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Diffstat (limited to 'scroll/README.md')
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1 files changed, 17 insertions, 4 deletions
diff --git a/scroll/README.md b/scroll/README.md index d24117d..be33f87 100644 --- a/scroll/README.md +++ b/scroll/README.md @@ -15,7 +15,20 @@ information), while allowing the rest of the screen to scroll as expected. In the end, it's the same example as `level.s` (same level to scroll), but the top part does not move and shows a "THIS DOES NOT MOVE" message. -Last but not least, the `mmc3.s` example shows how to configure the MMC3 chip -(e.g. Super Mario Bros. 3, Kirby's Adventure) to have better control on which -parts of the screen to scroll or not. To showcase this the example implements a -roulette mini-game (similar to Super Mario Bros. 3 but simpler). +## Scrolling in different ways in the same frame + +Some chips like the MMC3 give programmers a lot of flexibility when it comes to +mid-frame customization. That is, chips like the MMC3 give an interface in which +programmers can ask the chip to submit an IRQ on a given exact scanline. One +main usage of this was to allow a top section of the screen to scroll, while +leaving a small section at the bottom not to scroll. This way, games were no +longer required to have a status bar at the top and they could have it at the +bottom. But these chips allow for a lot of flexibility, so programmers can get +playful with it. One simple example is the roulette mini-game from Super Mario +Bros. 3. In here the game asks for two scanline IRQs and then the scroll +direction is changed on each given IRQ. This way, the background is split in +three sections that move in different directions/speed. Something similar (but +more simple) has been reproduced in [roulette.s](./roulette.s), giving the +following result: + + |