Glad it wasn't my fault! :P
If it becomes an issue in the future, the number 1 way to improve performance would be to have two different screen size constants, so the mask surfaces (the things that define how the view is sliced up) stay small, and each mask pixel is used by multiple screen pixels. You're gonna need to scale up/down coordinates in a couple places but it shouldn't be too hard to figure out, hiding the jagged edges on the screen (due to the larger pixels in the mask) might be a bit trickier though.