Euler angles/3D rotation problem

Newbie & Debugging Questions
#1

Hi all, I’ve been trying to make a 3D camera using Euler angles and I’ve been getting some unexpected results. I’m using LWJGL and I’ve plotted out a very basic flat scene to test whether the camera’s working properly. I used the algorithm at the end of the FAQ question below to create and multiply the 3 rotation matrices X, Y and Z.

http://www.cs.princeton.edu/~gewang/projects/darth/stuff/quat_faq.html#Q36

To transform to the perspective of the rotated viewport I have the method below:


public void transform(Player player) {
	float xcos = (float) Math.cos(Math.toRadians(xrot));
	float xsin = (float) Math.sin(Math.toRadians(xrot));
	float ycos = (float) Math.cos(Math.toRadians(yrot));
	float ysin = (float) Math.sin(Math.toRadians(yrot));
	float zcos = (float) Math.cos(Math.toRadians(zrot));
	float zsin = (float) Math.sin(Math.toRadians(zrot));
		
	float[] mat = new float[16];
	mat[0] = ycos * zcos;
	mat[1] = -ycos * zsin;
	mat[2] = ysin;
	mat[4] = xsin * ysin * zcos + xcos * zsin;
	mat[5] = -xsin * ysin * zsin + xcos * zcos;
	mat[6] = -xsin * ycos;
	mat[8] = -xcos * ysin * zcos + xsin * zsin;
	mat[9] = xcos * ysin * zsin + xsin * zcos;
	mat[10] = xcos * ycos;
	mat[3] = mat[7] = mat[11] = mat[12] = mat[13] = mat[14] = 0.0f;
	mat[15] = 1.0f;
	
	GL11.glMultMatrix((FloatBuffer) BufferUtils.createFloatBuffer(16).put(mat).flip());
}

With xrot, yrot and zrot being the rotation angles in degrees. I have some other methods that just add to these values to add/subtract from the angles.
The results are fairly hard to describe. When I only change one rotation angle the scene seems to rotate correctly, but when I add a second the scene seems to spiral out of control. Can anyone spot any errors that I’ve made?

Thanks

#2

Here you can use one of my old camera’s for reference: http://pastebin.java-gaming.org/4c7cb59245c
The big problem with that one though is that is recalculates the matrix every frame, you should have a camera.setPosition/Rotation which sets a boolean flag to true, then when the update is called if the boolean flag is true update the matrix, that will save performance.

#3

Cheers for the reply. Yeah, I’ve got a few optimisation methods in mind. I’m just stumped by this unexpected transformation it’s returning. It looks fairly straight forward in the article. I even double checked that all the matrix entries were being multiplied correctly. I’ll give your implementation a look. Thanks. :slight_smile:

#4

I’ve just tried implementing the same method from the code you provided, but I’m getting the same problem. If I rotate around one axis it’s fine, but if I include the second rotate it seems to spiral. Even if I don’t prompt it to rotate anymore, it continues to spiral.

#5

Sorry to keep posting, I’ve just realised something else. I’ve just replaced the contents of the method with this:


GL11.glRotatef(xrot, 1.0f, 0.0f, 0.0f);
GL11.glRotatef(yrot, 0.0f, 1.0f, 0.0f);
GL11.glRotatef(zrot, 0.0f, 0.0f, 1.0f);

But the problem persists, so it must not be the rotations that cause the problem.

#6

Make sure that it’s not rotating above 360, and also for the look up/look down make sure you limit the angle to 89/179 or the tan function will glitch.

For example in my camera:


if (cameraRot.x+mouseDX>=360) {
            cameraRot.x=cameraRot.x+mouseDX-360;
        } else if (cameraRot.x+mouseDX<0) {
            cameraRot.x=360-cameraRot.x+mouseDX;
        } else {
            cameraRot.x+=mouseDX;
        }
        if (cameraRot.y-mouseDY>=-90 && cameraRot.y-mouseDY<=90) {
            cameraRot.y+=-mouseDY;
        } else if (cameraRot.y-mouseDY<-90) {
            cameraRot.y=-90;
        } else if (cameraRot.y-mouseDY>0) {
            cameraRot.y=90;
        }

Also I would search up gimbal lock if your going to use euler angles (http://www.youtube.com/watch?v=zc8b2Jo7mno).

#7

Thanks for your reply. :slight_smile: I’ve added those checks, but it seems to still glitch. I think it may be the X axis rotation that’s causing the problems. If I drag the mouse down, the camera doesn’t appear to move down at all and when I drag the mouse up it’s very sensitive and spins around quickly and then continues to spin after I’ve stopped moving the mouse.

#8

It wasn’t even my camera class that was faulty, I was using Mouse.getY() instead of Mouse.getDY(). :’( I feel so foolish. Thanks to everybody for the help!