unit1.pas

这有很多Delphi应用的例子

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    procedure FormPaint(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormPaint(Sender: TObject);
Var
  i:Integer;
  x1,y1,x2,y2:Integer;
begin
  for i:=4 downto 1 do
  begin
    Canvas.Pen.Width:=2*i;
    x1:=trunc((ClientWidth/2)-(i+1)*30);
    x2:=trunc((ClientWidth/2)+(i+1)*30);
    y1:=trunc((ClientHeight/2)-(i+1)*30);
    y2:=trunc((ClientHeight/2)+(i+1)*30);
    Canvas.Rectangle(x1,y1,x2,y2);
  end
end;

end.