再学 GDI+[9]: DrawPolygon - 绘制多边形

本例效果图:

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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.

窗体文件:

---

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