unit Unit1;interfaceuses  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,  Dialogs, StdCtrls;type  TForm1 = class(TForm)    Button1: TButton;    Button2: TButton;    Button3: TButton;    Button4: TButton;    Button5: TButton;    procedure Button1Click(Sender: TObject);    procedure Button2Click(Sender: TObject);    procedure Button3Click(Sender: TObject);    procedure Button4Click(Sender: TObject);    procedure Button5Click(Sender: TObject);  end;var  Form1: TForm1;implementation{$R *.dfm}//使用 API 函数: SetRectprocedure TForm1.Button1Click(Sender: TObject);var  R: TRect;begin  SetRect(R, 20, 20, 80, 80);  Canvas.Pen.Color := clBlue;  Canvas.Rectangle(R);end;//使用 Classes.Rect 函数procedure TForm1.Button2Click(Sender: TObject);var  R: TRect;begin  R := Rect(20, 20, 80, 80);  Canvas.Pen.Color := clFuchsia;  Canvas.Rectangle(R);end;//使用 Classes.Rect 函数, 用两个点合成procedure TForm1.Button3Click(Sender: TObject);const  pt1: TPoint = (x:20; y:20);  pt2: TPoint = (x:80; y:80);var  R: TRect;begin  R := Rect(pt1, pt2);  Canvas.Pen.Color := clSkyBlue;  Canvas.Rectangle(R);end;//矩形常量procedure TForm1.Button4Click(Sender: TObject);const  R: TRect = (Left:20; Top:20; Right:80; Bottom:80);begin  Canvas.Pen.Color := clTeal;  Canvas.Rectangle(R);end;//使用 Classes.Bounds 函数, 我最喜欢这种办法procedure TForm1.Button5Click(Sender: TObject);var  R: TRect;begin  R := Bounds(20, 20, 60, 60);  Canvas.Pen.Color := clWhite;  Canvas.Rectangle(R);end;end.