XCRayt: the scene descriptor User's Guide
Contents
1. or if you have started to create a scene this is shown in the View sector under the default parameters of camera and the object list is abled It allows you to select any item in the scene see fig 1 3 The hierarchical structure of the objects is shown by an icon near to every item and indented on the left you will see its sub items To select an item click on it with the left mouse button All and only the functions regarding that item will then become active Its relevant textbox as well as the bars adds functionality enabling the user to select all the objects The associated textbox serves to select an object by name The following paragraphs describe all the functions provided according to object type in the object list 1 2 Camera When selecting Camera in the Object list this is the default selection that appears with the Object list sector all the functions relating to it are abled in the XCRayt window see fig 1 3 More precisely the Control sector and some of the buttons in the Buttons sector 1 2 1 Control sector The viewing direction is determined by the position of the camera and by a scene point As can be understood from the label the left four arrows cursor serves to position the camera while the right serves to position the scene point These two parameters are reported numerically in the textboxes below from which they may also be varied The X Y and Z textboxes on the right have a further function in helpi2. 2 Open Animation Control panel file which describes a scene or project From its directory site and name XCRayt deduces where to look for the scene components surfaces or objects are simple or trimmed NURBS surfaces or lists of simple or trimmed NURBS surfaces These are respectively stored in files with db dbe and obj extensions The file names are included in the scene description file md see Data file for mats section camera data consists of camera position scene point view up view volume included in a vw data file it is looked for in the same directory of the project rendering parameters consists of the parameters to define the ray tracer execution included in a data file arg it is found in the same project directory texture useful for texture mapping consists of image files with hr or ppm extensions The only essential file is the one that describes the scene md while the others arg e vw are optional and serve to provide a particular rendering of the set If you desire to load a vw or arg file use the correspondent buttons 1 1 3 New button This button opens a file request window that requires the name of the directory to be used to contain the project The camera ambient and background items with default values immediately appear in the box object list and it is possible to begin to describe a scene interactively from nothing WHat Is XCRayt 5 As soon as an md file has been loaded
3. Frame bar In this case the Save As button is unabled while the Export button is enabled Figure 2 2 Rendered image WHAT Is XCView 21 2 3 Export button This button allows to export an animation previously produced and loaded as hra file in an animated gif gif file To the pressure of the Export button it opens the file request in which the name of the file with which one wants to export the animation has to be given a panel which will allow to select a few parameters will be opened see fig 2 3 e transparency colour pixels which have the same selected colour will be given back in a transparent way this is useful in an image composi tion and in particular to present an animated object on a background image how often happens in realizing a web page e delay the delay in terms of second between the various frame e cyclic animation makes a cycle of frame to have an infinite animation or not Figure 2 3 Export a gif file xscrayt USER S GUIDE CHAPTER 3 Data file formats In this section the syntax of each file format used by XCRayt is given and explained The data files created or used by XCRayt are stored in xcmodel models directory as default The character in the following is a comment to the data in the file 3 1 Scene description The following example file is xcmodel models gc_chess gc_chess md gc_chess is the directory project gc_chess md is the scene graph file The extension md id
4. This algorithm is 2 How TO WORK WITH XCRayt based on an algorithm of ray surface intersection The present version of hrayt implements and gives the user the possibility to choose between three different ray surface intersection algorithms In order to run the program no specific knowledge of these algorithms or of how a ray tracer works is required Obviously a knowledge of how they work together with the possibility of setting many parameters allows the user to improve the performance in the rendering phase sometimes even by a few minutes For an introduction to ray tracing see GLAS89 In spite of it is possible to describe a scene interactively from nothing you are advised about the possibility to create the entire scene graph using the descriptor library see DESCRO7 and a script in C language This scene graph saved as an md file see section 4 can be successively opened with XCRayt modified interactively and rendered with the ray tracer 1 1 How to work with XCRayt When XCRayt is set up it opens the window shown in fig 1 1 Note that the GUI of XCRayt is made with xtools XTOOLS00 The work area is the large window its size is 1000 x 700 subdivided in six sectors that we call e Control top left that controls camera and lighting parameters Object list under the previous from which it is possible to select scene objects e Buttons two rows of buttons at the bottom which control a lot of operations th
5. intensity contribution 0 004 lighting Model amina aaa a Whitted depth cueing range oooooocooocooooo o 0 0 INFINITY SHA OWS uti a tee a OFF shadows cache oooooooocoooomo mm o ooo OFF number of light sources 243 number of primitive objects 7 4 28 STATISTICS FILE number of textured primitives 7 4 total number of patches 31 max uniform subdivision depth 0 min patch flatness 0000 1 00 number of rays traced ooooooo oo oooo o 38000 total number of ray extent checks 1710148 number of ray object intersections 11463 30 17 number of shadow ray object intersections O NaN number of ray patch intersections calls 79600 number of tests resolved with second extent 19786 24 86 Seads statistics Scene seads object tested per ray ccc eee eee eee eee 1 83 box tested per ray o oooommo rro cronos 4 00 object tested per normal ray 1 83 object tested per shadow ray NaN box tested per normal ray o o o oooooooo 4 00 box tested per shadow ray 00 0 000 NaN percentage empty voxel ooooooooocmo momo 0 00 average objects per noempty voxel 4 00 Seads statistics Second level object tested per ray oooooomooommoo cm o 1 75 box tested per ra
6. see fig 1 10 not yet implemented 1 6 2 Selector View sector This sector consists of 5 checkpoints see fig 1 3 their selection allows a special scene to be viewed or rather a selected object in the scene to be viewed The 5 views are e Perspective e Front e Side e Up e Quad The Perspective view is the default In each of these the selected object will appear drawn in white to be shown in the scene The Quad view consists in the subdivision of the View sector into four parts showing the previous views 1 6 3 Transformation sector If an object item or one of its subitems in the Object list has been selected the Transformation sector will be abled this allows to modifies in terms of position translation scaling rotation and share the selected object s geometry Numerical and interactive transformations using respectively the Keyboard and Mouse buttons are possible In the Numerical case be fore to execute the transformation by pressing the Keyboard button some numerical values have to be setted More precisely for each single trans formation the user has to provide the fixed point Information about the center of gravity Baricenter of the selected object which will be assumed to be as before unless specified will help the user to do this According to the chosen transformation through the checkpoints the user will be asked to insert the following parameters the degree of rotation the new position the sca
7. 0 eee ee 1 6 3 Transformation sector 00 2004 1 6 4 Texture space buttons 0004 Tee Attributes 3 acc cece we ee Ee ee hoe Oe 1 7 1 Buttons sector 0 0 000 eee eee eee 1 8 Other buttons in the Buttons sector 1 8 1 Set and Undo buttons 4 1 8 2 Reload Save and Save As buttons 1 8 3 Delete Dutti akg od a oe eis on a ee aS WIA Add DUO A ba a oe Baa Bs 1 8 5 Render button o o 1 8 6 Prefs button acia la ias a A R aA 1 9 Animation Control sector ii 2 What is XC View 2 1 Quit button 2 2 Open button 2 3 Export button Data file formats 3 1 Scene description 3 2 View parameters 3 3 Ray tracer parameters 3 4 Image file 3 5 Standard image file 3 6 Animation file 3 7 3d Animation file 3 8 Statistics fle List of Figures Bibliography LIST OF FIGURES xscrayt USER S GUIDE CHAPTER 1 What is XCRayt XCRayt is the scene desriptor of the XCModel system KCMODELO0 This program is self contained and executable from the XCModel console window It is distributed with the archive xcraytdev tar gz development version and xcraytusr tar gz executable version Downloading and installation instructions are in KCMODELOO XCRayt is a system allowing a virtual scene to be described interactively in order to represent it realistically usi
8. 2 000000e 01 2 000000e 01 6 400000e 01 HIERARCHY begin the hierarchy description OBJECT TYPE 1 root OBJECT NAME torre root name OBJECT TYPE 3 a left leaf PRIMITIVE NAME slice_4 left leaf surface name GEO SHAPE 11 surface geometric transform to apply TRANSFORM MATRIX TYPE 1 TRANSFORM MATRIX 4 846628e 15 1 000000e 00 0 000000e 00 1 000000e 00 4 846628e 15 0 000000e 00 0 000000e 00 0 000000e 00 1 000000e 00 2 500000e 01 1 750000e 00 0 000000e 00 16 0 TEXTURE MATRIX TYPE 1 surf material texture and attr TEXTURE MATRIX 1 864088e 14 3 846154e 00 0 000000e 00 3 846154e 00 1 864088e 14 0 000000e 00 0 000000e 00 0 000000e 00 1 000000e 00 0 000000e 00 0 000000e 00 0 000000e 00 TEXTURE DATA SIZE 1 TEXTURE DATA TYPE 3 00 00 2 352941e 03 3 137255e 03 DATA FILE FORMATS 25 0 000000e 00 0 000000e 00 0 000000e 00 0 000000e 00 marble_5_black hr texture file ATTRIBUTE N 2 attribute applied NURBS N O index NURBS surface loaded OBJECT TYPE 2 a right son node tree OBJECT TYPE 3 a left leaf PRIMITIVE NAME slice_3 left leaf surface name OBJECT TYPE 2 right son OBJECT TYPE 3 a left leaf PRIMITIVE NAME slice_2 left leaf surface name OBJECT TYPE 2 right son OBJECT TYPE 3 a left leaf PRIMITIVE NAME slice_1 left leaf surface name OBJECT TYPE O a right leaf 3 2 View parameters Contains the necessary information in order to define a 3D perspective view that can sim
9. 7 Ambient editor Detail button A window appears see fig 1 7 showing the present settings of the ambient light and enabling the colour to be changed this variation is interactive 1 4 Background If you select Background in the Object list some buttons in the Buttons sector will be abled WHAT 18 XCRayt 9 1 4 1 Buttons sector Detail button A window appears similar to the one in fig 1 7 showing the present settings of Background and enabling the colour to be changed and the background to be reflecting or not 1 5 Lights If you select a light source in the Object list some functions in the Control sector and some buttons in the Buttons sector will be abled and the scene will be viewed in the View sector according to the parameters set on the light source 1 5 1 Control sector As can be seen on the label see fig 1 8 the left cursor is abled and deter mines the position of the light source while the right cursor is unabled The gt gt Juez Figure 1 8 Control sector position is numerically reported in the textbox below which can be altered Immediately beneath the active cursor Distance is active which moves the light source nearer to or further from the scene point using Near Far 1 5 2 Buttons sector Detail button A window appears shown in fig 1 9 which contains a lot of information about the lights Type of light color Red Green and Blue Intensity etc The type of light sel
10. Distance Figure 1 3 XCRayt panel after a scene has been loaded has not been allowed a general setting because this would be of little inter est in the rendering Sometimes this is used to make the viewed object seem rotated while in fact it is the camera which is rotated This parameter is often 0 0 1 indicating a perfectly upright camera with respect to the WHAT IS XCRayt 7 scene pal second_cup handle 1 db cup db ceramic_cup handiet db cup db tabie db fsh_eye wide_angie standard middie_teie_1 middei teie 2 middie_teie 3 Figure 1 5 Select camera objective vertical axis The rotation buttons next to the above that only vary the rotation of the frame not the angle are of greater utility Focus Near Far has the same properties as Distance except that it acts on the scene point by moving it away from or towards the camera 1 2 2 Buttons sector Step button This button opens a window see fig 1 6 enabling the user to vary the step to modify the camera position the scene point and the lights The values viewed are in degrees In order to make the changes permanent press the 8 BACKGROUND Figure 1 6 Step editor Set button The default values will always be reset every time that the XCRayt program is run 1 3 Ambient If you select Ambient from the Object list some buttons in the Buttons sector will be abled 1 3 1 Buttons sector Figure 1
11. MODELOO0 XCView is a viewer for images produced by XCRayt or rather by hrayt It is therefore useful to view images that have previously been produced and saved but above all to view animations made using XCRayt which have been saved photogram by photogram but not viewed XCView also allows the image format of XCModel that is hr to be converted into a standard format such as ppm It can be executed from the console window of XCModel XCView ap pears with the window of fig 2 1 which has the functions described below AMOK Start reme Figure 2 1 XC View control panel 20 EXPORT BUTTON 2 1 Quit button This button allows the user to quit XC View 2 2 Open button This button opens a file request to load a hr or ppm image file or a file hra containing a list of images If an image file has been selected it will be viewed as follows see fig 2 2 This image file can then be saved again using the Save As button with a different name and or format from hr to ppm or viceversa If a list of images is selected hra file these will all be loaded in the memory and the sector of the window that manages the animations will be enabled Using the Rew Play and Fwd buttons it is possible respectively to rewind the film photogram by photogram to view the whole animation at the speed chosen by the Speed bar and to go through the animation photogram by photogram Rewind and Forward can also be performed using the
12. University of Bologna Department of Mathematics Piazza di Porta S Donato 5 40127 Bologna XCRayt the scene descriptor User s Guide Version 2 0 G CASCIOLA Department of Mathematics University of Bologna Bologna 2007 Abstract This report describes the XCRayt and XCView packages They are two separate programs executable independently but are to be considered part of a single working instrument to phisically describe a geometrically modelled scene in order to represent it realistically G CASCIOLA Department of Mathematics University of Bologna P zza di Porta S Donato 5 Bologna Italy E mail casciola dm unibo it 1 xscrayt USER S GUIDE Contents Contents What is XCRayt 1 1 How to work with XCRayt o 11 1 Quit button ss 4 2a wR Shee ae a A 1 1 2 Open button e ELS New button ee eae ee A es 1 20 Cameras weed bas Se Gee ee aS ne a ea 1 21 Control sectOrs wea ve hd oe ea ad tds 1 2 2 Buttons sector ea s rat ea aE A 13 ADDED ed 13 1 Buttows sector e iia eee eh ee a gy Bk eS 1 4 Background 4 2 3 6 6 03 zea a Sede ee aa A 1 4 1 Buttons sector 0 0 0 000 eee eee 1b eights da a a oe alee RA wey a ee aas La Control sectors ra a BAe ta RR eS 1 5 2 Buttons sector Gs dar a for Star ae A a E G 1 6 ODJECE ae eink RO ee Ris os Ha RO oe cd 1 6 1 Buttons sector 0 0 0 0 0000 eee 1 6 2 Selector View sector 2 0 000
13. an hr extension 3 5 Standard image file Standard image format common in Xwindow environments and known as ppm This is a binary RGB file for true color images 3 6 Animation file This contains the list in ASCII format of the frames hr or ppm files making up the animation hra file DATA FILE FORMATS 27 10 frame number framel hr follows the frames file names frame2 hr frame9 hr frame10 hr 3 7 3d Animation file This contains the list in ASCIT format of the scene graphs md vw and arg files making up the 3d animation ani file scacchi ani the file name 20 scene graph number 0 scacchiO md scacchi vw scacchi arg follows the scene graphs 1 scacchil md scacchi vw scacchi arg file names 2 scacchi2 md scacchi vw scacchi arg 19 scacchil9 md scacchi vw scacchi arg 20 scacchi20 md scacchi vw scacchi arg 3 8 Statistics file Statistics file for the image This contains information about image genera tion It is generated from XCRayt only if requested and if it already exists the information relating to the image in the rendering phase will be ap pended to the file As an example here is the Statistics file of the rendering of a scene GENERAL STATISTICS run length encoded image on models gc_chess gc_chess hr image resolution lines x pixels 200x200 maximum intersection tree depth 21 adaptive intersection tree depth control ON minimum
14. at we will see in detail View the large square area on the right where the scene is visualised in wire frame Selector View to select some usual view points e Transformation to control and management some object geometric transformations in the scene and in the texture space 3D texturing As soon as this window appears you will immediately see which actions are possible The buttons cursors textboxes bars etc are accompanied by one or more labels for convention if a label is drawn in black the related function is able whereas white means unable More labels near an xtools object mean multifunctionality Look now at the able buttons only 1 1 1 Quit button This button allows the user to quit XCRayt Wuat 18 XCRayt 3 0 086 2 008 2 808 8 688 108 008 166 000 100 008 6 808 6 088 8 808 0 088 6 888 8 888 8 808 8 888 8 008 SMS Sms z SS ES gt S S Ss S l Q 8 So S Figure 1 1 XCRayt panel before to load or create a scene 1 1 2 Open button This button opens a control panel useful to open a scene graph or a list of scene graphs that we will call an animation see Fig 1 2 In this section we describes the Open Scene button for the Animation How TO WORK WITH XCRayt control buttons see section 1 9 The Open Scene button opens a file request window to load a md EA EA E See SS A ee Figure 1
15. dden by a file i A COn parameters Scheer laa la AR o Sey sho 3 is teapotsia teapottr feapot arg g El El E ES ES E Figure 1 14 Render parameters with the same name as the project and with an arg extension If these files WhHar 18 XCRayt 17 do not exist the default parameters will be used It is possible to load an arg file with a different name from that of the project by setting the name and using the Load button The parameters are Image Size to set the dimensions of the image to be produced The information consists in the number of lines and columns of the discre tised grid of the screen in pixels or in the number of lines or pixels for a square grid Seads Subdivision Scene and Seads Subdivision Obj to de termine the number of divisions along each axis in order to subdivide the scene space and the NURBS objects The three dimensional grids are represented by a SEADS data structure which stands for Spatially Enumerated Auxiliary Data Structure Bezier Subdivision Level to determine the subdivision level of the parametric space of each surface as well as the basic one in Bezier patches Each of these patches is then evenly subdivided into 2 patches where k is the value of the object field Ray Depth Level sets the maximum depth of the ray tree Surface Flatness defines the tolerance with which a surface is con sidered flat in the Bezier subdivision process Mi
16. ected determines which elements of the GUI will be active 10 OBJECTS 4 8 c D E Figure 1 9 Light editor e A Distant light is a light source at an infinite distance from the scene on the direction defined by the X Y Z vector e A Point light is a light source in X Y Z with the intensity fading linerly to zero at the distance defined by Max Range if the Max Range value is zero the light intensity will not be dependent on the distant travelled e A Warn light is a Point light with a direction in order to aim a light at a particular area of an object Conc Exp defines the way in which light intensity decreases away from the aim direction a larger value means that the light decreases quicker than for smaller value Cone is an angular value used to restrict the path of the light it define a cone surrounding the light direction Flap On defines a plane equation Ax BY CZ D 0 the half space containing the light respect to the plane will be illuminated while the other will not Step button A window appears see fig 1 6 allowing the step changes of the camera position scene point and lighting to be modified The values viewed are in degrees In order to make the changes permanent press the Set button The default values will always be reset every time that the XCRayt program 1s run WHAT IS XCRayt 11 1 6 Objects If an object item or one of its subitems in the Object list has been selected so
17. entifies a scene model The format is self explanatory HEADER torre 3 3 1 scene name N lights N attrs 1 N file surf AMBIENT COLOR 1 000000e 00 1 000000e 00 1 000000e 00 ambient AMBIENT INTENSITY 7 000000e 01 ambient BKG COLOR 4 470000e 01 4 700000e 01 5 880000e 01 background BKG IS REFL 0 background LIGHT N O defines the first light of three NAME distant_light light name TYPE O LOCATION 0 000000e 00 0 000000e 00 0 000000e 00 DIRECTION 0 000000e 00 0 000000e 00 1 000000e 00 COLOR 1 000000e 00 1 000000e 00 1 000000e 00 INTENSITY 7 000000e 01 CONCENTRATION O MAX RANGE 0 000000e 00 CONE 1 000000e 00 FLAP O 0 000000e 00 0 000000e 00 0 000000e 00 0 000000e 00 LIGHT N 1 defines the second light of three NAME point_light light name 24 SCENE DESCRIPTION ATTRIBUTES N 1 defines the first attr of two NAME scacco_bianco attribute name COLOR 4 820000e 01 4 820000e 01 1 000000e 00 RGB values 5 000000e 01 ambient reflection 5 000000e 01 diffuse reflection 4 000000e 01 mirror reflection INDEX 1 000000e 00 1 000000e 00 refraction index 2 Phong s exponent 0 000000e 00 0 000000e 00 Min and Max transparency 0 transparency power ATTRIBUTES N 2 defines the second attr of two SURFACE N O defines the first surface of one NAME Qtorre db surface name IS SURFACE 1 NORMAL INSIDE O surface normal versus EXTENT surface bounding box 0 000000e 00 0 000000e 00 0 000000e 00
18. g the textbox relating to a Refraction Index the user can able a selection window containing a list of the most common materials However it is always possible to insert a generic material Also in this case a library file has been created refractionindex xclib nella directory 14 OTHER BUTTONS IN THE BUTTONS SECTOR xcmodel lib in ASCII format which can be edited by the user For more information about the parameters defining an attribute see DESCRO7 1 8 Other buttons in the Buttons sector 1 8 1 Set and Undo buttons The pair of buttons Set e Undo allow a minimum level of undo redo to be made on every object These are immediately enabled as soon as an object has been modified The first shows the wish to make the changes permanent in the scene in the memory but not on the file while the second replaces the previous values in the object If Set is chosen both this button and Undo will be unabled and the buttons Save and Save As will appear The Undo button is also useful to undo a transformation done using the Transformation sector 1 8 2 Reload Save and Save As buttons The Reload button allows the whole project to be reloaded without having to reopen file request again to repeat the selection This is useful in cases in which the scene has been recompiled using the descriptor library or you wish to start again from the last changes saved The Save As button is used to save the project on files the model is saved in a file wi
19. he first two once a name has been chosen the windows already viewed in fig 1 9 and fig 1 11 will be opened with their default values standard attribute and white Warn light This new attribute or light will appear at the bottom of the attributes and lights list The objects behave differently In fact they have several types of insertion surface add a simple surface file db or dbe in the tree object add an object list of surfaces included in a file obj copy of a leaf add a simple surface already presented in the hierarchy as a leaf copy of a subtree add an object already presented in the hierarchy as a subtree 1 85 Render button This button executes the rendering engine If it comes across a change in the project that has not yet been saved the user will be asked to save the project xhrayt will only run when the user has saved all the modifications The window shown in fig 1 13 front end image of hrayt is opened by xhrayt program which then runs hrayt the real ray tracer of XC Model the bar shows the progress of the rendering The system allows several types of rendering to be executed 1 8 6 Prefs button This button allows a series of parameters defining the ways in which the ray tracer must render the model to be varied interactively throught the window 16 OTHER BUTTONS IN THE BUTTONS SECTOR Figure 1 13 xhrayt execution of fig 1 14 The parameters contained when the window is opened are rea
20. ling factor the shear factors etc For the scaling it is possible to obtain a modification by varying the percentage of the different dimensions In the Interactive case press the Mouse button and then use the mouse according to the chosen transformation through the checkpoints in the View sector to set the transformation actions Wuat Is XCRayt 13 1 6 4 Texture space buttons These buttons allow the selected object in the Object list to be applied a texture image or to be put in a texture 3D space Pressing the Modify button the object transformation in the texture space mode will be abled a red cube which virtually represents the 3d texture space is shown the next transformations on the object will be inter preted as transformations of the object with respect to the texture space To go out of this mode press the Done button A matrix of texture trans formation which will be applied in rendering phase remains defined 1 7 Attributes If you select an attribute in the Object list some buttons in the Buttons sector will be abled 1 7 1 Buttons sector a 18 E ne EE l l Figure 1 11 Attribute editor Detail button The window shown in fig 1 11 appears enabling the parameters for the selected attribute to be defined These are the materials that can be associ ated with the objects in the scene the refraction indexes are very important for their definition By pressin
21. liography XCMODEL00 G Casciola remodel a system to model and render NURBS curves and surfaces User s Guide Version 1 0 Progetto MURST Analisi Numerica Metodi e Software Matematico Ferrara 2000 http www dm unibo it casciola html xcmodel html XCSURF07 G Casciola zcsurf the 3D modeller User s Guide Version4 0 http www dm unibo it casciola html xcmodel html XCBOOLO00 G Casciola xcbool the object composer User s Guide Ver sion 1 0 Progetto MURST Analisi Numerica Metodi e Software Matematico Ferrara 2000 http www dm unibo it casciola html xcmodel html XTOOLS00 S Bonetti G Casciola xtools library Programming Guide Version 2 0 2000 http www dm unibo it casciola html xcmodel html DESCRO7 G Casciola descriptor library Programming Guide Version 3 0 2007 http www dm unibo it casciola html xcmodel html FOVD90 J D Foley A VanDam S K Feiner J F Hughes Computer Graphics principles and practice II Edition Addison Wesley 1990 GLAS89 A S Glassner An introduction to ray tracing Academic Press 1989
22. me buttons in the Buttons Selector View and Transformation sectors will be abled and the scene will be viewed in the View sector from the point of view of the camera showing the selected object which will be drawn in white 1 6 1 Buttons sector standard atinbute glass angie texture border texture cross text laz s texture Z ceramic Pr Figure 1 10 Link attribute to object Detail button This function allows you to match the selected object with a material The materials to be used must already have been defined see Attributes in the next section Fig 1 10 shows how to carry out this operation The object will always be defined in a particular material which if unspecified will be the default The unmodifiable data concerning this material is provided in two sections according to type at the top if it is an attribute at the bottom if it is a texture If the selected object is not a leaf a surface in the hierarchy it is not possible to identify the material from which it has been made this is only possible by checking the leaves or the surfaces If you choose a texture only some of the GUI fields will be abled according to type With texture mapping it is possible to choose and load an image from the texture directory through a file request the image will be copied 12 OBJECTS into the project directory and viewed in the square in the bottom left of the screen
23. n Intensity Contribute defines the value below which the con tribution coming from a ray on the ray tree should not be considered Depth cueing Distance sets the maximum distance a surface point is viewed and then rendered Light Models determines the lighting model on which to base the rendering of the scene Intersector determines the type of algorithm intersector used by the ray tracer Shadows Effect allows shadows to be enabled Shadows Ray Cache allows caching of shadows to be improved Statistics Report enables the production of a file containing statis tical data about the execution of the ray tracer Statistics file and Output file specify the names of the related files The buttons Set and Cancel respectively enable the new parameters or return to the previous ones The Save button saves the parameters set in the specified arg file The Default button sets the default parameters 18 ANIMATION CONTROL SECTOR 1 9 Animation Control sector Pressing the Open button in XCRayt see fig 1 1 opens a control panel useful to control little animations by the Animation Control sector see Fig 1 2 Producing little animations starting from a scene graph or loading and modifying an animation previously created ani file by executing a C language code which make use of the descriptor library is possible In case of generation from a scene graph after loading one by the Open Scene button use the Save button in the Animation Con
24. ng the hrayt program XCRayt could be defined as the make up room and film director s office of a virtual film set The actors present on the set are the individual surfaces or objects list of surfaces that have been modelled and or put together using XCSurf see XCSURF07 and XCBool see KCBOOLO00 These surfaces are geomet rically described by NURBS and trimmed NURBS surfaces in parametric form The costumes and make up of the actors are defined by attributes of color and the visual properties of the materials and or by the application of tex ture The lighting for the set or scenery is divided into ambience lighting background colour and properties and different types of puntiform light sources The position of the actors on the set and the filming is respectively made by the application of geometric transformations and the setting of the pa rameters of the camera Obviously the system would be difficult to use for anyone not familiar with 3D transformations and the parameters regulating them Similarly some notions of optical physics and of the lighting models used to simulate realistic effects are essential For an introduction to these subjects see FOVD90 and GLAS89 However the system is quite simple so that even a user with little specific knowledge can learn to use it by experimentation XCRayt is supported by a program hrayt that implements a ray trac ing algorithm optimized for trimmed NURBS surfaces
25. ng the user to choose a scene point When they are pressed a window appears see fig 1 4 allowing the center of gravity of an object in the scene surfaces or objects consisting of surfaces to be chosen as a scene point or allowing the center of gravity co ordinates to be inserted The buttons present in the Control sector serve to vary the values of a fixed quantity position scene point and view volume Immediately below the cursors next to the Distance label there are two buttons and a textbox The latter provides the distance between camera and scene point while Near Far moves the camera nearer to or further from the scene point In order to position the camera at a fixed distance use the textbox The Zoom button and the angle textbox allow the user to vary the view volume Also in this case the buttons vary the angle by a certain step see Step button while a precise value is inserted using angle textbox If you click on this textbox a list of the most common objectives appears see fig 1 5 that are contained in the file camera xclib which you will find in the xcmodel 1lib directory The data in the bottom left of the window concerns the view up The user 6 CAMERA i iii EEE JL bk E tal a a EES A ale ou S S 3 E E S w oy Y Object pt X 8 343 ip ip handiel ab position Z 16 132 7 386 a e second cu ceramic Cuy Camera X 6 535 7
26. th an md extension and the viewing parameters in a file with an vw extension It is possible to save one or both see fig 1 12 and it is possible to choose an appropriate filename or directory The Save button modeisiteapot feapotind Figure 1 12 Save As files saves automatically both md and vw file with the chosen name and project directory 1 83 Delete button This option deletes an element from the scene the one selected in the ob ject list It is not possible to delete Camera Ambient or Background If WHAT IS XCRayt 15 these are superfluous for a particular project can be unabled by setting the intensity to zero or by setting them as though they were black As far as the other elements are concerned the selected object will be deleted In the case of the attributes it is not possible to delete an attribute of an object that is still being used First you need to delete the object or objects that refer to it or change its reference points As far as hierarchy is concerned this is a more difficult problem since the data structure is tree like The user must be particularly careful when deleting the final leaf of a node In this case the node will also have to be deleted to produce a new tree not yet implemented The Delete operation is permanent there is no Undo 1 8 4 Add button This option adds lights attributes or objects No other type of insertion is possible For t
27. trol sector to save a ani file made at this moment from a single frame Now through the gt but ton producing new frames as copy of the initial one is possible modifying these copies of the scene graph and saving the modifications by the Rec button allows to produce a little 3d animation In case of loading an ani mation previously created use the Load ani button As before through the buttons gt lt lt lt and gt gt running the frame and introducing possible modifications is possible The buttons present in this panel are e Load ani allows to load an animation previously saved which consists in a list of scene graphs e Rec saves the changes made on the current scene graph and joins it to a frame Del deletes the current scene graph and then the correspondent frame e Ins inserts a scene graph after the current one and then a frame creating a copy Save as saves with a name the 3d animation or the scene graph list e Save saves with the current name the 3d animation or the scene graph list Render renders all the scene graphs and creates a hra file xscrayt USER S GUIDE CHAPTER 2 What is XC View XCView is the viewer of the XCModel system KCMODELOQ It is self contained and executable from the XCModel console window It is dis tributed with the archive xcraytdev tar gz development version and xcray tusr tar gz executable version Downloading and installation instructions are in XC
28. ulate filming with a telecamera These files have an vw exten sion 14 03 11 72 1 60 camera point 0 20 0 80 0 45 scene point or object point 0 00 0 09 0 99 view up 26 00 view volume 1 00 aspect ratio x y 3 3 Ray tracer parameters These parameters define the arguments of the ray tracer These files have an arg extension 11 number of arguments follows the arg list L200 e0 004000 W B1 000000 26 ANIMATION FILE S gc_chess sta o gc_chess hr The arguments can be argument signify Bn min flat ratio b Blinn light model C no shadow cache Dn max 2 subdivision in Bezier patches ddepth max intersection tree depth X minimum intensity contribution Ln image resolution In first line to be processed MB Bezier Clipping intersector method MT Toth intersector method nn nurbs extent subdivisions o filename image filename Pn number of width pixels in the image the height is deduced by the aspect ratio pn first pixel to be processed rreach computed intensity is proportional to the distance between the camera and the point considered This is linearly scaled by a factor one at zero distance to a factor zero at the reach distance S filename statistical file name S shadow ON vn scene extent subdivisions W Whitted light model 3 4 Image file This is a compressed non standard format for images which can also be used for textures These files have
29. y o oooooo coro socorro 31 00 object tested per normal ray 1 75 object tested per shadow ray NaN box tested per normal ray oo o o oooooooo 31 00 box tested per shadow ray oooooococooooo oo NaN percentage empty voxel cece cee momo 0 00 average objects per noempty voxel 31 00 preprocessing time o oooooooooo Oh 0 0 00 ray tracing processing time Oh 0 12 00 total processing time Oh 0 12 00 xcrayt USER S GUIDE List of Figures 1 1 XCRayt panel before to load or create a scene 3 1 2 Open Animation Control panel 4 1 3 XCRayt panel after a scene has been loaded 6 1 4 Select a scene point object point 7 1 5 Select camera objective o 7 1 6 Step editor wora ai A BER di Pot E 8 1 7 Ambient editor e 8 1 8 Control sector ces ia as a a 9 1297 Die bre dior lo 6 dag Be a a de Ge ee eB 10 1 10 Link attribute to object o o e 11 1 11 Attribuitesediter ecc a a wy 13 110 Save As lesa tia a rad Sen aw pe 14 T 13 schrayt execution iaa e ta e ay aa 16 1 14 Render parameters o 16 2 1 XCView control panel o 19 2 2 Rendered Mage e 20 2 3 Exporta cif Mena a a a 21 xscrayt USER S GUIDE Bib
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