title: What causes frame rate loss?
body: <p>I'm writing a game with cocos2d and I have noticed that the frame rate drops as the game progresses. I've checked for leaks but everything looks fine so I'm at a loss as to what to do next. Sorry if this is a really basic question but what sort of factors cause frame rate loss? </p>
  
  <p>The problem seems to get worse when I clear the sprites from a layer. Sometimes the framerate jumps back to 60 but occasionally it drops down to 30 or lower and never recovers. After a few minutes the animations are noticably slower and the game pretty much grinds to a halt. I'm not sure if this is specific to cocos2d or a common issue in game development, but it renders the game unplayable :( </p>