2D Game Programming Tricks - Beginning Android Games - page 382

While not depicted in Figure 8-15 , this method also works for circles that completely contain the
rectangle. Here's the code:
public boolean overlapCircleRectangle(Circle c, Rectangle r) {
float closestX = c.center.x;
float closestY = c.center.y;
if if(c.center.x < r.lowerLeft.x) {
closestX = r.lowerLeft.x;
}
else if if(c.center.x > r.lowerLeft.x + r.width) {
closestX = r.lowerLeft.x + r.width;
}
if if(c.center.y < r.lowerLeft.y) {
closestY = r.lowerLeft.y;
}
else if if(c.center.y > r.lowerLeft.y + r.height) {
closestY = r.lowerLeft.y + r.height;
}
return c.center.distSquared(closestX, closestY) < c.radius * c.radius;
}
The description looked a lot scarier than the implementation. We determine the closest point on
the rectangle to the circle and then simply check whether the point lies inside the circle. If that's
the case, there is an overlap between the circle and the rectangle.
Note that we add an overloaded distSquared() method to Vector2 that takes two float
arguments instead of another Vector2 . We do the same for the dist() function.
Putting It All Together
Checking whether a point lies inside a circle or rectangle can also be useful. We can code up
two more methods and put them in a class called OverlapTester , together with the other three
methods we just defined. Listing 8-6 shows the code.
Listing 8-6. OverlapTester.java; Testing Overlap Between Circles, Rectangles, and Points
package com.badlogic.androidgames.framework.math;
public class OverlapTester {
public static boolean overlapCircles(Circle c1, Circle c2) {
float distance = c1.center.distSquared(c2.center);
float radiusSum = c1.radius + c2.radius;
return distance <= radiusSum * radiusSum;
}
public static boolean overlapRectangles(Rectangle r1, Rectangle r2) {
if (r1.lowerLeft.x < r2.lowerLeft.x + r2.width &&
r1.lowerLeft.x + r1.width > r2.lowerLeft.x &&
r1.lowerLeft.y < r2.lowerLeft.y + r2.height &&