CS 3723/3721 Programming Languages References & Access

Here is a sample postscipt file, stored using the filename abc.ps:

Sample Postscript Program	Output
%!PS-Adobe-2.0 /Times-Bold findfont 200 scalefont setfont 100 300 moveto (ABC) show showpage

You can create Postscipt files just using any editor. The names of such files should always end with .ps. If such files are directly sent to a Postscipt printer, the printer will follow the Postscript page description commands, rather than print it as a text file. The printer uses the first line to decide that this is a Postscript file. Otherwise you do not need this first line. You can also convert the file to .pdf format as illustrated below. This conversion produces error messages that can be very helpful in debugging. Finally, you can put a link to either the Postscipt file or the PDF file and open it through many browsers.

Convert to PDF, Produce Error Messages
% vi abc.ps -- create the file with editor % ps2pdf abc.ps abc.pdf -- convert to PDF, -- produces error messages, 2nd arg optional

Open a link to this file as:  abc.ps , or as  abc.pdf
(The .ps file may not open on Windows machines.)

Here is a session working with two erroneous postscript programs.

• Misspelled Postscript operator or function: This is by far the most common mistake, and is the main reason you must always convert to PDF in order to get error messages.

• No starting point specified: Postscript doesn't have a default starting position for items placed on a page. You must always specify the "current point".

Misspelled Postscript Operator	No Starting Point for Painting
% cat abc.bad.ps %!PS-Adobe-2.0 /Times-Bold findfont 200 scalefont setfont 100 300 movetto (ABC) show showpage % ps2pdf abc.bad.ps -- covert to PDF Error: /undefined in movetto Operand stack: 100 300 Execution stack: (blah, blah, lots of stuff)	% cat abc.bad2.ps %!PS-Adobe-2.0 /Times-Bold findfont 200 scalefont setfont (ABC) show showpage % ps2pdf abc.bad2.ps Error: /nocurrentpoint in --show-- Operand stack: (ABC) Execution stack: (blah, blah, lots of stuff)

Mr. John Whipple (a previous student) has called attention to a "Very nice PostScript IDE/Debugger". It is free to download and runs on all environments. (I haven't tried it out yet.) Whipple: "You can step through your program and see what's on the stack. Very helpful!"
http://sourceforge.net/projects/wxghostscript/.

• Postscript ``Blue'' book (by far the best introductory tutorial)
  Local copy (PDF, 847k)    Remote copy (PDF, 847k)   

• Programs from the Bluebook: Local copy, Remote copy

• Postscript ``Green'' Book (help for serious Postscript programmers)
  Local copy (PDF, 934K)   Remote copy (PDF, 934K)

• Postscript Language Reference Manual (hard, but has list of all operators)
  Local copy (PDF, 7.9 meg)   Remote copy (PDF, 7.9 meg)

• First Guide to Postscript (a reasonable and fairly short introduction)

• Small Postscript Manual (another short introduction)

1. Three types of graphics objects:
   1. Text: characters in many fonts, positioned and oriented in any way.
   2. Geometric figures: Drawn using powerful 2-dimensional graphics operators, using lines, curves, filled regions, color.
   3. Images: anything that can be digitized.
   (See Blue Book, pages 1-2.)
2. The imaging model:
   1. Current page: can place anything anywhere, overwriting old stuff
   2. Current path: a set of connected lines and curves making a path, often closed.
   3. Current clipping path: a closed path within which all drawing occurs.
   (See Blue Book, pages 2-3.)
3. Initial graphics: (See Blue Book, pages 3-4.)
4. The Stack: used for all computations and operators. Postfix notation. (See Blue Book, page 4, 7-15.)
5. Coordinate systems: x (horizontal) and y (vertical) coordinates, with (0, 0) in the lower left corner. Units are Postscipt points, where 1 point = 1/72 inch (in actual publishing, 1 point = 1/72.27 inch.) (See Blue Book, Chapter 3, pages 17-25.)
6. Variables and procedures: (It's getting harder now.) (See Blue Book, Chapter 4, pages 27-33.)
7. Text: (See Blue Book, Chapter 5, pages 35-46.)
8. More graphics: (See Blue Book, Chapter 6, pages 47-60.)
9. Conditionals and for loops: (See Blue Book, Section 7.1 and first page of 7.2, pages 61-68.)
10. Outline fonts: (See Blue Book, Section 9.4, pages 97-99.)
11. Clipping: (See Blue Book, Section 10.1, pages 101-104.)

( Revision date: 2015-01-03. Please use ISO 8601, the International Standard Date and Time Notation.)