Lab 3: PostScript

In this lab, you will get a quick introduction to the PostScript language, which you will be using in your project.

Before Lab

Before coming to lab, please do the following:

• Read both Project 3 and this lab handout.
• Read through the sections of the guide to PostScript listed below.
Install Ghostscript and Ghostview if you don't already have them. Ghostscript is a "PostScript previewer" -- an interpreter for programs written in PostScript. There are many interpreters available on a variety of platforms. Here are the recommended ones:
• Windows: install Ghostscript 8.54 and GhostView 4.8.
• MacOS: the Preview application acts as a PostScript viewer (by first translating from PostScript to PDF), but it does not report PostScript errors, so you will probably want to install Ghostscript. One version that's easy to install is EPS Ghostscript.
• Athena: already installed.
• Linux: find the ghostscript package for your Linux distribution and install it, if you don't already have it.

The Lab

Running your first PostScript programs

Ghostscript is an interpreter, which gives you a prompt and lets you type Postscript code interactively and see its results. Ghostview is file viewer, which runs a Postscript file and displays the resulting picture.

Start Ghostscript (on Athena/Linux/Mac, run the command gs). You should see a prompt. Type the following Postscript code:

2 3 add pstack

You should see it display 5. (The pstack command prints the current contents of the stack, which is useful for debugging.)

Now create a file called square.ps with the following contents, and open it in Ghostview (gv on Athena and Linux, Preview on Mac):

newpath
1.5 setlinewidth
72 72 moveto
72 0 rlineto
0 72 rlineto
-72 0 rlineto
closepath
stroke
showpage

This program creates a 1-inch square located 1 inch above and 1 inch to the right of the page's bottom left corner. (PostScript uses typographic units: 1 inch is 72 "points").

Working through a PostScript tutorial

Work through this guide to PostScript, focusing on the following sections:

• What is PostScript?
• Graphics Concepts in PostScript
• Language Concepts in PostScript
• Programming in PostScript
• Drawing and Filling Shapes
• Transformations

The first five sections are contiguous, so you can go from one to the other by starting at the first and just clicking "next page".

Do the following exercises:

• Modify the square drawing program so that one side of the square is left open (that is, without a visible stroke).
• Modify the program that draws a line at different rotations so that the line being drawn gets longer as the rotation progresses.
• Modify the program that draws a box using translation so that it draws a 3 by 3 array of boxes.
• Modify the program that draws two boxes and two lines so that the boxes appear to have roughly the same size. Then modify it again so that the last box is drawn several times at different rotations.

Creating your own PostScript program