- You say “pipes” and also “threads”. This is a small thing but I wonder if you can reconcile those metaphors. I think in terms of threads, but “pipes” makes more sense with your illustration. Also works better with the concept of a “pipeline” or “graphics/rendering pipeline”.
- clearly answer the "what is a fragment shader?" question in some sort of recap paragraph.
- beef up explanations around the compilation step (a brief overview will do).