再学 GDI+[69]: 路径画刷(9) - SetInterpolationColors 与 SetSurroundColors 的区别

本例效果图:

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代码文件:

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unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ComCtrls, StdCtrls, ExtCtrls;

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ, GDIPAPI;

procedure TForm1.FormPaint(Sender: TObject);
const
  colors: array[0..3] of TGPColor = (aclRed, aclYellow, aclGreen, aclBlue);
  pos: array[0..3] of Single = (0.0, 0.2, 0.6, 1.0); {好像两端数据必须要是 0 和 1}
var
  g: TGPGraphics;
  path: TGPGraphicsPath;
  pb: TGPPathGradientBrush;
  num: Integer;
  pts: array of TGPPoint;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  path := TGPGraphicsPath.Create;

  {建立椭圆路径, 并根据路径建立路径画刷, 再用 SetInterpolationColors 设置颜色}
  path.AddEllipse(MakeRect(10,10,150,150));
  pb := TGPPathGradientBrush.Create(path);
  pb.SetInterpolationColors(@colors, @pos, Length(pos));
  g.FillPath(pb, path);

  {根据椭圆路径建立路径画刷, 再用 SetSurroundColors 设置颜色}
  pb.Free;
  pb := TGPPathGradientBrush.Create(path);
  num := Length(pos);
  pb.SetSurroundColors(@colors, num);
  g.TranslateTransform(160, 0);
  g.FillPath(pb, path);

  {根据从椭圆路径中提取出的点数组建立路径画刷, 再用 SetSurroundColors 设置颜色}
  SetLength(pts, path.GetPointCount);
  path.GetPathPoints(PGPPoint(pts), Length(pts));
  pb.Free;
  pb := TGPPathGradientBrush.Create(PGPPoint(pts), Length(pts));
  pb.SetCenterColor(aclWhite); {此时中心会默认黑色, 我想要白色的}
  num := Length(colors);
  pb.SetSurroundColors(@colors, num);
  g.TranslateTransform(160, 0);
  g.FillPath(pb, path);

  {根据从椭圆路径中提取出的点数组建立路径画刷, 再用 SetInterpolationColors 设置颜色}
//  SetLength(pts, path.GetPointCount);
//  path.GetPathPoints(PGPPoint(pts), Length(pts));
  pb.Free;
  pb := TGPPathGradientBrush.Create(PGPPoint(pts), Length(pts));
//  pb.SetCenterColor(aclWhite); {这里不需要中心色}
  num := Length(colors);
  pb.SetInterpolationColors(@colors, @pos, Length(pos));
  g.TranslateTransform(160, 0);
  g.FillPath(pb, path);

  pb.Free;
  path.Free;
  g.Free;
end;

end.

窗体文件:

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object Form1: TForm1
  Left = 0
  Top = 0
  Caption = 'Form1'
  ClientHeight = 169
  ClientWidth = 649
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'Tahoma'
  Font.Style = []
  OldCreateOrder = False
  Position = poDesktopCenter
  OnPaint = FormPaint
  PixelsPerInch = 96
  TextHeight = 13
end