Making Pictures With GNU PIC
Contents
1. lt print arg gt TEXT lt expr gt lt position gt The current position and direction are saved on entry to a Y construction and restored on exit from it Note that in if constructions newlines can only occur in BALANCED BODY This means that if EE N else TES will fail You have to use the braces on the same line as the keywords if beige This restriction doesn t hold for the body after the do in a for construction lt any expr gt i lt expr gt lt text expr gt 32 lt any expr gt lt logical op gt lt any expr gt lt any expr gt lt logical op gt amp amp lt text expr gt i TEXT TEXT TEXT TEXT Pl Logical operators are handled specially by pic since they can deal with text strings also pic uses strcmp 3 to test for equality of strings an empty string is considered as false for amp amp and II lt primitive gt box circle ellipse arc line arrow spline move TEXT TEXT vss plot lt expr gt TEXT 7 7 lt command gt A closed object rectangle closed object circle closed object ellipse open object quarter circle open object line open object line with arrowhead open object spline curve text within invisible box formatted text Drawn objects within are treated as a single composite ob2. 35 lt object type gt box circle ellipse arc line arrow spline TETS TEXT As Kernighan notes since barbarisms like 1th and 3th are barbaric synonyms like 1st and 3rd are accepted as well Objects of a given type are numbered from 1 upwards in order of declaration the last modifier counts backwards The th form which allows you to select a previous object with an expression as opposed to a numeric literal is not documented in DWB s pic 1 The xxx of rule is special The lexical parser checks whether xxx is followed by the token of without eliminating it so that the grammar parser can still see of Valid examples of specifying a place with corner and label are thus A n n of A nA north of A while north A A north both cause a syntax error DWB pic also allows the weird form A north of Here the special rules for the with keyword using a path lt path gt lt relative path gt lt relative path gt lt relative path gt lt relative path gt lt corner gt LABEL LABEL lt corner gt The following style variables control output Style Variable Default What It Does boxht 0 5 Default height of a box boxwid 0 75 Default height of a box lineht 0 5 Default length of vertical line linewid 0 75 Default length of horizontal line arcrad 0 25 Default radius of an arc circlerad 0 25 Default radius of a circle e
3. Block Composites A block composite object is created a series of commands enclosed by square brackets The compos ite can be treated for most purposes like a single closed object with the size and shape of its bounding box Here is an example The program fragment A circle line up 1 at last circle n line down 1 at last circle s line right 1 at last circle e line left 1 at last circle w box dashed with nw at last circle se 0 2 0 2 Caption center of last box yields the block in figure 11 1 which we show both with and without its attachment points The block s location becomes the value of A 18 _ a Figure 11 1 A sample composite object To refer to one of the composite s attachment points you can say for example A s For purposes of object naming composites are a class You could write last s as an equivalent reference usable any where a location is needed This construction is very important for putting together large multi part dia grams Blocks are also a variable scoping mechanism like a groff 1 environment All variable assignments done inside a block are undone at the end of it To get at values within a block write a name of the block followed by a dot followed by the label you want For example we could refer the the center of the box in the above composite as last Caption or A Caption This kind of reference to a label can be used in any way any
4. VARIABLE A String starting with a character from the set a z optionally followed by one or more charac ters of the set a zA Z0 9_ Values of variables are preserved across pictures LABEL A string starting with a character from the set A Z optionally followed by one or more char acters of the set a zA Z0 9_ COMMAND LINE A line starting with a command character in groff mode V in TEX mode BALANCED TEXT A String either enclosed by and Y or with X and X where X doesn t occur in the string BALANCED BODY Delimiters as in BALANCED TEXT the body will be interpreted as command FILENAME The name of a file This has the same semantics as TEXT MACRONAME Either VARIABLE or LABEL Semi Formal Grammar Tokens not enclosed in are literals except n is a newline Three dots is a suffix meaning replace with 0 or more repetitions of the preceding element s An enclosure in square brackets has its usual meaning of this clause is optional Square bracket enclosed portions within tokens are optional Thus h eigh t matches either height or ht If one of these special tokens has to be referred to literally it is surrounded with single quotes The top level pic object is a picture lt picture gt PS NUMBER NUMBER n lt statement gt PE n The arguments if present represent the width and height of the picture causing pic to att
5. g format strings 14 Macros You can define macros in pic This is useful for diagrams with repetitive parts In conjunction with the scope rules for block composites it effectively gives you the ability to write functions The syntax is define name replacement text This defines name as a macro to be replaced by the replacement text not including the braces The macro may be called as name arg1 arg2 argn The arguments if any will be substituted for tokens 1 2 n appearing in the replacement text As an example of macro use consider this 27 PS Plot a single jumper in a box 1 is the on off state define jumper shrinkfactor 0 8 Outer box invis wid 0 45 ht 1 Count on end to reset these boxwid Outer wid shrinkfactor 2 boxht Outer ht shrinkfactor 2 box fill 1 with s at center of Outer box fill 1 with n at center of Outer Plot a block of six jumpers define jumperblock jumper 1 jumper 2 jumper jumper Ja jumper 3 4 5 jumper 6 jwidth last Outer wid jheight last Outer ht box with nw at 6th last nw wid 6 jwidth ht jheight Use to avoid changing position from last box draw This is necessary so move in any direction will work as expected Jumpers in state 1 2 3S4S5S6 at last box s 0 0 2 Sample macro invocations jumperblock 1 1 0 0 1 0 mov
6. mand For example the program PS A box first object move B ellipse second object move arrow right at A r PE declares labels A and B for its first and second objects Here s what that looks like 13 first second object object Figure 9 1 Example of label use The at statement in the fourth line uses the label A the behavior of at will be explained in the next sec tion We ll see later on that labels are most useful for referring to block composite objects Labels are not constants but variables you can view colon as a sort of assignment You can say something like A A 1 0 and the effect will be to reassign the label A to designate a position one inch to the right of its old value 10 Describing locations The location of points can be described in many different ways All these forms are interchangeable as for as the pic language syntax is concerned where you can use one any of the others that would make semantic sense are allowed The special label Here always refers to the current position 10 1 Absolute Coordinates The simplest is absolute coordinates in inches pic uses a Cartesian system with 0 0 at the lower left corner of the virtual drawing surface for each picture that is X increases to the right and Y increases upwards An absolute location may always be written in the conventional form as two comma separated numbers surrounded by parentheses and this is recommen
7. original pic is referred to as DWB pic Details on the history of the program are given at the end of this document In this document the gpic 1 extensions will be marked as such 2 Invoking PIC Every pic description is a little program which gets compiled by pic 1 into gtroff 1 macros Pro grams that process or display gtroff 1 output need not know or care that parts of the image began life as pic descriptions The pic 1 program tries to translate anything between PS and PE markers and passes through everything else The normal definitions of PS and PE in the ms macro package and elsewhere have also the side effect of centering the pic output on the page 2 1 PIC Error Messages If you make a pic syntax error gpic 1 will issue an error message in the standard gcc 1 like syntax A typical error message looks like this 2 pic pic ms lt nnn gt parse error before lt token gt pic pic ms lt nnn gt giving up on this picture where nnn is a line number and token is a token near usually just after the error location 3 Basic PIC Concepts Pictures are described procedurally as collections of objects connected by motions Normally pic tries to string together objects left to right in the sequence they are described joining them at visually natu ral points Here is an example illustrating the flow of data in pic processing Ros srt a ee z gtbl 1 or geqn 1 gpic 1 7 opt
8. already seen how to change the direction in which objects are composed from rightwards to downwards Here are some more illustrative examples right box arrow circle arrow ellipse left box arrow circle arrow ellipse Figure 8 1 Effects of different motion directions right and left i down box arrow circle arrow ellipse up box arrow circle arrow ellipse Figure 8 2 Effects of different motion directions up and down Something that may appear surprising happens if you change directions in the obvious way Figure 8 3 box arrow circle down arrow ellipse You might have expected that program to yield this Figure 8 4 More intuitive But in fact to get Figure 8 3 you have to do this lt 12 zS box arrow circle move to last circle s down arrow ellipse JPE Why is this Because the exit point for the current direction is already set when you draw the object The second arrow in Figure 8 2 dropped downwards from the circle s attachment point for an object to be joined to the right The meaning of the command move to last circle s should be obvious In order to see how it gener alizes we ll need to go into detail on two important topics locations and object names 9 Naming Objects The most natural way to name locations in pic is relative to objects In order to do this you have to be able yo
9. eai 0S ht 0 75 Williewoat last oE Figure 10 7 Using the with modifier for attachments 10 5 The chop Modifier When drawing lines between circles that don t intersect them at a compass point it is useful to be able to shorten a line by the radius of the circle at either or both ends Consider the following program eye PS circle x circle y at lst circle 0 4 0 6 circle z at lst circle 0 4 0 6 arrow from 1st circle to 2nd circle chop arrow from 2nd circle to 3rd circle chop arrow from 3rd circle to lst circle chop PE It yields the following Figure 10 8 The chop modifier Notice that the chop attribute moves arrowheads rather than stepping on them By default the chop modi fier shortens both ends of the line by circlerad By suffixing it with a number you can change the amount of chopping If you say line chop r chop r2 with r and r2 both numbers you can vary the amount of chop ping at both ends You can use this in combination with trigonometric functions to write code that will deal with more complex intersections 11 Object Groups There are two different ways to group objects in pic brace grouping and block composites 11 1 Brace Grouping The simpler method is simply to group a set of objects within curly bracket or brace characters On exit from this grouping the current position and direction are restored to their value when the opening brace was encountered 11 2
10. to dot or dash ellipses circles and arcs and splines in TEX mode only some versions of DWB may only permit dashing of lines and boxes It too can be suffixed with a number to specify the interval between dots default 0 05 0 1 0 15 0 2 Figure 6 2 Dotted objects 6 3 Rounding Box Corners It is also possible in GNU gpic only to modify a box so it has rounded corners Figure 6 3 box rad with increasing radius values Radius values higher than half the minimum box dimension are silently truncated to that value 6 4 Arrowheads Lines and arcs can be decorated as well Any line or arc and any spline as well can be decorated with arrowheads by adding one or more as modifiers _ __b Figure 6 4 Double headed line made with line lt gt In fact the arrow command is just shorthand for line gt And there is a double head modifier lt gt so the figure above could have been made with line lt gt Arrowheads have a width attribute the distance across the rear and a height attribute the length of the arrowhead along the shaft Arrowhead style is controlled by the style variable arrowhead The DWB and GNU versions inter pret it differently DWB defaults to open arrowheads and an arrowhead value of 2 the Kernighan paper says a value of 7 will make solid arrowheads GNU gpic defaults to solid arrowheads and an arrowhead value of 1 a value of 0 will produce open arrowheads Note that solid arrowheads are alway
11. 12 Style Variables There are a number of global style variables in pic that can be used to change its overall behavior We ve mentioned several of them in previous sections They re all described here For each variable the default is given Style Variable Default What It Does boxht 0 5 Default height of a box boxwid 0 75 Default width of a box lineht 0 5 Default length of vertical line linewid 0 75 Default length of horizontal line linethick 1 Default line thickness arcrad 0 25 Default radius of an arc circlerad 0 25 Default radius of a circle ellipseht 0 5 Default height of an ellipse ellipsewid 0 75 Default width of an ellipse moveht 0 5 Default length of vertical move movewid 0 75 Default length of horizontal move textht 0 Default height of box enclosing a text object textwid 0 Default width of box enclosing a text object arrowht 0 1 Length of arrowhead along shaft arrowwid 0 05 Width of rear of arrowhead arrowhead 1 Enable disable arrowhead filling 20 Style Variable Default What It Does dashwid 0 05 Interval for dashed lines maxpswid 11 Maximum width of picture maxpsht 8 5 Maximum height of picture scale 1 Unit scale factor fillval 0 5 Default fill value Any of these variables can be set with a simple assignment statement For example Figure 12 1 boxht 1 boxwid 0 3 movewid 0 2 box move box move box move box In GNU pic setting the sc
12. Making Pictures With GNU PIC Eric S Raymond esr snark thyrsus com ABSTRACT The pic language is a troff extension that makes it easy to create and alter box and arrow diagrams of the kind frequently used in technical papers and textbooks This paper is both an introduction to and reference for gpic 1 the implementation distributed by the Free Software Foundation for use with groff 1 1 Introduction to PIC 1 1 Why PIC The pic language provides an easy way to write procedural box and arrow diagrams to be included in troff documents The language is sufficiently flexible to be quite useful for state charts Petri net diagrams flow charts simple circuit schematics jumper layouts and other kinds of illustration involving repetitive uses of simple geometric forms and splines Because these descriptions are procedural and object based they are both compact and easy to modify The gpic 1 implementation of pic is distributed by the Free Software Foundation for use with their groff 1 implementation of troff Because both implementations are widely available in source form for free they are good bets for writing very portable documentation 1 2 PIC Versions The original 1984 pre ditroff 1 version of pic is long obsolete The rewritten 1991 version is still available as part of the Documenter s Work Bench module of System V Where differences between Documenter s Work Bench 1991 pic and GNU pic need to be described
13. The GNU incarnation of the ms macro package for example includes the following definitions de PS oka sp n DD u ie n lt 2 error bad arguments to PS not preprocessed with pic Lel ds need u 1 1v in u n 1 n i 2 2 gt 0 sN de PE par reset sp n DD u 5m Equivalent definition will be supplied by GNU pic 1 if you use the mpic option this should make it usable with macro pages other than ms 1 If PF is used instead of PE the troff position is restored to what it was at the picture start Kernighan notes that the F stands for flyback The invocation PS lt file causes the contents of file to replace the PS line This feature is deprecated use copy file instead By default input lines that begin with a period are passed to the postprocessor embedded at the cor responding point in the output Messing with horizontal or vertical spacing is an obvious recipe for bugs but point size and font changes will usually be safe Point sizes and font changes are also safe within text strings as long as they are undone before the end of string 26 The state of gt roff s fill mode is preserved across pictures The Kernighan paper notes that there is a subtle problem with complicated equations inside pic pic tures they come out wrong if egn 1 has to leave extra vertical space for the equation If your equation involves more than subscripts and superscripts you m
14. a single object resembling a box for many purposes We ll describe both of these later on The box ellipse circle and block composite objects are closed lines arrows arcs and splines are open This distinction will often be important in explaining command modifiers Figure 3 2 was produced by the following pic program which introduces some more basic concepts PS box box move line line move arrow arrow move circle circle move llipse ellipse move arc down move arc PE The first thing to notice is the move command which moves a default distance 1 2 inch in the cur rent movement direction Secondly see how we can also decorate lines and arrows with text The line and arrow commands each take two arguments here specifying text to go above and below the object If you wonder why one argument would not do contemplate the output of arrow ow owle Figure 3 3 Text centered on an arrow When a command takes one text string pic tries to place it at the object s geometric center As you add more strings pic treats them as a vertical block to be centered The program line 1 line maw T2 line poe woqw Poa line uH woqw TZN wan line wat non an wan Wo for example gives you this e N A UIN Re nAnBRWNe Figure 3 4 Effects of multiple text arguments The last line of Figure 3 2 s program are down move arc describing the c
15. ain a PostScript copy of the revised version 1 by sending a mail message to netlib research att com with a body of send 116 from research cstr There have been two revisions in 1984 and 1991 The document you are reading effectively subsumes Kernighan s description it was written to fill in lacune in the exposition and integrate in descriptions of the GNU gpic 1 features The GNU gpic implementation was written by James Clark jjc jclark com It is currently main tained by Werner Lemberg w gnu org 23 Bibliography 1 Kernighan B W PIC A Graphics Language for Typesetting Revised User Manual Bell Labs Computing Science Technical Report 116 December 1991 2 Van Wyk C J A high level language for specifying pictures ACM Transactions On Graphics 1 2 1982 163 182
16. ale variable re scales all size related state variables so that their values remain equivalent in the new units The command reset resets all style variables to their defaults You can give it a list of variable names as arguments optionally separated by commas in which case it resets only those State variables retain their values across pictures until reset 13 Expressions Variables and Assignment A number is a valid expression of course all numbers are stored internally as floating point Deci mal point notation is acceptable in GNU gpic scientific notation in C s e format like 5e 2 is accepted Anywhere a number is expected the language will also accept a variable Variables may be the built in style variable described in the last section or new variables created by assignment DWB pic supports only the ordinary assignment via which defines the variable on the left side of the equal sign in the current block if it is not already defined there and then changes the value on the right side in the current block The variable is not visible outside of the block This is similar to the C program ming language where a variable within a block shadows a variable with the same name outside of the block GNU gpic supports an alternate form of assignment using The variable must already be defined and the value will be assigned to that variable without creating a variable local to the current block For example th
17. ame way as for anormal text object Be very careful that you specify an appropriate format string pic does only very lim ited checking of the string This is deprecated in favour of sprintf 20 Some Larger Examples Here are a few larger examples with complete source code One of our earlier examples is generated in an instructive way using a for loop a1 PS Draw a demonstration up left arrow with grid box overlay define gridarrow move right 0 1 arrow up left 1 box wid 0 5 ht 0 5 dotted with nw at last arrow end for i 2 to 1 0 5 do box wid 0 5 ht 0 5 dotted with sw at last box se move down from last arrow center if 1 boxht then fBline up left fP else sprintf fBarrow up left g fP 1 move right 0 1 from last e gridarrow 0 5 gridarrow 1 gridarrow 1 5 gridarrow 2 undef gridarrow SPE line up left arrow up left 1 arrow up left 1 5 arrow up left 2 Figure 20 1 Diagonal arrows dotted boxes show the implied 0 5 inch grid Here s an example concocted to demonstrate layout of a large multiple part pattern 28 lt PS define filter box ht 0 25 rad 0 125 lineht 0 25 Top right box fBms fR move box fBHTML f R move box fBlinuxdoc sgml fP move box fBTexinfo fP sources sources sources line down from 1st box s lineht A line down line down from 2nd box B line dow
18. aptioned arc intro duces several new ideas Firstly we see how to change the direction in which objects are joined Had we written arc move arc omitting down the caption would have been joined to the top of the arc like this arc ey Figure 3 5 Result of arc move This is because drawing an arc changes the default direction to the one its exit end points at To rein force this point consider arc Figure 3 6 Result of are cw move All we ve done differently here is specify cw for a clockwise arc ccw specifies counter clock wise direction Observe how it changes the default direction to down rather than up Another good way to see this via with the following program line arc arc cw line which yields Figure 3 7 Result of line arc arc cw line Notice that we did not have to specify up for the second arc to be joined to the end of the first Finally observe that a string alone is treated as text to be surrounded by an invisible box of a size either specified by width and height attributes or by the defaults textwid and textht Both are initially zero because we don t know the default font size 4 Sizes and Spacing Sizes are specified in inches If you don t like inches it s possible to set a global style variable scale that changes the unit Setting scale 2 54 will effectively change the internal unit to centimeters all other size variable values will be scaled corre
19. ave up to 9 arguments The replacement text may be delimited by braces or by a pair of instances of any character not appearing in the rest of the text If you write copy thru macro omitting the filename lines to be parsed are taken from the input source up to the next PE In either of the last two copy commands GNU gpic permits a trailing until word clause to be added which terminates the copy when the first word matches the argument the default behavior is there fore equivalent to until PE Accordingly the command JPS copy thru circle at 1 2 until END 12 3 4 6 Flo oO N bo P x tH is equivalent to VES circle at 1 2 circle at 3 4 circle at 5 6 box JB m 15 2 Debug Messages The command print accepts any number of arguments concatenates their output forms and writes the result to standard error Each argument must be an expression a position or a text string 24 15 3 Escape to Post Processor If you write command arg pic concatenates the arguments and pass them through as a line to troff or T X Each arg must be an expression a position or text This has a similar effect to a line beginning with or but allows the values of variables to be passed through 15 4 Executing Shell Commands The command sh anything macro expands the text in braces then executes it as a shell command This could be used to generate images or
20. data tables for later inclusion The delimiters shown as here may also be two copies of any one character not present in the shell command text In either case the body may contain balanced pairs Strings in the body may contain balanced or unbalanced braces in any case 16 Control flow constructs The pic language provides conditionals and looping For example pi atan2 0 1 for i 0to2 pi by 0 1 do Wo at 123 0 3 at 1 2 sin i 2 Wen at 1 2 cos 1 2 3 which yields this Figure 16 1 Plotting with a for loop The syntax of the for statement is for variable expr1 to expr2 by expr3 do X body X The semantics are as follows Set variable to expr1 While the value of variable is less than or equal to expr2 do body and increment variable by expr3 if by is not given increment variable by 1 If expr3 is prefixed by then variable will instead be multiplied by expr3 X can be any character not occurring in body or the two Xs may be paired braces as in the sh command The syntax of the if statement is as follows if expr then X if true X else Y if false Y Its semantics are as follows Evaluate expr if it is non zero then do if true otherwise do if false X can be any character not occurring in if true Y can be any character not occurring in if false Eithe or both of the X or Y pairs may instead be balanced pairs of braces and as in the sh com mand In either case the if true may contai
21. ded for clarity In contexts where it creates no ambiguity the pair of X and Y coordinates suffices without parentheses It is a good idea to avoid absolute coordinates however They tend to make picture descriptions diffi cult to understand and modify Instead there are quite a number of ways to specify locations relative to pic objects and previous locations 10 2 Locations Relative to Objects The symbol Here always refers to the position of the last object drawn or the destination of the last move Alone and unqualified a last circle or any other way of specifying a closed object or arc location refers as a position to the geometric center of the object Unqualified the name of a line or spline object refers to the position of the object start Also pic objects have quite a few named locations associated with them One of these is the object center which can be indicated redundantly with the suffix center or just c Thus last circle center is equivalent to last circle 10 2 1 Locations Relative to Closed Objects Every closed object box circle ellipse or block composite also has eight compass points associ ated with it 14 hw n ne Ww C e SW S se Figure 10 1 Compass points these are the locations where eight compass rays from the geometric center would intersect the figure So when we say last circle s we are referring to the south compass point of the last circle drawn The ex
22. e jJumperblock 1 0 1 0 1 1 PE It yields the following Jumpers in state 110010 Jumpers in state 101011 Figure 14 1 Sample use of a macro This macro example illustrates how you can combine brace grouping and variable assignment to write true functions One detail the example above does not illustrate is the fact that macro argument parsing is not token oriented If you call jumper 1 the value of 1 will be 1 You could even call jumper big string to give 1 the value big string 23 If you want to pass in a coordinate pair you can avoid getting tripped up by the comma by wrapping the pair in parentheses Macros persist through pictures To undefine a macro say undef name for example undef jumper undef jumperblock would undefine the two macros in the jumper block example 15 Import Export Commands Commands that import or export data between pic and its environment are described here 15 1 File and Table Insertion The statement copy filename inserts the contents of filename in the pic input stream Any PS PE pair in the file will be ignored This you can use this to include pre generated images A variant of this statement replicates the copy thru feature of grap 1 The call copy filename thru macro calls macro which may be either a name or replacement text on the arguments obtained by breaking each line of the file into blank separated fields The macro may h
23. empt to scale it to the given dimensions in inches In no case however will the X and Y dimensions of the picture exceed the values of the style variables maxpswid and maxpsheight which default to the normal 8 5i by 11i page size 31 If the ending PE is replaced by PF the page vertical position is restored to its value at the time PS was encountered Another alternate form of invocation is PS lt FILENAME which replaces the PS line with a file to be interpreted by pic but this feature is deprecated The PS PE and PF macros to perform centering and scaling are normally supplied by the post processor In the following either I or a new line starts an alternative lt statement gt lt command gt lt command gt n lt command gt lt primitive gt lt attribute gt LABEL lt command gt LABEL lt command gt lt position gt lt command gt VARIABLE lt any expr gt up down left right COMMAND LINE command lt print arg gt print lt print arg gt sh BALANCED TEXT copy FILENAME copy FILENAME thru MACRONAME until TEXT copy FILENAME thru BALANCED BODY until TEXT for VARIABLE lt expr gt to lt expr gt by lt expr gt do BALANCED BODY if lt any expr gt then BALANCED BODY else BALANCED BODY reset VARIABLE VARIABLE
24. g radii The move command can also take a dimension which just tells it how many inches to move in the current direction Ellipses are sized to fit in the rectangular box defined by their axes and can be resized with width and height like boxes You can also change the radius of curvature of an arc with rad ius which specifies the radius of the circle of which the arc is a segment Larger values yield flatter arcs oe wth 0 1 0 2 0 3 Figure 4 4 are rad with increasing radii Observe that because an arc is defined as a quarter circle increasing the radius also increases the size of the arc s bounding box 4 5 The same Keyword In place of a dimension specification you can use the keyword same This gives the object the same size as the previous one of its type As an example the program PS box box wid 1 ht 1 box same box PE gives you Figure 4 5 The same keyword 5 Generalized Lines and Splines 5 1 Diagonal Lines It is possible to specify diagonal lines or arrows by adding multiple up down left and right modi fiers to the line object Any of these can have a multiplier To understand the effects think of the drawing area as being gridded with standard sized boxes line up left arrow up left 1 arrow up left 1 5 arrow up left 2 Figure 5 1 Diagonal arrows dotted boxes show the implied 0 5 inch grid 5 2 Multi Segment Line Objects A line or arro
25. given by the stule variable fillval DWB pic and gpic have opposite conventions for fill values and different defaults DWB fillval defaults to 0 3 and smaller values are darker GNU fillval uses 0 for white and 1 for black Figure 6 5 circle fill move circle fill 0 4 move circle fill 0 9 GNU gpic makes some additional guarantees A fill value greater than 1 can also be used this means fill with the shade of gray that is currently being used for text and lines Normally this will be black but output devices may provide a mechanism for changing this The invisible attribute does not affect the fill ing of objects Any text associated with a filled object will be added after the object has been filled so that the text will not be obscured by the filling The closed object modifier solid is equivalent to fill with the darkest fill value DWB pic had this capability but mentioned it only in a reference section 6 8 Colored Objects As a GNU extension three additional modifiers are available to specify colored objects outline sets the color of the outline shaded the fill color and color sets both All three keywords expect a suffix speci fying the color Example Figure 6 6 box color yellow arrow color cyan circle shaded green outline black Alternative spellings are colour colored coloured and outlined Currently color support is not available in TEX mode Predefined color names for groff 1 are in the device
26. intf may contain gtn roff font changes size changes and local motions provided those changes are undone before the end of the current item A position is an x y coordinate pair There are lots of different ways to specify positions 34 lt position gt lt position not place gt lt place gt lt position not place gt lt expr pair gt lt position gt lt expr pair gt lt position gt lt expr pair gt lt position gt lt position gt lt expr gt of the way between lt position gt and lt position gt lt expr gt lt lt position gt lt position gt gt lt expr pair gt lt expr gt lt expr gt expr pair lt place gt lt label gt lt label gt lt corner gt lt corner gt of lt label gt Here lt label gt LABEL LABEL lt nth primitive gt lt corner gt m se aw ss ne se nw sw cfenter start end tfop b ot tom l eft rlight left right lt top of gt lt bottom of gt lt north of gt lt south of gt lt east of gt lt west of gt lt center of gt lt start of gt lt end of gt upper left lower left upper right lower right lt xxx oOf gt XXX followed by of lt nth primitive gt lt ordinal gt lt object type gt lt ordinal gt last lt object type gt lt ordinal gt INT th INT st INT nd INT rd lt any expr gt th
27. inuxdoc sgml sources Texinfo sources format ms intermediate form texi2roff HTML Figure 20 2 Hypothetical production flow for dual mode publishing 21 PIC Reference This is an annotated grammar of pic 21 1 Lexical Items These tools don t yet exist In general pic is a free format token oriented language that ignores whitespace outside strings But certain lines and contructs are specially interpreted at the lexical level A comment begins with and continues to n comments may also follow text in a line A line beginning with a period or backslash may be interpreted as text to be passed through to the post processor depending on command line options An end of line backslash is interpreted as a request to continue the 30 line the backslash and following newline are ignored 21 2 se Here are the grammar terminals INT A positive integer NUMBER A floating point numeric constant May contain a decimal point or be expressed in scientific notation in the style of printf 3Y s e escape A trailing i or T indicating the unit inch is ignored TEXT A string enclosed in double quotes A double quote within TEXT must be preceded by a back slash Instead of TEXT you can use sprintf TEXT lt expr gt except after the until and last keywords and after all ordinal keywords th and friends
28. ional R gtroff 1 E oss a eves za Figure 3 1 Flow of pic data This was produced from the following pic program PS ellipse document arrow box width 0 6 fIpic fP 1 arrow box width 1 1 fIgtbl fP 1 or fIgeqn f P 1 optional dashed arrow box width 0 6 flIgtroff fP 1 arrow ellipse PostScript PE This little program illustrates several pic basics Firstly we see how to invoke three object types ellipses arrows and boxes We see how to declare text lines to go within an object and that text can have font changes in it We see how to change the line style of an object from solid to dashed And we see that a box can be made wider than its default size to accommodate more text we ll discuss this facility in detail in the next section We also get to see pic s simple syntax Statements are ended by newlines or semicolons String quotes are required around all text arguments whether or not they contain spaces In general the order of command arguments and modifiers like width 1 2 or dashed doesn t matter except that the order of text arguments is significant Here are all but one of the basic pic objects at their default sizes line arrow J box arc Figure 3 2 Basic pic objects The missing simple object type is a spline There is also a way to collect objects into block compos ites which allows you to treat the whole group as
29. is a F9 K X x 3 y 3 prink x2 y prints 3 5 You can use the height width radius and x and y coordinates of any object or corner in expressions If A is an object label or name all the following are valid 21 A X x coordinate of the center of A A ne y y coordinate of the northeast corner of A A wid the width of A A ht and its height 2nd last circle rad the radius of the 2nd last circle Note the second expression showing how to extract a corner coordinate Basic arithmetic resembling those of C operators are available and So is for exponen tiation Grouping is permitted in the usual way using parentheses GNU gpic allows logical operators to appear in expressions logical negation not factorial amp amp gt lt lt gt Various built in functions are supported sin x cos x log x exp x sqrt x max x y atan2 x y min x y int x rand and srand Both exp and log are base 10 int does integer truncation rand returns a random number in 0 1 and srand sets the seed for a new sequence of pseudo random numbers to be returned by rand srand is a GNU extension GNU gpic also documents a one argument form or rand rand x which returns a random number between 1 and x but this is deprecated and may be removed in a future version The function sprintf behaves like a C sprintf 3 function that only takes e f and
30. ject with a rectangular shape that of the bounding box of all the elements Variable and label assignments within a block are local to the block Current direction of motion is restored to the value at start of block upon exit Position is not restored unlike instead the current position becomes the exit position for the current direction on the block s bounding box lt attribute gt h eigh t lt expr gt wid th lt expr gt rad ius lt expr gt diam eter lt expr gt up lt expr gt down lt expr gt left lt expr gt right lt expr gt from lt position gt to lt position gt at lt position gt with lt path gt with lt position gt by lt expr pair gt 33 set height of closed figure set width of closed figure set radius of circle arc set diameter of circle arc move up move down move left move right set from position of open figure set to position of open figure set center of open figure fix corner named point at specified location fix position of object at specified location set object s attachment point then sequential segment composition dotted lt expr gt set dotted line style dashed lt expr gt set dashed line style thick ness lt expr gt set thickness of lines chop lt expr gt chop end s of segment t gt 7 lt lt gt decorate with arrows invis ible make primitive invisible solid ma
31. ke closed figure solid fill ed lt expr gt set fill density for figure colo u r ed TEXT set fill and outline color for figure outline d TEXT shaded TEXT set outline color for figure set fill color for figure same copy size of previous object cw CCW set orientation of curves ljust rjust adjust text horizontally above below adjust text vertically aligned align parallel to object TEXT TEXT text within object lt expr gt motion in the current direction Missing attributes are supplied from defaults inappropriate ones are silently ignored For lines splines and arcs height and width refer to arrowhead size The at primitive sets the center of the current object The with attribute fixes the specified feature of the given object to a specified location Note that with is incorrectly described in the Kernighan paper The by primitive is not documented in the tutorial portion of the Kernighan paper and should prob ably be considered unreliable The primitive arrow is a synonym for line gt Text is normally an attribute of some object in which case successive strings are vertically stacked and centered on the object s center by default Standalone text is treated as though placed in an invisible box A text item consists of a string or sprintf expression optionally followed by positioning information Text or strings specified with spr
32. llipseht 0 5 Default height of an ellipse ellipsewid 0 75 Default width of an ellipse moveht 0 5 Default length of vertical move movewid 0 75 Default length of horizontal move textht 0 Default height of box enclosing a text object 36 Style Variable Default What It Does textwid 0 Default width of box enclosing a text object arrowht 0 1 Length of arrowhead along shaft arrowwid 0 05 Width of rear of arrowhead arrowhead 1 Enable disable arrowhead filling dashwid 0 05 Interval for dashed lines maxpswid 11 Maximum width of picture maxpsht 8 5 Maximum height of picture scale 1 Unit scale factor fillval 0 5 Default fill value Any of these can be set by assignment or reset using the reset statement Style variables assigned within L blocks are restored to their beginning of block value on exit top level assignments persist across pic tures Dimensions are divided by scale on output All pic expressions are evaluated in floating point units are always inches a trailing i or T is ignored Expressions have the following simple grammar with semantics very similar to C expressions lt expr gt i VARIABLE NUMBER lt place gt lt place attribute gt lt expr gt lt op gt lt expr gt lt expr gt lt any expr gt lt expr gt lt funcl gt lt any expr gt lt func2 gt lt any expr gt lt any expr gt rand lt place attribute gt x y h eigh t wid
33. macro files for example ps tmac additional colors can be defined with the defcolor request see the manual page of GNU troff 1 for more details pic assumes that at the beginning of a picture both glyph and fill color are set to the default value 7 More About Text Placement By default text is centered at the geometric center of the object it is associated with The modifier ljust causes the left end to be at the specified point which means that the text lies to the right of the speci fied place the modifier rjust puts the right end at the place The modifiers above and below center the text one half line space in the given direction Text attributes can be combined 10 i F ljust above just text rjust tex i rjust below Figure 7 1 Text attributes What actually happens is that n text strings are centered in a box that is textwid wide by textht high Both these variables are initially zero that is pic s way of not making assumptions about tg roff 1 s default point size In GNU gpic objects can have an aligned attribute This will only work when the postprocessor is grops Any text associated with an object having the aligned attribute will be rotated about the center of the object so that it is aligned in the direction from the start point to the end point of the object Note that this attribute will have no effect for objects whose start and end points are coincident 8 More About Direction Changes We ve
34. n line down from 3rd box C line down line down from 4th box D line down s filter s filter Ss filter move down 1 from last s Anchor box wid 1 ht 0 75 fBms fR arrow from Top A end to Anchor arrow from Top B end to 1 3 of arrow from Top C end to 2 3 of arrow from Top D end to Anchor nw ne PostScript column move to Anchor line down left then down gt filter fBpic fP arrow filter arrow filter arrow filter arrow box PostScript SW fBeqn fP fBtb1l fP fBgroff fP HTML column move to Anchor se line down right then down gt A filter dotted fBpic2img fP arrow B filter dotted fBeqn2html1 fP arrow C filter dotted fBtbl2html1 P arrow filter fBms2html fP arrow box HTML Nonexistence caption box dashed wid 1 at B 2 0 intermediate These line chop 0 chop 0 1 dashed from last box line chop 0 chop 0 1 dashed from last box sources wid 1 5 fBhtml2ms fP fBformat fP fBtexi2roff fP form the way between Anchor nw and Anchor ne the way between Anchor nw and Anchor ne tools don t yet exist n nw to A e gt w to B e gt ms sources 29 line chop 0 chop 0 1 dashed from last box HTML sources html2ms A iy eqn groff PostScript Sw to C e gt l
35. n balanced pairs of braces None of these delimiters will be 25 seen inside strings All the usual relational operators my be used in conditional expressions logical negation not fac torial amp amp gt lt lt gt String comparison is also supported using and String comparisons may need to be parenthe sized to avoid syntactic ambiguities 17 Interface To gt roff The output of pic is gt roff drawing commands The GNU gpic 1 command warns that it relies on drawing extensions present in groff 1 that are not present in troff 1 17 1 Scaling Arguments The DWB pic 1 program will accept one or two arguments to PS which is interpreted as a width and height in inches to which the results of pic 1 should be scaled width and height scale independently If there is only one argument it is interpreted as a width to scale the picture to and height will be scaled by the same proportion GNU gpic is less general it will accept a single width to scale to or a zero width and a maximum height to scale to With two non zero arguments it will scale to the maximum height 17 2 How Scaling is Handled When pic processes a picture description on input it passes PS and PE through to the postproces sor The PS gets decorated with two numeric arguments which are the X and Y dimensions of the picture in inches The post processor can use these to reserve space for the picture and center it
36. other location can be For example if we added Hi at A Caption the result would look like this _ uy Figure 11 2 Adding a caption using interior labeling You can also use interior labels in either part of a with modifier This means that the example com posite could be placed relative to its caption box by a command containing with A Caption at Note that both width and height of the block composite object are always positive 19 box wid 0 5 ht 0 5 box wid 0 75 ht 0 75 box wid 0 5 ht 0 5 box wid 0 75 ht 0 75 Figure 11 3 Composite block objects always have positive width and height Blocks may be nested This means you can use block attachment points to build up complex dia grams hierarchically from the inside out Note that last and the other sequential naming mechanisms don t look inside blocks so if you have a program that looks like PS P box foo ellipse bar Q box baz ellipse quxx random text arrow from 2nd last PE PE the arrow in the last line will be attached to object P not object Q In DWB pic only references one level deep into enclosed blocks were permitted GNU gpic removes this restriction The combination of block variable scoping assignability of labels and the macro facility that we ll describe later on can be used to simulate functions with local variables just wrap the macro body in block braces
37. pful in placing an object at one of the corners of the virtual box defined by two other objects A B A is here A B is here B Figure 10 5 Using x y composition 10 4 Using Locations There are four ways to use locations at from to and with All three are object modifiers that is you use them as suffixes to a drawing command 16 The at modifier says to draw a closed object or arc with its center at the following location or to draw a line spline arrow starting at the following location The to modifier can be used alone to specify a move destination The from modifier can be used alone in the same way as at The from and to modifiers can be used with a line or arc command to specify start and end points of the object In conjunction with named locations this offers a very flexible mechanism for connecting objects For example the following program PS box from move 0 75 ellipse to arc cw from 1 3 of the way between last box n and last box ne to last ellipse n PE yields from to Figure 10 6 A tricky connection specified with English like syntax The with modifier allows you to identify a named attachment point of an object or a position within the object with another point This is very useful for connecting objects in a natural way For an example consider these two programs box wid 0 5 ht 0 5 bord 0 5 aeS Dox wid OSE
38. pla nation of Figure 7 3 s program is now complete In case you dislike compass points the names top bottom left and right are synonyms for n s e and w respectively they can even be abbreviated to t b l and r The names center top bottom left right north south east and west can also be used without the leading dot in a prefix form marked by of thus center of last circle and top of 2nd last ellipse are both valid object references Finally the names left and right can be prefixed with upper and lower which both have the obvious meaning Arc objects also have compass point they are the compass points of the implied circle 10 2 2 Locations Relative to Open Objects Every open object line arrow arc or spline has three named points start center or c and end They can also be used without leading dots in the of prefix form The center of an arc is the center of its circle but the center of a line path or spline is halfway between its endpoints end Start center Start center 7 end Start end center center 7 end Start Figure 10 2 Special points on open objects 10 3 Ways of Composing Positions Once you have two positions to work with there are several ways to combine them to specify new positions 10 3 1 Vector Sums and Displacements Positions may be added or subtracted to yield a new position to be more precise you can only add a position and an expression pair the la
39. s filled with the current outline color 6 5 Line Thickness It s also possible to change the line thickness of an object this is a GNU extension DWB pic doesn t support it The default thickness of the lines used to draw objects is controlled by the linethick variable This gives the thickness of lines in points A negative value means use the default thickness in TRX output mode this means use a thickness of 8 milliinches in T X output mode with the c option this means use the line thickness specified by ps lines in troff output mode this means use a thickness proportional to the pointsize A zero value means draw the thinnest possible line supported by the output device Initially it has a value of 1 There is also a thickness attribute which can be abbreviated to thick For example cir cle thickness 1 5 would draw a circle using a line with a thickness of 1 5 points The thickness of lines is not affected by the value of the scale variable nor by any width or height given in the PS line 6 6 Invisible Objects The modifier invis ible makes an object entirely invisible This used to be useful for positioning text in an invisible object that is properly joined to neighboring ones Newer DWB versions and GNU pic treat stand alone text in exactly this way 6 7 Filled Objects It is possible to fill boxes circles and ellipses The modifier fill ed accomplishes this You can suf fix it with a fill value the default is
40. spondingly 4 1 Default Sizes of Objects Here are the default sizes for pic objects Object Default Size box 0 75 wide by 0 5 high circle 0 5 diameter ellipse 0 75 wide by 0 5 high arc 0 5 radius Object Default Size line 0 5 long arrow 0 5 long The simplest way to think about these defaults is that they make the other basic objects fit snugly into a default sized box 4 2 Objects Do Not Stretch Text is rendered in the current font with normal troff line spacing Boxes circles and ellipses do not automatically resize to fit enclosed text Thus if you say box this text far too long for a default box you ll get this this text is far too long for a default box Figure 4 1 Boxes do not automatically resize which is probably not the effect you want 4 3 Resizing Boxes To change the box size you can specify a box width with the width modifier this text is far too long for a default box Figure 4 2 Result of box width 3 This modifier takes a dimension in inches There is also a height modifier that will change a box s height The width keyword may be abbreviated to wid the height keyword to ht 4 4 Resizing Other Object Types To change the size of a circle give it a rad ius or diam eter modifier this changes the radius or diameter of the circle according to the numeric argument that follows ee ie Figure 4 3 Circles with increasin
41. th rad lt op gt pam x eget m gt Need gt lt funcl gt sin cos log exp sqrt int rand srand lt func2 gt atan2 max min Both exp and log are base 10 int does integer truncation and rand returns a random number in 0 1 There are define and undef statements which are not part of the grammar they behave as pre proces sor macros to the language These may be used to define pseudo functions define name replacement text This defines name as a macro to be replaced by the replacement text not including the braces The macro may be called as name arg1 arg2 argn The arguments if any will be substituted for tokens 1 2 n appearing in the replacement text To undefine a macro say undef name specifying the name to be undefined 37 22 History and Acknowledgements Original pic was written to go with Joseph Ossanna s original troff 1 by Brian Kernighan and later re written by Kernighan with substantial enhancements apparently as part of the evolution of troff 1 into ditroff 1 to generate device independent output The language had been inspired by some earlier graphics languages including ideal and grap Kernighan credits Chris van Wyk the designer of ideal with many of the ideas that went into pic delim The pic language was originally described by Brian Kernighan in Bell Labs Computing Sci ence Technical Report 116 you can obt
42. tter must be on the right side of the addition or subtraction sign The result is the conventional vector sum or difference of coordinates For example last box ne 0 1 0 is a valid position This example illustrates a common use to define a position slightly offset from a named one say for captioning purposes 15 10 3 2 Interpolation Between Positions A position may be interpolated between any two positions The syntax is fraction of the way between position and position2 For example you can say 1 3 of the way between here and last ellipse ene The fraction may be in numerator denominator form or may be an ordinary number values are not restricted to 0 1 As an alternative to this verbose syntax you can say fraction lt positionl position2 gt thus the example could also be written as 1 3 lt here last ellipse gt Figure 10 3 P 1 3 of the way between last arrow start and last arrow end This facility can be used for example to draw double connections yin yang Figure 10 4 Doubled arrows You can get Figure 10 4 from the following program PS A box yin move B box yang arrow right at 1 4 lt A e A ne gt arrow left at 1 4 lt B w B sw gt PE Note the use of the short form for interpolating points 10 3 3 Projections of Points Given two positions p and q the position p q has the X coordinate of p and the Y coordinate of q This can be hel
43. u have to be able to name objects The pic language has rich facilities for this that try to emulate the syntax of English 9 1 Naming Objects By Order Of Drawing The simplest and generally the most useful way to name an object is with a last clause It needs to be followed by an object type name box circle ellipse line arrow spline or the last type refers to a composite object which we ll discuss later So for example the last circle clause in the program attached to Figure 9 1 3 refers to the last circle drawn More generally objects of a given type are implicitly numbered starting from 1 You can refer to say the third ellipse in the current picture with 3rd ellipse or to the first box as 1st box or to the fifth text string which isn t an attribute to another object as 5th Objects are also numbered backwards by type from the last one You can say 2nd last box to get the second to last box or 3rd last ellipse to get the third to last ellipse In places where nth is allowed expr th is also allowed Note that th is a single token no space is allowed between the and the th For example for i 1 to 4 do line from i th box nw to itl th box se 9 2 Naming Objects With Labels You can also specify an object by referring to a label A label is a word which must begin with a capital letter followed by a colon you declare it by placing it immediately before the object drawing com
44. ust add to the beginning of each equation the extra information space 0 He gives the following example arrow box Sspace 0 H omega over 1 H omega S arrow delim space 0 Htomega over HCamega Figure 17 1 Equations within pictures 18 Interface to TeX TEX mode is enabled by the t option In TEX mode pic will define a vbox called graph for each picture You must yourself print that vbox using for example the command centerline box graph Actually since the vbox has a height of zero this will produce slightly more vertical space above the picture than below it centerline raise lem box graph would avoid this You must use a TEX driver that supports the tpic specials version 2 Lines beginning with are passed through transparently a is added to the end of the line to avoid unwanted spaces You can safely use this feature to change fonts or to change the value of baselineskip Anything else may well produce undesirable results use at your own risk Lines beginning with a period are not given any special treatment The TeX mode of pic 1 will not translate troff font and size changes included in text strings 19 Obsolete Commands GNU gpic 1 has a command plot expr text This is a text object which is constructed by using text as a format string for sprintf with an argument of expr If text is omitted a format string of g is used Attributes can be specified in the s
45. w object may actually be a path consisting of any number of segments of varying lengths and directions To describe a path connect several line or arrow commands with the keyword then Figure 5 2 line right 1 then down 5 left 1 then right 1 5 3 Spline Objects If you start a path with the spline keyword the path vertices are treated as control points for a spline curve fit z p VEE The spline curve with tangents displayed Figure 5 3 spline right 1 then down 5 left 1 then right 1 You can describe many natural looking but irregular curves this way For example aS spline right then up then left then down gt spline left then up right then down right gt Figure 5 4 Two more spline examples Note the arrow decorations Arrowheads can be applied naturally to any path based object line or spline We ll see how in the next section 6 Decorating Objects 6 1 Dashed Objects We ve already seen that the modifier dashed can change the line style of an object from solid to dashed GNU gpic permits you to dot or dash ellipses circles and arcs and splines in TEX mode only some versions of DWB may only permit dashing of lines and boxes It s possible to change the dash inter val by specifying a number after the modifier default 0 05 0 1 0 15 0 2 Figure 6 1 Dashed objects 6 2 Dotted Objects Another available qualifier is dotted GNU gpic permits you
Download Pdf Manuals
Related Search