创建一个应用程序，在 Form1 的 OnPaint 事件里面添加如下一段代码：
      procedure TForm1.FormPaint(Sender: TObject);
      var
       i:word;
       dy,y:real;
      begin
       dy:=clientheight/256;
       y:=0;
       for i:=255 downto 0 do
       begin
        canvas.brush.color:=$00000000 + i*$10000;
        canvas.fillrect(rect(0,round(y),clientwidth,round(y+dy)));
        y:=y+dy;
       end;
     end;