Proper horizontal scrolling is now in place. It is updating both the tiles graphics as well as the attribute table (colors) dynamically as the player walks.
I'm debating if I want to implement backtracking or only allow moving left to right. Currently it allows you to backtrack to the edge of the currently visible nametable, and to go beyond that would require more complex tile streaming logic.
I also haven't decided if I want to take on vertical scrolling as well. That is notoriously difficult on the NES, and I think it might not be worth the effort for this compo entry. I would probably do something more like Mega Man, where there are some vertical sections, but they are only one screen high.
As you may have noticed, there isn't actually any collision yet, and in reality the player has no logic at all (beyond playing a walking animation). I'll be getting her moving around for real next, and hopefully start on world collision too.