Processing: Creative Coding and Computational Art

A lot more can be done with this code, including creating an autonomous prey object and
using it instead of the mouse. A simple tank game could be created, with a computercontrolled
tank and a user-controlled one. The atan2() function will ensure that the tanks
(or the tanks’ gun turrets) stay oriented in the correct direction as they move.
Springing
Another fun effect to experiment with is springing. In the last few examples, the predator
followed the prey, but never overshot it. There are times, though, when you might want an
object to slingshot past another object and eventually come to rest. Think about a
small rubber ball on an elastic string, and how it bounces around before coming to rest.
Working with accurate spring equations is somewhat involved, and more than you need
for most aesthetics-based creations. We can very easily simulate spring behavior just by
tweaking the code used in the predator/prey scenario. In fact, the tweak we need is very
similar to the tweak used to add acceleration (with gravity) to the speed example earlier in
the chapter.
Here’s the Ravenous Triangle I sketch converted to use a springy (yet still ravenous)
triangle:
// Ravenous Triangle II
float predCntrX, predCntrY;
float predX[] = new float[3];
float predY[] = new float[3];
float predLen = 8.0;
float predAng, predRot;
// springing variables
float accelX, accelY;
float springing = .01, damping = .95;
void setup(){
size(400, 400);
predCntrX = width/2;
predCntrY = height/2;
smooth();
}
void draw(){
// repaint background
fill(255, 40);
rect(0, 0, width, height);
/* find distance for x and y
between prey and predator */
float deltaX = (pmouseX-predCntrX);
float deltaY = (pmouseY-predCntrY);
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