticity incre ment specified in the view file or by the given value value Tp Prevent twist This command adjusts the turtle s up and left vector to minimize the twist 3 This command operates locally i e it adjusts the turtle s vectors only at the current point Tf Force the twist If the orientation of a segment following symbols or is adjusted due to a tropism which as a default adjusts the segment s up vector to prevent twist the effect of the symbols or is nullified In such cases it is necessary to add the symbol Tf to force the twist This command operates localy i e it prevents twist only for symbols or to the left of
126. or near only l or n can be used When set to linear texture image is smoothed while setting to near makes the texture pixels visible The default is near L filter for textures with texels smaller than image pixels The pa rameter filter is either linear or near only l or n can be used When set to linear more texture pixels are used to compute the given pixel while for near just one texture pixel is used to com pute the given pixel which may result in aliasing It is also possible to use mipmaps in which case the OpenGL library creates a smaller version of the texture down to a size of 1 x 1 and for smaller objects uses the smaller texture resulting in faster dis playing There are four modes of operation when selectin a proper textel pixel mnn take the nearest mipmap image and the nearest pixel in this mipmap Produces some artefacts visible especially when moving object around or scaling it but it is the fastest mln take the nearest mipmap image and the linearly interpolate between neighboring pixels still produces some artefacts mnl take the nearest pixels in both best choices of pixmaps and interpolate between the values 41 mll linearly interpolate between neighboring pixels in both best choices of pixmaps and interpolate between the values Pro duces the best result but may be slower If just m is used the mll mode is selected The default is near E The parameter mode is one of the following
127. ordinates the environmental process sends the value O to the plant model Otherwise the parameter of the communication module stays unchanged and there is no reply by the environment 8 4 6 Troubleshooting During the design of a model it may be necessary to find out whether proper data are transferred between the environment and the plant simulator To view the exchanged data it is possible to use the file communication and to display the content of files to fieldXXXX 0 and to fiel dXXXX 0 If the amount of transferred data is too large though the data are transferred from one process to the other in several chunks each stored in a file with the same name Thus the user can access only the last chunk of data The maximum size in the number of modules of the data file is predefined but it is possible to increase it to a value large enough so that there is only one communication file used during the data exchange by adding a number behind the keyword file in the specification file Often it is also necessary to debug the environmental program The debugging is much easier if the program is running in a stand alone mode without the plant simu lator To achieve this it is possible to use the pipe communication and to run only the environmental program while inputing the data to the standard input and receiving the response on the standard output The input data can also be redirected from a file This file can be either created in a te
128. ormat_string turtle heading format_string turtle left format_string turtle up format_string turtle line width format_string turtle scale factor format_string These commands define C like format strings for those turtle parameters which are sent to the environment currently only the parameters listed above can be transferred Often only the position and the heading vector are necessary and the rest can be omitted Since the information is being sent in a text format it may be desirable to use only a few decimal places or to omit the z axis when possible For example commands turtle position P 3f 3f turtle heading H 1f 5f Tn the current version of the program cpfg the default value is yes 67 specify that only the x and y coordinates of the turtle position and heading vector are transferred to the environment as floating point numbers with the precision of 1 3 or 5 decimal places Letters in format strings are helpful for debugging purposes when using files for the communication but they are not mandatory interpreted modules all or M n1 M n2 Mn mn Itis possible to include a set of polygons representing module X following the communication module E with the data transferred to the environmental process The module X is interpreted when e only the word all is specified e n is not present and M X or e M X and X has n parameters currently it is not possible to specify ni g
129. oses Figure 5a Now the environment re ceives two modules address 4 E 0 position 0 5 0 866 0 address 7 E 0 position 0 5 0 866 0 These two points do not collide and the environment again does not reply Step 2 In the next derivation step production p is applied to both modules E result ing in the string F 180 F 180 E 0 F2E 0 F F 180 E 0 F E 0 visualized in Figure 5b In the following environmental step the environment receives four modules address 8 E address 11 E address 18 E address 21 E position 0 1 7321 0 position 1 1 7321 0 position 0 1 7321 0 position 1 1 7321 0 61 A A KA M Figure 5 Sierpinski triangle generated by open L system 3 in 1 2 6 and 32 steps Since the first and third module occupy the same point the environment returns a mes sage in the form address 8 E 1 address 18 E 1 The plant simulator receives this message and updates the parameters of the specified communication modules resulting in the string F 180 F 180 E 1 F2E 0 F F 180 E 1 F E 0 Step 3 In the next derivation step only the second and fourth module F is replaced by a pair of branches resulting in a structure shown in Figure Sc The simulation then continues generating a branching structure which is similar to the Sierpinski gasket Figure 5g The implementation issues related to
130. otated How about having the system call incorporate additional variable values using an sprintf Make it possible to access view parameters from productions 97 Part II Examples This section contains examples of many models created by cpfg The input files for these examples are included with cpfg and can be conveniently examined and experimented with using the Virtual Laboratory framework vlab Instructions for getting the Virtual Laboratory distribution are given in Section 3 12 Quadratic Koch island Figure 9 shows several approximations of the quadratic Koch island from The Algo rithmic Beauty of Plants 7 page 8 They were generated with the command cpfg koch l koch v The files contents are detailed in the following sections 12 1 koch l lsystem 0 derivation length 3 axiom F F F F E gt PEF E EPHEFPSE endlsystem This L system introduces three turtle symbols F and The F symbol causes the turtle to move forward and draw a straight line The and symbols cause the turtle to turn counter clockwise and clockwise respectively The amount that the turtle turns 90 in this example is specified in the viewing file Section 12 2 The axiom F F F F draws a square The production F gt F F F FF F F F replaces each line segment with a shape as shown in Figure 10 Note that there are no productions for the and symbols Symbols with no replacement productions are replaced w
131. our for diffuse color four for specular color four for emissive color and one for specular exponent a value between 0 and 128 The alpha value controls the opacity of the surface 1 for opaque O for transparent This material is applied to all subsequently defined primitives Transformations All primitives are defined with respect to a local coordinate system The system can be modified by transformation statements listed below The coordinate system is expressed by a single matrix specifying the transformation necessary to map the world coordinate system into the current local system Thus every rotation translation or scaling modifies only the current transformation matrix This approach is equivalent to the use of the modelview matrix in OpenGL 8 loadidentity sets the current transformation matrix to identity i e the current local coordinate system is equal to the world coordinate system loadmatrix a dg 416 sets the current matrix The first four values spec ify the first column of the matrix next four the second column etc pushmatrix stores the current transformation matrix on a matrix stack popmatrix retrieves a matrix from the stack and sets it as the current transforma tion matrix translate txtytz translates the local coordinate system by vector tx ty tz by modifying the current transformation matrix rotate angle vx vy vz_ rotates the coordinate system around vector vx vy vz by angle degree
132. pecial working modes g pipestrb Performs an off screen rendering A colormap or a material file must be specified i e the off screen rendering does not work with hardware colormaps If the switch a is not included cpfg will generate the string up to the last generation step defined in L system_file and save particular files as specified by rgb ras etc With switch a all frames as defined in the animate file are saved It is recommended to specify filenames as format strings e g plant 03d rgb ADD Format strings are used in a few other places It would be nice to have a section explaining the general setup along with us age examples The program uses the off screen mode and converts a binary L system string file coming on stdin into a desired format as spec ified by options rgb ras etc which can be output also to stdout except for image formats by specifying the word stdout as a filename for a selected format If a is present further generation as specified by animate file is performed The option pipestrb can be used for example to pipe stored strings directly to rayshade and avoid keeping big rayshade files C communication_setup_string Specifies connections to other processes in a dis S socketnum 4 4 Output rgb rgb_file tributed simulations The communication setup string is a single string with no spaces Each connection starts with a symbol z where x is one of m s and c follo
133. r the whole polygon Otherwise the colormap is used In the 36 case of cylinders or generalized cylinders the color of the polygon is chosen from interval col dif f_refl col dif fre fl where col is the color index associated with the surface and dif f_refl is a range defined using command diffuse reflection see below The color is chosen according to the position of the polygon with respect to the direction towards the first light source other sources are ignored In the case of surfaces and tsurfaces the color selection is more com plicated see command surface reflection below shaded similar to mode flat If materials are specified the normal for each polygon representing a surface can be different at each vertex of the polygon resulting in a smooth shading If colormap is used a color is computed for each vertex of the polygon see the commands diffuse reflectionand surface diffuse below z buffer flag a string identifying whether hidden surface elimination using z buffer should be provided on or not of cue range x anumber specifying the range of color indices used for depth cue ing A value of 0 indicates no depth cueing Usual values of n are 10 to 100 Depth cueing is not used in versions 3 0 and higher font Xfont Xfont specifies the font type to be used in UL interpretation using the X font specification If the font is not found or not specified the default is courier bold r 2 HH
134. rams loadmap and savemap do not recognize the type of the screen and try to load or save the second 256 entries Thus it maybe necessary to use command line parameter c0 both with Lloadmap and savemap You can also use command line switch m with a colormap file or switch M with a material file but in this case the low number of bits per pixel will significantly reduce the quality of the output the image will be dithered At least use a single buffer mode command line switch sb to increase the number of bit planes allocated for each pixel in double buffered mode the number is divided by two e g 4 bits per front and 4 bits per back buffer as compared with 8 bits in a ingle buffer mode 10 3 Use of symbol in the L system file Make sure that the symbol does not appear as the first symbol on the line in an L system file or the first symbol after tabs or spaces Otherwise the preprocessor tries to recognize it as its command and the reading of the file fails If you would like to use a production with as the predecessor add an empty left context such as in x lt wid gt wid x 0 9 Also make sure that in the case of multiple line successors the new line does not starts with and move the module to the previous line 10 4 Transparent objects The support of transparent objects is not very strong in OpenGL To render transparent objects correctly it is necessary to perform two passes through the objects first draw t
135. res sure gives a lot more scope for making images but its slow on old machines It d be nice to have textures off during rotations or something It would be nice to enhance rotation speed by allowing for a different mode while the object is being rotated Sub L systems should have names instead of the cryptic numbers Fixes to the manual Section 7 4 need to say under what conditions which of the statements appear assumedly by reference to the view file parameters Although currently cpfg outputs the viewing parameters in a single projection matrix Format strings are used in a few places It would be nice to have a section explaining the general setup along with usage examples It would be nice to include an example of rayshade instancing o gt productions where turtle s parameters are considered Regarding the manual describing environmental programs it may be nice to in clude an example of the environment argument file in the description this is optional because an example is a part of the vlab object that you point to an example anyway Suggestions for future extensions or improvements It would be nice to have an option for having interpretation step both before and after the environmental step only before it or only after it Global homomorphism is not implemented Right now each L system has its own homomorphism productions page 24 Extend the programming language by incorporating structures user defi
136. ring takes precedence because buffer ing has to be set at the point of execution using command line parameters and cannot be changed afterwards The only effect the command double buffer has is to set single buffering even if the program starts with two buffers clear between frames flag specifies whether screen clearing between frames is on or of f The default is on scale between frames flag Ifthe flag is on the view is adjusted in paral lel projection only so the whole structure fits into the window before the scaling is applied see command scale in the view file The default is off new view between frames on off Ifthe flag is on the view file is reread after each simulation step Consequently the view textures and all parame ters specified in the view file are updated Used for example for updating a background scene or a texture used for visualizing the environmental field The default is of f swap interval i minimum time in tenth of a second between swapping of buffers in double buffer mode The time is measured from the moment cpfg begins to draw the frame to the moment it begins to draw the next frame If it takes longer to draw a frame the delay between frames is then longer The default is 1 first frame i derivation step of the L system string to be interpreted as the first frame The default is 1 last frame i derivation step of the L system string to be interpreted as the last frame The def
137. rmation about the model to the environment Usually however only partial information about the state of a plant is needed as input to the environment as illustrated in the example below In addition the use of addresses makes it possible to send replies from the environment only to selected communication modules Proper placement of communication modules in the model combined with careful selection of the information to be exchanged provide a means for keeping the amount of transferred information at a manageable level You can use the communication modules in homomorphism productions but only to send information to the environment The environment will not be able to respond because these modules exists only temporarily during the application of homomor phism to a given module It is fine to use the communication modules in decomposition productions The following simple example illustrates the operation of an open L system The model creates a branching structure consisting of straight line segments The structure grows by adding a pair of segments to the end of existing branches unless a branch col lides with another one The occurrence of a collision is determined by the environment To accomplish its task the environment receives the information about the position of segment s end points and tests whether two points occupy the same place or not The listing of the environmental process can be found in Section 8 4 5 60 hofs Thesis
138. ropisms 53 k a AS a OM ee oP eS Animation file como e eA ee k bd 2s Other input Mes ae ce ek ii a aA A drby rn 6 4 1 Surface specification file 6 4 2 Contour specification file 6 4 3 Tsurface specification file 6 4 4 Textureimagefile o a 6 4 5 Background scene specification file 7 Output files 7 1 Rayshade OU put soe ae ee ae ew Vello Materials y seg 5 dates ta DA Srb LE 7 1 2 View parameters and lights 7 1 3 BOUDIN Boxes cri s a a sk Be a ola 7 1 4 Predefined surfaces o o 7 1 5 Instantiated Objects o o 7 1 6 The main object o o 7 2 Postscript output e 73 L system Sting cra ee Soke ee oby la 7 4 Graphics Library Statements format TO Inventoroutput 6 6 4 4 sed 1578 WA EE A Sk ee dk M 8 Communication with environmental process 8 1 Open L systems z 4 k u 4 de ke bd eee AA SEES 8 2 Implementation of the modeling framework 8 3 Visualization of the environment o 8 4 Two process communication lt lt lt lt lt 8 4 1 Specification of the communication 8 4 2 Environmental process o e 6 43 DatasSthuctures 2 oo ta nb B e RA t 8 44 Library functions lt lt SAD Examples s 08 diia a EES 8 4 6 Troubles
139. rtle parameters of the interpreted and stored module differ the module s geometry is output to the file If the module is found in the hash table only the reference to the predefined object is included in the rayshade file To properly position and orient the object the reference to the object is followed by a transformation matrix capturing the current turtle position and orientation 9 2 Sending commands to cpfg through sockets It is possible to control the interactive operation of the plant simulator cpfg by sending the commands through sockets Each menu item has a corresponding command This functionality allows the user for example to modify the L system file view file or any other input file by an external program and then send a command corresponding to the cpfg menu items New L system or New View Thus the displayed model can be updated without interactive participation of the user Note that this functionality is available only in the interactive mode of operation 89 hoofs cpfg3 4 exam ples socket commands To be able to send the commands to cpfg it is necessary to execute it with a com mand line switch S followed by an arbitrary number specifying the socket cpf y M plant mat S 3000 plant plant v Afterwards the user can send an arbitrary command representing a menu item to the plant simulator by using a program command_client The program has two pa rameters the first one specifies the network name of the ma
140. s scale sx sy sz_ scales the local coordinate system by factors sz sy and sz in axis x y and z multmatrix aj az dig multiplies the current transformation matrix by specified matrix Example A sample background scene is specified below material 0 1 0 1 0 1 1 subsequent surfaces are grey 0 16 0 21 0 27 1 with no specular reflections 0001 and no emissive color 00 10 0 50 pushmatrix translate 3 20 3 scale 1 0 7 0 7 sphere 15 ellipsoid popmatrix pushmatrix translate 14 55 0 8 cone 15 2 14 cone popmatrix translate 10 65 0 box 30 5 30 box The file is preprocessed by cpfg thus macros or comments can be part of it The format of the background scene file is also used in transferring the polygons representing selected modules from the plant simulator to the model of the environ ment In addition the same format can be used for the output of the generated struc tures from the plant simulator in which case the file also includes statements specifying light sources and the projection Section 7 4 51 7 Output files The cpfg menu allows the user to save output files in a number of different formats Output file names can be specified on the command line with defaults derived by re placing the suffix of the L system file with a different suffix rgb ras tga rle ray ps str strb gls vv or iv depending on the format chosen The file nam
141. scaled when the cpfg window is resized If pixels or just p is listed flat shaded lines are drawn with their width in pixels or screen units If shaded or simply s is listed lines are drawn as shaded cylinders in world units In versions 3 0 and higher line style should 34 be set by command line style see below in Section Lines surfaces and generalized cylinders line width increment x a number specifying the line width increment as sociated with the symbols and with units taken from the initial line width specification initial scale x the parameter x specifies the initial scale factor associated with the turtle the default is 1 All geometry will be scaled by this factor This initial value can be modified by modules D Di and Dd scale multiplier x modifies the default value 1 of the multiplicative factor by which the turtle scale is multiplied or divided when module Di or Dd 1s interpreted 6 2 2 Setting the view viewpoint x y z x y and z coordinates of the view point in world space view reference point x y z x y and z coordinates of the view reference point in world space twist 1 tenths of degrees to rotate the image on the screen projection type type identifies the desired projection either parallel or perspective Perspective viewing mode is the preferred mode to use if you intend to save a rayshade format object since rayshade also uses perspec tive viewing Auto centering and auto s
142. seed i derivation length d ignore symbols axiom axiom Icontext lt predecessor gt rcontext a C 8 gt successor p Icontext lt predecessor gt rcontext a C B Y gt successor po Icontext lt predecessor gt rcontext a C B gt successor Pn endlsystem The new first line specifies the integer seed 2 for the random number generator Each production has a probability factor represented by the floating point value p associated with it See The Algorithmic Beauty of Plants 7 page 28 for more information 6 1 1 Variables Variable names are defined as in C There are two types of variables float and character string but character strings require special handling as they are passed by reference The variables are defined in the whole scope of an L system Often if a variable is used in a production it has to be defined in There is a block structure controlling their scope There is a special definition section for arrays which are indexed as in C Section 6 1 4 ADD Jim an explanation of the external statement that can now appear in the define section of cpfg Basic syntax is the keyword external followed by a comma separated list of variable names and array definitions The arrays require their dimen sions to be specified I believe 6 1 2 Programming statements There are three types of statements which can be included in L system productions e The first type is represent
143. shown below lsystem label derivation length d ignore symbols axiom axiom Icontext lt predecessor gt rcontext a CY B gt successor Icontext lt predecessor gt rcontext a y C B gt successor Icontext lt predecessor gt rcontext fa C B gt successor homomorphism no warnings seed s maximum depth d Icontext lt predecessor gt rcontext a C B gt successor 22 hofs cpfg3 0 features homomorphism Icontext lt predecessor gt rcontext a C 4 B gt successor Icontext lt predecessor gt rcontext a C 4 B gt successor endlsystem It is possible to repeatedly apply the homomorphism productions to the resulting homomorphism image of a module To enable this operation the keyword maximum depth should follow the keyword homomorphism The value d then specifies the maximum depth of application of homomorphism productions to avoid an infinite recursion A warning is issued if the maximum depth is reached and it is possible to further apply the homomorphism productions only in version 3 4 and higher This warn ing can be avoided by specifying an optional keyword no warnings following the keyword homomorphism homomorphism no warnings which is equivalent to homomorphism kept for backward compatibility It is possible to use only the keyword warnings to specify that the warnings are switched on homomorphism warnings A
144. size in number of voxels In this case there are several objects defined and the main object is defined at the end of the rayshade file as a list of the parts specified by the 2J module The objects use references to surfaces and instantiated parts defined earlier in the rayshade file In addition itis possible to define a reference to a rayshade object defined in another file by specifying the name of the object as a parameter of the module see also Section 6 1 9 In this case an instance of the object with the given name is created at the current position with the orientation given by the turtle and the scale specified as the second parameter of module EJ Before the instance of the main object is defined at the end of the rayshade file after the ifdef NOHEADERS statement the object is possibly scaled using the scale param eter defined in the cpfg s view file using the command rayshade scale Note 1t is usually better to use the parameter turtle scale the view file command initial scale which affects all primitives and the final scaling is not necessary Note that cylinders and cones are defined as a single primitive thus they always appear smoothly shaded Also the rayshade format does not support double sided surfaces thus if a sur face has associated two different materials in cpfg in the rayshade file only the top material is specified for this surface Rayshade reports triangles with edges shorter than 0 00001
145. stantiation 25 128 maximum depth 24 warnings 24 inventor output 10 L system environmentally sensitive 34 main 22 open 34 62 sub L system 22 L system file 7 light 42 line 40 material table 7 8 menu animation 15 main 13 menu bar 8 overlay menu 8 module communication 34 62 off screen rendering 8 pixmap 8 polygon specification 30 postscript output 10 preprocessor 6 production multiple sets 22 programming statement 18 projection 37 rayshade 40 rayshade output 10 string input from stdin 9 output 10 59 surface 41 drawing 31 specification file 48 texture 43 tropism 45 changing parameters 33 tsurface 41 specification file 49 turtle parameters changing 28 setting 36 rotations 27 scale 29 37 variable global 20 verbose mode 6 view file 7 36 view parameters 37 warning mode 6 window position 8 size 8 13 title 8 129
146. ster if CMSendCommSymbol slave module_id two_modules amp turtle send graphics while CSGetString amp master string sizeof string CMSendString slave string check for possible response while CMGetCommunicationModule slave amp module_id amp comm_module retrieve the master master comm_module params 0 value do not change the first parameter comm_module params 0 set 0 CSSendData master module id comm module F M ndTransmission module id process the rest for slave 0 slave lt CMGetNumberOfSlaves slave while CMGetCommunicationModule slave module_id amp comm_module retrieve the master master comm module params 0 value do not change the first parameter comm_module params 0 set 0 CSSendData master module id comm module 82 if CSEndTransmission break BOK KKK oko k KK k kok I k kok k kok k K I kk k X k X k X k kk k void main int argc char argv establishes all connections according to C parameter CSInitialize amp argce amp argv MainLoop CTerminate The two sections below describes the function of an initialization program start and a simple drawing program draw 8 5 2 Initialization program Program start reads in a text specification file and executes a set of communicating processes The program takes as a parameter the name o
147. t 6 If homomorphism or decomposition productions can be applied to the module X Section 6 1 7 all geometry created by these productions is sent to the environ ment The geometry is transferred as a set of polygons in a text format see the output format of OpenGL like commands described in Section 7 4 verbose on off Switches on or off the verbose mode which informs the user about the details of the communication 8 4 2 Environmental process Flow of information An environmental process communicating with the plant simulator operates as a slave i e the communication is controlled by the plant simulator the master Gen erally the environmental process waits for the data from the plant simulator The data consists of a communication module its address and possibly turtle parameters or the module following the communication module Afterwards the process sends back the communication modules with modified parameters and waits for new input in a loop There are two possible modes of operation of an environmental process Figure 8 1 immediate answer the parameters of a communication module obtained from the plant simulator can be updated immediately because the results depend on the local properties of the environment and do not depend on the other communi cation modules This mode of operation is suitable for example for simulation of static environments that are too complex to be expressed in environmentally sensi
148. t correspond to the view in the cpfg window e Textures are supported although Inventor always smoothens the texture image Consequently it is not possible to have a sharp chessboard texture for example e Regardless the used rendering mode shaded flat wireframe etc the resulting objects are always smoothly shaded e Cpfg generated Inventor files have sometimes too big memory requirements possibly related to too many items in a group e Directional lights do not convert properly to Inventor output they are defined as a very distant point source e If a predefined surface is not included in the view file the created input file cannot be viewed the viewer does not read such a file ADD Specify under what conditions which of the statements appear assumedly by reference to the view file parameters Although currently cpfg outputs the viewing parameters in a single projection matrix 58 8 Communication with environmental process 8 1 Open L systems Open L systems are a generalization of the concept of query modules P H L and U used in environmentally sensitive L systems 6 see also Section 6 1 9 Com munication modules of the form E x1 tm are used both to send and receive environmental information represented by the values of parameters 21 m Fig ure 4 Specifically parameters x m act as an interface between the plant and the environment They can be set by the plant model and transferr
149. te 6 4 2 Contour specification file A contour specification file defines the cross section contour of a generalized cylin der As a default the contour is a disk It is possible to use an arbitrary contour defined as an open or closed three dimensional parametric curve consisting of several B spline segments The contour curve is specified by a set of control points Each control point is defined by two coordinates in which case the third coordinate is assigned to be 0 or by three coordinates The file starts with a single header line num_points dimension type where value num_pomts specifies the number of control points in the file value dimension controls the dimension of the contour 2 or 3 and word type is either open for open contours or closed for closed contours An example of a contour file follows 12 3 closed 0 16 1 12 2 0 0 41 1 04 1 0 0 38 033 05 1 08 0 04 0 2 1 08 0 49 0 0 0 49 0 54 0 0 0 33 0491 01 0 37 1 04 0 3 0 70 0 62 0 2 1 12 0 16 0 1 0 87 0 74 0 3 0 41 0 66 1 0 It is recommended to specify the control points in the counter clockwise order with respect to the point 0 0 0 because interpolation between clockwise and counter clockwise contour results in a twisted generalized cylinder Note that ff a contour includes some singularity e g a sharp edge created by having three control points at the same location the normals are not correct 6 4 3 Tsurface specification file
150. the environment This menu item appears only if a switch e environmentfile is included in the command line cpfg communicates with an environmental program May cause problems if the environmental programs relies on the data from previous simulation steps Window size Allows the user to set the size of the output window Output Allows access to a sub menu of output file formats 13 Input Image Saves the image in the window in various image for mats RGB SGI rgb format RAS SGI colormap format TGA TrueVision Targa format RLE Utah Raster Toolkit image format Rayshade rayshade 4 0 scene description file Postscript Postscript scene description file String current string in two formats text simple text format binary internal representation GLS format graphics library statements format View Volume bounding volume information Inventor SGI Inventor format object See Section 6 and Section 7 for more detail on file formats Each of these entries invoke a sub menu allowing the user to save using a default filename the name of the L system file with an appropriate extension or the file specified on the command line or to save under a different name In the second case a special window is opened allowing the user to browse through the current directory and select the output file or to type in the name The modified filename is then stored and it appears as the default output name next time user want to output the structure usi
151. them by translating or scaling the coordinate system using transformation statements see below polygon 11 Y 21 Un Yn Zn specifies a polygon with n vertices a1 41 21 to En Yn Zn n gt 3 hofs cpfg3 0 features interpretation gen_cylinders background_scene polygonuv 1 Y 21 NT NY NZI Tn Yn Zn NEn NYn NZn Specifies a polygon with n vertices 1 Y1 21 to n Yn Zn n gt 3 Each vertex 7 has also associated a normal nzi nyi nzi rectangleab defines a rectangle with one vertex in 0 0 0 and edges of length a b along the positive axes x y respectively mesh 11 Y1 21 En Yn Zn specifies a rectangular mesh vertices 2k 2k 1 2k 3 and 2k 2 define a single rectangle of the mesh n 4 2k k gt 0 boxabc specifies a box with one vertex in 0 0 0 and edges of length a b and c along the positive axes x y and z respectively cone r1 ra h specifies a cone with its axis along y axis radius at the base equal to r radius at the top equal to r2 and height A cylinder r h specifies a cylinder with its axis along y axis radius r and height h sphere r specifies a sphere with center at 0 0 0 and radius r Material specification There is only one statement in this group 49 material ni n2 n17 specifies the current material using 17 values that follow the keyword material four values for ambient color red green blue and al pha all in the range of 0 1 f
152. tions 13 1 snowflake l lsystem 0 derivation length 3 100 Figure 11 Snowflake curves axiom F F F F gt F F F F endlsystem The axiom F F F draws a triangle The production Basso PLP PFE replaces each line segment with the shape shown in Figure 12 101 Figure 12 The production F gt F F F F 13 2 snowflake v angle increment 60 The and commands for this L system rotate the turtle by 60 The viewing file for the snowflake is identical to that for the Quadratic Koch island except for the different angle increment 14 Combination of islands and lakes Figure 13 illustrates an application of the turtle symbol which moves the turtle forward but does not draw a line The L system used to generate this image is shown below 14 1 lakes l lsystem 0 derivation length 2 axiom F F F F E gt F f FF F FF Ff FF f FF F FEF FfC FFF E gt EFEFEF endlsystem The axiom F F F F draws a square The production E gt F f FF F FF Ff FF f FF F FF Ff FFF replaces each line segment with the shape shown in Figure 14 102 E P a o ean aa o Tea keane s Teer eva aaa e qa ar z geo a a au JU J Oo Figure 13 Islands and Lakes Figure 14 The production F gt F f FF F FF Ff FF 1 FF F FF Ff FFF 1
153. tive L systems 68 hofs environment MonteCarlo test runs after new simulation step CSBeginTransmission Input comm module CSGetData CSGetString 5 new module simulation step is irrelevant AnswerQuery Input comm module CSGetData CSGetString Y Process Process Update environment Output comm module CSSendData Output comm module CSSendData El CSEndTransmission Immediate answer Delayed answer Figure 8 Two possible modes of operation of an environmental process 2 delayed answer the reply depends on the information obtained from other communication modules in the string due to the propagation of information through the environment Thus all communication modules from the string have to be first input and stored in internal data structures before the parameters of the communication modules can be properly set This mode of operation is usu ally used in the case the plant is affecting the environment because the response then depends on changes in the environment introduced by other communication modules The functions used to control the flow of information to receive the data from the plant simulator and to send data back shown in Figure 8 are discussed below 8 4 3 Data structures Let us first overview the data structures used for the data exchange The information about selected turtle parameters is received in the structure CTURT
154. uery master module id two modules amp turtle store all or some of the queries do not forget to store values of master and module_id while CSGetString 6master str sizeof str ProcessGraphics master str process the graphical representation of the module following the communication module DetermineResponse determine the answers SendBackResponse send back modified communication modules using CSSendData master module_id amp two_modules 0 if CSEndTransmission break Functions StoreQuery ProcessGraphics DetermineResponse and SendBackResponse have to be defined by the user depending on the data structures chosen for storing and processing the incoming communication modules In the case of a two process com munication the parameter master may be ignored and for function CSSendData set to 0 To be able to use the program in a multiprocess environment see Section 8 5 the parameter master should be stored as well The second example in the following section illustrates the use of the functions listed above 8 4 5 Examples Two simple examples of an environmental process are presented below The first ex ample illustrates the case when the parameters of the received communication module can be set immediately thus the program uses the function C S Main Loop include lt stdio h gt include comm_lib h int Answer Cmodule_type two_m
155. wed by several parameters divided by commas The three types of connections are m fora master connection cpfg controls the data exchange with the given program The switch m is followed by a communication specification file for the given connection and a socket number m comm_spec file socketnum The same file and socket number has to be specified for the slave process s fora slave connection the other program controls the data exchange The switch s is followed by a communication specification file for the given connection a socket number and the name of the machine on which the master process 1s running s comm _spec_file socket num master machine The same file and socket number has to be specified for the master process c connection to a process controlling the whole simulation The program cpfg confirms its successful execution by sending a predefined character through this connection The switch c is followed by a socket number and the name of hoofs cpfg3 2 exam ples Distr environ the machine where the main process is running c socket_num machine See an example in Section 4 5 and more details on the distributed simulations in Section 8 5 The program is able to process text commands corresponding to menu items coming through the specified socket using program command _client see Section 9 2 Specify name for the 24 bit SGI RGB image file Note that any window that appears on top
156. xt editor or obtained from files exchanged between the processes during a regular simulation which uses the file communication Running the environmental process in the stand alone mode then follows these steps 1 The simulation is first run with the plant simulator using the file communication Each time the simulation is stopped it is possible to concatenate the data file to fieldXXXX 0 the data sent to the environment in the last data exchange to a file to_field which is of zero length at the beginning of the simulation It is also possible to choose the data file from only one simulation step 2 The user may change the content of the file e g edit some values or add a message terminating the environmental process by including a line containing the string Control 8 to the end of the file to_field 3 The environmental process can then be run separately by setting the communi cation type to pipes and redirecting the file to_field to the standard input environment e comm_spec file lt to field The program writes all modified communication modules to the standard output in a text format 77 8 5 Distributed system In a distributed system several plant models can communicate with different environ mental processes and then send the graphical interpretation of the models into a single drawing window Each program in the system has to be compiled with the provided communication library Since the programs can

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