本例效果图:

代码文件:

unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    RadioGroup1: TRadioGroup;
    procedure FormPaint(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure RadioGroup1Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  RadioGroup1.Items.CommaText := 'TRANSPARENT,OPAQUE';
  RadioGroup1.ItemIndex := 0;
  RadioGroup1.Columns := RadioGroup1.Items.Count;
end;

procedure TForm1.FormPaint(Sender: TObject);
const
  str = 'Delphi 2007';
var
  x,y: Integer;
begin
  Canvas.Font.Size := 36;
  Canvas.Font.Style := [fsBold];
  x := (ClientWidth - Canvas.TextWidth(str)) div 2;
  y := (ClientHeight - Canvas.TextHeight(str)) div 4;

  Canvas.Pen.Color := clRed;
  Canvas.Brush.Color := clWhite;

  case RadioGroup1.ItemIndex of
    0: SetBkMode(Canvas.Handle, TRANSPARENT); {透明模式}
    1: SetBkMode(Canvas.Handle, OPAQUE);      {非透明模式}
  end;

  {也可以用下面一句话代替上面的 case 语句}
  //SetBkMode(Canvas.Handle, RadioGroup1.ItemIndex + 1);

  BeginPath(Canvas.Handle);
  Canvas.TextOut(x, y, str);
  EndPath(Canvas.Handle);

  StrokeAndFillPath(Canvas.Handle);
end;

procedure TForm1.RadioGroup1Click(Sender: TObject);
begin
  Repaint;
end;

end.