As a follow up to my least effort solution, here is a demo showing the solution that I actually needed all along, with multiple cameras blitting to just a single bitmap data. Multiple BitmapDatas (and Bitmaps) could be convenient from a strictly AS3 viewpoint, but that would make the code itself unportable. The current code *is* portable, and I'm going to clean it up and then post it when I'm back from Vegas.

I did have a brief problem because I was trying to render subpixels which is of course silly. And when I say brief, I mean I've had essentially working code for fricking ages and it took me way too long to realize that I was trying to render fractional pixels using the COPY !*$ing PIXELS method of BitmapData. Ah well, it's working now so I can finally implement two player split screen in SUPERAWESOMETANKSSSSSSS!!111!!111111oneone.

Oooh, DEMO - should be visually exactly the same as previous, but with just the one BitmapData.

*Edit* - slightly different, does a fill of white so we don't get nasty "smudging" :)