An implementation of Conway's Game of Life for the GameBoy.

Press START to pause and enter edit mode.

In edit mode:

• use the d-pad to move the cursor
• press A to toggle a cell's state
• press B to trigger one step of the automata
• press SELECT to clear all the cells

Press START again to resume animation of the automata.

I started this as my first real programming written entirely in assembly. I thought the gameboy was a good fit for that, with its not too complex instruction set. I chose Conway's Game of Life because it's quite a classic of CS exercises and I thought it would be simple enough to do.

Boy, I was wrong.

I know the gameboy is far from fast enough to update all pixels on screen in between each frame. Who would have thought it would also not be fast enough to just update its 20x18 tiles? That's only 360 bytes! In the v-blank, the time between two frames are rendered by the Picture Processing Unit or PPU, and where you have access to Video RAM, there's barely enough time to write to a quarter of the tilemap. And that's without reading from it!

But there's hope: first, the gameboy has enough video ram to hold two tilemaps, so we can double buffer. Second, the v-blank is not the only time where you can write to Video RAM, you can also write in between the PPU rendering lines! That requires synchronising code with rendering but it should be doable.

The first working version I got looked like this: