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

Now that the function is complete, we can test it with data from ball1 and ball2.
Algorithms 173
boolean intersecting = intersect(ball1.x,ball1.y,ball2.x,ball2.y,ball1.r,ball2.r);
if (intersecting) {
println( "The circles are intersecting! ");
}
Th e above code is somewhat awkward and it will be useful to take the function one step further,
incorporating it into the ball class itself. Let’s fi rst look at the entire main program as it stands.
// Two ball variables
Ball ball1;
Ball ball2;
void setup() {
size(400,400);
framerate(30);
smooth();
// Initialize balls
ball1 = new Ball(64);
ball2 = new Ball(32);
}
void draw() {
background(0);
// Move and display balls
ball1.move();
ball2.move();
ball1.display();
ball2.display();
boolean intersecting = intersect(ball1.x,ball1.y,ball2.x,ball2.y,ball1.r,ball2.r);
if (intersecting) {
println( “The circles are intersecting! ”);
}
}
// A function that returns true or false based on whether two circles intersect
// If distance is less than the sum of radii the circles touch
boolean intersect(float x1, float y1, float x2, float y2, float r1, float r2) {
float distance = dist(x1,y2,x2,y2); // Calculate distance
if (distance < r1 + r2) { // Compare distance to r1 + r2
return true;
} else {
return false;
}
}
Since we have programmed the balls in an object-oriented fashion, it is not terribly logical to suddenly
have an intersect( ) function that lives outside of the ball class. A ball object should know how to test if it
is intersecting another ball object. Our code can be improved by incorporating the intersect logic into the
class itself, saying “ ball1.intersect (ball2); ” or, does Ball 1 intersect Ball 2?
void draw() {
background(0);
// Move and display balls
ball1.move();
ball2.move();
ball1.display();
ball2.display();