Why is this OpenGL ES code slow on iPhone?

Question

I\'ve slightly modified the iPhone SDK\'s GLSprite example while learning OpenGL ES and it turns out to be quite slow. Even in the simulator (on the hw worst) so I must be doing

Answer 1

I guess my first try was just a bad (or very good) test. iPhone has a PowerVR MBX Lite which has a tile based graphics processor. It subdivides the screen into smaller tiles and renders them parallel. Now in the first case above the subdivision might got a bit exhausted because of the very high overlapping. More over, they couldn't be clipped because of the same distance and so all texture coordinates had to calculated (This could be easily tested by changing the translation in the loop). Also because of the overlapping the parallelism couldn't be exploited and some tiles were sitting doing nothing and the rest (1/3) were working a lot.

So I think, while memory bandwidth could be a bottleneck, this wasn't the case in this example. The problem is more because of how the graphics HW works and the setup of the test.