note on using PALETTE_SIZE as offset. normally it's `256 colors * 3 bytes per color = 768`, but in our headless mode it's 256. upstream does `SDL_SetPaletteColors(screen->format->palette, playpal_data->colours + 256 * pal, 0, 256);` when palette is updated, so clearly it means offsetting by 256 colors=bytes. but PALETTE_SIZE I used as my offset is not for stuff upstream uses it for. just something better than a magic number.
feos