/vr/ - Retro Games

>>7934228
interesting. the game is using horizontal mirroring, which isn't what you think it'd be using. it's loading all of the horizontal movement tile by tile into the 8x8 mask area on "the left side of the screen" as you scroll right. this allows it to use two stacked screens without penalty or moving the status bar or changing how the code works, which is how it's achieving limited vertical scrolling.
Many sidescrolling games like Super Mario Bros will use vertical mirroring and preload pieces of the screen into the unused nametable: this isn't the case here. the game does scroll slowly so it can easily get away with it.
i didn't delve into the code or anything but the PPU viewer here tells alot of the story.