blurHashDecode function

Future<Uint8List> blurHashDecode({ required String blurHash, required int width, required int height, double punch = 1.0, })

Implementation

Future<Uint8List> blurHashDecode({
  required String blurHash,
  required int width,
  required int height,
  double punch = 1.0,
}) {
  _validateBlurHash(blurHash);

  final sizeFlag = _decode83(blurHash[0]);
  final numY = (sizeFlag / 9).floor() + 1;
  final numX = (sizeFlag % 9) + 1;

  final quantisedMaximumValue = _decode83(blurHash[1]);
  final maximumValue = (quantisedMaximumValue + 1) / 166;

  final colors = []..length = numX * numY;

  for (var i = 0; i < colors.length; i++) {
    if (i == 0) {
      final value = _decode83(blurHash.substring(2, 6));
      colors[i] = _decodeDC(value);
    } else {
      final value = _decode83(blurHash.substring(4 + i * 2, 6 + i * 2));
      colors[i] = _decodeAC(value, maximumValue * punch);
    }
  }

  final bytesPerRow = width * 4;
  final pixels = Uint8List(bytesPerRow * height);

  int p = 0;
  for (int y = 0; y < height; y++) {
    for (int x = 0; x < width; x++) {
      var r = .0;
      var g = .0;
      var b = .0;

      for (int j = 0; j < numY; j++) {
        for (int i = 0; i < numX; i++) {
          final basis = cos((pi * x * i) / width) * cos((pi * y * j) / height);
          var color = colors[i + j * numX];
          r += color[0] * basis;
          g += color[1] * basis;
          b += color[2] * basis;
        }
      }

      final intR = _linearTosRGB(r);
      final intG = _linearTosRGB(g);
      final intB = _linearTosRGB(b);

      pixels[p++] = intR;
      pixels[p++] = intG;
      pixels[p++] = intB;
      pixels[p++] = 255;
    }
  }

  return Future.value(pixels);
}