How do I get started?
We recommend that you do this problem set on an Athena machine. It is possible to do it on your machine at home (as long as it is Java 1.1 compliant), though you will have to then transfer files to your space on imagery in order to get credit for it (plus, we will not be actively supporting the PC platform).

Downloading the files:
Download assignment2.tar by clicking here. Save it to your /mit/imagery4/6.837/F99/students/uid/WWW/ directory. Then type:

athena% cd /mit/imagery4/6.837/F99/students/uid/WWW/
athena% tar xvf assignment2.tar

This will create a new directory for you: assignment2. In that directory you will see a number of files:

• Bresenham.java and CohenSutherland.java: The source files that you need to fill in and compile.
• Bresenham.html and CohenSutherland.html: The web pages you will load to see your code in action. These were written for you so all you need to do is load them into your browser.
• setupJava: a setup script (see below)
• A bunch of .class files: these are the pre-compiled infrastructure files which take care of the graphics output etc. You do not need to worry about this stuff at all.
• display/: a directory full of more .class files that you don't need to worry about.

Setting up java:
Source the script setupJava:

athena% cd assignment2
athena% source setupJava

This script adds the Java Athena locker (which gives you access to the Java executables) and sets your CLASSPATH environment variable appropriately (which lets Java know to look for compiled .class files it needs in your imagery directory).
Important Note: You must source this script once every time you log on.

Using Java for this Assignment
Java is a great programming language. It's easy to use and flexible. Don't worry if you haven't used Java before. The syntax is close enough to C/C++ that knowing either of these, you know 90% of Java. For some information on the language, including tutorials, API references and language specifications, check out the Sun Java page at http://www.javasoft.com.
For the purposes of this problem set, here are the important Java commands to know:

• javac: This invokes the Java compiler, taking .java files and producing .class files (which can then be run by the Java interpreter or a web browser, etc.). The argument it takes is the name of the file(s) to compile. So to compile your .java files you could cd into the directory which holds them and type

  athena% javac *.java

• appletviewer: This invokes the Java appletviewer, which is a program which takes a web page, and then runs any applets it finds on that web page in a separate window. Although we will be looking at a web page to verify your final solution, it is a good idea to use appletviewer for debugging purposes. This is because there is a problem with Netscape in which byte code, once cached, cannot be reloaded. This means that you need to quit and restart netscape every time you change your code!
  The single argument to appletviewer is the name of an html file. So, for example, when you are testing your Bresenham solution, you might type (given that the page Bresenham.html holds the applet):

  athena% appletviewer Bresenham.html

A TODO List

The Bresenham algorithm
• Fill in the file Bresenham.java with correct code for the Bresenham algorithm.
• Compile your Bresenham.java and leave the compiled readable Bresenham.class file in your assignments2/ directory. Verify that the applets works correctly by loading the page:
  http://imagery.mit.edu/imagery4/6.837/F99/students/uid/WWW/assignment2/Bresenham.html

The Cohen-Sutherland Algorithm
• Fill in the file CohenSutherland.java with code for the Cohen-Sutherland algorithm.
• Compile your CohenSutherland.java and leave the compiled readable CohenSutherland.class file in your assignments2/ directory. Verify that the applet works correctly by loading the page: http://imagery.mit.edu/imagery4/6.837/F99/students/uid/WWW/assignment2/CohenSutherland.html

Both
• Turn in the code for both parts of the problem set by executing the command:

  athena% turnin -course 6.837 2 Bresenham.{java,class} CohenSutherland.{java,class}

For more detailed information on implementing the algorithms, including inputs and outputs to the method you must fill in etc., check the comments in Bresenham.java and CohenSutherland.java.

Don't Forget:
Scan converting and clipping line segments is fun! Think of the applications!