I modified the Apple sample program Touches to do some simple polygon drawing on an iPad. The strange thing is: when I first draw a polygon, it almost always has glitches in it (you can see what I mean in this YouTube video: http://www.youtube.com/watch?v=oNgXJ1oEDv8 ), but after a few seconds (with the program doing nothing, no user interaction), they always go away (also shown in the video). My first thought was that it might be a hardware problem, but it does the same thing on an iPhone. Since I'm a newbie in iPad/iPhone programming, I'm guessing that I'm just making some stupid mistake, but I have no idea what it might be. I can post the code for my test program if you're interested.