Drawing images off-screen results in performance drop

Question

Im writing an IOS game using AS3. Here's the problem- I have an image on the screen that moves around. When the image's y value goes negative (the image is partly off the screen), the frame rates bottom out. I've gone over my code pretty thoroughly, even threw together a few test projects just to experiment. In all the test I do, whenever there is an object that is off screen, even partially, the frame rates drop. It's making scrolling backgrounds impossible. BTW, I'm using Packager for iPhone and a 3G (not 3GS). Frame rates are normally 24 with no problems

Answer 1

What technique do you use to hide the invisible part of the screen? Mask + scrolling content, scrolling content or scroll rect? You should consider using scroll rect if that's not the technique you are using right now.

Answer 2

You need to clip all drawing to the visible image. Anytime you draw offscreen you lose hardware acceleration, which only works on video memory.