Direct2D (20) : 图层之 TD2D1LayerParameters.opacityBrush (为图层指定蒙版画刷)

uses Direct2D, D2D1;

procedure TForm1.FormPaint(Sender: TObject);
var
  cvs: TDirect2DCanvas;
  iLayer: ID2D1Layer;
  rLayerParameters: TD2D1LayerParameters;
  wic: TWICImage;
  R: TRect;
  iLinearGradientBrush: ID2D1LinearGradientBrush;
  rLinear: TD2D1LinearGradientBrushProperties;
  arrGradientStop: array[0..2] of TD2D1GradientStop;
  iGradientStops: ID2D1GradientStopCollection;
begin
  wic := TWICImage.Create;
  wic.LoadFromFile('C:\Temp\Test.png');
  R := Rect(0, 0, wic.Width, wic.Height);
  cvs := TDirect2DCanvas.Create(Canvas, ClientRect);

  {建立线性渐变画刷}
  rLinear.startPoint := D2D1PointF(0, 0);
  rLinear.endPoint := D2D1PointF(0, wic.Height);
  arrGradientStop[0].position := 0.0;
  arrGradientStop[0].color := D2D1ColorF(clBlack, 1.0);
  arrGradientStop[1].position := 0.6;
  arrGradientStop[1].color := D2D1ColorF(clWhite, 0.0);
  arrGradientStop[2].position := 1.0;
  arrGradientStop[2].color := D2D1ColorF(clBlack, 1.0);
  cvs.RenderTarget.CreateGradientStopCollection(@arrGradientStop[0], Length(arrGradientStop), D2D1_GAMMA_2_2, D2D1_EXTEND_MODE_CLAMP, iGradientStops);
  cvs.RenderTarget.CreateLinearGradientBrush(rLinear, nil, iGradientStops, iLinearGradientBrush);

  cvs.RenderTarget.SetTransform(TD2DMatrix3x2F.Translation((ClientWidth-wic.width)/2, (ClientHeight-wic.height)/2));
  cvs.BeginDraw;
  cvs.Brush.Color := clBlack;
  cvs.Rectangle(R);

  {在图层中绘制图像}
  cvs.RenderTarget.CreateLayer(nil, iLayer);
  rLayerParameters.contentBounds := R;
  rLayerParameters.geometricMask := nil;
  rLayerParameters.maskAntialiasMode := D2D1_ANTIALIAS_MODE_PER_PRIMITIVE;
  rLayerParameters.maskTransform := TD2DMatrix3x2F.Identity;
  rLayerParameters.opacity := 1.0;
  rLayerParameters.opacityBrush := iLinearGradientBrush; //!
  rLayerParameters.layerOptions := D2D1_LAYER_OPTIONS_NONE;
  cvs.RenderTarget.PushLayer(rLayerParameters, iLayer);
  cvs.StretchDraw(R, wic);
  cvs.RenderTarget.PopLayer;

  cvs.EndDraw;
  cvs.Free;
  wic.Free;
end;

procedure TForm1.FormResize(Sender: TObject);
begin
  Repaint;
end;

效果图：