Programming Assignment Checklist: Recursive Graphics

Frequently Asked Questions

What do I need to do to get full credit for the artistic part of the assignment? This part is meant to be fun, but here are some guidelines in case you're not so artistic. A very good approach is to choose a self-referential pattern as a target output. Check out the graphics exercises in Section 2.7 for still more possibilities. See also the Famous Fractals in Fractals Unleashed for some ideas. Here are some more ideas. Then, try to figure out a recursive scheme that will generate it. Some pictures are harder to generate than others; consult a preceptor for advice if you're unsure.

What will cause me to lose points on the artistic part? We'll deduct points if your picture is overly boring or too similar to HTree.java. You will also lose points if your artwork could easily be created without recursion, e.g., it is tail-recursive: a single recursive call at the very end of the function.

Can I use GIF or JPEG files in my artistic creation? Yes. If so, be sure to submit them along with your other files. Make it clear in your readme.txt what part of the design is yours and what part is borrowed from the image file.

Can I rescale GIF or JPEG images in Turtle.java? Not currently.

I get the error java.lang.NullPointerException. What am I doing wrong? Perhaps you forget Turtle.create(512, 512).

I get a blank gray screen. What am I doing wrong? Perhaps you forget Turtle.destroy().

Testing and Submission

readme.txt. Use the following readme file template and answer all questions.

Submission. If you don't follow these instructions, you risk upsetting your grader and losing a significant number of points.

• Your main function must call Turtle.destroy as the last line.
• Your Art.java program must take exactly one integer command line input (expect it to be between 1 and 6).
• Your Art.java must fit within a 512-by-512 box.

Extra Credit

Although it is not mentioned in the assignment, we'll award extra credit if you follow the above instructions to create an image for the Display Wall in the Frist Student Center. This requires no programming and can be alot of fun! Follow these display wall instructions to show off your artwork and earn 2 points of extra credit at the same time. Name your jpg file login.jpg where login is replaced by your arizona login name.

Here are the display wall submissions from Spring 2001, Fall 2001, Spring 2002, Fall 2002, and Spring 2003.

Possible Progress Steps

These are purely suggestions for how you might make progress. You do not have to follow these steps. Note that your final HTree.java program should not be very long (ours is 21 lines, not including commments and blank lines).

• Review the Koch snowflake from lecture.

• Download Turtle.java to your working directory.

• Write a (nonrecursive) function void drawH(double x, double y, double size) that plots an H, centered on (x, y) with each of the 3 line segments having length size. Use Turtle.fly and Turtle.go. To debug and test your function, write main so that it calls drawH a few times, with different parameters. You will want to use this function exactly as is in HTree.java.

• Write a recursive function recur that plots an H-tree pattern of order n. Consider creating this function in several steps.

  • Write a recursive function void recur(int n) that prints the value n, and then calls itself four times with the value n-1. The recursion should stop when n becomes 0. To test this function out, write main so that it reads one integer N from the command line and calls recur(N). Modulo the line wraps, you should get the following output when you call recur with N = 0, 1, 2, 3, 4, 5. Make sure you understand how this function works, and why it prints the numbers in the order it does.

  • Modify recur so that instead of printing n, it prints the size of the H to be plotted. Your function should now have the signature void recur(int n, double size), and the initial call from main should be to recur(N, 256.0) since the big H has side length 256.0. Each successive level of recursion halves the length. Your function should produce the following output.

  • Modify recur so that it plots a recursive H pattern of order N, centered on (x, y) of the given size.. Your function should now have the signature void recur(double x, double y, int n, double size). Start by drawing H's with pencil and paper. Do some calculations to figure out the geometry of where the smaller H's should go.

• Now that you have the H-tree pattern drawn, it is easy to animate. Append the command Turtle.pause(10) to the end of the drawH function.