再学GDI+[9]: DrawPolygon

本例效果图:

代码文件: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);
　{如果是动态数组的话, 需要 @PtArr, 但动态数组本身就是个指针}
　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.