GDI+ 学习记录(10): 线性渐变画刷 LinearGradientBrush

//线性渐变画刷
var
  g: TGPGraphics;
  lb: TGPLinearGradientBrush;
  rect: TGPRect;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  rect := MakeRect(11,11,222,111);
  lb := TGPLinearGradientBrush.Create(rect, aclBlue, aclGreen, LinearGradientModeHorizontal);

  g.FillEllipse(lb, rect);

  lb.Free;
  g.Free;
end;


//定义渐变的位置与颜色
var
  g : TGPGraphics;
  p: TGPPen;
  lb: TGPLinearGradientBrush;
  p1,p2: TGPPoint;
  c1,c2: TGPColor;
begin
  g := TGPGraphics.Create(Canvas.Handle);

  p1 := MakePoint(0, 0);
  p2 := MakePoint(200, 100);
  c1 := MakeColor(255, 0, 0, 255);
  c2 := MakeColor(255, 0, 255, 0);

  lb := TGPLinearGradientBrush.Create(p1, p2, c1, c2);

  p:= TGPPen.Create(lb, 10);

  g.DrawLine(p, 0, 0, 600, 300);
  g.FillEllipse(lb, 10, 100, 200, 100);

  lb.Free;
  p.Free;
  g.Free;
end;


//自定义渐变过渡效果
var
  g : TGPGraphics;
  lb: TGPLinearGradientBrush;
  p1,p2: TGPPoint;
  c1,c2: TGPColor;
const
  Factors: array[0..2] of Single = (0.0, 0.5, 1.0);   {颜色比例}
  Positions: array[0..2] of Single = (0.0, 0.2, 1.0); {位置比例, 两个数组元素须相同}
begin
  g := TGPGraphics.Create(Canvas.Handle);

  p1 := MakePoint(0, 10);
  p2 := MakePoint(200, 10);
  c1 := aclBlack;
  c2 := aclRed;

  lb := TGPLinearGradientBrush.Create(p1, p2, c1, c2);

  lb.SetBlend(@Factors, @Positions, 3); {设置渐变因子}

  g.FillEllipse(lb, 0, 30, 200, 100);
  g.FillRectangle(lb, 0, 155, 500, 30);

  lb.Free;
  g.Free;
end;

线性渐变的方向参数:

Delphi	微软	说明
LinearGradientModeBackwardDiagonal	BackwardDiagonal	指定从右上到左下的渐变。
LinearGradientModeForwardDiagonal	ForwardDiagonal	指定从左上到右下的渐变。
LinearGradientModeHorizontal	Horizontal	指定从左到右的渐变。
LinearGradientModeVertical	Vertical	指定从上到下的渐变。