procedure TForm1.Button1Click(Sender: TObject);var  cvs: TCanvas;begin  {PaintBox1 就像窗体一样, 也有 Canvas 属性}  PaintBox1.Canvas.Brush.Color := clRed;  PaintBox1.Canvas.FillRect(PaintBox1.ClientRect);  {像 Panel1 这样没有 Canvas 属性的控件, 也可以绕道获取}  cvs := TCanvas.Create;  cvs.Handle := GetDC(Panel1.Handle);  cvs.Brush.Color := clBlue;  cvs.FillRect(Panel1.ClientRect);  cvs.Free;end;         //执行前后对比图: