The smaller your blocks, or metatiles, the more ROM space a level takes up, but the more flexibility you have in laying out your levels. For this game, I'm planning to use 32x32 blocks. (which I've built the whole engine around, so if that changes for some reason, I'm in for a lot of work)
|Here's a picture of Super Mario Bros. By this time your eyes are glazing over|
and you don't even remember why I was talking about Super Mario Bros anyway.
Warning: the next paragraph is even worse.
The reason I chose 32x32 is because of how the NES handles palettes. In memory, there's a byte for each 8x8 pixel space on the screen, to indicate which tile should be drawn there. But each tile can have one of 4 palettes, and that byte doesn't include any palette information. There's another block of video memory where you assign palettes to tiles. BUT, there's a few limitations. You can only assign one palette for every 16x16 pixel block (group of 4 tiles), which is one reason it's so common to have blocks that size in games. AND 4 of those groups (a 32x32 pixel block) shares a byte in memory (2 bits for each 16x16 block). So in my case, each 32x32 metatile can map to a byte of palette memory, which simplifies writing palettes.
So between the ROM savings for large levels (64 bytes to represent a single screen) and the ease of writing palettes (also called attribute tables), I picked 32x32 metatiles.
Now the problem is that I need a better tool for designing my metatiles. There are a few tools out there (NES Screen tool by Shiru, Sumez's editor, etc). But for one reason or another, none of them quite did want I wanted. So it was time to start tool building, which is a sometimes-miserable, sometimes-nice distraction in the middle of a project.
I considered forcing myself to use Kotlin or Clojure for the sake of learning another language, but once again, the pragmatism of getting something done quickly set in, so I cranked it out in java. Java 8's lambdas makes gui programming a little less unpleasant, so it didn't take long to have my metatile designer working but ugly.
Now it's time to actually try to put together some decent-looking metatiles and start building a cool demo level.