An arc-ball camera

While building Cube Chaser, we implemented an FPS or First Person Shooter style camera. For Tank Battles, we want to take a different approach. The player will not be moving around on the terrain from a first person perspective, but will instead hover over the playfield, with the ability to rotate the camera around while focusing on the center of the game area.

Imagine a dome covering the play area, with the camera being able to slide along the dome to any position while still pointing inward at the center of the action. This kind of camera is known as an arc-ball camera, and acts as if the camera rides around on a ball surrounding the target point, as seen in the following image:

No matter where the camera is placed on the surface of the dome, it rotates to face the target point in the center. In order to implement our arc-ball camera, we will construct a class similar to the camera we created in Cube Chaser, but with modified controls for positioning the camera to maintain...