Testing Again for Fill Limitation

Testing Again for Fill Limitation

If you now shrink the window, performance increases again. This indicates that the program is again fill-limited. To increase performance further, you need to fill fewer pixels, or make pixel-fill less expensive by changing the pixel-drawing mode.

This particular application uses just one special per-fragment drawing mode: depth buffering. Depth buffering can be eliminated in a variety of special cases, including convex objects, backdrops, ground planes, and height fields.

Fortunately, since the program is drawing a sphere, you can eliminate depth buffering and still render a correct image by discarding quads that face away from the viewer (the "front" faces, given the orientation of quads in this model):

    glDisable(GL_DEPTH_TEST);
    glEnable(GL_CULL_FACE);
    glCullFace(GL_FRONT);

This pushes performance up to nearly 260 frames per second. Further improvements are possible. The program's performance is still far from the upper limit determined by the rate at which the screen can be cleared.