I have a simple program that consists of many colored circles. When the radius of the circles is increased, the speed of the drawing also decreases - quite dramatically. What would be the reason for this? Sample can be found at http://jlslate.posterous.com/coloration
Stroked circles are probably the least efficient primitives to draw going by number of operations-per-pixel. Followed by no-stroke circles. Generally you’ll find you get the largest performance hit by filling the screen with a lot of blended pixels, even if they overlap. iPad 2 is less susceptible to this slowdown as it has a much higher fill-rate.
We’re looking at improving the rendering speed in a future update. There’s a lot of room for improvement on our end, so we’re hoping these sorts of performance bottlenecks won’t be as prominent in the future.