Hi,all,
I have recently made a camera class for my project. Although all the code has been written and it works perfectly, I still have some questions. The key code section in the class is from http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=Quaternion_Camera_Class, and it looks like:
void glCamera::SetPrespective()
{
GLfloat Matrix[16];
glRotatef(m_HeadingDegrees, 0.0f, 1.0f, 0.0f);
glRotatef(m_PitchDegrees, 1.0f, 0.0f, 0.0f);
glGetFloatv(GL_MODELVIEW_MATRIX, Matrix);
m_DirectionVector.i = Matrix[8];
m_DirectionVector.k = Matrix[10];
glLoadIdentity();
glRotatef(m_PitchDegrees, 1.0f, 0.0f, 0.0f);
glGetFloatv(GL_MODELVIEW_MATRIX, Matrix);
m_DirectionVector.j = Matrix[9];
glRotatef(m_HeadingDegrees, 0.0f, 1.0f, 0.0f);
// Scale the direction by our speed.
m_DirectionVector *= m_ForwardVelocity;
// Increment our position by the vector
m_Position.x += m_DirectionVector.i;
m_Position.y += m_DirectionVector.j;
m_Position.z += m_DirectionVector.k;
// Translate to our new position.
glTranslatef(-m_Position.x, -m_Position.y, m_Position.z);
}
This code sets up the model/view matrix using the camera’s heading and pitch degrees. It works perfectly. What I do not get is the way it gets the direction vector from the model/view matrix using glGetFloat. Can anybody explain this a little bit or introduce some theoretic materials? Can I get the up vector in the similar way? Thanks a lot.