RomTile.cs

namespace RomTile;

using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;

internal static class Program
{
    private const int TileWidth = 8;
    private const int TileHeight = 8;
    private const int NumberOfPixelsInATile = TileWidth * TileHeight;

    private const int NumberOfTilesAcross = 32;

    private static readonly Rgba32[] Palette =
    {
        new(0x09, 0x18, 0x20),
        new(0x35, 0x67, 0x56),
        new(0x88, 0xC0, 0x70),
        new(0xE0, 0xF8, 0xD0),
    };

    private static void Main(string[] args)
    {
        var rom = File.ReadAllBytes(args[0]);

        var numberOfPixelsInRom = rom.Length / 2 * TileWidth;

        var numberOfTilesInRom = numberOfPixelsInRom / NumberOfPixelsInATile;

        var numberOfTilesTall = (int)Math.Ceiling((double)numberOfTilesInRom / NumberOfTilesAcross);

        var image = new Image<Rgba32>(NumberOfTilesAcross * TileWidth, numberOfTilesTall * TileHeight);

        var pixelCount = 0;
        for (var i = 0; i < rom.Length; i += 2)
        {
            var b0 = rom[i];
            var b1 = rom[i + 1];

            var pixelLine = new int[TileWidth];
            for (var j = pixelLine.Length - 1; j >= 0; j--)
            {
                var mask = 1 << j;
                var p = 2 * ((b1 & mask) == 0 ? 0 : 1) + ((b0 & mask) == 0 ? 0 : 1);
                pixelLine[pixelLine.Length - 1 - j] = p;

                var indexOfPixelInTile = pixelCount % NumberOfPixelsInATile;
                var tileIndex = pixelCount / NumberOfPixelsInATile;

                var yInTile = indexOfPixelInTile / TileWidth;
                var xInTile = indexOfPixelInTile % TileWidth;

                var y0 = tileIndex / NumberOfTilesAcross * TileHeight;
                var x0 = tileIndex % NumberOfTilesAcross * TileWidth;

                var x = x0 + xInTile;
                var y = y0 + yInTile;

                image[x, y] = Palette[p];

                pixelCount += 1;
            }
        }

        image.SaveAsPng("/tmp/tiles.png");
    }
}