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

14.9
Example 14-17: Nested push and pop
// Global angle for rotation
float theta = 0;
void setup() {
size(200, 200);
smooth();
}
void draw() {
background(100);
stroke(255);
// Translate to center of window
translate(width/2,height/2);
// Loop from 0 to 360 degrees (2*PI radians)
for(float i = 0; i < TWO_PI; i + = 0.2) {
// Push, rotate and draw a line!
pushMatrix();
rotate(theta + i);
line(0,0,100,0);
// Loop from 0 to 360 degrees (2*PI radians)
for(float j = 0; j < TWO_PI; j + = 0.5) {
// Push, translate, rotate and draw a line!
pushMatrix();
translate(100,0);
rotate(–theta–j);
line(0,0,50,0);
// We're done with the inside loop, pop!
popMatrix();
}
// We're done with the outside loop, pop!
popMatrix();
}
endShape();
// Increment theta
theta + = 0.01;
}
Translation and Rotation (in 3D!) 249
Exercise 14-9: Take either your pyramid or your cube shape and make it into a class. Have
each object make its own call to pushMatrix( ) and popMatrix( ) . Can you make an array
of objects all rotating independently in 3D?
A Processing Solar System
Using all the translation, rotation, pushing, and popping techniques in this chapter, we are ready to build
a Processing solar system. Th is example will be an updated version of Example 14-16 in the previous
section (without any moons), with two major changes:
• Every planet will be an object, a member of a Planet class.
• An array of planets will orbit the sun.
fi g. 14.30
The transformation state is saved
at the beginning of each cycle
through the for loop and restored
at the end. Try commenting out
these lines to see the difference!