Quietust posted here previously that changes in the fine horizontal scroll value via $2005 (low 3 bits) take effect immediately, even in the middle of a scanline. The coarse scroll value (high 5 bits) would obviously not be implemented until the next scanline when the tile index would be reloaded. I'm having trouble understanding how changing the fine X scroll value in mid-scanline would work. Would the PPU render the same pixels from a tile twice if it were decremented? I thought the shift register only worked 1 way. I initially assumed that the fine X scroll just told the PPU how many bits to throw away from the left edge of the first tile rendered, but apparently that's not the case. Can anyone shed some light on how this would actually work? It was stated that some games (e.g. SMB3 during the matching subgame) rely upon this behavior. Does Nintendulator currently emulate this?