Learning XNA 3.0

Collision Detection

So, you've got a pretty good thing going thus far. Players can interact with your game and move the three rings around the screen—but still there's not a lot to do. You need to add some collision detection in order to take the next step.

Collision detection is a critical component of almost any game. Have you ever played a shooter game where you seem to hit your target but nothing happens? Or a racing game where you seem to be far away from a wall but you hit it anyway? This kind of gameplay is infuriating to players, and it's a result of poorly implemented collision detection.

Collision detection can definitely make or break a gameplay experience. The reason it's such a make-or-break issue is because the more precise and accurate you make your collision-detection algorithms, the slower your gameplay becomes. There is a clear trade-off between accuracy and performance when it comes to collision detection.

One of the simplest and fastest ways to implement collision detection is through the bounding-box algorithm. Essentially, when using a bounding-box algorithm, you "draw" a box around each object on the screen and then check to see whether the boxes themselves intersect. If they do, you have a collision. Figure 3-3 shows the three rings and skull ball sprites with these invisible boxes surrounding the two objects.

Figure 3-3. Bounding boxes around your objects

To implement ...