Question

I have my object’s rotation and translation in a quaternion, which I’ve converted to a matrix[16].

How do I feed that matrix to OpenGL? I’d-a thought I could just glLoadMatrix() with my new, fancy-pants matrix and all would be good, but I’m getting a blank screen.

(I’m a bit of a GL n00b, so type slowly and use small words 😉

My code looks something like this:

glPushMatrix();

[quaternion makeIdentity];         // reset quat
[quaternion setPitch: rotation.x yaw: rotation.y roll: rotation.z];  // Set up with rotation coords (NOTE: setPitch:yaw:roll: is smart about degrees->radians)

GLdouble matrix[16];
[quaternion matrix: &matrix[0]];   // get quat -> matrix
matrix[12] =  location.x;          // fill in the translation
matrix[13] =  location.y;
matrix[14] =  location.z;

glLoadMatrixd(matrix);

glScaled(scale.x, scale.y, scale.z);

// draw geometry here -- snip

glPopMatrix();

I think I’m pretty close but, when I use this code, I get a blank display (everything is glClearColor.)

NOTE: when I skip the quaternion part and do something like this:

glPushMatrix();

glTranslatef(location.x, location.y, location.z);

glRotated(rotation.z,   0,   0, 1.0);
glRotated(rotation.x, 1.0,   0,   0);
glRotated(rotation.y,   0, 1.0,   0);

// draw geometry here -- snip

glPopMatrix();

the display is as expected. The only problem is that my rotations are screwy, due to being applied sequentially. Hence my desire to use quaternions.

Answer 1

If you don’t forgot to set current matrix mode to GL_MODELVIEW, your matrix should be loaded correctly. Check your quat -> matrix calculations. I’d start from rotation by zero angle and comparing result with identity matrix.