How do I turn individual pixels on & off (i.e. APA graphics) instead of drawing with tiles ?
The ability to turn individual pixels on & off on the screen is often called APA (or All Points Addressable) graphics. On the GBC you can do this by putting a unique tile at each screen map location. Since the GBC can have 512 unique tiles, 360 of these are enough to cover the entire screen (20×18 tiles.) Then you can set individual screen pixels to any colo(u)r by writing to tile memory. On the other GBs (pocket, classic, super) you only have access to 256 tiles at one tile which is less than the 360 unique tiles required to fill the screen. But, by using a mid-screen LYC interrupt you can switch from tile set #1 to tile set #2 midscreen. This effectively allows you to display up to 384 unique tiles (since tile set #1 & #2 half overlap each other) which is enough to fill the screen to allow APA graphics.
