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:
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; m_DirectionVector.k = Matrix; glLoadIdentity(); glRotatef(m_PitchDegrees, 1.0f, 0.0f, 0.0f); glGetFloatv(GL_MODELVIEW_MATRIX, Matrix); m_DirectionVector.j = Matrix; 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.