我想做出只留当前一条线的效果,这段代码的重影为什么不消失?

[coolcoffee4051982]

	if ((nFlags&MK_LBUTTON)==MK_LBUTTON)
	{
		CDC *dc=GetDC();
		CDC *db;
		CDC *da;
		db=new CDC;
		da=new CDC;
		db->CreateCompatibleDC(dc);
		da->CreateCompatibleDC(db);
		
		if (first)
		{
			first=FALSE;
			at.CreateCompatibleBitmap(dc,300,300);
			bt.CreateCompatibleBitmap(dc,300,300);
			db->SelectObject(bt);
			db->BitBlt(0,0,300,300,dc,0,0,SRCCOPY);
		}
		da->SelectObject(at);
		da->BitBlt(0,0,300,300,db,0,0,SRCCOPY);
		da->MoveTo(50,50);
		da->LineTo(point.x,point.y);
		dc->BitBlt(0,0,300,300,da,0,0,SRCCOPY);
		delete da;
		delete db;
		ReleaseDC(dc);
	}

[coolcoffee4051982]

忘了说了,这是在一个对话框中的OnMouseMove(UINT nFlags, CPoint point) 函数中.

[ZM]

CDC::SetROP2(R2_NOTXORPEN);

[coolcoffee4051982]

自己解决了,虽然不是楼上的问题