canvas_shadow_wrapper.dart

part of '../display_ex.dart';

/// This class is a replacement for the deprecated shadow property of the
/// DisplayObject class. Please consider to use the DropShadowFilter class
/// which is the recommended technique to render shadows in WebGL.
///
/// The CanvasShadowWrapper takes an arbitrary DisplayObject and renders
/// it with a drop shadow if the render engine is Canvas2D (not WebGL).
///
/// Example with deprecated shadow property:
///
///     var spaceship = new Spaceship();
///     spaceship.x = 160;
///     spaceship.y = 200;
///     spaceship.shadow = new Shadow(Color.Black, 10, 10, 5);
///     stage.addChild(spaceship);
///
/// Example with the CanvasShadowWrapper class:
///
///     var spaceship = new Spaceship();
///     spaceship.x = 160;
///     spaceship.y = 200;
///     var shadow = new CanvasShadowWrapper(spaceship, Color.Black, 10, 10, 5);
///     stage.addChild(shadow);
///
class CanvasShadowWrapper extends DisplayObject {
  final DisplayObject displayObject;

  int shadowColor;
  num shadowOffsetX;
  num shadowOffsetY;
  num shadowBlur;

  CanvasShadowWrapper(this.displayObject,
      [this.shadowColor = Color.Black,
      this.shadowOffsetX = 10.0,
      this.shadowOffsetY = 10.0,
      this.shadowBlur = 0.0]);

  //-----------------------------------------------------------------------------------------------

  void _throwUnsupportedError() {
    throw UnsupportedError(
        'CanvasShadowWrapper does not implement this property or method.');
  }

  @override
  set x(num value) {
    _throwUnsupportedError();
  }

  @override
  set y(num value) {
    _throwUnsupportedError();
  }

  @override
  set pivotX(num value) {
    _throwUnsupportedError();
  }

  @override
  set pivotY(num value) {
    _throwUnsupportedError();
  }

  @override
  set scaleX(num value) {
    _throwUnsupportedError();
  }

  @override
  set scaleY(num value) {
    _throwUnsupportedError();
  }

  @override
  set skewX(num value) {
    _throwUnsupportedError();
  }

  @override
  set skewY(num value) {
    _throwUnsupportedError();
  }

  @override
  set rotation(num value) {
    _throwUnsupportedError();
  }

  @override
  set alpha(num value) {
    _throwUnsupportedError();
  }

  @override
  set mask(Mask? mask) {
    _throwUnsupportedError();
  }

  //-----------------------------------------------------------------------------------------------

  @override
  DisplayObject? hitTestInput(num localX, num localY) {
    final matrix = displayObject.transformationMatrix;
    final deltaX = localX - matrix.tx;
    final deltaY = localY - matrix.ty;
    final childX = (matrix.d * deltaX - matrix.c * deltaY) / matrix.det;
    final childY = (matrix.a * deltaY - matrix.b * deltaX) / matrix.det;
    return displayObject.hitTestInput(childX, childY);
  }

  //-----------------------------------------------------------------------------------------------

  @override
  void render(RenderState renderState) {
    final renderContext = renderState.renderContext;
    if (renderContext is RenderContextCanvas) {
      final rawContext = renderContext.rawContext;
      final shadowMatrix = renderState.globalMatrix;
      rawContext.save();
      rawContext.shadowColor = color2rgba(shadowColor);
      rawContext.shadowBlur = sqrt(shadowMatrix.det) * shadowBlur;
      rawContext.shadowOffsetX =
          shadowOffsetX * shadowMatrix.a + shadowOffsetY * shadowMatrix.c;
      rawContext.shadowOffsetY =
          shadowOffsetX * shadowMatrix.b + shadowOffsetY * shadowMatrix.d;
      renderState.renderObject(displayObject);
      rawContext.restore();
    } else {
      renderState.renderObject(displayObject);
    }
  }
}