`PaintStyle` for `Paint` of `sky_engine`

PaintStyle.dart

import 'dart:ui';

/// A description of the style to use when drawing on a [Canvas].
///
/// Most APIs on [Canvas] take a [Paint] object to describe the style
/// to use for that operation. [PaintStyle] allows to be const 
/// constructed and later in runtime forged into the [Paint] object.
class PaintStyle {
  /// Whether to apply anti-aliasing to lines and images drawn on the
  /// canvas.
  ///
  /// Defaults to true.
  final bool isAntiAlias;

  // Must be kept in sync with the default in paint.cc.
  static const int _kColorDefault = 0xFF000000;

  /// The color to use when stroking or filling a shape.
  ///
  /// Defaults to opaque black.
  ///
  /// See also:
  ///
  ///  * [style], which controls whether to stroke or fill (or both).
  ///  * [colorFilter], which overrides [color].
  ///  * [shader], which overrides [color] with more elaborate effects.
  ///
  /// This color is not used when compositing. To colorize a layer, use
  /// [colorFilter].
  final Color color;

  // Must be kept in sync with the default in paint.cc.
  static final int _kBlendModeDefault = BlendMode.srcOver.index;

  /// A blend mode to apply when a shape is drawn or a layer is composited.
  ///
  /// The source colors are from the shape being drawn (e.g. from
  /// [Canvas.drawPath]) or layer being composited (the graphics that were drawn
  /// between the [Canvas.saveLayer] and [Canvas.restore] calls), after applying
  /// the [colorFilter], if any.
  ///
  /// The destination colors are from the background onto which the shape or
  /// layer is being composited.
  ///
  /// Defaults to [BlendMode.srcOver].
  ///
  /// See also:
  ///
  ///  * [Canvas.saveLayer], which uses its [Paint]'s [blendMode] to composite
  ///    the layer when [restore] is called.
  ///  * [BlendMode], which discusses the user of [saveLayer] with [blendMode].
  final BlendMode blendMode;

  /// Whether to paint inside shapes, the edges of shapes, or both.
  ///
  /// Defaults to [PaintingStyle.fill].
  final PaintingStyle style;

  /// How wide to make edges drawn when [style] is set to
  /// [PaintingStyle.stroke]. The width is given in logical pixels measured in
  /// the direction orthogonal to the direction of the path.
  ///
  /// Defaults to 0.0, which correspond to a hairline width.
  final double strokeWidth;

  /// The kind of finish to place on the end of lines drawn when
  /// [style] is set to [PaintingStyle.stroke].
  ///
  /// Defaults to [StrokeCap.butt], i.e. no caps.
  final StrokeCap strokeCap;

  /// The kind of finish to place on the joins between segments.
  ///
  /// This applies to paths drawn when [style] is set to [PaintingStyle.stroke],
  /// It does not apply to points drawn as lines with [Canvas.drawPoints].
  ///
  /// Defaults to [StrokeJoin.miter], i.e. sharp corners.
  ///
  /// Some examples of joins:
  ///
  /// {@animation 300 300 https://flutter.github.io/assets-for-api-docs/assets/dart-ui/miter_4_join.mp4}
  ///
  /// {@animation 300 300 https://flutter.github.io/assets-for-api-docs/assets/dart-ui/round_join.mp4}
  ///
  /// {@animation 300 300 https://flutter.github.io/assets-for-api-docs/assets/dart-ui/bevel_join.mp4}
  ///
  /// The centers of the line segments are colored in the diagrams above to
  /// highlight the joins, but in normal usage the join is the same color as the
  /// line.
  ///
  /// See also:
  ///
  ///  * [strokeMiterLimit] to control when miters are replaced by bevels when
  ///    this is set to [StrokeJoin.miter].
  ///  * [strokeCap] to control what is drawn at the ends of the stroke.
  ///  * [StrokeJoin] for the definitive list of stroke joins.
  final StrokeJoin strokeJoin;

  // Must be kept in sync with the default in paint.cc.
  static const double _kStrokeMiterLimitDefault = 4.0;

  /// The limit for miters to be drawn on segments when the join is set to
  /// [StrokeJoin.miter] and the [style] is set to [PaintingStyle.stroke]. If
  /// this limit is exceeded, then a [StrokeJoin.bevel] join will be drawn
  /// instead. This may cause some 'popping' of the corners of a path if the
  /// angle between line segments is animated, as seen in the diagrams below.
  ///
  /// This limit is expressed as a limit on the length of the miter.
  ///
  /// Defaults to 4.0.  Using zero as a limit will cause a [StrokeJoin.bevel]
  /// join to be used all the time.
  ///
  /// {@animation 300 300 https://flutter.github.io/assets-for-api-docs/assets/dart-ui/miter_0_join.mp4}
  ///
  /// {@animation 300 300 https://flutter.github.io/assets-for-api-docs/assets/dart-ui/miter_4_join.mp4}
  ///
  /// {@animation 300 300 https://flutter.github.io/assets-for-api-docs/assets/dart-ui/miter_6_join.mp4}
  ///
  /// The centers of the line segments are colored in the diagrams above to
  /// highlight the joins, but in normal usage the join is the same color as the
  /// line.
  ///
  /// See also:
  ///
  ///  * [strokeJoin] to control the kind of finish to place on the joins
  ///    between segments.
  ///  * [strokeCap] to control what is drawn at the ends of the stroke.
  final double strokeMiterLimit;

  /// A mask filter (for example, a blur) to apply to a shape after it has been
  /// drawn but before it has been composited into the image.
  ///
  /// See [MaskFilter] for details.
  final MaskFilter maskFilter;

  /// Controls the performance vs quality trade-off to use when applying
  /// filters, such as [maskFilter], or when drawing images, as with
  /// [Canvas.drawImageRect] or [Canvas.drawImageNine].
  ///
  /// Defaults to [FilterQuality.none].
  // TODO(ianh): verify that the image drawing methods actually respect this
  final FilterQuality filterQuality;

  /// The shader to use when stroking or filling a shape.
  ///
  /// When this is null, the [color] is used instead.
  ///
  /// See also:
  ///
  ///  * [Gradient], a shader that paints a color gradient.
  ///  * [ImageShader], a shader that tiles an [Image].
  ///  * [colorFilter], which overrides [shader].
  ///  * [color], which is used if [shader] and [colorFilter] are null.
  final Shader shader;

  /// A color filter to apply when a shape is drawn or when a layer is
  /// composited.
  ///
  /// See [ColorFilter] for details.
  ///
  /// When a shape is being drawn, [colorFilter] overrides [color] and [shader].
  final ColorFilter colorFilter;

  /// Whether the colors of the image are inverted when drawn.
  ///
  /// Inverting the colors of an image applies a new color filter that will
  /// be composed with any user provided color filters. This is primarily
  /// used for implementing smart invert on iOS.
  final bool invertColors;

  const PaintStyle({
    this.isAntiAlias = true, 
    this.color = const Color(_kColorDefault), 
    this.blendMode = BlendMode.srcOver,
    this.style = PaintingStyle.fill,
    this.strokeWidth = 0.0, 
    this.strokeCap = StrokeCap.butt, 
    this.strokeJoin = StrokeJoin.miter, 
    this.strokeMiterLimit = 4.0, 
    this.maskFilter, // null 
    this.filterQuality = FilterQuality.none, 
    this.shader, // null
    this.colorFilter, // null
    this.invertColors = false,
  });

  @override
  String toString() {
    final StringBuffer result = StringBuffer();
    String semicolon = '';
    result.write('Paint(');
    if (style == PaintingStyle.stroke) {
      result.write('$style');
      if (strokeWidth != 0.0)
        result.write(' ${strokeWidth.toStringAsFixed(1)}');
      else
        result.write(' hairline');
      if (strokeCap != StrokeCap.butt)
        result.write(' $strokeCap');
      if (strokeJoin == StrokeJoin.miter) {
        if (strokeMiterLimit != _kStrokeMiterLimitDefault)
          result.write(' $strokeJoin up to ${strokeMiterLimit.toStringAsFixed(1)}');
      } else {
        result.write(' $strokeJoin');
      }
      semicolon = '; ';
    }
    if (isAntiAlias != true) {
      result.write('${semicolon}antialias off');
      semicolon = '; ';
    }
    if (color != const Color(_kColorDefault)) {
      if (color != null)
        result.write('$semicolon$color');
      else
        result.write('${semicolon}no color');
      semicolon = '; ';
    }
    if (blendMode.index != _kBlendModeDefault) {
      result.write('$semicolon$blendMode');
      semicolon = '; ';
    }
    if (colorFilter != null) {
      result.write('${semicolon}colorFilter: $colorFilter');
      semicolon = '; ';
    }
    if (maskFilter != null) {
      result.write('${semicolon}maskFilter: $maskFilter');
      semicolon = '; ';
    }
    if (filterQuality != FilterQuality.none) {
      result.write('${semicolon}filterQuality: $filterQuality');
      semicolon = '; ';
    }
    if (shader != null) {
      result.write('${semicolon}shader: $shader');
      semicolon = '; ';
    }
    if (invertColors)
      result.write('${semicolon}invert: $invertColors');
    result.write(')');
    return result.toString();
  }

  Paint toPaint() {
    Paint paint = Paint();
    if (this.isAntiAlias != true)
      paint.isAntiAlias = this.isAntiAlias;
    if (this.color != const Color(_kColorDefault))
      paint.color = this.color;
    if (this.blendMode != BlendMode.srcOver)
      paint.blendMode = this.blendMode;
    if (this.style != PaintingStyle.fill)
      paint.style = this.style;
    if (this.strokeWidth != 0.0)
      paint.strokeWidth = this.strokeWidth;
    if (this.strokeCap != StrokeCap.butt)
      paint.strokeCap = this.strokeCap;
    if (this.strokeJoin != StrokeJoin.miter)
      paint.strokeJoin = this.strokeJoin;
    if (this.strokeMiterLimit != 4.0)
      paint.strokeMiterLimit = this.strokeMiterLimit;
    if (this.maskFilter != null)
      paint.maskFilter = this.maskFilter;
    if (this.filterQuality != FilterQuality.none)
      paint.filterQuality = this.filterQuality;
    if (this.shader != null)
      paint.shader = this.shader;
    if (this.colorFilter != null)
      paint.colorFilter = this.colorFilter;
    if (this.invertColors != false)
      paint.invertColors = this.invertColors;
    return paint;
  }
}