iPhone + OpenGL + Touches: FPS drop

Question

Hey there,

Recently I ran into a very strange issue: touching the screen of the iPhone and moving a finger around can eat up to 50% of my FPS. Yeah, I checked my code for possible bottlenecks – not the issue. The last resort I tried before writing this post – commenting out all the touch processing code and looking at FPS then. Results are: no touches – 58-60. Touching and moving the finger – 35-40 FPS instantly.

The rendering is done in a separate thread, so that no main runloop events shall collide with it. However, it's very crushial for me (and the game I develop) to resolve this issue, because such FPS drop is really noticeable.

Thank you for your help in advance.

UPDATE: seems that setting rendering thread's priority to higher value helps a bit...

Answer 1

The iPhone, iPod Touch, and iPad are all single-processor, single-core devices. Simply putting your rendering code on a separate thread from touch event handling—though a good idea—won't prevent the touch processing from eating up CPU cycles. The only way to make your framerates go up will be to either make the touch handling code faster or make the rendering faster. Which you pursue depends on the specifics of your application.