I mean that enemies/objects tend to appear and disappear just before they enter the screen, new tiles for scrolling backgrounds can be done long before or just before the edge of the screen. (In some cases, just after, like the attribute glitching you see in SMB3.) If you were to extend the background, you still don't know where to put the sprites at the edges.Mr. Blah wrote:>Well, most NES games tend to be doing a lot of work "just off screen".
What kind of work? Preparing code and loading it from the VRAM?
If the game keeps track of enemies offscreen, whatever format that's in will have nothing to do with what's displayed onscreen, so there's no automatable way to pick up that information (presuming it even exists). Onscreen sprites have 8-bit values for their coordinates, there's no way to specify one that should be offscreen, so you can't get it from the PPU's sprite position data.Mr. Blah wrote:>And as rainwarrior mentioned, sprites will pop in and out of visibility as they go through the extended background.Why's this? Imperfect extending?
As I said, the only thing to do, really, is rewrite the game. Either rebuild it on some non-NES platform, or extend an NES emulator with new (fake) hardware capabilities and rewrite as much of the game as you need to do this.