如何使用鼠标在Delphi图像上绘制多边形？

unit MainForm;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ExtCtrls, StdCtrls;

type
  TForm1 = class(TForm)
    Image1: TImage;
    Button1: TButton;
    Shape1: TShape;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormMouseMove(Sender: TObject; Shift: TShiftState; X,
      Y: Integer);
    procedure FormMouseUp(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormPaint(Sender: TObject);
  private
    { Private declarations }
    PolyPoints: array of TPoint;
    Drawing: Boolean;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  // 加载图像
  Image1.Picture.LoadFromFile('image.jpg');
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  // 清空多边形坐标
  SetLength(PolyPoints, 0);
  // 开始绘制多边形
  Drawing := True;
end;

procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Drawing then
  begin
    // 记录鼠标按下时的坐标
    SetLength(PolyPoints, Length(PolyPoints) + 1);
    PolyPoints[High(PolyPoints)].X := X;
    PolyPoints[High(PolyPoints)].Y := Y;
    // 更新多边形形状
    Shape1.Shape := stPolygon;
    Shape1.Pen.Color := clRed;
    Shape1.Brush.Style := bsClear;
    Shape1.Brush.Color := clWhite;
    Shape1.Polygon := PolyPoints;
  end;
end;

procedure TForm1.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  if Drawing then
  begin
    // 根据鼠标移动的坐标更新多边形形状
    PolyPoints[High(PolyPoints)].X := X;
    PolyPoints[High(PolyPoints)].Y := Y;
    Shape1.Polygon := PolyPoints;
  end;
end;

procedure TForm1.FormMouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if Drawing then
  begin
    // 结束绘制多边形
    Drawing := False;
  end;
end;

procedure TForm1.FormPaint(Sender: TObject);
begin
  // 绘制已保存的多边形
  if Length(PolyPoints) > 0 then
  begin
    Canvas.Pen.Color := clRed;
    Canvas.Brush.Style := bsClear;
    Canvas.Polygon(PolyPoints);
  end;
end;

end.