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

172 Learning Processing
// Move and display balls
ball1.move();
ball2.move();
ball1.display();
ball2.display();
}
Now that we have set up our system for having two circles moving around the screen, we need to develop
an algorithm for determining if the circles intersect. In Processing , we know we can calculate the distance
between two points using the dist( ) function (see Chapter 7). We also have access to the radius of each
circle (the variable r inside each object). Th e diagram in Figure 10.3 shows how we can compare the
distance between the circles and the sum of the radii to determine if the circles overlap.
fi g. 10.3
R 1
OK, so assuming the following:
• x 1, y 1: coordinates of circle one
• x 2, y 2: coordinates of circle two
• r 1: radius of circle one
• r 2: radius of circle two
We have the statement:
DIST
R 2
DIST > (R1 + R2)
NOT INTERSECTING
R 1
DIST
R 2
DIST < (R1 + R2)
INTERSECTING
If the distance between (x 1,y 1 ) and (x 2,y 2 ) is less than the sum of r 1 and r 2, circle one intersects
circle two.
Our job now is to write a function that returns true or false based on the above statement.
// 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;
}
}