Pymapper doesn't have to deal with screen rotation. Pymapper probably does the same thing that Maemo Mapper v1.x did, which is load a 4x3 grid of maps into a 1024x768 buffer (or larger?) and pan the view around it. You can't take advantage of the same initial assumption when you're rotating the viewpoint, because now you have to load maps into non-parallel pixel spaces. For example, to load the same 5x4 grid of maps into a buffer to draw (and pan around) on the screen, you'd need 1280x1280 pixels (> 6.5 MB of buffer). And to have the same pannability as the non-rotated situation, you'd need more than 4x3 grid panels, increasing the number of panels that have to be accessed from the (relatively slow) database.

I'm not saying it's not possible to do it more efficiently. It just wouldn't be easy to do now, given the current codebase. I can look into reducing some of the blackness without increasing the memory requirements (by too much), but right now my focus is on stability and features.