很简单的问题，却总没找到最简单的实现方法

Question

问题很简单：在Canvas内部要动态划一根线，如果不清空Canvas，那么每个MouseMove事件中画出来的线都会留在Canvas上，如果清空，那么整个Canvas就会闪烁，该如何解决呢？

Answer 1

其实在Image上绘图，是首先在内存中绘好，然后再整个画到Image.Canvas上；
直接在Image.Canvas绘图会产生闪烁。同时设置pen.mode
比如在内存中建立临时Canvas.
然后CopyRect或者Draw到目标.

Answer 2

bcb代码，如果你要的是思路，这就足够了！
void __fastcall TForm1::Image1MouseDown(TObject *Sender,
      TMouseButton Button, TShiftState Shift, int X, int Y)
{
Drawing =true;
Image1->Canvas->MoveTo(0,0);
 Origin=Point(X,Y);
tPoint=Origin;
}
//---------------------------------------------------------------------------
void __fastcall TForm1::Image1MouseMove(TObject *Sender, TShiftState Shift,
      int X, int Y)
{
if(Drawing)
{
 Image1->Canvas->Brush->Style=bsClear;
    Image1->Canvas->Pen->Color=clLime;
 Image1->Canvas->Pen->Mode =pmXor;
 Image1->Canvas->Rectangle(Rect(Origin.x,Origin.y,tPoint.x,tPoint.y));
 tPoint=Point(X,Y); Image1->Canvas->Pen->Mode =pmXor;
 Image1->Canvas->Rectangle(Rect(Origin.x,Origin.y,tPoint.x,tPoint.y));
 }
}
//---------------------------------------------------------------------------void __fastcall TForm1::Image1MouseUp(TObject *Sender, TMouseButton Button,
      TShiftState Shift, int X, int Y){
if(Drawing)
{
Image1->Canvas->Pen->Color=clBlue;
Image1->Canvas->Pen->Mode =pmCopy;
Image1->Canvas->Rectangle(Rect( Origin.x,Origin.y,X,Y));
Drawing=false;
}
}
//---------------------------------------------------------------------------void __fastcall TForm1::FormCreate(TObject *Sender)
{
DoubleBuffered=true;
Image1->Picture->Bitmap->PixelFormat=pf24bit;
Image1->Canvas->Pen->Color=clRed;
}
//----------------------------------------------------------------