Alright so we can do some basic "movement", but we left a big trail in the video memory of everywhere we went. Most of the time that's not what we want at all. If we want more hardware support we're going to have to use a new video mode. So far we've only used Mode 3, but modes 4 and 5 are basically the same. Instead, we'll switch focus to using a tiled graphical mode.

First we will go over the complete GBA memory mapping. Part of this is the memory for tiled graphics, but also things like all those IO registers, where our RAM is for scratch space, all that stuff. Even if we can't put all of them to use at once, it's helpful to have an idea of what will be available in the long run.

Tiled modes bring us two big new concepts that each have their own complexity: backgrounds and objects. They share some concepts, but fundamentally the background is for creating a very large static space that you can scroll around the view within, and the objects are about having a few moving bits that appear over the background. Careful use of backgrounds and objects is key to having the best looking GBA game, so we won't even be able to cover it all in a single chapter.

And, of course, since most games are pretty boring if they're totally static we'll touch on the kinds of RNG implementations you might want to have on a GBA. Most general purpose RNGs that you find are rather big compared to the amount of memory we want to give them, and they often use a lot of u64 operations, so they end up much slower on a 32-bit machine like the GBA (you can lower 64-bit ops to combinations of 32-bit ops, but that's quite a bit more work). We'll cover a few RNG options that size down the RNG to a good size and a good speed without trading away too much in terms of quality.

To top it all off, we'll make a simple "memory game" sort of thing. There's some face down cards in a grid, you pick one to check, then you pick the other to check, and then if they match the pair disappears.