How do I implement a quaternion based camera?
- by kudor gyozo
I looked at several tutorials about this and when I thought I understood I tried to implement a quaternion based camera. The problem is it doesn't work correctly, after rotating for approx. 10 degrees it jumps back to -10 degrees. I have no idea what's wrong. I'm using openTK and it already has a quaternion class. I'm a noob at opengl, I'm doing this just for fun, and don't really understand quaternions, so probably I'm doing something stupid here. Here is some code: (Actually almost all the code except the methods that load and draw a vbo (it is taken from an OpenTK sample that demonstrates vbo-s))
I load a cube into a vbo and initialize the quaternion for the camera
protected override void OnLoad(EventArgs e) {
base.OnLoad(e);
cameraPos = new Vector3(0, 0, 7);
cameraRot = Quaternion.FromAxisAngle(new Vector3(0,0,-1), 0);
GL.ClearColor(System.Drawing.Color.MidnightBlue);
GL.Enable(EnableCap.DepthTest);
vbo = LoadVBO(CubeVertices, CubeElements);
}
I load a perspective projection here. This is loaded at the beginning and every time I resize the window.
protected override void OnResize(EventArgs e) {
base.OnResize(e);
GL.Viewport(0, 0, Width, Height);
float aspect_ratio = Width / (float)Height;
Matrix4 perpective = Matrix4.CreatePerspectiveFieldOfView(MathHelper.PiOver4, aspect_ratio, 1, 64);
GL.MatrixMode(MatrixMode.Projection);
GL.LoadMatrix(ref perpective);
}
Here I get the last rotation value and create a new quaternion that represents only the last rotation and multiply it with the camera quaternion. After this I transform this into axis-angle so that opengl can use it. (This is how I understood it from several online quaternion tutorials)
protected override void OnRenderFrame(FrameEventArgs e) {
base.OnRenderFrame(e);
GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);
double speed = 1;
double rx = 0, ry = 0;
if (Keyboard[Key.A]) {
ry = -speed * e.Time;
}
if (Keyboard[Key.D]) {
ry = +speed * e.Time;
}
if (Keyboard[Key.W]) {
rx = +speed * e.Time;
}
if (Keyboard[Key.S]) {
rx = -speed * e.Time;
}
Quaternion tmpQuat = Quaternion.FromAxisAngle(new Vector3(0,1,0), (float)ry);
cameraRot = tmpQuat * cameraRot;
cameraRot.Normalize();
GL.MatrixMode(MatrixMode.Modelview);
GL.LoadIdentity();
Vector3 axis;
float angle;
cameraRot.ToAxisAngle(out axis, out angle);
GL.Rotate(angle, axis);
GL.Translate(-cameraPos);
Draw(vbo);
SwapBuffers();
}
Here are 2 images to explain better:
I rotate a while and from this:
it jumps into this
Any help is appreciated.
Update1: I add these to a streamwriter that writes into a file:
sw.WriteLine("camerarot: X:{0} Y:{1} Z:{2} W:{3} L:{4}", cameraRot.X, cameraRot.Y, cameraRot.Z, cameraRot.W, cameraRot.Length);
sw.WriteLine("ry: {0}", ry);
The log is available here: http://www.pasteall.org/26133/text. At line 770 the cube jumps from right to left, when camerarot.Y changes signs. I don't know if this is normal.
Update2 Here is the complete project.
