twonly-app-dependencies/flutter_blurhash/lib/src/blurhash.dart

import 'dart:async';
import 'dart:math';
import 'dart:ui' as ui;

import 'package:flutter/foundation.dart';

/// Optimization modes for BlurHash decoder
enum BlurHashOptimizationMode {
  /// Original algorithm
  none,

  /// Optimized with better cache locality
  standard,

  /// Approximation with faster sRGB conversion + cache locality
  approximation
}

// Optimized BlurHash decode implementation
Future<Uint8List> optimizedBlurHashDecode({
  required String blurHash,
  required int width,
  required int height,
  double punch = 1.0,
  BlurHashOptimizationMode optimizationMode = BlurHashOptimizationMode.standard,
}) {
  _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;

  // Preallocate colors array with fixed size
  final colors = List<List<double>>.filled(numX * numY, [0, 0, 0]);

  // Decode DC component (first component)
  final dcValue = _decode83(blurHash.substring(2, 6));
  colors[0] = _decodeDC(dcValue);

  // Decode AC components (remaining components)
  final adjustedPunch = maximumValue * punch;
  for (var i = 1; i < colors.length; i++) {
    final value = _decode83(blurHash.substring(4 + i * 2, 6 + i * 2));
    colors[i] = _decodeAC(value, adjustedPunch);
  }

  // Precalculate cosine values for x and y
  final cosinesX = List<List<double>>.generate(
    numX,
    (i) => List<double>.generate(
      width,
      (x) => cos((pi * x * i) / width),
    ),
  );

  final cosinesY = List<List<double>>.generate(
    numY,
    (j) => List<double>.generate(
      height,
      (y) => cos((pi * y * j) / height),
    ),
  );

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

  // Process image in chunks to improve cache locality
  const chunkSize = 32;

  // Process the image in tiles for better cache performance
  for (int yChunk = 0; yChunk < height; yChunk += chunkSize) {
    final yEnd = min(yChunk + chunkSize, height);

    for (int xChunk = 0; xChunk < width; xChunk += chunkSize) {
      final xEnd = min(xChunk + chunkSize, width);

      for (int y = yChunk; y < yEnd; y++) {
        int p = (y * width + xChunk) * 4;

        for (int x = xChunk; x < xEnd; x++) {
          var r = 0.0, g = 0.0, b = 0.0;

          // Use precalculated cosine values
          for (int j = 0; j < numY; j++) {
            final cosY = cosinesY[j][y];

            for (int i = 0; i < numX; i++) {
              final basis = cosinesX[i][x] * cosY;
              final color = colors[i + j * numX];

              r += color[0] * basis;
              g += color[1] * basis;
              b += color[2] * basis;
            }
          }

          // Convert linear RGB to sRGB space based on optimization mode
          switch (optimizationMode) {
            case BlurHashOptimizationMode.approximation:
              pixels[p++] = _approximatedLinearTosRGB(r);
              pixels[p++] = _approximatedLinearTosRGB(g);
              pixels[p++] = _approximatedLinearTosRGB(b);
              break;
            case BlurHashOptimizationMode.standard:
            case BlurHashOptimizationMode.none:
              pixels[p++] = _linearTosRGB(r);
              pixels[p++] = _linearTosRGB(g);
              pixels[p++] = _linearTosRGB(b);
              break;
          }

          pixels[p++] = 255; // Alpha is always 255
        }
      }
    }
  }

  return Future.value(pixels);
}

// Create this once as a static variable
final List<double> _sRGBLookupTable = _createSRGBLookupTable(256);

List<double> _createSRGBLookupTable(int size) {
  final table = List<double>.filled(size, 0);
  for (int i = 0; i < size; i++) {
    final v = i / (size - 1);
    if (v <= 0.0031308) {
      table[i] = v * 12.92;
    } else {
      table[i] = 1.055 * pow(v, 1 / 2.4) - 0.055;
    }
  }
  return table;
}

int _approximatedLinearTosRGB(double value) {
  final v = max(0.0, min(1.0, value));

  // Find the closest indices in the lookup table
  final pos = v * (_sRGBLookupTable.length - 1);
  final idx = pos.floor();
  final fract = pos - idx;

  // Edge case for the maximum value
  if (idx >= _sRGBLookupTable.length - 1) {
    return (_sRGBLookupTable[_sRGBLookupTable.length - 1] * 255 + 0.5).toInt();
  }

  // Linear interpolation between the two closest values
  final result =
      _sRGBLookupTable[idx] * (1 - fract) + _sRGBLookupTable[idx + 1] * fract;
  return (result * 255 + 0.5).toInt();
}

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);
}

Future<ui.Image> blurHashDecodeImage({
  required String blurHash,
  required int width,
  required int height,
  double punch = 1.0,
  BlurHashOptimizationMode optimizationMode = BlurHashOptimizationMode.standard,
}) async {
  _validateBlurHash(blurHash);

  final completer = Completer<ui.Image>();

  final Uint8List pixels;
  if (optimizationMode != BlurHashOptimizationMode.none) {
    pixels = await optimizedBlurHashDecode(
      blurHash: blurHash,
      width: width,
      height: height,
      punch: punch,
      optimizationMode: optimizationMode,
    );
  } else {
    pixels = await blurHashDecode(
      blurHash: blurHash,
      width: width,
      height: height,
      punch: punch,
    );
  }

  if (kIsWeb) {
    completer.complete(_createBmp(pixels, width, height));
  } else {
    ui.decodeImageFromPixels(
        pixels, width, height, ui.PixelFormat.rgba8888, completer.complete);
  }

  return completer.future;
}

Future<ui.Image> _createBmp(Uint8List pixels, int width, int height) async {
  int size = (width * height * 4) + 122;
  final bmp = Uint8List(size);
  final ByteData header = bmp.buffer.asByteData();
  header.setUint8(0x0, 0x42);
  header.setUint8(0x1, 0x4d);
  header.setInt32(0x2, size, Endian.little);
  header.setInt32(0xa, 122, Endian.little);
  header.setUint32(0xe, 108, Endian.little);
  header.setUint32(0x12, width, Endian.little);
  header.setUint32(0x16, -height, Endian.little);
  header.setUint16(0x1a, 1, Endian.little);
  header.setUint32(0x1c, 32, Endian.little);
  header.setUint32(0x1e, 3, Endian.little);
  header.setUint32(0x22, width * height * 4, Endian.little);
  header.setUint32(0x36, 0x000000ff, Endian.little);
  header.setUint32(0x3a, 0x0000ff00, Endian.little);
  header.setUint32(0x3e, 0x00ff0000, Endian.little);
  header.setUint32(0x42, 0xff000000, Endian.little);
  bmp.setRange(122, size, pixels);
  final codec = await ui.instantiateImageCodec(bmp);
  final frame = await codec.getNextFrame();
  return frame.image;
}

double _sRGBToLinear(int value) {
  final v = value / 255;
  if (v <= 0.04045) {
    return v / 12.92;
  } else {
    return pow((v + 0.055) / 1.055, 2.4) as double;
  }
}

int _linearTosRGB(double value) {
  final v = max(0, min(1, value));
  if (v <= 0.0031308) {
    return (v * 12.92 * 255 + 0.5).round();
  } else {
    return ((1.055 * pow(v, 1 / 2.4) - 0.055) * 255 + 0.5).round();
  }
}

void _validateBlurHash(String blurHash) {
  if (blurHash.length < 6) {
    throw Exception('The blurhash string must be at least 6 characters');
  }

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

  if (blurHash.length != 4 + 2 * numX * numY) {
    throw Exception(
        'blurhash length mismatch: length is ${blurHash.length} but '
        'it should be ${4 + 2 * numX * numY}');
  }
}

int _sign(double n) => (n < 0 ? -1 : 1);

num _signPow(double val, double exp) => _sign(val) * pow(val.abs(), exp);

int _decode83(String str) {
  var value = 0;
  final units = str.codeUnits;
  final digits = _digitCharacters.codeUnits;
  for (var i = 0; i < units.length; i++) {
    final code = units.elementAt(i);
    final digit = digits.indexOf(code);
    if (digit == -1) {
      throw ArgumentError.value(str, 'str');
    }
    value = value * 83 + digit;
  }
  return value;
}

List<double> _decodeDC(int value) {
  final intR = value >> 16;
  final intG = (value >> 8) & 255;
  final intB = value & 255;
  return [_sRGBToLinear(intR), _sRGBToLinear(intG), _sRGBToLinear(intB)];
}

List<double> _decodeAC(int value, double maximumValue) {
  final quantR = (value / (19 * 19)).floor();
  final quantG = (value / 19).floor() % 19;
  final quantB = value % 19;

  final rgb = [
    _signPow((quantR - 9) / 9, 2.0) * maximumValue,
    _signPow((quantG - 9) / 9, 2.0) * maximumValue,
    _signPow((quantB - 9) / 9, 2.0) * maximumValue
  ];

  return rgb;
}

bool validateBlurhash(String blurhash) {
  if (blurhash.isEmpty || blurhash.length < 6) {
    debugPrint('Blurhash should be at least 6 characters');
    return false;
  }

  final sizeFlag = _decode83(blurhash[0]);
  final y = ((sizeFlag / 9) + 1).floor();
  final x = (sizeFlag % 9) + 1;

  if (blurhash.length != 4 + 2 * x * y) {
    debugPrint(
        "blurhash length mismatch: length is ${blurhash.length} but it should be ${4 + 2 * x * y}");
    return false;
  }

  return true;
}

const _digitCharacters =
    "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz#\$%*+,-.:;=?@[]^_{|}~";