'adding' two angles

Question

Alright, so I got two angles. One is the joystick's angle, and the other is the camera to player angle. The camera's angle. Now I want it so when I press up on the joystick it moves the player away from the camera. How would I do this? And is there a easy way to do it in Java or Ardor3d?

edit: Here is the code of how I get my angles.

float camDegree = (float) Math.toDegrees(Math.atan2(
                     _canvas.getCanvasRenderer().getCamera().getLocation().getXf() - colladaNode.getTranslation().getXf(),
                     _canvas.getCanvasRenderer().getCamera().getLocation().getYf()) - colladaNode.getTranslation().getYf());

            player.angle = (float) Math.toDegrees(Math.atan2(padX, padY));
            Quaternion camQ = new Quaternion().fromAngleAxis(camDegree, Vector3.UNIT_Y);

Answer 1

I have to say that I don't really understand your question, but it seems to be about how to implement camera-relative control using a joystick.

The most important piece of advice I can give you is that it's better not to compute angles, but to work directly with vectors.

Suppose that the camera is looking in the direction v (in some types of game this vector will be pointing directly at the player, but not all types of game, and not always):

Typically you don't care about the vertical component of this vector, so remove it to get the horizontal component, which I'll call y for reasons that will become apparent later:

y = v − (v · up) up

where up is a unit vector pointing vertically upwards.

We can find the horizontal vector that's perpendicular to y using the cross product (and remembering the right hand rule):

x = v × up

Now you can see that y is a vector in the plane pointing forwards (away from the camera), and x a vector in the plane pointing right (sideway with respect to the camera). If you normalise these vectors:

x̂ = x / |x|

ŷ = y / |y|

then you can use x̂ and ŷ as the coordinate basis for camera-relative motion of the player. If your joystick readings are Jx and Jy, then move the player by

s (Jx x̂ + Jy ŷ)

where s is an appropriate scalar value proportional to the player's speed.

(Notice that no angles were computed at any point in this answer!)