procedure TForm1.FormPaint(Sender: TObject);//编程form1的onPaint事件代码如下
var
  g:TGPGraphics; //定义绘图表面类变量
  p:TGPPen; //定义画笔类变量
begin
  g:=TGPGraphics.Create(Canvas.Handle); //创建绘图表面对象
  p:=TGPPen.Create(aclRed,2); //创建画笔对象
  g.Clear(aclWhite); //清除整个绘图面并以白色填充

  g.DrawPie(p,10,10,200,100,0,350); //在绘图表面画一个饼形（也可以叫扇形）

  p.Free; //用完成对象记得释放
  g.Free; //用完成对象记得释放
end;

unit Unit1;

interface

uses //系统自动生成
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, Spin, ExtCtrls;

type        //在窗体上添加了一个TPanel，两个TLabel，两个TSpinEdit。
  TForm1 = class(TForm)
    Panel1: TPanel;
    Label1: TLabel;
    Label2: TLabel;
    SpinEdit1: TSpinEdit;
    SpinEdit2: TSpinEdit;
    procedure FormCreate(Sender: TObject);
    procedure FormPaint(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses GDIPOBJ, GDIPAPI; //加入这两个GDI+要用到的单元

var
  a1,a2: Integer; //声明两个本单元文件内要用到的全局变量(用于起始角度和旋转角度)

procedure TForm1.FormCreate(Sender: TObject);
begin
  a1 := 0;    //初始化起始角度
  SpinEdit1.Text := IntToStr(a1);
  a2 := 30;  //初始化旋转角度
  SpinEdit2.Text := IntToStr(a2);
  SpinEdit1.Increment := 10; //步进
  SpinEdit2.Increment := 10;
  SpinEdit1.OnChange := FormPaint; //组件OnChange指向FormPaint
  SpinEdit2.OnChange := FormPaint;
end;

procedure TForm1.FormPaint(Sender: TObject);
var
  g: TGPGraphics;
  p: TGPPen;
  x,y,w,h: Integer;
begin
  g := TGPGraphics.Create(Canvas.Handle);
  p := TGPPen.Create(aclRed, 2);
  g.Clear(aclWhite);

  x := ClientWidth div 6;
  y := ClientHeight div 6;
  w := x * 4;
  h := y * 3;
  a1 := StrToIntDef(SpinEdit1.Text, 0); //此函数用于检查用户在SpinEdit输入的数值
  a2 := StrToIntDef(SpinEdit2.Text, 30); //如果用户输入英文之类的字符SpinEdit将回复为参数2

  g.DrawPie(p, x, y, w, h, a1, a2); //画扇形

  g.Free;
  p.Free;
end;

end.