Function makePng

packages/engine/src/utils/alphaBlit.test.ts:58–87

* Build a minimal RGBA PNG for testing. * pixels: flat RGBA array (row-major, 8-bit per channel)

(width: number, height: number, pixels: number[])

 * pixels: flat RGBA array (row-major, 8-bit per channel)
 */
function makePng(width: number, height: number, pixels: number[]): Buffer {
  // IHDR
  const ihdr = Buffer.allocUnsafe(13);
  ihdr.writeUInt32BE(width, 0);
  ihdr.writeUInt32BE(height, 4);
  ihdr[8] = 8; // bit depth
  ihdr[9] = 6; // color type RGBA
  ihdr[10] = 0; // compression
  ihdr[11] = 0; // filter method
  ihdr[12] = 0; // interlace none

  // Raw scanlines with filter byte 0 (None)
  const scanlines: number[] = [];
  for (let y = 0; y < height; y++) {
    scanlines.push(0); // filter type None
    for (let x = 0; x < width; x++) {
      const i = (y * width + x) * 4;
      scanlines.push(pixels[i] ?? 0, pixels[i + 1] ?? 0, pixels[i + 2] ?? 0, pixels[i + 3] ?? 0);
    }
  }

  const idatData = deflateSync(Buffer.from(scanlines));

  return Buffer.concat([
    PNG_SIG,
    makeChunk("IHDR", ihdr),
    makeChunk("IDAT", idatData),
    makeChunk("IEND", Buffer.alloc(0)),
  ]);
}

// ── decodePng tests ──────────────────────────────────────────────────────────