Direct2D (11) : 画刷之 ID2D1LinearGradientBrush

TDirect2DCanvas.Brush 的类型是 TDirect2DBrush，它和 GDI 的 TBrush 的区别主要有两点：
1、只保留了 TBrush.Style 中的 bsSolid、bsClear 选项，弃用了：bsHorizontal、bsVertical、bsFDiagonal、bsBDiagonal、bsCross、bsDiagCross。
2、其 Handle 属性是 Direct2D 中的 ID2D1Brush。

Direct2D 提供有四种画刷：

ID2D1SolidColorBrush     //纯色画刷；TDirect2DBrush 默认使用了它

ID2D1LinearGradientBrush //线性渐变画刷

ID2D1RadialGradientBrush //放射渐变画刷

ID2D1BitmapBrush         //位图画刷



ID2D1Brush //是它们的父接口，它提供了透明色和 2D 变换的基础能力。



{相关方法}

TDirect2DCanvas.RenderTarget.CreateSolidColorBrush();     //建立纯色画刷

TDirect2DCanvas.RenderTarget.CreateLinearGradientBrush(); //建立线性渐变画刷

TDirect2DCanvas.RenderTarget.CreateRadialGradientBrush(); //建立放射渐变画刷

TDirect2DCanvas.RenderTarget.CreateBitmapBrush();         //建立位图画刷



TDirect2DCanvas.RenderTarget.CreateGradientStopCollection(); //建立画刷需要的 ID2D1GradientStopCollection 对象

  //ID2D1GradientStopCollection 中包含渐变需要的颜色及位置数组和位图排列规则参数等

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ID2D1LinearGradientBrush : 线性渐变画刷

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{建立函数}

function CreateLinearGradientBrush(

  const linearGradientBrushProperties: TD2D1LinearGradientBrushProperties; //描述渐变轴的结构体

  brushProperties: PD2D1BrushProperties;               //描述透明度及 2D 变换的结构指针

  gradientStopCollection: ID2D1GradientStopCollection; //通过该接口传递 TD2D1GradientStop 结构(颜色及位置)的数组

  out linearGradientBrush: ID2D1LinearGradientBrush    //输出建立的对象

): HResult; stdcall;



{描述渐变轴的结构体}

TD2D1LinearGradientBrushProperties = record

  startPoint: D2D1_POINT_2F;

  endPoint: D2D1_POINT_2F;

end;

{描述透明度及 2D 变换的结构体}

TD2D1BrushProperties = record

  opacity: Single;

  transform: D2D1_MATRIX_3X2_F;

end;

{描述位置与颜色的结构体}

TD2D1GradientStop = record

  position: Single;

  color: D2D1_COLOR_F;

end;

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测试代码：

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uses Direct2D, D2D1;



procedure TForm1.FormPaint(Sender: TObject);

var

  cvs: TDirect2DCanvas;

  iBrush: ID2D1LinearGradientBrush;

  R: TRect;

  rLinear: TD2D1LinearGradientBrushProperties;

  arrGradientStop: array[0..2] of TD2D1GradientStop;

  iGradientStops: ID2D1GradientStopCollection;

begin

  cvs := TDirect2DCanvas.Create(Canvas, ClientRect);



  R := ClientRect;

  InflateRect(R, -ClientWidth div 6, -ClientHeight div 6);



  {对角线轴}

  rLinear.startPoint := D2D1PointF(R.Left, R.Top);

  rLinear.endPoint := D2D1PointF(R.Right, R.Bottom);



  {横向轴}

//  rLinear.startPoint := D2D1PointF(R.Left, ClientHeight / 2);

//  rLinear.endPoint := D2D1PointF(R.Right, ClientHeight / 2);



  arrGradientStop[0].position := 0.0;

  arrGradientStop[0].color := D2D1ColorF(clRed);

  arrGradientStop[1].position := 0.5;

  arrGradientStop[1].color := D2D1ColorF(clYellow);

  arrGradientStop[2].position := 1.0;

  arrGradientStop[2].color := D2D1ColorF(clGreen);



  cvs.RenderTarget.CreateGradientStopCollection(

    @arrGradientStop[0], Length(arrGradientStop), D2D1_GAMMA_2_2, D2D1_EXTEND_MODE_CLAMP, iGradientStops

  );



  cvs.RenderTarget.CreateLinearGradientBrush(rLinear, nil, iGradientStops, iBrush);

  cvs.Brush.Handle := iBrush;



  cvs.BeginDraw;

  cvs.Rectangle(R);

  cvs.EndDraw;

  cvs.Free;

end;



procedure TForm1.FormResize(Sender: TObject);

begin

  Repaint;

end;

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效果图：

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