Smooth Camera Rotation around 90 degrees

Question

I'm developing a third person 3D platformer in XNA. My problem is when I try to rotate the camera around the player.
I would like to rotate (and animate) the camera 90 degrees around the player. So the camera should rotate until it has reached 90 degrees from the starting position.
I cannot figure out how to keep track of the rotation, and when the rotation has made the full 90 degrees.

Currently my cameras update:

public void Update(Vector3 playerPosition) {
    if (rotateCamera) {
        position = Vector3.Transform(position - playerPosition, Matrix.CreateRotationY(0.1f)) + playerPosition;
    }
    this.viewMatrix = Matrix.CreateLookAt(position, playerPosition, Vector3.Up);
}

The initial position of the camera is set in the constructor.
The "rotateCamera" bool is set on keypress.

Thanks for the help in advance.

Cheers.

Answer 1

You can have a variable in your class that store the rotation angle that your camera have already done. In your code it seems you rotate around Y by 0.1 each frame. So you set the initial value of the variable to 0 and increment it by 0.1 each time you rotate. You check the value before rotating, if it's under 90 you continue, else you stop to rotate. The value 0.1 is in radians, wether you convert it back in degrees and compared with 90, or you can keep it in radians and compared with rad(90).