Function encodePng

server.js:229–248

(width, height, rgba)

}

function encodePng(width, height, rgba) {
  const ihdr = Buffer.alloc(13);
  ihdr.writeUInt32BE(width, 0);
  ihdr.writeUInt32BE(height, 4);
  ihdr[8] = 8;
  ihdr[9] = 6;
  const scanlineLength = width * 4 + 1;
  const scanlines = Buffer.alloc(scanlineLength * height);
  for (let y = 0; y < height; y += 1) {
    const sourceStart = y * width * 4;
    const targetStart = y * scanlineLength + 1;
    rgba.copy(scanlines, targetStart, sourceStart, sourceStart + width * 4);
  }
  return Buffer.concat([
    Buffer.from([0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a]),
    pngChunk("IHDR", ihdr),
    pngChunk("IDAT", zlib.deflateSync(scanlines)),
    pngChunk("IEND")
  ]);
}

function glyphFor(char) {
  return LABEL_FONT[char] || LABEL_FONT["?"];