class DropShadowFilter extends BitmapFilter {

 num distance;
 num angle;
 int color;
 num alpha;
 int blurX;
 int blurY;
 bool knockout;
 bool hideObject;

 DropShadowFilter(this.distance, this.angle, this.color, this.alpha, this.blurX, this.blurY, {
                  this.knockout: false, this.hideObject: false }) {

   if (blurX < 1 || blurY < 1)
     throw new ArgumentError("Error #9004: The minimum blur size is 1.");

   if (blurX > 64 || blurY > 64)
     throw new ArgumentError("Error #9004: The maximum blur size is 64.");
 }

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

 BitmapFilter clone() => new DropShadowFilter(distance, angle, color, alpha, blurX, blurY,
     knockout: knockout, hideObject: hideObject);

 Rectangle get overlap {
   var shiftX = (this.distance * cos(this.angle)).round();
   var shiftY = (this.distance * sin(this.angle)).round();
   var sRect = new Rectangle(0, 0, 0, 0);
   var dRect = new Rectangle(shiftX - blurX, shiftY - blurY, 2 * blurX, 2 * blurY);
   return sRect.union(dRect);
 }

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

 void apply(BitmapData bitmapData, [Rectangle rectangle]) {

   RenderTextureQuad renderTextureQuad = rectangle == null
       ? bitmapData.renderTextureQuad
       : bitmapData.renderTextureQuad.cut(rectangle);

   ImageData sourceImageData =
       this.hideObject == false || this.knockout ? renderTextureQuad.getImageData() : null;

   ImageData imageData = renderTextureQuad.getImageData();
   List<int> data = imageData.data;
   int width = _ensureInt(imageData.width);
   int height = _ensureInt(imageData.height);
   int shiftX = (this.distance * cos(this.angle)).round();
   int shiftY = (this.distance * sin(this.angle)).round();

   num pixelRatio = renderTextureQuad.renderTexture.storePixelRatio;
   int blurX = (this.blurX * pixelRatio).round();
   int blurY = (this.blurY * pixelRatio).round();
   int alphaChannel = _isLittleEndianSystem ? 3 : 0;
   int stride = width * 4;

   _shiftChannel(data, 3, width, height, shiftX, shiftY);

   for (int x = 0; x < width; x++) {
     _blur2(data, x * 4 + alphaChannel, height, stride, blurY);
   }

   for (int y = 0; y < height; y++) {
     _blur2(data, y * stride + alphaChannel, width, 4, blurX);
   }

   if (this.knockout) {
     _setColorKnockout(data, this.color, this.alpha, sourceImageData.data);
   } else if (this.hideObject) {
     _setColor(data, this.color, this.alpha);
   } else {
     _setColorBlend(data, this.color, this.alpha, sourceImageData.data);
   }

   renderTextureQuad.putImageData(imageData);
 }

}