Processing: Creative Coding and Computational Art

PROCESSING: CREATIVE CODING AND COMPUTATIONAL ART
500
Object interactions
The last sketch can be thought of as a very (very) simplified particle system. Particle
systems are used to render organic effects and phenomena usually without a discrete and
rigid form. For example, by generating a group of particles moving in certain wave patterns,
we can simulate things like waving grass, a sheet blowing in the wind, or even liquid.
Aside from the type of speed and acceleration variables we’ve been looking at, particle
systems might also include more complex calculations for inter-particle attraction/
repulsion, inertia, and so on.
We’ll begin by considering the interaction between just two particles and build from there.
One simple but interesting type of interaction is following behavior, as exhibited in a
simple predator/prey dynamic. In the next two sketches, I’ll make the mouse the prey and
a ravenous ellipse its predator. The first example simply has the ellipse follow the mouse
with a slight delay. Notice that I used Processing’s pmouseX and pmouseY variables, which
hold the coordinate values of the mouse one frame in the past.
Easing
// Ravenous ellipse I
float x, y;
void setup(){
size(400, 400);
x = width/2;
y = 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-x);
float deltaY = (pmouseY-y);
x += deltaX;
y += deltaY;
ellipse(x, y, 15, 15);
}
The core principle in this last (pretty dull) sketch is that we are calculating deltaX and
deltaY each frame in the draw() loop, with the following lines: