Generates mipmaps for a single channel image by processing 4 pixels in the order they appear in the underlying buffer as opposed to visually.

packed-1d-mipmaps.ts

interface SingleChannelImage {
    width: number;
    height: number;
    data: Uint8ClampedArray
}

function mipmaps(source: SingleChannelImage, fn = Math.max): SingleChannelImage[] {
  if (source.width === 1 && source.height === 1) {
    return [source];
  }

  const width = Math.max(source.width / 2, 1);
  const height = Math.max(source.height / 2, 1);

  const length = width * height;
  const data = new Uint8ClampedArray(length);
  for (let i = 0; i < length; i++) {
    const offset = i * 4;
    data[i] = fn(...source.data.slice(offset, offset + 4));
  }

  const result = { width, height, data };
  return [source, ...mipmaps(result)];
}