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Camera rotation problem

Started by bah Oct 24, 2005 at 8:38 AM 9 replies 1k views
Original Post
bah
bah
Hi I am having a problem with my FPS-style camera; it doesn't rotate properly. I calculate the pitch and yaw angles within an "UpdateByMouse"-type of function so that at the end, both of the angles are in degrees and in the range [-360, 360]. Once you've calculated these 2 angles, how do you apply them to the camera's view vector?
bah
bah
I integrated the function RotateCamera into the camera class, but i am still getting errors.

cam->Rotate( yawRadians, 0.0f, 1.0f, 0.0f );
cam->Rotate( pitchRadians, 0.0f, 0.0f, 1.0f );
Zakwayda
Zakwayda
You don't need quaternions for this. You could construct an Euler-angle rotation matrix from your yaw and pitch rotations, or construct the basis vectors directly using trig. Which would be easier kind of depends on what you've already got going. If you need more specific advice, you might post some of your camera code.

The one other thing I'll say is that you'll want to apply the rotations in the order pitch->yaw.
bah
bah
The following is an excerpt from the camera member function, UpdateByMouse:

if( MouseX < CenterX){	DeltaMouse = GLfloat(CenterX - MouseX);	Cam.ChangeHeading(-0.2f * DeltaMouse);}else if(MouseX > CenterX){	DeltaMouse = GLfloat(MouseX - CenterX);	Cam.ChangeHeading(0.2f * DeltaMouse);}if(MouseY < CenterY){	DeltaMouse = GLfloat(CenterY - MouseY);	Cam.ChangePitch(-0.2f * DeltaMouse);}else if(MouseY > CenterY){	DeltaMouse = GLfloat(MouseY - CenterY);	Cam.ChangePitch(0.2f * DeltaMouse);}Mat4x4 rotY, rotZ, combinedMat; // matrices are initiliased to zeroV3D newViewVector;rotZ->Rotate( pitchInDegrees, 0.0f, 0.0f, 1.0f ); // operation affects ALL elementsrotY->Rotate( yawInDegrees, &Y, 0.0f, 1.0f, 0.0f );combinedMat = rotZ * rotY;// multiply the current view vector by the combined Xform matrix and add it to itselfview += combinedMat * view;


If all the math is correct, shouldn't this code work properly?

Note that I found the camera on Nehe.
Zakwayda
Zakwayda
It looks like you're using column vectors, so I'd think you'd want this:
combinedMat = rotY * rotZ;
Instead of this:
combinedMat = rotZ * rotY;
Also, I may be missing something, but I don't understand what this line is supposed to do:
view += combinedMat * view;
Setting aside the fact that the direction vectors can be extracted directly from the matrix, I'd think the above should just be:
view = combinedMat * world_forward_axis;
where 'world_forward_axis' is whatever world axis is considered forward in local space.
bah
bah
How do you extract the direction vector directly from the matrix?
bah
bah 
Mat4x4 mat;float oglModelview[16] = { 0 };glMatrixMode( GL_MODELVIEW_MATRIX );glPushMatrix();glLoadIdentity();glRotatef( pitchDegrees, 0.0f, 0.0f, 1.0f );glRotatef( yawDegrees, 0.0f, 1.0f, 0.0f );glGetFloatv( GL_MODELVIEW_MATRIX, oglModelview );glPopMatrix();mat->SetFromArray( oglModelview );mat->TransformV3D( &viewVector, &viewVector ); //viewVector will hold the result


Ok, I am using OpenGL to calculate the composite rotation matrix and then transform the current view vector by it (i.e. the direction the camera is facing).

Shouldn't this work?
Zakwayda
Zakwayda
One observation. You probably need to change this:
glRotatef( pitchDegrees, 0.0f, 0.0f, 1.0f );glRotatef( yawDegrees, 0.0f, 1.0f, 0.0f );
To this:
glRotatef( yawDegrees, 0.0f, 1.0f, 0.0f );glRotatef( pitchDegrees, 0.0f, 0.0f, 1.0f );
In OpenGL, transforms are applied in the opposite of the order that they appear in the code, and you want pitch to be applied first.

Also, if you want to just extract the direction vectors directly, they are the first three columns of the matrix.
bah
bah
Applying the rotations is the least of the problems. I've tried rotating about just the Y or Z axis, but the result is still wrong.

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