procedure TForm1.PaintBox1Paint(Sender: TObject; Canvas: TCanvas);

var bitmap :TBitMap;

    pt1, pt2 :TPointF;

begin

  pt1 := TPointF.Create(, );

  pt2 := TPointF.Create(PaintBox1.Width, PaintBox1.Width);

  //ShowMessage('yes');

  bitmap := TBitMap.Create(Trunc(PaintBox1.Width), Trunc(PaintBox1.Width));

  try

    bitmap.Canvas.BeginScene(); // ZC: 做画图工作时，这一句必须要

    bitmap.Canvas.Stroke.Kind := TBrushKind.bkSolid;

    bitmap.Canvas.Stroke.Color := TAlphaColorRec.Black;

    bitmap.Canvas.DrawLine(pt1, pt2, );

    bitmap.Canvas.EndScene;     // ZC: 做画图工作时，这一句必须要

    //TCanvas.CopyBitmap(bitmap, Canvas.Bitmap);

    //PaintBox1.Canvas.BeginScene(); // ZC: 这里，可以不执行这一句

    PaintBox1.Canvas.DrawBitmap(

      bitmap,

      TRectF.Create(, , PaintBox1.Width, PaintBox1.Width),

      TRectF.Create(, , PaintBox1.Width, PaintBox1.Width),

      );

    //PaintBox1.Canvas.EndScene;     // ZC: 这里，可以不执行这一句

  finally

    if Assigned(bitmap) then

      bitmap.Free;

  end;

end;