再學 GDI+[9]: DrawPolygon - 繪制多邊形

本例效果圖:

　　代碼文件:unit Unit1;
interface
uses
　Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
　Dialogs, StdCtrls;
type
　TForm1 = class(TForm)
　　Button1: TButton;
　　Button2: TButton;
　　procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
　　　Shift: TShiftState; X, Y: Integer);
　　procedure FormPaint(Sender: TObject);
　　procedure Button1Click(Sender: TObject);
　　procedure Button2Click(Sender: TObject);
　end;
var
　Form1: TForm1;
implementation
{$R *.dfm}
uses GDIPOBJ, GDIPAPI;
var
　PtArr: array of TGPPoint;
　i: Integer = 0;
procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
　Shift: TShiftState; X, Y: Integer);
begin
　Canvas.Ellipse(X-2, Y-2, X+2, Y+2);
　Inc(i);
　SetLength(PtArr, i);
　PtArr[i-1].X := X;
　PtArr[i-1].Y := Y;
　Text := IntToStr(i);
end;
procedure TForm1.FormPaint(Sender: TObject);
var
　g: TGPGraphics;
　p: TGPPen;
begin
　g := TGPGraphics.Create(Canvas.Handle);
　p := TGPPen.Create(aclRed, 2);
　g.Clear(aclWhite);
　{如果是動態數組的話, 需要 @PtArr, 但動態數組本身就是個指針}
　g.DrawPolygon(p, PGPPoint(PtArr), Length(PtArr));
　g.Free;
　p.Free;
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
　i := 0;
　SetLength(PtArr, i);
　Repaint;
　Text := IntToStr(i);
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
　Repaint;
end;
end.窗體文件:object Form1: TForm1
　Left = 0
　Top = 0
　Caption = 'Form1'
　ClIEntHeight = 188
　ClIEntWidth = 264
　Color = clBtnFace
　Font.Charset = DEFAULT_CHARSET
　Font.Color = clWindowText
　Font.Height = -11
　Font.Name = 'Tahoma'
　Font.Style = []
　OldCreateOrder = False
　Position = poDesktopCenter
　OnMouseUp = FormMouseUp
　OnPaint = FormPaint
　PixelsPerInch = 96
　TextHeight = 13
　object Button1: TButton
　　Left = 98
　　Top = 155
　　Width = 75
　　Height = 25
　　Caption = #25830#38500
　　TabOrder = 0
　　OnClick = Button1Click
　end
　object Button2: TButton
　　Left = 179
　　Top = 155
　　Width = 75
　　Height = 25
　　Caption = #32472#21046
　　TabOrder = 1
　　OnClick = Button2Click
　end
end