为何在这样在内存中画图这么慢呢？？

Question

这样比直接在PaintBox上画图居然要慢许多， 是什么原因呢？？？？
var 
  BackMap : TBitMap;
begin
  BackMap := TBitMap.Create;
  BackMap.Width := PaintBox.Width;
  BackMap.Height := PaintBox.Height;
  BackMap.Canvas.CopyRect(Rect(0,0,PaintBox.Width,PaintBox.Height),PaintBox.Canvas
                          Rect(0,0,PaintBox.Width,PaintBox.Height));  BackMap.Canvas.Pen.Color := clLime;
  BackMap.Canvas.Pen.Mode :=pmCopy;  BackMap.Canvas.MoveTo(x,y);
  BackMap.Canvas.LineTo(x,y);
  ......  PaintBox.Canvas.CopyRect(Rect(0,0,PaintBox.Width,PaintBox.Height),BackMap.Canvas
                           Rect(0,0,BackMap.Width,BackMap.Height));
  BackMap.Free;
end;

Answer 1

直接画的话少画了一次,当然快了

Answer 2

肯定慢，但是内存画图不会闪屏