Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
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This example isn’t too exciting, but it does illustrate the power and simplicity of doing
matrix transformations in Processing. In the example, I used the rect() command three
times, using the same four arguments; yet I got three rectangles with different sizes and
positions. If you run this example, you should notice four tables of numbers output in the
Processing console. Each table is composed of two rows and three columns. These mysterious
numbers are the actual matrices at different states in the program. You’ll notice that
the first and last table of numbers are identical:
1.0000 0.0000 0.0000
0.0000 1.0000 0.0000
These tables represent the base, or identity, matrix, without any transformation applied.
The first rectangle I created used this matrix, before I called the first translate() function,
and that’s why what I input with regard to the arguments is what I got out. The other
two rectangles have different transforms, and thus look different. In going over this
sketch, you should take the time to see what parts of the matrix get changed after each
transformation.
Another strange concept to deal with is the matrix stack. A stack is a temporary data structure
that operates following the last in, first out (LIFO) principal. Stacks are utilized in
many areas of computing, including managing transformation matrices. The pushMatrix()
and popMatrix() functions alter the matrix stack, allowing different transformations to
happen in a seemingly independent fashion. When you want to create a localized transformation
(not affecting everything following the transformation call), you first call
pushMatrix(), which adds any transformations that follow it onto the matrix stack. Then,
when you’re done, you call popMatrix(), which restores the matrix to its previous form.
This is the reason that the first and last tables of values shown previously were identical—
the first table represented the untransformed matrix and the last table represented the
matrix after popMatrix() was called—which removed the last transformation pushed onto
the stack.
This next example (shown in Figure A-13) is much more interesting than the last, and really
illustrates the power of this whole matrix business. But it’s also pretty complex and long;
so watch it, play with it, and don’t worry about understanding all the code yet. After you
get a sense of what the sketch does (visually), try messing with some of the values; it’s a
great way to see what’s going on programatically (and don’t worry about breaking the
sketch, either). After you launch the example, let it run for a while, as there are some
really interesting patterns that form and change in interesting and unpredictable ways
over time.
//Example 2:
/*
PushPop
Ira Greenberg, November 8, 2005
*/
/*Need to import opengl library to use OPENGL
rendering mode. You can also try running
in P3D mode*/
import processing.opengl.*;