Camera rotation issues (z-axis drift solved!)

[ppardee]

I am trying to get the camera to rotate as it would in a first person shooter, but if I pan, tilt and then pan again, the camera has rolled along the Z axis.  I think this is due to the fact that the camera is using its own rotation (myRotation) quaternion to make the matrix and after it tilts, the Y axis is no longer aligned with the world's and it causes the pan do to wonky things, but I don't know how to fix this.  Any suggestions would be appreciated!! (Great tutorials!!!!!!)

Thanks!

Paul

[mikeschuld]

This has been a source of much confusion for a long time on these forums (one that has bugged me quite a bit actually ) You can modify the rotate function to accomplish this sort of action for you. I'm not positive as to how you would want to go about this, but I'll work on a version myself and let you know when I get it working It shouldn't take too long.

[Chr0n1x]

Source code for Riemer's book, chapter 2 part 3 is about a FPS camera. You will find in this case you DO want Gimbal Lock, so using Vectors for a FPS camera rotation is appropriate. Playing around in a FPS game, you'll find you encounter gimbal lock in most FPS games.

You create your X rotation before your Y rotation from the 2 vectors, and always transform your Up and Target vectors by the rotation. (The target is so that it retargets based on your movement, like in FPS.)

[mikeschuld]

I figured out you can set the z component of the quaternion to 0 and then normalize it again. It messes up the revolve functionality, but the rotate works pretty well.

[mikeschuld]

Even better... Add these to your camera:

        public void RotateGlobal(Vector3 axis, float angle) {
            myRotation = Quaternion.Normalize(Quaternion.CreateFromAxisAngle(axis, angle) * myRotation);

            Update();
        }

        public void TranslateGlobal(Vector3 distance) {
            myPosition += distance;

            Update();
        }

        public void RevolveGlobal(Vector3 axis, float angle) {
            Quaternion rotate = Quaternion.CreateFromAxisAngle(axis, angle);
            myPosition = Vector3.Transform(myPosition - myTarget, Matrix.CreateFromQuaternion(rotate)) + myTarget;

            RotateGlobal(axis, angle);
        }

Then just use RotateGlobal for your Y. Works for revolve too I'll add these into the XNA 3.0 versions of the tutorials.

[ppardee]

Thanks for the replies!


Mike, the RotateGlobal works only when looking directly down the world's Z-axis, unfortunately.  If you turn 90 degrees and look up and down, the camera rotates on its Z-axis instead of its X-axis because it is now aligned with the world's Z axis.   

But I will keep looking, you gave me some ideas to try and I will get back to you on them

[ppardee]

Here is my solution... I think it works....

I added to the HMCamera class:

private float yRotation = 0;
private float xRotation = 0;

        public void Rotate(float xAngle, float yAngle)
        {
            xRotation += xAngle;
            yRotation += yAngle;
            myRotation = Quaternion.CreateFromRotationMatrix(Matrix.CreateRotationX(yRotation) *
                Matrix.CreateRotationY(xRotation));
        }


And then in HMDemo:

        static void mouse_OnMove(Vector2 move)
        {
            HMCameraManager.ActiveCamera.Rotate(move.X * -0.005f, move.Y * -0.005f);
            //HMCameraManager.ActiveCamera.Rotate(new Vector3(1, 0, 0), move.Y * -0.005f);
            //HMCameraManager.ActiveCamera.Rotate(new Vector3(0, 1, 0), move.X * -0.005f);
        }

Let me know if there are any bugs (or if you know why this works because I stole it from Riemers' XNA Tutorial)

// Edit

Or even more flexible... HMCamera

        private float xRotation = 0;
        private float yRotation = 0;
        private float zRotation = 0;

        public void Rotate(Vector3 axis, float angle)
        {
            xRotation += MathHelper.Clamp((float)axis.X, 0.0f, 1.0f) * angle;
            yRotation += MathHelper.Clamp((float)axis.Y, 0.0f, 1.0f) * angle;
            zRotation += MathHelper.Clamp((float)axis.Z, 0.0f, 1.0f) * angle;

            myRotation = Quaternion.CreateFromRotationMatrix(
                Matrix.CreateRotationX(xRotation) *
                Matrix.CreateRotationY(yRotation) *
                Matrix.CreateRotationZ(zRotation));

            Update();
        }

Everything else stays the same as it was in the tutorial...

[mikeschuld]

I am not sure you are understanding the rotateglobal meaning. If you turn the camera so it's local Z is on the world X and rotate world X... it is supposed to be rotating on the camera's Z. It rotates on the global X. to get the first person type of camera you are talking about with my functions you need to do:

            HMCameraManager.ActiveCamera.Rotate(new Vector3(1, 0, 0), move.Y * 0.01f);
            HMCameraManager.ActiveCamera.RotateGlobal(new Vector3(0, 1, 0), move.X * 0.01f);

That is working for me just fine Try adding the skybox and playing around with it.

[ppardee]

Not sure where my typo was yesterday, but it works today and that is all I care about

[mikeschuld]

Sorry for all the hassle this one has caused everyone. This solution should be the real final true actual one (disclaimer: some statements may be exaggerated) that will go into the final camera class used in the engine.

It at least is going to be in the XNA 3.0 tutorials (already is in fact) and will be released as soon as I finish the updates.

[inbreed]

i still could point to my quakelike fix http://www.thehazymind.com/smf/index.php?topic=270.0 if i wanted, but i got no time :/