NeHe 5 steps for the OpenGL Graphics Pipeline

NeHe Productions_ Prep_ The Graphics Pipeline
This article gives us a brief idea on how does OpenGL make your triangles display on the screen. Well, it is simplified one, and some information missing here. Some important information like, early z test, z test, alpha test are missing. I think the early z test will happen in the step 2. Because the depth already computed here. The higher part in the pipe-line, the less time will be used.
And for the z test and alpha test should happen after the step 4, after the final value compute out. And the alpha value may come from some texture maps. The depth value may be override by GLSL when we specify the depth will be output in the fragment-shader.