flutter_svg/lib/src/vector_drawable.dart

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

import 'package:meta/meta.dart';
import 'package:path_drawing/path_drawing.dart';
import 'package:vector_math/vector_math_64.dart';

import 'render_picture.dart' as render_picture;
import 'svg/parsers.dart' show affineMatrix;

/// Paint used in masks.
final Paint _grayscaleDstInPaint = Paint()
  ..blendMode = BlendMode.dstIn
  ..colorFilter = const ColorFilter.matrix(<double>[
    0, 0, 0, 0, 0, //
    0, 0, 0, 0, 0,
    0, 0, 0, 0, 0,
    0.2126, 0.7152, 0.0722, 0, 0,
  ]); //convert to grayscale (https://www.w3.org/Graphics/Color/sRGB) and use them as transparency

/// Base interface for vector drawing.
@immutable
abstract class Drawable {
  /// A string that should uniquely identify this [Drawable] within its [DrawableRoot].
  String? get id;

  /// Whether this [Drawable] would be visible if [draw]n.
  bool get hasDrawableContent;

  /// Draws the contents or children of this [Drawable] to the `canvas`, using
  /// the `parentPaint` to optionally override the child's paint.
  ///
  /// The `bounds` specify the area to draw in.
  void draw(Canvas canvas, Rect bounds);
}

/// A [Drawable] that can have a [DrawableStyle] applied to it.
@immutable
abstract class DrawableStyleable extends Drawable {
  /// The [DrawableStyle] for this object.
  DrawableStyle? get style;

  /// The 4x4 transform to apply to this [Drawable], if any.
  Float64List? get transform;

  /// Creates an instance with merged style information.
  DrawableStyleable mergeStyle(DrawableStyle newStyle);
}

/// A [Drawable] that can have child [Drawables] and [DrawableStyle].
abstract class DrawableParent implements DrawableStyleable {
  /// The child [Drawables] of this [DrawableParent].
  ///
  /// Each child may itself have children.
  List<Drawable>? get children;

  /// The default color used to provide a potential indirect color value
  /// for the `fill`, `stroke` and `stop-color` of descendant elements.
  ///
  /// See: https://www.w3.org/TR/SVG11/color.html#ColorProperty
  Color? get color;
}

/// Styling information for vector drawing.
///
/// Contains [Paint], [Path], dashing, transform, and text styling information.
@immutable
class DrawableStyle {
  /// Creates a new [DrawableStyle].
  const DrawableStyle({
    this.stroke,
    this.dashArray,
    this.dashOffset,
    this.fill,
    this.textStyle,
    this.pathFillType,
    this.groupOpacity,
    this.clipPath,
    this.mask,
    this.blendMode,
  });

  /// Used where 'dasharray' is 'none'
  ///
  /// This will not result in a drawing operation, but will clear out
  /// inheritance.
  static final CircularIntervalList<double> emptyDashArray =
      CircularIntervalList<double>(const <double>[]);

  /// If not `null` and not `identical` with [DrawablePaint.empty], will result in a stroke
  /// for the rendered [DrawableShape]. Drawn __after__ the [fill].
  final DrawablePaint? stroke;

  /// The dashing array to use for the [stroke], if any.
  final CircularIntervalList<double>? dashArray;

  /// The [DashOffset] to use for where to begin the [dashArray].
  final DashOffset? dashOffset;

  /// If not `null` and not `identical` with [DrawablePaint.empty], will result in a fill
  /// for the rendered [DrawableShape].  Drawn __before__ the [stroke].
  final DrawablePaint? fill;

  /// The style to apply to text elements of this drawable or its chidlren.
  final DrawableTextStyle? textStyle;

  /// The fill rule to use for this path.
  final PathFillType? pathFillType;

  /// The clip to apply, if any.
  final List<Path>? clipPath;

  /// The mask to apply, if any.
  final DrawableStyleable? mask;

  /// Controls group level opacity. Will be [BlendMode.dstIn] blended with any
  /// children.
  final double? groupOpacity;

  /// The blend mode to apply, if any.
  ///
  /// Setting this will result in at least one [Canvas.saveLayer] call.
  final BlendMode? blendMode;

  /// Creates a new [DrawableStyle] if `parent` is not null, filling in any null
  /// properties on this with the properties from other (except [groupOpacity],
  /// is not inherited).
  static DrawableStyle mergeAndBlend(
    DrawableStyle? parent, {
    DrawablePaint? fill,
    DrawablePaint? stroke,
    CircularIntervalList<double>? dashArray,
    DashOffset? dashOffset,
    DrawableTextStyle? textStyle,
    PathFillType? pathFillType,
    double? groupOpacity,
    List<Path>? clipPath,
    DrawableStyleable? mask,
    BlendMode? blendMode,
  }) {
    return DrawableStyle(
      fill: DrawablePaint.merge(fill, parent?.fill),
      stroke: DrawablePaint.merge(stroke, parent?.stroke),
      dashArray: dashArray ?? parent?.dashArray,
      dashOffset: dashOffset ?? parent?.dashOffset,
      textStyle: DrawableTextStyle.merge(textStyle, parent?.textStyle),
      pathFillType: pathFillType ?? parent?.pathFillType,
      groupOpacity: groupOpacity,
      // clips don't make sense to inherit - applied to canvas with save/restore
      // that wraps any potential children
      clipPath: clipPath,
      mask: mask,
      blendMode: blendMode,
    );
  }

  @override
  String toString() {
    return 'DrawableStyle{$stroke,$dashArray,$dashOffset,$fill,$textStyle,$pathFillType,$groupOpacity,$clipPath,$mask}';
  }
}

/// A wrapper class for Flutter's [Paint] class.
///
/// Provides non-opaque access to painting properties.
@immutable
class DrawablePaint {
  /// Creates a new [DrawablePaint] object.
  const DrawablePaint(
    this.style, {
    this.color,
    this.shader,
    this.blendMode,
    this.colorFilter,
    this.isAntiAlias,
    this.filterQuality,
    this.maskFilter,
    this.strokeCap,
    this.strokeJoin,
    this.strokeMiterLimit,
    this.strokeWidth,
  });

  /// Will merge two DrawablePaints, preferring properties defined in `a` if they're not null.
  ///
  /// If `a` is `identical` with [DrawablePaint.empty], `b` will be ignored.
  static DrawablePaint? merge(DrawablePaint? a, DrawablePaint? b) {
    if (a == null && b == null) {
      return null;
    }

    if (b == null && a != null) {
      return a;
    }

    if (identical(a, DrawablePaint.empty) ||
        identical(b, DrawablePaint.empty)) {
      return a ?? b;
    }

    if (a == null) {
      return b;
    }

    // If we got here, the styles should not be null.
    assert(a.style == b!.style,
        'Cannot merge Paints with different PaintStyles; got:\na: $a\nb: $b.');

    b = b!;
    return DrawablePaint(
      a.style ?? b.style,
      color: a.color ?? b.color,
      shader: a.shader ?? b.shader,
      blendMode: a.blendMode ?? b.blendMode,
      colorFilter: a.colorFilter ?? b.colorFilter,
      isAntiAlias: a.isAntiAlias ?? b.isAntiAlias,
      filterQuality: a.filterQuality ?? b.filterQuality,
      maskFilter: a.maskFilter ?? b.maskFilter,
      strokeCap: a.strokeCap ?? b.strokeCap,
      strokeJoin: a.strokeJoin ?? b.strokeJoin,
      strokeMiterLimit: a.strokeMiterLimit ?? b.strokeMiterLimit,
      strokeWidth: a.strokeWidth ?? b.strokeWidth,
    );
  }

  /// An empty [DrawablePaint].
  ///
  /// Used to assist with inheritance of painting properties.
  static const DrawablePaint empty = DrawablePaint(null);

  /// Returns whether this paint is null or equivalent to SVG's "none".
  static bool isEmpty(DrawablePaint? paint) {
    return paint == null || identical(empty, paint) || paint.color == null;
  }

  /// The color to use for this paint when stroking or filling a shape.
  final Color? color;

  /// The [Shader] to use  when stroking or filling a shape.
  final Shader? shader;

  /// The [BlendMode] to use when stroking or filling a shape.
  final BlendMode? blendMode;

  /// A color filter to apply when a shape is drawn or layer is composited.
  final ColorFilter? colorFilter;

  /// Whether to apply anti-aliasing to the lines and images drawn.
  ///
  /// Defaults to true.
  final bool? isAntiAlias;

  /// 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].
  final FilterQuality? filterQuality;

  /// 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;

  /// Whehter to fill or stroke when drawing this shape.
  final PaintingStyle? style;

  /// The [StrokeCap] for this shape.
  final StrokeCap? strokeCap;

  /// The [StrokeJoin] for this shape.
  final StrokeJoin? strokeJoin;

  /// The stroke miter limit.  See [Paint.strokeMiterLimit].
  final double? strokeMiterLimit;

  /// The width of strokes for this paint.
  final double? strokeWidth;

  /// Creates a [Paint] object from this [DrawablePaint].
  Paint toFlutterPaint() {
    final Paint paint = Paint();

    // Null chekcs are needed here because the setters assert.
    if (blendMode != null) {
      paint.blendMode = blendMode!;
    }
    if (color != null) {
      paint.color = color!;
    }
    if (colorFilter != null) {
      paint.colorFilter = colorFilter;
    }
    if (filterQuality != null) {
      paint.filterQuality = filterQuality!;
    }
    if (isAntiAlias != null) {
      paint.isAntiAlias = isAntiAlias!;
    }
    if (maskFilter != null) {
      paint.maskFilter = maskFilter;
    }
    if (shader != null) {
      paint.shader = shader;
    }
    if (strokeCap != null) {
      paint.strokeCap = strokeCap!;
    }
    if (strokeJoin != null) {
      paint.strokeJoin = strokeJoin!;
    }
    if (strokeMiterLimit != null) {
      paint.strokeMiterLimit = strokeMiterLimit!;
    }
    if (strokeWidth != null) {
      paint.strokeWidth = strokeWidth!;
    }
    if (style != null) {
      paint.style = style!;
    }

    return paint;
  }

  @override
  String toString() {
    if (identical(this, DrawablePaint.empty)) {
      return 'DrawablePaint{}';
    }
    return 'DrawablePaint{$style, color: $color, shader: $shader, blendMode: $blendMode, '
        'colorFilter: $colorFilter, isAntiAlias: $isAntiAlias, filterQuality: $filterQuality, '
        'maskFilter: $maskFilter, strokeCap: $strokeCap, strokeJoin: $strokeJoin, '
        'strokeMiterLimit: $strokeMiterLimit, strokeWidth: $strokeWidth}';
  }
}

/// A wrapper class for Flutter's [TextStyle] class.
///
/// Provides non-opaque access to text styling properties.
@immutable
class DrawableTextStyle {
  /// Creates a new [DrawableTextStyle].
  const DrawableTextStyle({
    this.decoration,
    this.decorationColor,
    this.decorationStyle,
    this.fontWeight,
    this.fontFamily,
    this.fontSize,
    this.fontStyle,
    this.foreground,
    this.background,
    this.letterSpacing,
    this.wordSpacing,
    this.height,
    this.locale,
    this.textBaseline,
    this.anchor,
  });

  /// Merges two drawable text styles together, prefering set properties from [b].
  static DrawableTextStyle? merge(DrawableTextStyle? a, DrawableTextStyle? b) {
    if (b == null) {
      return a;
    }
    if (a == null) {
      return b;
    }
    return DrawableTextStyle(
      decoration: a.decoration ?? b.decoration,
      decorationColor: a.decorationColor ?? b.decorationColor,
      decorationStyle: a.decorationStyle ?? b.decorationStyle,
      fontWeight: a.fontWeight ?? b.fontWeight,
      fontStyle: a.fontStyle ?? b.fontStyle,
      textBaseline: a.textBaseline ?? b.textBaseline,
      fontFamily: a.fontFamily ?? b.fontFamily,
      fontSize: a.fontSize ?? b.fontSize,
      letterSpacing: a.letterSpacing ?? b.letterSpacing,
      wordSpacing: a.wordSpacing ?? b.wordSpacing,
      height: a.height ?? b.height,
      locale: a.locale ?? b.locale,
      background: a.background ?? b.background,
      foreground: a.foreground ?? b.foreground,
      anchor: a.anchor ?? b.anchor,
    );
  }

  /// The [TextDecoration] to draw with this text.
  final TextDecoration? decoration;

  /// The color to use when drawing the decoration.
  final Color? decorationColor;

  /// The [TextDecorationStyle] of the decoration.
  final TextDecorationStyle? decorationStyle;

  /// The weight of the font.
  final FontWeight? fontWeight;

  /// The style of the font.
  final FontStyle? fontStyle;

  /// The [TextBaseline] to use when drawing this text.
  final TextBaseline? textBaseline;

  /// The font family to use when drawing this text.
  final String? fontFamily;

  /// The font size to use when drawing this text.
  final double? fontSize;

  /// The letter spacing to use when drawing this text.
  final double? letterSpacing;

  /// The word spacing to use when drawing this text.
  final double? wordSpacing;

  /// The height of the text.
  final double? height;

  /// The [Locale] to use when drawing this text.
  final Locale? locale;

  /// The background to use when drawing this text.
  final DrawablePaint? background;

  /// The foreground to use when drawing this text.
  final DrawablePaint? foreground;

  /// The [DrawableTextAnchorPosition] to use when drawing this text.
  final DrawableTextAnchorPosition? anchor;

  /// Creates a Flutter [TextStyle], overriding the foreground if specified.
  TextStyle toFlutterTextStyle({DrawablePaint? foregroundOverride}) {
    return TextStyle(
      decoration: decoration,
      decorationColor: decorationColor,
      decorationStyle: decorationStyle,
      fontWeight: fontWeight,
      fontStyle: fontStyle,
      textBaseline: textBaseline,
      fontFamily: fontFamily,
      fontSize: fontSize,
      letterSpacing: letterSpacing,
      wordSpacing: wordSpacing,
      height: height,
      locale: locale,
      background: background?.toFlutterPaint(),
      foreground:
          foregroundOverride?.toFlutterPaint() ?? foreground?.toFlutterPaint(),
    );
  }

  @override
  String toString() =>
      'DrawableTextStyle{$decoration,$decorationColor,$decorationStyle,$fontWeight,'
      '$fontFamily,$fontSize,$fontStyle,$foreground,$background,$letterSpacing,$wordSpacing,$height,'
      '$locale,$textBaseline,$anchor}';
}

/// How to anchor text.
enum DrawableTextAnchorPosition {
  /// The offset specifies the start of the text.
  start,

  /// The offset specifies the midpoint of the text.
  middle,

  /// The offset specifies the end of the text.
  end,
}

/// A [Drawable] for text objects.
class DrawableText implements Drawable {
  /// Creates a new [DrawableText] object.
  ///
  /// One of fill or stroke must be specified.
  DrawableText(
    this.id,
    this.fill,
    this.stroke,
    this.offset,
    this.anchor, {
    this.transform,
  }) : assert(fill != null || stroke != null);

  @override
  final String? id;

  /// The offset for positioning the text. The [anchor] property controls
  /// how this offset is interpreted.
  final Offset offset;

  /// The anchor for the offset, i.e. whether it is the start, middle, or end
  /// of the text.
  final DrawableTextAnchorPosition anchor;

  /// If specified, how to draw the interior portion of the text.
  final Paragraph? fill;

  /// If specified, how to draw the outline of the text.
  final Paragraph? stroke;

  /// A transform to apply when drawing the text.
  final Float64List? transform;

  @override
  bool get hasDrawableContent =>
      (fill?.width ?? 0.0) + (stroke?.width ?? 0.0) > 0.0;

  @override
  void draw(Canvas canvas, Rect bounds) {
    if (!hasDrawableContent) {
      return;
    }
    if (transform != null) {
      canvas.save();
      canvas.transform(transform!);
    }
    if (fill != null) {
      canvas.drawParagraph(fill!, resolveOffset(fill!, anchor, offset));
    }
    if (stroke != null) {
      canvas.drawParagraph(stroke!, resolveOffset(stroke!, anchor, offset));
    }
    if (transform != null) {
      canvas.restore();
    }
  }

  /// Determines the correct location for an [Offset] given laid-out
  /// [paragraph] and a [DrawableTextPosition].
  static Offset resolveOffset(
    Paragraph paragraph,
    DrawableTextAnchorPosition anchor,
    Offset offset,
  ) {
    assert(paragraph != null); // ignore: unnecessary_null_comparison
    assert(anchor != null); // ignore: unnecessary_null_comparison
    assert(offset != null); // ignore: unnecessary_null_comparison
    switch (anchor) {
      case DrawableTextAnchorPosition.middle:
        return Offset(
          offset.dx - paragraph.longestLine / 2,
          offset.dy - paragraph.alphabeticBaseline,
        );
      case DrawableTextAnchorPosition.end:
        return Offset(
          offset.dx - paragraph.longestLine,
          offset.dy - paragraph.alphabeticBaseline,
        );
      case DrawableTextAnchorPosition.start:
        return Offset(
          offset.dx,
          offset.dy - paragraph.alphabeticBaseline,
        );
      default:
        return offset;
    }
  }
}

/// Contains reusable drawing elements that can be referenced by a String ID.
class DrawableDefinitionServer {
  final Map<String, DrawableGradient> _gradients = <String, DrawableGradient>{};
  final Map<String, List<Path>> _clipPaths = <String, List<Path>>{};
  final Map<String, DrawableStyleable> _drawables =
      <String, DrawableStyleable>{};

  /// An empty IRI for SVGs.
  static const String emptyUrlIri = 'url(#)';

  /// Attempt to lookup a [Drawable] by [id].
  DrawableStyleable? getDrawable(String id, {bool nullOk = false}) {
    assert(id != null); // ignore: unnecessary_null_comparison
    final DrawableStyleable? value = _drawables[id];
    if (value == null && nullOk != true) {
      throw StateError('Expected to find Drawable with id $id.\n'
          'Have ids: ${_drawables.keys}');
    }
    return value;
  }

  /// Add a [Drawable] that can later be referred to by [id].
  void addDrawable(String id, DrawableStyleable drawable) {
    assert(id != null); // ignore: unnecessary_null_comparison
    assert(drawable != null); // ignore: unnecessary_null_comparison
    assert(id != emptyUrlIri);
    _drawables[id] = drawable;
  }

  /// Attempt to lookup a pre-defined [Shader] by [id].
  ///
  /// [id] and [bounds] must not be null.
  Shader? getShader(String id, Rect bounds) {
    assert(id != null); // ignore: unnecessary_null_comparison
    assert(bounds != null); // ignore: unnecessary_null_comparison
    final DrawableGradient? srv = _gradients[id];
    return srv != null ? srv.createShader(bounds) : null;
  }

  /// Retreive a gradient from the pre-defined [DrawableGradient] collection.
  T? getGradient<T extends DrawableGradient?>(String id) {
    assert(id != null); // ignore: unnecessary_null_comparison
    return _gradients[id] as T?;
  }

  /// Add a [DrawableGradient] to the pre-defined collection by [id].
  void addGradient(String id, DrawableGradient gradient) {
    assert(id != null); // ignore: unnecessary_null_comparison
    assert(gradient != null); // ignore: unnecessary_null_comparison
    _gradients[id] = gradient;
  }

  /// Get a [List<Path>] of clip paths by [id].
  List<Path>? getClipPath(String id) {
    assert(id != null); // ignore: unnecessary_null_comparison
    return _clipPaths[id];
  }

  /// Add a [List<Path>] of clip paths by [id].
  void addClipPath(String id, List<Path> paths) {
    assert(id != null); // ignore: unnecessary_null_comparison
    assert(paths != null); // ignore: unnecessary_null_comparison
    _clipPaths[id] = paths;
  }
}

/// Determines how to transform the points given for a gradient.
enum GradientUnitMode {
  /// The gradient vector(s) are transformed by the space in the object containing the gradient.
  objectBoundingBox,

  /// The gradient vector(s) are taken as is.
  userSpaceOnUse,
}

/// Basic information describing a gradient.
@immutable
abstract class DrawableGradient {
  /// Initializes basic values.
  const DrawableGradient(
    this.offsets,
    this.colors, {
    this.spreadMethod = TileMode.clamp,
    this.unitMode = GradientUnitMode.objectBoundingBox,
    this.transform,
  });

  /// Specifies where `colors[i]` begins in the gradient.
  ///
  /// Number of elements must equal the number of elements in [colors].
  final List<double>? offsets;

  /// The colors to use for the gradient.
  final List<Color>? colors;

  /// The [TileMode] to use for this gradient.
  final TileMode spreadMethod;

  /// The [GradientUnitMode] for any vectors specified by this gradient.
  final GradientUnitMode unitMode;

  /// The transform to apply to this gradient.
  final Float64List? transform;

  /// Creates a [Shader] (i.e. a [Gradient]) from this object.
  Shader createShader(Rect bounds);
}

/// Represents the data needed to create a [Gradient.linear].
@immutable
class DrawableLinearGradient extends DrawableGradient {
  /// Creates a new [DrawableLinearGradient].
  const DrawableLinearGradient({
    required this.from,
    required this.to,
    required List<double> offsets,
    required List<Color> colors,
    required TileMode spreadMethod,
    required GradientUnitMode unitMode,
    Float64List? transform,
  }) : super(
          offsets,
          colors,
          spreadMethod: spreadMethod,
          unitMode: unitMode,
          transform: transform,
        );

  /// The starting offset of this gradient.
  final Offset from;

  /// The ending offset of this gradient.
  final Offset to;

  @override
  Shader createShader(Rect bounds) {
    final bool isObjectBoundingBox =
        unitMode == GradientUnitMode.objectBoundingBox;

    Matrix4 m4transform = transform == null
        ? Matrix4.identity()
        : Matrix4.fromFloat64List(transform!);

    if (isObjectBoundingBox) {
      final Matrix4 scale =
          affineMatrix(bounds.width, 0.0, 0.0, bounds.height, 0.0, 0.0);
      final Matrix4 translate =
          affineMatrix(1.0, 0.0, 0.0, 1.0, bounds.left, bounds.top);
      m4transform = translate.multiplied(scale)..multiply(m4transform);
    }

    final Vector3 v3from = m4transform.transform3(
      Vector3(
        from.dx,
        from.dy,
        0.0,
      ),
    );
    final Vector3 v3to = m4transform.transform3(
      Vector3(
        to.dx,
        to.dy,
        0.0,
      ),
    );

    return Gradient.linear(
      Offset(v3from.x, v3from.y),
      Offset(v3to.x, v3to.y),
      colors!,
      offsets,
      spreadMethod,
    );
  }
}

/// Represents the information needed to create a [Gradient.radial].
@immutable
class DrawableRadialGradient extends DrawableGradient {
  /// Creates a [DrawableRadialGradient].
  const DrawableRadialGradient({
    required this.center,
    required this.radius,
    required this.focal,
    this.focalRadius = 0.0,
    required List<double> offsets,
    required List<Color> colors,
    required TileMode spreadMethod,
    required GradientUnitMode unitMode,
    Float64List? transform,
  }) : super(
          offsets,
          colors,
          spreadMethod: spreadMethod,
          unitMode: unitMode,
          transform: transform,
        );

  /// The center of the radial gradient.
  final Offset center;

  /// The radius of the radial gradient.
  final double? radius;

  /// The focal point, if any, for a two point conical gradient.
  final Offset focal;

  /// The radius of the focal point.
  final double focalRadius;

  @override
  Shader createShader(Rect bounds) {
    final bool isObjectBoundingBox =
        unitMode == GradientUnitMode.objectBoundingBox;

    Matrix4 m4transform = transform == null
        ? Matrix4.identity()
        : Matrix4.fromFloat64List(transform!);

    if (isObjectBoundingBox) {
      final Matrix4 scale =
          affineMatrix(bounds.width, 0.0, 0.0, bounds.height, 0.0, 0.0);
      final Matrix4 translate =
          affineMatrix(1.0, 0.0, 0.0, 1.0, bounds.left, bounds.top);
      m4transform = translate.multiplied(scale)..multiply(m4transform);
    }

    return Gradient.radial(
      center,
      radius!,
      colors!,
      offsets,
      spreadMethod,
      m4transform.storage,
      focal,
      0.0,
    );
  }
}

/// Contains the viewport size and offset for a Drawable.
@immutable
class DrawableViewport {
  /// Creates a new DrawableViewport, which acts as a bounding box for the Drawable
  /// and specifies what offset (if any) the coordinate system needs to be translated by.
  ///
  /// Both `rect` and `offset` must not be null.
  const DrawableViewport(
    this.size,
    this.viewBox, {
    this.viewBoxOffset = Offset.zero,
  })  : assert(size != null), // ignore: unnecessary_null_comparison
        assert(viewBox != null), // ignore: unnecessary_null_comparison
        assert(viewBoxOffset != null); // ignore: unnecessary_null_comparison

  /// The offset for all drawing commands in this Drawable.
  final Offset viewBoxOffset;

  /// A [Rect] representing the viewBox of this DrawableViewport.
  Rect get viewBoxRect => Offset.zero & viewBox;

  /// The viewBox size for the drawable.
  final Size viewBox;

  /// The viewport size of the drawable.
  ///
  /// This may or may not be identical to the
  final Size size;

  /// The width of the viewport rect.
  double get width => size.width;

  /// The height of the viewport rect.
  double get height => size.height;

  @override
  String toString() => 'DrawableViewport{$size, viewBox: $viewBox, '
      'viewBoxOffset: $viewBoxOffset}';
}

/// Tests whether a [DrawableRoot] should be cache invalidated given old and new
/// external parameter changes.
///
/// For example, an SVG needs to be invalidated if it actually uses `em` units
/// and the font size changes, but not if it only uses `px` units.
class CacheCompatibilityTester {
  /// Creates a tester that always returns true.
  const CacheCompatibilityTester();

  /// Determine whether a cached [DrawableRoot] should be invalidated given
  /// old and new data.
  ///
  /// By default, the data is always treated as compatible.
  bool isCompatible(Object oldData, Object newData) => true;
}

/// The root element of a drawable.
class DrawableRoot implements DrawableParent {
  /// Creates a new [DrawableRoot].
  const DrawableRoot(
    this.id,
    this.viewport,
    this.children,
    this.definitions,
    this.style, {
    this.transform,
    this.color,
    this.compatibilityTester = const CacheCompatibilityTester(),
  });

  /// The expected coordinates used by child paths for drawing.
  final DrawableViewport viewport;

  /// Used to test whether ambient parameter changes should invalidate a cached
  /// version of this drawable.
  ///
  /// For example, if the drawable was constructed using an ambient font size
  /// or color, the tester will return false when the font size or color change.
  final CacheCompatibilityTester compatibilityTester;

  @override
  final String? id;

  @override
  final Float64List? transform;

  @override
  final Color? color;

  @override
  final List<Drawable> children;

  /// Contains reusable definitions such as gradients and clipPaths.
  final DrawableDefinitionServer definitions;

  /// The [DrawableStyle] for inheritence.
  @override
  final DrawableStyle? style;

  /// Scales the `canvas` so that the drawing units in this [Drawable]
  /// will scale to the `desiredSize`.
  ///
  /// If the `viewBox` dimensions are not 1:1 with `desiredSize`, will scale to
  /// the smaller dimension and translate to center the image along the larger
  /// dimension.
  void scaleCanvasToViewBox(Canvas canvas, Size desiredSize) {
    final Matrix4 transform = Matrix4.identity();
    if (render_picture.scaleCanvasToViewBox(
      transform,
      desiredSize,
      viewport.viewBoxRect,
      viewport.size,
    )) {
      canvas.transform(transform.storage);
    }
  }

  /// Clips the canvas to a rect corresponding to the `viewBox`.
  void clipCanvasToViewBox(Canvas canvas) {
    canvas.clipRect(viewport.viewBoxRect);
  }

  @override
  bool get hasDrawableContent =>
      children.isNotEmpty == true && !viewport.viewBox.isEmpty;

  /// Draws the contents or children of this [Drawable] to the `canvas`, using
  /// the `parentPaint` to optionally override the child's paint.
  ///
  /// The `bounds` is not used.
  @override
  void draw(Canvas canvas, Rect bounds) {
    if (!hasDrawableContent) {
      return;
    }

    if (transform != null) {
      canvas.save();
      canvas.transform(transform!);
    }

    if (viewport.viewBoxOffset != Offset.zero) {
      canvas.translate(viewport.viewBoxOffset.dx, viewport.viewBoxOffset.dy);
    }
    for (Drawable child in children) {
      child.draw(canvas, viewport.viewBoxRect);
    }

    if (transform != null) {
      canvas.restore();
    }
  }

  /// Creates a [Picture] from this [DrawableRoot].
  ///
  /// Be cautious about not clipping to the ViewBox - you will be
  /// allowing your drawing to take more memory than it otherwise would,
  /// particularly when it is eventually rasterized.
  Picture toPicture({
    Size? size,
    bool clipToViewBox = true,
    ColorFilter? colorFilter,
  }) {
    if (viewport.viewBox.width == 0) {
      throw StateError('Cannot convert to picture with $viewport');
    }

    final PictureRecorder recorder = PictureRecorder();
    final Canvas canvas = Canvas(recorder, viewport.viewBoxRect);
    if (colorFilter != null) {
      canvas.saveLayer(null, Paint()..colorFilter = colorFilter);
    } else {
      canvas.save();
    }
    if (size != null) {
      scaleCanvasToViewBox(canvas, size);
    }
    if (clipToViewBox == true) {
      clipCanvasToViewBox(canvas);
    }

    draw(canvas, viewport.viewBoxRect);
    canvas.restore();
    return recorder.endRecording();
  }

  @override
  DrawableRoot mergeStyle(DrawableStyle newStyle) {
    assert(newStyle != null); // ignore: unnecessary_null_comparison
    final DrawableStyle mergedStyle = DrawableStyle.mergeAndBlend(
      style,
      fill: newStyle.fill,
      stroke: newStyle.stroke,
      clipPath: newStyle.clipPath,
      mask: newStyle.mask,
      dashArray: newStyle.dashArray,
      dashOffset: newStyle.dashOffset,
      pathFillType: newStyle.pathFillType,
      textStyle: newStyle.textStyle,
    );

    final List<Drawable> mergedChildren =
        children.map<Drawable>((Drawable child) {
      if (child is DrawableStyleable) {
        return child.mergeStyle(mergedStyle);
      }
      return child;
    }).toList();

    return DrawableRoot(
      id,
      viewport,
      mergedChildren,
      definitions,
      mergedStyle,
      transform: transform,
    );
  }
}

/// Represents a group of drawing elements that may share a common `transform`,
/// `stroke`, or `fill`.
class DrawableGroup implements DrawableStyleable, DrawableParent {
  /// Creates a new DrawableGroup.
  const DrawableGroup(
    this.id,
    this.children,
    this.style, {
    this.transform,
    this.color,
  });

  @override
  final String? id;

  @override
  final List<Drawable>? children;
  @override
  final DrawableStyle? style;
  @override
  final Float64List? transform;
  @override
  final Color? color;

  @override
  bool get hasDrawableContent => children != null && children!.isNotEmpty;

  @override
  void draw(Canvas canvas, Rect bounds) {
    if (!hasDrawableContent) {
      return;
    }

    final Function innerDraw = () {
      if (style!.groupOpacity == 0) {
        return;
      }
      if (transform != null) {
        canvas.save();
        canvas.transform(transform!);
      }

      bool needsSaveLayer = style!.mask != null;

      final Paint blendingPaint = Paint();
      if (style!.groupOpacity != null && style!.groupOpacity != 1.0) {
        blendingPaint.color = Color.fromRGBO(0, 0, 0, style!.groupOpacity!);
        needsSaveLayer = true;
      }
      if (style!.blendMode != null) {
        blendingPaint.blendMode = style!.blendMode!;
        needsSaveLayer = true;
      }
      if (needsSaveLayer) {
        canvas.saveLayer(null, blendingPaint);
      }

      for (Drawable child in children!) {
        child.draw(canvas, bounds);
      }

      if (style!.mask != null) {
        canvas.saveLayer(null, _grayscaleDstInPaint);
        style!.mask!.draw(canvas, bounds);
        canvas.restore();
      }
      if (needsSaveLayer) {
        canvas.restore();
      }
      if (transform != null) {
        canvas.restore();
      }
    };

    if (style?.clipPath?.isNotEmpty == true) {
      for (Path clipPath in style!.clipPath!) {
        if (transform != null) {
          clipPath = clipPath.transform(transform!);
        }

        canvas.save();
        canvas.clipPath(clipPath);
        if (children!.length > 1) {
          canvas.saveLayer(null, Paint());
        }

        innerDraw();

        if (children!.length > 1) {
          canvas.restore();
        }
        canvas.restore();
      }
    } else {
      innerDraw();
    }
  }

  @override
  DrawableGroup mergeStyle(DrawableStyle newStyle) {
    assert(newStyle != null); // ignore: unnecessary_null_comparison
    final DrawableStyle mergedStyle = DrawableStyle.mergeAndBlend(
      style,
      fill: newStyle.fill,
      stroke: newStyle.stroke,
      clipPath: newStyle.clipPath,
      dashArray: newStyle.dashArray,
      dashOffset: newStyle.dashOffset,
      pathFillType: newStyle.pathFillType,
      textStyle: newStyle.textStyle,
    );

    final List<Drawable> mergedChildren =
        children!.map<Drawable>((Drawable child) {
      if (child is DrawableStyleable) {
        return child.mergeStyle(mergedStyle);
      }
      return child;
    }).toList();

    return DrawableGroup(
      id,
      mergedChildren,
      mergedStyle,
      transform: transform,
    );
  }
}

/// A raster image (e.g. PNG, JPEG, or GIF) embedded in the drawable.
class DrawableRasterImage implements DrawableStyleable {
  /// Creates a new [DrawableRasterImage].
  const DrawableRasterImage(
    this.id,
    this.image,
    this.offset,
    this.style, {
    this.size,
    this.transform,
  })  : assert(image != null), // ignore: unnecessary_null_comparison
        assert(offset != null); // ignore: unnecessary_null_comparison

  @override
  final String? id;

  /// The [Image] to draw.
  final Image image;

  /// The position for the top-left corner of the image.
  final Offset offset;

  /// The size to scale the image to.
  final Size? size;

  @override
  final Float64List? transform;

  @override
  final DrawableStyle style;

  @override
  void draw(Canvas canvas, Rect bounds) {
    final Size imageSize = Size(
      image.width.toDouble(),
      image.height.toDouble(),
    );
    Size? desiredSize = imageSize;
    double scale = 1.0;
    if (size != null) {
      desiredSize = size;
      scale = math.min(
        size!.width / image.width,
        size!.height / image.height,
      );
    }
    if (scale != 1.0 || offset != Offset.zero || transform != null) {
      final Size halfDesiredSize = desiredSize! / 2.0;
      final Size scaledHalfImageSize = imageSize * scale / 2.0;
      final Offset shift = Offset(
        halfDesiredSize.width - scaledHalfImageSize.width,
        halfDesiredSize.height - scaledHalfImageSize.height,
      );
      canvas.save();
      if (transform != null) {
        canvas.transform(transform!);
      }
      canvas.translate(offset.dx + shift.dx, offset.dy + shift.dy);
      canvas.scale(scale, scale);
    }
    canvas.drawImage(image, Offset.zero, Paint());
    if (scale != 1.0 || offset != Offset.zero || transform != null) {
      canvas.restore();
    }
  }

  @override
  bool get hasDrawableContent => image.height > 0 && image.width > 0;

  @override
  DrawableRasterImage mergeStyle(DrawableStyle newStyle) {
    assert(newStyle != null); // ignore: unnecessary_null_comparison
    return DrawableRasterImage(
      id,
      image,
      offset,
      DrawableStyle.mergeAndBlend(
        style,
        fill: newStyle.fill,
        stroke: newStyle.stroke,
        clipPath: newStyle.clipPath,
        mask: newStyle.mask,
        dashArray: newStyle.dashArray,
        dashOffset: newStyle.dashOffset,
        pathFillType: newStyle.pathFillType,
        textStyle: newStyle.textStyle,
      ),
      size: size,
      transform: transform,
    );
  }
}

/// Represents a drawing element that will be rendered to the canvas.
class DrawableShape implements DrawableStyleable {
  /// Creates a new [DrawableShape].
  const DrawableShape(this.id, this.path, this.style, {this.transform})
      : assert(path != null), // ignore: unnecessary_null_comparison
        assert(style != null); // ignore: unnecessary_null_comparison

  @override
  final String? id;

  @override
  final Float64List? transform;

  @override
  final DrawableStyle style;

  /// The [Path] describing this shape.
  final Path path;

  /// The bounds of this shape.
  Rect get bounds => path.getBounds();

  // can't use bounds.isEmpty here because some paths give a 0 width or height
  // see https://skia.org/user/api/SkPath_Reference#SkPath_getBounds
  // can't rely on style because parent style may end up filling or stroking
  // TODO(dnfield): implement display properties - but that should really be done on style.
  @override
  bool get hasDrawableContent => bounds.width + bounds.height > 0;

  @override
  void draw(Canvas canvas, Rect bounds) {
    if (!hasDrawableContent) {
      return;
    }

    path.fillType = style.pathFillType ?? PathFillType.nonZero;
    // if we have multiple clips to apply, need to wrap this in a loop.
    final Function innerDraw = () {
      if (transform != null) {
        canvas.save();
        canvas.transform(transform!);
      }
      if (style.blendMode != null) {
        canvas.saveLayer(null, Paint()..blendMode = style.blendMode!);
      }
      if (style.mask != null) {
        canvas.saveLayer(null, Paint());
      }
      if (style.fill?.color != null) {
        assert(style.fill!.style == PaintingStyle.fill);
        canvas.drawPath(path, style.fill!.toFlutterPaint());
      }

      if (style.stroke?.color != null &&
          (style.stroke!.strokeWidth == null ||
              (style.stroke!.strokeWidth != null &&
                  style.stroke!.strokeWidth! > 0))) {
        assert(style.stroke!.style == PaintingStyle.stroke);
        if (style.dashArray != null &&
            !identical(style.dashArray, DrawableStyle.emptyDashArray)) {
          canvas.drawPath(
            dashPath(
              path,
              dashArray: style.dashArray!,
              dashOffset: style.dashOffset,
            ),
            style.stroke!.toFlutterPaint(),
          );
        } else {
          canvas.drawPath(path, style.stroke!.toFlutterPaint());
        }
      }

      if (style.mask != null) {
        canvas.saveLayer(null, _grayscaleDstInPaint);
        style.mask!.draw(canvas, bounds);
        canvas.restore();
        canvas.restore();
      }

      if (style.blendMode != null) {
        canvas.restore();
      }
      if (transform != null) {
        canvas.restore();
      }
    };

    if (style.clipPath?.isNotEmpty == true) {
      for (Path clip in style.clipPath!) {
        canvas.save();
        canvas.clipPath(clip);
        innerDraw();
        canvas.restore();
      }
    } else {
      innerDraw();
    }
  }

  @override
  DrawableShape mergeStyle(DrawableStyle newStyle) {
    assert(newStyle != null); // ignore: unnecessary_null_comparison
    return DrawableShape(
      id,
      path,
      DrawableStyle.mergeAndBlend(
        style,
        fill: newStyle.fill,
        stroke: newStyle.stroke,
        clipPath: newStyle.clipPath,
        mask: newStyle.mask,
        dashArray: newStyle.dashArray,
        dashOffset: newStyle.dashOffset,
        pathFillType: newStyle.pathFillType,
        textStyle: newStyle.textStyle,
      ),
      transform: transform,
    );
  }
}