Held: Thursday, 13 February 2014
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Summary
We explore the basics of the graphics language PostScript.
Related Pages
Overview
- PostScript basics.
- Important drawing commands.
- Program control.
- Sample procedures.
- Why study PostScript?
Administrivia
PostScript
- From Adobe.
- A comparatively old language - developed around 1982.
- A language designed for two purposes
- High-resolution printers
- Interactive displays ("display postscript")
- It's a programming language, not just a markup language.
- These days, mostly used for printers
- Almost every laser printer has a built-in postscript interpreter.
- PostScript is also at the core of PDF.
- Programs generate PostScript for you.
- But you can write PostScript on your own.
- Programming model: Stack based.
- Each value you enter goes on the stack.
- Operations remove values from the stack (and put new values on the stack).
- Preview with Ghostview or ps2pdf or ...
ps2pdf -dEPSCrop file.eps
- We'll mostly use encapulsated postscript
- Vector oriented.
- Two essential books, one additional book (all free these days)
- The Green Book - Tutorial and Cookbook - Where you (might) go
to learn.
- The Red Book - The Language Guide - Where you find details.
- The Blue Book - Program Design - Where you get better.
- Disclaimer: I am a toy program PostScript programmer, at best
General File Format
This is for encapsulated PostScript, which is really nice for figures.
%!PS-Adobe-3.0 EPSF-3.0
%%BoundingBox: 0 0 576 792
%%DocumentNeededResources: font Times-Roman
%%EndComments
...
showpage
%%EOF
Drawing Commands
Setting the color
*r* *g* *b* setrgbcolor
1 0 0 setrgbcolor % red
*g* setgray
0 setgray % black
Setting the line width for strokes
*w* setlinewidth
1.0 setlinewidth
Moving to a particular position
*x* *y* moveto
100 100 moveto
Specifying lines (not shown until stroked)
*x* *y* lineto
100 120 lineto
*x* *y* rlineto
15 15 rlineto
Stroking everything since the last stroke or fill
stroke
Filling figures (if possible
closepath
fill
Saving and restoring context
gsave
grestore
Creating a circle (or arc)
*x* *y* *r* *theta1* *theta2* arc
Creating a bezier curve
*x1* *y1* *xc* *yc* *x2* *y2* curveto
Typical mechanism for setting the font
/Times-Roman findfont
12 scalefont setfont
Showing text
(TEXT) show
Changing the Environment
*a* rotate
*x* *y* scale
*x* *y* translate
More Fun with Programming
Define a variable
/*var* *exp* def
/destx 72 def
Group instructions (which can go on the stack)
{ *instructions * }
Repeat instructions
*n* { *instructions* } repeat
Define a set of instructions
/*name* { *instructions* } def
Rotate the top of the stack
*size* *amt* roll
Copy an element at some offset
*offset* index
Copy the top element
dup
Switch the top two elements of the stack
exch
Negate the top value on the stack
neg
Sample Code
How Sam Draws Rectangles
% left bottom width height rect
% Draw the specified rectangle.
/rect { % l b w h
4 2 roll % w h l b
moveto % w h
1 index % w h w
0 % w h w 0
rlineto % w h
dup % w h h
0 exch % w h 0 h
rlineto % w h
exch % h w
neg 0 % h -w 0
rlineto % h
neg % -h
0 exch % 0 -h
rlineto %
stroke %
} def
Right-justifying text
% string showright
/showright { % str
dup % str str
stringwidth % str str-width str-height
pop % str str-width
neg % str -str-width
0 % str -str-width 0
rmoveto % str
show
} def
Why Study PostScript?
- A new way of thinking.
- Fun.
- Long term: Can we use vector graphics as a similar model?
- Long term: Can we use PostScript as an output mechanism?
