lib/web_ui/lib/src/engine/color_filter.dart

// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// @dart = 2.6
part of engine;

/// A description of a color filter to apply when drawing a shape or compositing
/// a layer with a particular [Paint]. A color filter is a function that takes
/// two colors, and outputs one color. When applied during compositing, it is
/// independently applied to each pixel of the layer being drawn before the
/// entire layer is merged with the destination.
///
/// Instances of this class are used with [Paint.colorFilter] on [Paint]
/// objects.
class EngineColorFilter implements ui.ColorFilter {
  /// Creates a color filter that applies the blend mode given as the second
  /// argument. The source color is the one given as the first argument, and the
  /// destination color is the one from the layer being composited.
  ///
  /// The output of this filter is then composited into the background according
  /// to the [Paint.blendMode], using the output of this filter as the source
  /// and the background as the destination.
  const EngineColorFilter.mode(ui.Color color, ui.BlendMode blendMode)
      : _color = color,
        _blendMode = blendMode,
        _matrix = null,
        _type = _TypeMode;

  /// Construct a color filter that transforms a color by a 5x5 matrix, where
  /// the fifth row is implicitly added in an identity configuration.
  ///
  /// Every pixel's color value, repsented as an `[R, G, B, A]`, is matrix
  /// multiplied to create a new color:
  ///
  /// ```text
  /// | R' |   | a00 a01 a02 a03 a04 |   | R |
  /// | G' |   | a10 a11 a22 a33 a44 |   | G |
  /// | B' | = | a20 a21 a22 a33 a44 | * | B |
  /// | A' |   | a30 a31 a22 a33 a44 |   | A |
  /// | 1  |   |  0   0   0   0   1  |   | 1 |
  /// ```
  ///
  /// The matrix is in row-major order and the translation column is specified
  /// in unnormalized, 0...255, space. For example, the identity matrix is:
  ///
  /// ```
  /// const ColorMatrix identity = ColorFilter.matrix(<double>[
  ///   1, 0, 0, 0, 0,
  ///   0, 1, 0, 0, 0,
  ///   0, 0, 1, 0, 0,
  ///   0, 0, 0, 1, 0,
  /// ]);
  /// ```
  ///
  /// ## Examples
  ///
  /// An inversion color matrix:
  ///
  /// ```
  /// const ColorFilter invert = ColorFilter.matrix(<double>[
  ///   -1,  0,  0, 0, 255,
  ///    0, -1,  0, 0, 255,
  ///    0,  0, -1, 0, 255,
  ///    0,  0,  0, 1,   0,
  /// ]);
  /// ```
  ///
  /// A sepia-toned color matrix (values based on the [Filter Effects Spec](https://www.w3.org/TR/filter-effects-1/#sepiaEquivalent)):
  ///
  /// ```
  /// const ColorFilter sepia = ColorFilter.matrix(<double>[
  ///   0.393, 0.769, 0.189, 0, 0,
  ///   0.349, 0.686, 0.168, 0, 0,
  ///   0.272, 0.534, 0.131, 0, 0,
  ///   0,     0,     0,     1, 0,
  /// ]);
  /// ```
  ///
  /// A greyscale color filter (values based on the [Filter Effects Spec](https://www.w3.org/TR/filter-effects-1/#grayscaleEquivalent)):
  ///
  /// ```
  /// const ColorFilter greyscale = ColorFilter.matrix(<double>[
  ///   0.2126, 0.7152, 0.0722, 0, 0,
  ///   0.2126, 0.7152, 0.0722, 0, 0,
  ///   0.2126, 0.7152, 0.0722, 0, 0,
  ///   0,      0,      0,      1, 0,
  /// ]);
  /// ```
  const EngineColorFilter.matrix(List<double> matrix)
      : _color = null,
        _blendMode = null,
        _matrix = matrix,
        _type = _TypeMatrix;

  /// Construct a color filter that applies the sRGB gamma curve to the RGB
  /// channels.
  const EngineColorFilter.linearToSrgbGamma()
      : _color = null,
        _blendMode = null,
        _matrix = null,
        _type = _TypeLinearToSrgbGamma;

  /// Creates a color filter that applies the inverse of the sRGB gamma curve
  /// to the RGB channels.
  const EngineColorFilter.srgbToLinearGamma()
      : _color = null,
        _blendMode = null,
        _matrix = null,
        _type = _TypeSrgbToLinearGamma;

  final ui.Color _color;
  final ui.BlendMode _blendMode;
  final List<double> _matrix;
  final int _type;

  // The type of SkColorFilter class to create for Skia.
  static const int _TypeMode = 1; // MakeModeFilter
  static const int _TypeMatrix = 2; // MakeMatrixFilterRowMajor255
  static const int _TypeLinearToSrgbGamma = 3; // MakeLinearToSRGBGamma
  static const int _TypeSrgbToLinearGamma = 4; // MakeSRGBToLinearGamma

  @override
  bool operator ==(dynamic other) {
    if (other is! EngineColorFilter) {
      return false;
    }
    final EngineColorFilter typedOther = other;

    if (_type != typedOther._type) {
      return false;
    }
    if (!_listEquals<double>(_matrix, typedOther._matrix)) {
      return false;
    }

    return _color == typedOther._color && _blendMode == typedOther._blendMode;
  }

  SkColorFilter _toSkColorFilter() {
    switch (_type) {
      case _TypeMode:
        if (_color == null || _blendMode == null) {
          return null;
        }
        return SkColorFilter.mode(this);
      case _TypeMatrix:
        if (_matrix == null) {
          return null;
        }
        assert(_matrix.length == 20, 'Color Matrix must have 20 entries.');
        return SkColorFilter.matrix(this);
      case _TypeLinearToSrgbGamma:
        return SkColorFilter.linearToSrgbGamma(this);
      case _TypeSrgbToLinearGamma:
        return SkColorFilter.srgbToLinearGamma(this);
      default:
        throw StateError('Unknown mode $_type for ColorFilter.');
    }
  }

  @override
  int get hashCode => ui.hashValues(_color, _blendMode, ui.hashList(_matrix), _type);

  @override
  String toString() {
    switch (_type) {
      case _TypeMode:
        return 'ColorFilter.mode($_color, $_blendMode)';
      case _TypeMatrix:
        return 'ColorFilter.matrix($_matrix)';
      case _TypeLinearToSrgbGamma:
        return 'ColorFilter.linearToSrgbGamma()';
      case _TypeSrgbToLinearGamma:
        return 'ColorFilter.srgbToLinearGamma()';
      default:
        return 'Unknown ColorFilter type. This is an error. If you\'re seeing this, please file an issue at https://github.com/flutter/flutter/issues/new.';
    }
  }

  List<dynamic> webOnlySerializeToCssPaint() {
    throw UnsupportedError('ColorFilter for CSS paint not yet supported');
  }
}