Interesting cross-browser behaviour

I've discovered another interesting quirk between the way that IE and FF handle flash.

I'm building a site that has a huge (3200x2100) scrolling bitmap for a background, the site itself is 1000x570, so there's a pretty big scrolling area as well. It's basically a bit of a processor fryer, and no, it wasn't my idea.

Movie is set to 25fps and I get the following behaviours:

FF: When the background is totally at rest, nothing is happening except a tiny amount of code for the fps monitor. Processor use reads 0% and I'm getting just over 21fps, consistently. Now if I start to scroll the background, the framerate goes down, hovers between 16 and 20 fps. Processor use hovers between 65 and 80 %

IE: Same thing, and I get EXACTLY the same when it's at rest - 0% processor use, consistently just over 21fps. Now if I start to scroll, the fps goes UP to 23-24 fps and the processor usage maxes out to 99/100

Weird

someone told me that FF limits the CPU usage of flash so that its hard for the swf to run higher than 30fps.

IE puts out.

Yes, I've said the very same in another thread, but it's insane that IE increases the fps when things get intensive.

Just cut the large bitmap into chunks and disable them when outside the viewing area. See if that helps any

Good idea. The schedule's really tight though, so I'm gonna have to leave optimisation until last. Client just wants to see shiny sparkly stuff as soon as possible.

Turning bitmap smoothing off has given me an extra 2-3 fps, the difference is only noticeable when the background comes to a stop (the bitmap snaps to pixels instead of moving between them gradually)