Learning Processing: A Beginner's Guide to Programming Images ...

246 Learning Processing
Although technically not required, it is a good habit to place pushMatrix( ) and popMatrix( ) around
the second rectangle as well (in case we were to add more to this code). A nice rule of thumb when
starting is to use pushMatrix( ) and popMatrix( ) before and after translation and rotation for all shapes
so that they can be treated as individual entities. In fact, this example should really be object oriented,
with every object making its own calls to pushMatrix( ), translate( ), rotate( ) , and popMatrix( ) .
See Example 14-5 .
Example 14-15: Rotating many things using objects
// An array of Rotater objects
Rotater[] rotaters;
void setup() {
size(200,200);
rotaters = new Rotater[20];
// Rotaters are made randomly
for (int i = 0; i < rotaters.length; i + + ) {
rotaters[i] = new Rotater(random(width),random(height),random(–0.1,0.1),random(48));
}
}
void draw() {
background(255);
// All Rotaters spin and are displayed
for (int i = 0; i < rotaters.length; i + + ) {
rotaters[i].spin();
rotaters[i].display();
}
}
// A Rotater class
class Rotater {
float x,y; // x,y location
float theta; // angle of rotation
float speed; // speed of rotation
float w; // size of rectangle
Rotater(float tempX, float tempY, float tempSpeed, float tempW) {
x = tempX;
y = tempY;
theta = 0; // Angle is always initialized to 0
speed = tempSpeed;
w = tempW;
}
// Increment angle
void spin() {
theta + = speed;
}
// Display rectangle
void display() {
rectMode(CENTER);
stroke(0);
fi g. 14.27