unit Unit1;

interface

uses
  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 FormCreate(Sender: TObject);
    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}

var
  btn: TButton;
const
  y1 = 10;
  y2 = 80;


{先设置画笔画刷}
procedure TForm1.FormCreate(Sender: TObject);
begin
  Canvas.Pen.Width := 4;
  Canvas.Pen.Color := clRed;
  Canvas.Brush.Color := clWhite;
end;


{给出左上角和右下角的坐标就可以绘制矩形}
procedure TForm1.Button1Click(Sender: TObject);
begin
  btn := TButton(Sender);
  Canvas.Rectangle(btn.Left, y1, btn.Left+btn.Width, y2);
end;


{给出一个矩形结构做参数也可以绘制矩形}
procedure TForm1.Button2Click(Sender: TObject);
var
  R: TRect; {定义一个矩形结构}
begin
  btn := TButton(Sender);
  R := Rect(btn.Left, y1, btn.Left+btn.Width, y2);
  Canvas.Rectangle(R);
end;


{绘制圆角矩形; 最后两个参数是设置圆角的}
procedure TForm1.Button3Click(Sender: TObject);
begin
  btn := TButton(Sender);
  Canvas.RoundRect(btn.Left, y1, btn.Left+btn.Width, y2, 20,20);
end;


{绘制焦点矩形; 它不受画笔的影响; 它的颜色是和画刷的颜色进行某种运算得来的}
procedure TForm1.Button4Click(Sender: TObject);
var
  R: TRect;
begin
  btn := TButton(Sender);
  R := Rect(btn.Left, y1, btn.Left+btn.Width, y2);
  Canvas.DrawFocusRect(R);
end;


{矩形描边, 用的不是画笔是画刷}
procedure TForm1.Button5Click(Sender: TObject);
var
  R: TRect;
begin
  btn := TButton(Sender);
  R := Rect(btn.Left, y1, btn.Left+btn.Width, y2);
  Canvas.FrameRect(R);
end;

end.


//效果图: