Antialiasing

That would probably be pain-stakingly slow. Pixel read and write operations are pretty slow, that's why most folks tend to do things on a screen basis. Like copyrect etc. It takes a while for instance (in computer time) to lock and unlock buffers, to access textures to read and write, so add that onto the execution time of the code, the time it takes to tranfer textures to and from memory etc.

Your best bet is some sort of full screen, or rectangle chunk of the screen effect.