PIC A Graphics Language for Typesetting Revised User Manual
Contents
1. Notice how the second argument may be used to pass in arbitrary contents Coordinates like x y may be enclosed in parentheses as in x y so they can be included in a macro argument 11 File Copy The statement copy filename inserts the contents of the named file at that point in the input Any PS or PE lines within the file are ignored so previously prepared pictures can be used as parts of larger ones without editing PIC also provides the copy thru mechanism found in GRAP copy file thru macro name copies file treating each line as an invocation of the named macro each field being an argument A literal macro may be used instead of a name copy file thru X macro replacement text X and if no file name is given the remainder of the input until the next PE is used So to plot a set of circles at points whose coordinates and radii are included in line copy thru circle rad 3 at 1 2 OO 205 1 le tll 16 The sh command executes an arbitrary commandline sh X anything X As always X is any character not in anything 12 Loops and Conditionals PIC provides an if statement and a for loop piSe lt a2 pi atan2 0 1 for i 0 to 2 pi by 0 1 do X MoM atiy O s at i 2 sin i 2 toun at i 2 cos i 2 ps 2 The by clause is optional if the value is preceded by a the steps are multiplicative not additive The body of the loop is delimited by any character not found within2. 10 Sometimes it is desirable to have a line intersect a circle at a point which is not one of the eight com pass points that PIC knows about In such cases the proper visual effect can be obtained by using the attribute chop to chop off part of the line circlerad circle a circle b circle c arrow from arrow from 0 15 at lst circle at lst circle lst circle to lst circle to arrowhead 7 0 4 0 6 0 4 0 6 2nd circle chop 3rd circle chop a So By default the line is chopped by circlerad at each end This may be changed line chop r chops both ends by r and line chop rl chop r2 chops the beginning by r and the end by r2 More complicated intersections can be computed with the built in trigonometric functions listed in the next section There is one other form of positioning that is sometimes useful to refer to a point some fraction of the way between two other points This can be expressed in PIC as fraction of the way between position and position2 fraction is any expression and position and position2 are any positions You can abbreviate this rather windy phrase of the way is optional and the whole thing can be written instead as fraction lt position position2 gt As a pair of examples box arrow right from 1 3 of the way between last box ne and last box se arrow right from 2 3 lt last box ne last box se gt J A ellipse ellipse ht 2 wi
3. a box we ti creates a standard box 3 4 inch wide 1 2 inch high and centers the two pieces of text in it this is a box Each line of text is a separate quoted string Quotes are mandatory even if the text contains no blanks Of course there needn t be any text at all Each line will be printed in the current size and font centered horizontally and separated vertically by the current TROFF line spacing PIC does not center the complete drawing itself but the default definitions of PS and PE in the ms macro package do You can use circle or ellipse in place of box Text is centered on lines and arrows if there is more than one line of text the lines are centered above and below line this is a line this is a line arrow this is an arrow this is geet Wee aa an arrow Boxes and lines may be dashed or dotted just add the word dashed or dotted after box or line line dashed dashed line dashed line Arcs by default turn 90 degrees counterclockwise from the current direction you can make them turn clockwise by saying arc cw line arc arc cw arrow A spline might well do this job better we will return to that shortly As you might guess arc arc arc arc draws a circle though not very efficiently Notice that several commands can be put on a single line if they are separated by semicolons Objects are normally drawn one after another left to right and connected at
4. box C box box wid 2 boxwid D box Block boxht 2 dw boxwid 2 dw movewid 2 dh A box move B box move C box move box invis wid 2 boxwid move D box with t at Ptr s 0 h 2 arrow from Ptr A to Block A nw dh 0 arrow from Ptr B to Block B nw dh 0 arrow from Ptr C to Block C nw dh 0 arrow from Ptr D to Block D nw dh 0 box dashed ht last ht tdw wid last wid dw at last This produces O nila rt ae Porc re q l J i EEES TER oe E E hegre a 10 Macros PIC provides a basic macro facility In the simplest form define name X replacement text X defines name to be the replacement text X is any character that does not appear in the replacement Any subsequent occurrence of name will be replaced by replacement text Macros may have arguments If the replacement text of a macro definition contains occurrences of 1 2 etc these will be replaced by the corresponding actual arguments when the macro is invoked The invocation for a macro with arguments is name argl arg2 Non existent arguments are replaced by null strings Macro definitions last from picture to picture a macro 15 definition can be removed by undef macro name As an example one might define a square by define square X box ht 1 wid 1 2 X and use it as square 1l one inch square 0 5 square 0 25 s 4tiny s 4 dashed one moa x tiny inch eae
5. 5 lineht 0 5 movewid 0 5 moveht 0 5 textwid 0 textht 0 arrowwid 0 05 arrowht 0 1 dashwid 0 1 arrowhead 2 scale 1 These may be changed at any time and the new values remain in force from picture to picture until changed again or reset by a reset statement Variables changed within and revert to their previous value upon exit from the block Dimensions are divided by scale during output Expressions Expressions in PIC are evaluated in floating point All numbers representing dimensions are taken to be in inches 957 expr expr op expr expr expr expr variable number place x place y place ht place wid place rad Sin expr cos expr atan2 expr expr log expr exp expr sqrt expr max expr expr min expr expr int expr rand op Definitions The define and undef statements are not part of the grammar define define name X replacement text X undef undef name Occurrences of 1 2 etc in the replacement text will be replaced by the corresponding arguments if name is invoked as name argl arg2 Non existent arguments are replaced by null strings Replacement text may contain newlines The undef statement removes the definition of a macro The PS and PE Macros This is the default definition of the PS and PE macros de PS start picture 1 is height 2 is width in inches sp 3 ein n lu 2 2u ene S 1 de PE end of picture
6. Attributes like ht and wid and positions like at can be written out in any order So box ht 0 2 wid 0 2 at 0 0 box at 0 0 wid 0 2 ht 0 2 box ht 0 2 at 0 0 wid 0 2 are all equivalent though the last is harder to read and thus less desirable The from and to attributes are particularly useful with arcs to specify the endpoints By default arcs are drawn counterclockwise at 0 0 ate gt from 0 5 0 to 0 0 lt 5 arc gt cw from 0 0 to T035 The radius can be made large to provide flat arcs arc gt ecw from 0 0 to 2 0 rad 15 If the circle is under specified PIC guesses a radius and or center you will have to provide them explicitly if the guess is wrong We said earlier that objects are normally connected left to right This is an over simplification The truth is that objects are connected together in the direction specified by the most recent up down left or right either alone or as part of some object Thus in arrow left box arrow circle arrow the left implies connection towards the left This could also be written as left arrow box arrow circle arrow Objects are joined in the order determined by the last up down etc with the entry point of the sec ond object attached to the exit point of the first which is fixed at the time of entry Entry and exit points for boxes circles and ellipses are on opposite sides This automatic connection and direction selection works well if the d
7. PIC variables this will be discussed in Section 6 The attributes of height which you can abbreviate to ht and width or wid apply to boxes circles ellipses and to the head on an arrow The attributes of radius or rad and diameter or diam can be used for circles and arcs if they seem more natural Lines and arrows are most easily drawn by specifying the amount of motion from where one is right now in terms of directions Accordingly the words up down left and right and an optional distance can be attached to line arrow and move line up 1 right 2 arrow left 2 move left 0 1 line lt gt down 1 height rjust height The notation lt gt indicates a two headed arrow use gt for a head on the end and lt for one on the start Lines and arrows are really the same thing in fact arrow is a synonym for line gt If you don t specify any distance after up down etc PIC uses the standard distance line up right line down line down left line up If you omit the direction associated with a distance the current direction is used Boxes and lines may be dotted or dashed box dotted line dotted move line dashed box dashed If there is a number after dot the dots will be approximately that far apart You can also control the size of the dashes at least somewhat if there is a length after the word dashed the dashes will be that long and the intervening spaces will be as close as possible to th
8. it or in a special dispensation for program mers by braces which may also be used for definitions copy sh and if statements The if statement is if expression then X anything X else X anything X where the else clause is optional The expression may use the usual relational operators gt gt lt lt amp amp and pi atan2 0 1 for i 0 to pi by 0 1 do if s sin i gt 0 8 then s 0 8 Wx at 17 27 S72 A string comparison using or is also permitted to compare quoted strings if stringl string2 then 13 TROFF Interface PIC is usually run as a TROFF preprocessor pic file troff ms Run it before EQN if it is also present If the PS line looks like PS lt file x Fs then the contents of file are inserted in place of the PS line whether or not the file contains PS or PE This feature is deprecated in favor of the copy statement PIC copies the PS and PE lines from input to output intact except that it adds two things on the same line as the PS PS hw h and w are the picture height and width in units The ms macro package has simple definitions for PS and PE that cause pictures to be centered and offset a bit from surrounding text See the appendix If PF is used instead of PE the position after printing is restored to where it was before the pic ture started instead of being at the bottom F is for fl
9. reset to default values with reset The undef statement removes a macro definition Arrowheads may be filled with the arrowhead variable their positioning is improved on arcs The width and height of the generated picture may be set independently from the PS line The state of fill or no fill mode is preserved around a picture Input numbers may be expressed in E notation Numerous internal changes have been made as well Any number of objects text strings etc may be used the only limit is total available memory Output is now produced in inches instead of units for a particular typesetter so most need for the T option has gone away
10. 9 diagnostic symbol message Ss a table printer lexical syntactic corrector corrector source lexical tokens intermediate semantic pe a parser Hae code analyzer code checker PSS ps 8 arrow source code LA box lexical analyzer arrow tokens above P box parser arrow intermediate code Sem box semantic checker arrow arrow lt gt up from top of LA LC box lexical corrector arrow lt gt up from top of P Syn box syntactic corrector arrow up DMP box diagnostic message printer arrow lt gt right from right of DMP ST box symbol table arrow from LC ne to DMP sw arrow from Sem nw to DMP se arrow lt gt from Sem top to ST bot PE There are eighteen objects boxes and arrows in the picture and one line of PIC input for each this seems like an acceptable level of verbosity 20 input OO rollers CPU 16 bit mini character CRT Paper Basic Digital Typesetter PS ps 2 circle DISK arrow character defns CPU box CPU 16 bit mini arrow lt from top of CPU up input rjust arrow CRT CRT ljust line from CRT 0 0 075 up 0 15 then right 0 5 then right 0 5 up 0 25 then down 0 5 0 15 then left 0 5 up 0 25 then left 0 5 Paper CRT 1 05 0 75 arrow lt from Paper down 1 5 l paper ljust at end
11. B and 2nd last box refers to box A Numbering of objects can also be done from the beginning so boxes A and C are 1st box and 2nd box respectively To cut down the need for explicit coordinates objects have corners named by compass points B box B c ht 1 wid 1 5 B e at B e ljust B ne at B ne ljust B se at B se ljust B s at B s below B n at B n above B sw at B sw rjust B w at B w rjust B nw at B nw rjust B nw Bi B ne B w B c B e B sw Bs B se Note the use of 1just rjust above and below to alter the default positioning of text and of a blank within some strings to help space them away from a vertical line Lines and arrows have a start an end and a center in addition to corners Circles and ellipses have corners too an arc has the same corners as the circle of which it is a part The words left right top and bottom are synonyms for west east north and south It is sometimes easiest to position objects by positioning some part of one at some part of another for example the northwest corner of one at the southeast corner of another The with attribute permits this kind of positioning box ht 0 75 wid 0 75 box ht 0 5 wid 0 5 with sw at last box se Notice that the corner after with is written sw As another example consider ellipse ellipse ht 2 wid 3 with se at 1st ellipse nw ellipse ht 2 wid 3 with sw at 1st ellipse ne
12. December 1984 Bell Laboratories Murray Hill New Jersey 07974 Computing Science Technical Report No 116 PIC A Graphics Language for Typesetting Revised User Manual Brian W Kernighan PIC A Graphics Language for Typesetting Revised User Manual Brian W Kernighan Bell Laboratories Murray Hill New Jersey 07974 ABSTRACT PIC is a language for drawing simple figures on a typesetter The basic objects in PIC are boxes circles ellipses lines arrows arcs spline curves and text These may be placed anywhere at positions specified absolutely or in terms of previous objects The example below illustrates the style and basic capabilities of the language TBL EQN Be optional TROFF typesetter This picture was created with the input PS ellipse document arrow box PIC arrow box TBL EQN optional dashed arrow box TROFEF arrow llipse typesetter PE PIC is a TROFF preprocessor it passes most of its input through untouched but translates commands between PS and PE into TROFF commands that draw the pic tures This manual describes the version of PIC made available in December 1984 December 1984 PIC A Graphics Language for Typesetting Revised User Manual Brian W Kernighan Bell Laboratories Murray Hill New Jersey 07974 1 Introduction PIC is a language for drawing pictures It operates as yet another TROFF R Comp
13. Paks at sp 6 Summary of New Features The built in functions sin cos atan2 log exp sqrt max min int and rand are avail able The copy statement includes data from a file or that follows immediately copy filename copy thru macro copy filename thru macro The macro may be either the name of a defined macro or the body of a macro enclosed in some character not part of the body If no filename is given copy copies the input until the next PE 26 The for and if statements provide loops and decision making for var expr to expr by expr do X anything X if expr then X anything X else X anything X The by and else clauses are optional The expr in an if may use the usual relational operators or the tests str or str2 for two quoted strings The sh command executes any sequence of commands sh X anything X In all of the above braces may be used in place of X X Text strings are now first class citizens a statement beginning with a sequence of text strings is treated as an invisible box with the strings positioned at its center The variable textht and textwid may be set to any values to control positioning The height of n such strings is n X textht It is possible to convert expressions to formatted strings sprintf format expr expr is equivalent to a quoted string in any context Variants of f and g are the only sensible format conver sions Built in variables may be
14. Sci Tech Rept 54 I Bell Laboratories C Murray Hill New Jersey A J F Ossanna T NROFF TROFF User s Manual D October 1976 C Murray Hill N J D January 1979 preprocessor in the same style as EQN A Brian W Kernighan A Lorinda L Cherry T A System for Typesetting Mathematics J Commu nications of the ACM V 18 N 3 D 1975 P 151 157 K cacm acm TBL R Comp Sci Tech Rept 49 I Bell Laboratories C Murray Hill New Jersey A M E Lesk T Tbl A Program to For mat Tables D September 1976 J UNIX Programmer s Manual V 2 O Section 10 I Bell Laborato ries C Murray Hill N J D January 1979 and REFER R Comp Sci Tech Rept 69 A M E Lesk T Some Applications of Inverted Indexes on the UNIX System D 1978 J UNIX Programmer s Man ual V 2 O Section 11 I Bell Laboratories C Murray Hill N J D January 1979 with pictures marked by PS and PE PIC was inspired partly by Chris Van Wyk s early work on IDEAL T A High Level Language for Specifying Pictures A C J Van Wyk J ACM Transactions on Graphics V 1 N 2 D 1982 P 163 182 it has somewhat the same capabilities but quite a different flavor In particular PIC is much more procedural a picture is drawn by specifying sometimes in painful detail the motions that one goes through to draw it Other direct influences include the PICTURE language A John C Beatty T PIC TURE A picture drawing language for the Trix Red Report Editor R Lawrence Liverm
15. as in pic Taps The typesetter type may also be set with the environment variable TYPESETTER 14 Some Examples Herewith a handful of larger examples ndtable hashtab ndblock ea define ndblock box wid boxwid 2 ht boxht 2 down box same with t at bottom of last box box same boxht 2 boxwid 3 circlerad 3 dx 0 05 down box box boxe box ht 3 boxht Tem eo L box box box invis wid 2 boxwid hashtab with e at lst box w right Start box wid 5 with sw at lst box ne 4 2 Nl box wid 2 nl Dl box wid 3 dl N3 box wid 4 n3 D3 box wid 3 d3 box wid 4 N2 box wid 5 n2 D2 box wid 2 d2 arrow right from 2nd box ndblock spline gt right 2 from 3rd las spline gt right 3 from 2nd las arrow right from last box ndblock spline gt right 2 from 3rd las spline gt right 3 from 2nd las arrow right 2 linewid from L ndblock box then to Nl sw dx 0 box then to Dl sw dx 0 ct ct box to N2 sw dx 2 to N2 ct ct spline gt right 2 from 3rd last box to N3 sw dx 0 spline gt right 3 from 2nd last box to D3 sw dx 0 circlerad 3 circle invis ndblock at last box e 1 2 2 arrow dashed from last circle w to last box chop 0 chop 3 box invis wid 2 boxwid ndtable with e at Start w swt dx 0 box to D2 ssw dx lt 2 to D24 swt dx 0 1
16. at size line right 5 dashed move left 5 down 25 right line right 5 dashed 0 25 move left 5 down 25 right line right 5 dashed 0 5 move left 5 down 25 right line right 5 dashed 1 Dotted or dashed attributes apply only to lines and boxes You can make any object invisible by adding the word invis after it This is particularly useful for positioning things correctly near text box invis input arrow box invis output input output Text may be positioned on lines and arrows arrow on top of move arrow above below move arrow above above mov arrow below below move arrow above on top of below 6 above above SPONE F below below F The width of an arrowhead is the distance across its tail the height is tel PMance along the shaft The arrowheads in this picture are default size and shape As we said earlier arcs go 90 degrees counterclockwise from where you are right now and arc cw changes this to clockwise The default radius is the same as for circles but you can change it with the rad attribute It is also easy to draw arcs between specific places this will be described in the next section To put an arrowhead on an arc use one of lt gt or lt gt as with lines In all cases unless an explicit dimension for some object is specified you will get the default size If you want an object to have the same size as the previo
17. ay actually be a path that is it may consist of connected segments line right 1 then down 5 left 1 then right 1 A spline is a smooth curve guided by a set of straight lines just like the line above It begins at the same place ends at the same place and in between is tangent to the mid point of each guiding line The syntax for a spline is identical to a path line except for using spline instead of line line dashed right 1 then down 5 left 1 then right 1 spline from start of last line right 1 then down 5 left 1 then right 1 Long input lines can be split by ending each piece with a backslash 13 The elements of a path whether for line or spline are specified as a series of points either in absolute terms or by up down etc If necessary to disambiguate the word then can be used to separate compo nents as in spline right then up then left then down gt which is evidently not the same as spline right then up left then down gt A Notice that arrowheads may be put on the ends of a line or spline 9 Blocks Any sequence of PIC statements may be enclosed in brackets to form a block which can then be treated as a single object and manipulated rather like an ordinary box box Al box 2 arrow 3 above box 4 with n at last box s 0 0 1 Thing 2 rjust at last w 1 3 Thing 2 2 4 Notice that last type constructs treat blocks as a u
18. block troff command is any line that begins with a period Such a line is assumed to make sense in the con text where it appears accordingly if it doesn t work don t call Primitives The primitive objects are yaz primitive box circle ellipse arc line arrow spline move text list arrow isa synonym for line gt Attributes An attribute list is a sequence of zero or more attributes each attribute consists of a keyword per haps followed by a value attribute h eigh t expr wid th expr rad ius expr diam eter expr up opt expr down opt expr right opt expr left opt expr from position to position at position with corner by expr expr then dotted opt expr dashed opt expr chop opt expr gt lt lt gt invis same text list expr Missing attributes and values are filled in from defaults Not all attributes make sense for all primitives irrelevant ones are silently ignored The attribute at causes the geometrical center to be put at the specified place with causes the position on the object to be put at the specified place For lines splines and arcs height and width refer to arrowhead size A bare expr implies motion in the current direction Text Text is normally an attribute of some primitive by default it is placed at the geometrical center of the object Stand alone text is also permitted A text list is a list of text items a text item is a quoted string optionally followed by positioning reque
19. d 3 with se at 1st ellipse nw ellipse ht 2 wid 3 with sw at 1st ellipse ne circle rad 05 at 0 5 lt A nw A c gt circle rad 05 at 0 5 lt A ne A c gt arc from 0 25 lt A w A e gt to 0 75 lt A w A e gt Naturally the distance given by fraction can be greater than 1 or less than 0 6 Variables Expressions and Built in Functions It s generally a bad idea to write everything in absolute coordinates if you are likely to change things PIC variables let you parameterize your picture a 0 5 b 1 box wid a ht b ellipse wid a 2 ht 1 5 b Box2 Boxl a 2 b 2 Expressions may use the standard operators and and parentheses for grouping The most important variables are the predefined ones for controlling the default sizes of objects listed in Section 3 These may be set at any time in any picture and retain their values from picture to pic ture until reset You can use the height width radius and x and y coordinates of any object or corner in an expres sion Boxl x the x coordinate of the center of Boxl Boxl ne y the y coordinate of the northeast corner of Boxl Boxl wid the width of Boxl Boxl ht and its height 2nd last circle rad the radius of the 2nd last circle Any pair of expressions enclosed in parentheses defines a position furthermore such positions can be added or subtracted to yield new positions x y Xir Yi X2 Yo If p and p are positions then p41 p2 ref
20. ers to the point p x Dp y PIC provides a small collection of standard functions sin expr cos expr atan2 y x angle in radians log expr exp expr Beware both base 10 sqrt expr max e e min e e gt int expr integer part of expr rand random number between 0 and 1 7 More on Text Normally text is centered at the geometric center of the object it is associated with The attribute ljust causes the left end to be at the specified point which means that the text lies to the right of the specified place and rjust puts the right end at the place above and below center the text one half line space in the given direction x 2 Text attributes can be compounded arrow 1 ljust above ljust above ljust above Text is most often an attribute of some other object but you can also have self standing text origin 0 0 at 0 0 this is 1 1 at 1 box ht 1 wid 1 dotted with sw at 0 0 this is In effect n text strings are contained in an invisible box of width textwid and height n x textht The variables text wid and textht may be set to any values they are normally zero A list of numeric expressions can be converted to a formatted string with the sprintf function and used anywhere a quoted string can be B box wid log 20 sprintf width g height g B wid B ht rjust at B w width 1 30103 height 0 5 8 Lines and Splines A line m
21. irection doesn t change but it will occasionally surprise you arrow circle down arrow The arrow comes out of the right side of the circle not the bottom as might be expected If a set of commands is enclosed in braces the current position and direction of motion when the group is finished will be exactly where it was when entered Nothing else is restored There is also a more general way to group objects using and which is discussed in Section 9 5 Labels and Corners Objects can be labelled or named so that you can talk about them later For example Boxl box other stuff move to Boxl Place names must begin with an upper case letter to distinguish them from variable names which begin with lower case letters The name refers to the center of the object which is the geometric center for most things Other combinations also work line from Boxl to Box2 move to Boxl up 0 1 right 0 2 move to Boxl 0 2 0 1 same as previous line to Boxl 0 5 0 The reserved name Here may be used to record the current position of some object Boxl Here Labels are variables they can be reset several times in a single picture so a statement like Boxl Boxl 1 1 is perfectly legal You can also refer to previously drawn objects of each type using the word last For example given the input box A Girele BN box TOY then last box refers to box C last circle refers to circle
22. ith textual descriptions Finally and perhaps most important it is possible to generate PIC input from a program GRAP is merely the most recent in a set of such programs none of which would be feasible with the inter active systems I know of 72 In any case the issue is far from settled comments and suggestions are welcome Acknowledgements I am indebted to Chris Van Wyk for ideas from several versions of IDEAL He and Doug McIlroy have also contributed algorithms for line and circle drawing and made useful suggestions on the design of PIC Theo Pavlidis contributed the basic spline algorithm Eric Grosse provided code to compute the bounding box of an arc Charles Wetherell pointed out reference 6 to me and made several valuable criti cisms on an early draft of the language and manual The exposition in this manual has been greatly improved by suggestions from Jim Blinn and Mark Miller I am grateful to my early users Brenda Baker Dottie Luciani and Paul Tukey for their suggestions and cheerful use of an often shaky and clumsy system The most recent version of PIC has benefited greatly from adventurous use by Jon Bentley and Ravi Sethi their comments on this edition of the manual are also much appreciated References LIST D2 Appendix A PIC Reference Manual Pictures The top level object in PIC is the picture picture PS optional width optional height element list PE If optiona
23. l width is present the picture is made that many inches wide regardless of any dimensions used internally The height is scaled in the same proportion unless optional height is present If instead the line is PS lt f the file f is inserted in place of the PS line If PF is used instead of PE the position after printing is restored to what it was upon entry Elements An element list is a list of elements what else the elements are element primitive attribute list placename element placename position var expr direction element list element list for var expr to expr by expr do X anything X if expr then X anything X else X anything X copy file copy thru macro copy file thru macro sh X commandline X print expr reset optional var list troff command Elements are separated by newlines or semicolons a long element may be continued by ending the line with a backslash Comments are introduced by a and terminated by a newline Variable names begin with a lower case letter place names begin with upper case Place and variable names retain their values from one picture to the next The current position and direction of motion are saved upon entry to a block and restored upon exit Elements within a block enclosed in are treated as a unit the dimensions are determined by the extreme points of the contained objects Names variables and direction of motion within a block are local to that
24. nit and don t look inside for objects last box s refers to box 1 not box 2 or 4 You can use last etc just like last box Blocks have the same compass corners as boxes determined by the bounding box It is also possi ble to position a block by placing either an absolute coordinate like 0 0 or an internal label like A at some external point as in yee CAE yee hes TCO 4 Fe BE By default blocks join with other things as boxes do at the center of the appropriate side Names of variables and places within a block are local to that block and thus do not affect variables and places of the same name outside In particular that includes the built in variables like boxwid etc if they are set within a block they revert to their original values when the block is left You can get at the internal place names with constructs like last A or B A where B is a name attached to a block 14 B De phi SBS ater ae When combined with define statements next section blocks provide a reasonable simulation of a pro cedure mechanism Although blocks nest it is currently possible to look only one level deep with constructs like B A although A may be further qualified by a corner name i e B A sw or top of B A are legal The following example illustrates most of the points made above about how blocks work Pir boxht h boxwid dw A box B
25. of last arrow 0 0 25 circle rad 0 05 at Paper 0 055 0 25 circle rad 0 05 at Paper 0 055 0 25 n rollers ljust at Paper 0 1 0 25 ps 2 PE ce Basic Digital Typesetter 15 Final Observations The fundamental approach in PIC Cartesian coordinates and real measurements is not the easi est thing in the world to work with although it does have the merit of being in some sense sufficient Much of the syntactic sugar or corn syrup corners joining things implicitly etc is aimed at making posi tioning and sizing automatic or at least relative to previous things rather than explicit Nonetheless PIC does offer some positive values Most notably it is integrated with the rest of the standard Unix document preparation software In particular it positions text correctly in relation to graphi cal objects this is not true of any of the interactive graphical editors that I am aware of It can even deal with equations in a natural manner modulo the space 0 nonsense alluded to in Section 13 A standard question is Wouldn t it be better if it were interactive The answer seems to be both yes and no If one has a decent input device such as a mouse interaction is certainly better for sketching out a figure But it is hard to state and preserve relationships between objects with purely graphical input and it is tedious to do precision drafting especially of repetitive constructs These are easy w
26. ore Laboratory Report UCID 30156 D April 1977 the V viewgraph language A Anon T V A viewgraph gener ating language R Bell Laboratories internal memorandum D May 1979 and more recently new fea tures from the GRAP language A J L Bentley A B W Kernighan T GRAP A Language for Typesetting Graphs R Bell Laboratories Comp Sci Tech Rept 114 D December 1984 for typesetting graphs This paper is primarily a user s manual for PIC a discussion of design issues and user experience may be found in A B W Kernighan T PIC A Language for Typesetting Graphics J Software Practice amp Experience D January 1982 V 12 N 1 P 1 21 The next section shows how to use PIC in the most simple way Subsequent sections describe how to change the sizes of objects when the defaults are wrong and how to change their positions when the standard positioning rules are wrong An appendix describes the language succinctly and summarizes changes since the last manual 2 Basics PIC provides boxes lines arrows circles ellipses arcs and splines smooth curves plus facilities for positioning and labeling them The picture below shows all of the fundamental objects except for splines in their default sizes line arrow box a oy Each picture begins with PS and ends with PE between them are commands to describe the picture Each command is typed on a line by itself For example PS box this is
27. rticular size even when coordinates have been given in inches Experience indicates that a good way to get a picture of the right size is to enter its dimensions in inches then if neces sary add a width to the PS line Once set variables like boxht retain their values from one picture to the next You can reset vari ables to their default values by listing them ina reset statement reset boxht boxwid A bare reset resets all variables 4 Controlling Positions You can place things anywhere you want PIC provides a variety of ways to talk about positions PIC uses a standard Cartesian coordinate system so any point or object has an x and y position measured in inches The first object is placed with its start at position 0 0 by default The x y position of a box circle or ellipse is its geometrical center the position of a line or motion is its beginning the position of an arc is the center of the corresponding circle Position modifiers like from to by and at are followed by an x y pair and can be attached to boxes circles lines motions and so on to specify or modify a position You can also use up down right and left with line and move box ht 0 2 wid 0 2 at 0 0 1 move right 0 5 or move to 0 5 0 box ht 0 2 wid 0 2 2 move right 0 5 or move 0 5 or move same box ht 0 2 wid 0 2 3 Comments can be used in pictures they begin with a and end at the end of the line
28. sts text item positioning sprintf format expr positioning positioning center ljust rjust above below If there are multiple text items for some primitive they are centered vertically except as qualified Posi tioning requests apply to each item independently Text items can contain TROFF commands for size and font changes local motions etc but make sure that these are balanced so that the entering state is restored before exiting Positions and places A position is ultimately an x y coordinate pair but it may be specified in other ways 24 position expr expr place expr expr place expr expr position position expr of the way between position and position expr lt position position gt position place placename _ optional corner corner of placename nth primitive optional corner corner of nth primitive Here An optional corner is one of the eight compass points or the center or the start or end of a primitive optional corner ot we Ww S ne soe NW SW lt z sstart end corner top bot left right start end Each object in a picture has an ordinal number nth refers to this nth nth nth last Since barbarisms like 1th and 3th are barbaric synonyms like 1st and 3st are accepted as well Variables The built in variables and their default values are boxwid 0 75 boxht 0 5 circlerad 0 25 arcrad 0 25 ellipsewid 0 75 ellipseht 0 5 linewid 0
29. the invalid input box arrow box will draw the message pic syntax error near line 5 file context is box gt gt gt arrow lt lt lt box The brackets point to the place where the error was first noted it sometimes follows the word in error although in this example it s right on target 3 Controlling Sizes This section deals with how to control the sizes of objects when the default sizes are not what is wanted The next section deals with positioning them when the default positions are not right Each object that PIC knows about boxes circles etc has associated dimensions like height width radius and so on By default PIC tries to choose sensible default values for these dimensions so that sim ple pictures can be drawn with a minimum of fuss and bother All of the figures and motions shown so far have been in their default sizes box 34 wide x 1 2 high circle 4 diameter ellipse 34 wide x 1 2 high arc 1 2 radius line or arrow 1 2 long move 12 in the current direction When necessary you can make any object any size you want box width 3 height 0 1 circle radius 0 1 All positions and dimensions are in inches so the box is 3 inches wide and 1 10 inch high and the circle has radius 1 10 inch An attribute like width changes only the one instance of the object You can also change the default size for all objects of a particular type by assigning values to
30. the obvious places arrow box input arrow box process arrow box output arrow input gt process output One way to leave a space is with move box move box move box Although objects are normally connected left to right this can be changed If you specify a direction as a separate object subsequent objects will be joined in that direction down box arrow ellipse arrow circle left box arrow ellipse arrow circle Each new picture begins going to the right Normally figures are drawn at a fixed scale with objects of a standard size It is possible however to arrange that a figure be expanded or shrunk to fit a particular width If the PS line contains a number the drawing is forced to be that many inches wide with the height scaled proportionately Thus apo B85 causes the picture to be 3 5 inches wide PIC is pretty dumb about the size of text in relation to the size of boxes circles and so on There is no way to say make a box that just fits around this text or make this text fit inside this circle or draw a line as long as this text Tight fitting of text can generally only be done by trial and error Speaking of errors if you make a grammatical error in the way you describe a picture PIC will com plain and try to indicate where For example
31. us one of that kind add the word same Thus in the set of boxes given by down box ht 0 2 wid 1 5 move down 0 15 box same move same box same the dimensions set by the first box are used several times similarly the amount of motion for the second move is the same as for the first one You can change the default sizes of objects by assigning values to the variables that define their val ues Here is the list with their default values boxwid 0 75 boxht 0 5 linewid 0 75 lineht 0 5 circlerad 0 25 arcrad 0 25 ellipsewid 0 75 ellipseht 0 5 movewid 0 75 moveht 0 5 textwid 0 textht 0 arrowwid 0 05 arrowht 0 1 These refer to the arrowhead dashwid 0 05 arrowhead 2 Arrowhead fill style So if you want all your boxes to be long and skinny and relatively close together boxwid 0 1 boxht 1 movewid 0 2 box move box move box Setting the variable arrowhead to a value like 7 causes arrowheads to be filled by overstriking the default is 2 arrowhead 7 arrow move arrowhead 2 arrow PIC works internally in inches Setting the variable scale to some value causes all dimensions to be scaled down by that value Thus for example scale 2 54 causes dimensions to be interpreted as cen timeters The number given as a width in the PS line overrides the dimensions given in the picture this can be used to force a picture to a pa
32. yback Any input line that begins with a period is assumed to be a TROFF command that makes sense at that point it is copied to the output at that point in the document It is asking for trouble to add vertical space or in any way fiddle with the line spacing here but point size and font changes are generally harmless ps 24 circle radius 4 at 0 0 ps 12 circle radius 2 at 0 0 ps 8 circle radius 1 at 0 0 ps 6 circle radius 05 at 0 0 ps 10 don t forget to restore siz PIC does preserve the state of TROFF s fill mode across pictures It is also safe to include sizes fonts and local motions within quoted strings in PIC so long as whatever changes are made are unmade before exiting the string For example to print text in Old English 2 points larger ellipse s 2 f OESmile fP s 2 This is essentially the same rule as applies in EON There is a subtle problem with complicated equations inside PIC pictures they come out wrong if EQN has to leave extra vertical space for the equation If your equation involves more than subscripts and superscripts you must add to the beginning of each equation the extra information space 0 arrow box Sspace 0 H omega over 1 H omega arrow H w 1 H w 18 PIC output is largely independent of any particular typesetter but in the rare case that you have to say something to it the T option makes the choice
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