Recursive doodling.

This week's assignment has two parts, each of which involves writing a recursive program.

Fortunately, Java's drawing resolution is good enough that if we get it to do this kind of doodling, we can produce things quite a bit more interesting than a big blob. For example, repeatedly dividing triangles into smaller triangles can lead to a picture like that shown above.

This image was formed by first drawing a triangle and connecting the midpoints. This breaks the triangle into four smaller triangles (at the top, center, lower-left, and lower-right).

How to Proceed

Drag the starter folder to your directory as usual. Inside the starter, you will find two subfolders: Triangulate is the starter for Part 1, Stairs is the starter for Part 2.

Because this triangle doodle is going to be a recursive structure, you will need to design an interface for the doodle (called TriangleDoodle), a base class (called EmptyTriangleDoodle), and a recursive class (called ComplexTriangleDoodle). The only method that will be needed for triangle doodles is a move method, so design the interface appropriately.

The EmptyTriangleDoodle class represents an empty doodle. Like the empty scribble, nothing is drawn on the screen, so the constructor and move method are both pretty trivial.

The ComplexTriangleDoodle is more complicated. It will need instance variables for the lines composing the outer triangle as well as instance variables for the three triangle doodles inside.

Its constructor will take parameters for the vertices of the triangle (in the order left, right, and top), and the drawing canvas. It should then draw lines between the vertices to form a triangle. It will also construct three more triangle doodles inside this triangle. If any of the edges of the new triangle are long enough (say, with length greater than or equal to 12 pixels), then the constructor should find the midpoints of each of the sides and then create complex triangle doodles in the top, lower-left, and lower-right portions of the triangle (leaving the middle blank). If none of the edges are long enough, then just create three empty triangle doodles for the instance variables (as we did with scribbles). The move method should move the lines forming the triangle as well as the contained triangle doodles.

We have provided you with a main program that extends WindowController. The begin method constructs a new object from class ComplexTriangleDoodle. The onMousePress and onMouseDrag methods use the move method to drag the triangle doodle around (even when the mouse is not in the triangle doodle).

To start out, it often a good idea to do a simpler version of the problem. For example, first have the constructor of ComplexTriangleDoodle just draw a simple triangle out of lines. Then try drawing only the triangle doodles in the top part of the triangle. Then add the lower right, then finally adding those in the lower left portion.

The window should be set to be 400 pixels square for this problem. You will also find the distanceTo method defined in the Location class useful to solve this problem:

   public double distanceTo(Location point)

Once this is working, you can experiment with a color scheme to achieve a picture like that shown above. This extension will require the addition of a color parameter to the triangle doodle constructors (and the addition of such a parameter to the construction in the begin method of the Triangulate class).

If you are not careful in writing this program (and the next one), you may get a StackOverflowError. This will occur if your program continues to construct new triangle doodles without ever terminating. You can avoid this if you make sure you have written the base class correctly and that the complex doodle invokes its constructor only to create simpler doodles, eventually creating only empty doodles.

Part 2:

As above, you will need to create an interface, StairsInterface, and two classes, EmptyStairs and VariegatedStairs. We have provided the class StairController, which extends WindowController. This time that class will only drag the stairs around if the user presses the mouse down on the stairs. Thus you will need to create methods contains and move. The constructor call in the begin method is:

    stairs = new VariegatedStairs(lowerLeft, initialSize, initialColor, canvas);

We made it look nicer by drawing the first square in a color created by new Color(225,225,255). At each level of recursion, the color of the first two components (the red and green components) are decreased by 30. That results in nice shading.

You can obtain the red, green, and blue components from a color with the methods:

    int getRed();
    int getGreen();
    int getBlue();
 

The window for this problem is 450 pixels wide and 400 pixels tall.

Submitting Your Work

I hope you will turn in your programs before you leave lab for the day. If not, labs are due Thursday at 11 PM, though it is likely that you will complete this during your lab period.

When your work is complete you should deposit in the appropriate dropoff folder a single folder containing a subfolder for each program. Make sure the folder name includes your name and the phrase "Lab 7". Also make sure that your name is included in the comment at the top of each Java source file.

Before turning in your work, be sure to double check both its logical organization and your style of presentation. Make your code as clear as possible and include appropriate comments describing major sections of code and declarations.

Computer Science 051
Department of Math & Computer Science
Pomona College