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

174 Learning Processing
boolean intersecting = ball1.intersect(ball2);
if (intersecting) {
println( " The circles are intersecting! " );
}
}
Following this model and the algorithm for testing intersection, here is a function for inside the ball class
itself. Notice how the function makes use of both its own location ( x and y ) as well as the other ball’s
location ( b.x and b.y ).
// A function that returns true or false based on whether two Ball objects intersect
// If distance is less than the sum of radii the circles touch
boolean intersect(Ball b) {
float distance = dist(x,y,b.x,b.y); // Calculate distance
if (distance < r + b.r) { // Compare distance to sum of radii
return true;
} else {
return false;
}
}
Putting it all together, we have the code in Example 10-3 .
Example 10-3: Bouncing ball with intersection
// Two ball variables
Ball ball1;
Ball ball2;
void setup() {
size(400,400);
smooth();
// Initialize balls
ball1 = new Ball(64);
ball2 = new Ball(32);
}
void draw() {
background(255);
// Move and display balls
ball1.move();
ball2.move();
if (ball1.intersect(ball2)) {
ball1.highlight();
ball2.highlight();
}
ball1.display();
ball2.display();
}
class Ball {
float r; // radius
float x,y;
float xspeed,yspeed;
color c = color(100,50);
fi g. 10.4
Assumes a function intersect() inside
the Ball class that returns true or false.
New! An object can have a function that takes
another object as an argument. This is one
way to have objects communicate. In this case
they are checking to see if they intersect.