Performance of a game is very important, it is important to maintain a constant frame rate of a game. So I will talk about how I keep track of the performance of the game. However, the game is not finished, I can only profile the engine with sample placeholder assets, the profiled data might not be match with the final data after the game is finished. Anyway, I will try to talk about my first attempt to profile my engine. (All the data are measured with iPhone 3G).
XCode OpenGL ES Analysis
For profiling the graphics performance on iPhone, there is an OpenGL ES analyzer that comes with Xcode 4. It can detect redundant state changes and give some advice to improve rendering performance. It also help me to spot some bugs such as forgetting to set the texture states to use mip-map.
After using the analyzer, I discover that 2 recommendations that improve my engine rendering performance significantly. The first suggestion is to use the EXT_discard_framebuffer extension after rendering each frame.
Before using the analyzer, I did not notice iPhone have this OpenGL extension. This helps the frame rate from 20.8ms per frame to 19.2ms per frame. The second suggestion is to use a more compact back-buffer format to reduce the fill rate.