cgm_mperspective(proj_matrix, cgm_deg_to_rad(40.0), win_aspect, 0.5, 500.0);
glMatrixMode(GL_PROJECTION);
glLoadMatrixf(proj_matrix);
cgm_mperspective(proj_matrix, cgm_deg_to_rad(40.0), win_aspect, 0.5, 500.0);
glMatrixMode(GL_PROJECTION);
glLoadMatrixf(proj_matrix);