Learning XNA 3.0

Rotations in a First-Person Camera

All camera rotations are related to the same rotations that were discussed previously in relation to the rotation of 3D objects in XNA. Essentially, a camera can yaw, pitch, and roll just like an object can. As a reminder, yaw, pitch, and roll rotations are pictured in Figure 11-4.

Figure 11-4. Yaw, pitch, and roll apply not only to objects, but to cameras as well

In the classes in which I've taught XNA, one of the things that has traditionally been difficult for some students to understand is the fact that yaw, pitch, and roll rotations when applied to objects or cameras that move and rotate in 3D don't necessarily correspond to rotations around the X-, Y-, and Z-axes.

For example, picture the camera you currently have in your game. The camera sits on the Z-axis and faces in the negative Z direction. If you wanted to rotate the camera in a roll, you could rotate the camera around the Z-axis. However, what would happen if the camera rotated to turn 90° and was now looking in the direction of positive X? If you performed a rotation around the Z-axis at this point, you'd rotate in a pitch rather than a roll.

It's easier to think of yaw, pitch, and roll as related to the vectors available to you in your camera. For example, a yaw, rather than rotating around the Y-axis, rotates around the camera's up vector. Similarly, a roll rotates around the camera's ...