再学 GDI+[9]: DrawPolygon - 绘制多边形

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.

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