vc6内存位图绘制图形怎么设置背景透明?

[ljhhh0123]

我画的圆里面怎么都是填充的是白色的,怎么才能不填充?请高手指教.

void CTView::OnPrepareDC(CDC* pDC, CPrintInfo* pInfo) 
{
	// TODO: Add your specialized code here and/or call the base class
	CRect rect;
	GetClientRect(rect);
	pDC->SetMapMode(MM_ISOTROPIC);
	pDC->SetWindowExt(rect.Width(),rect.Height());
	pDC->SetViewportExt(rect.Width(),-rect.Height());
	pDC->SetViewportOrg(rect.Width()/2,rect.Height()/2);

}
void CTView::OnLButtonDblClk(UINT nFlags, CPoint point) 
{
	// TODO: Add your message handler code here and/or call default
	CBitmap bitmap;
	CDC memdc;
	CClientDC dc(this);
	OnPrepareDC(&dc);
	CRect rect;
	GetClientRect(rect);
	bitmap.CreateCompatibleBitmap(&dc,rect.Width(),rect.Height());
	memdc.CreateCompatibleDC(&dc);
	memdc.SelectObject(bitmap);
	OnPrepareDC(&memdc);
	memdc.DPtoLP(&rect);

	memdc.SetBkMode(TRANSPARENT);//此处并不管用.
 CBrush brush(RGB(255,0,0));
 memdc.FillRect(rect,&brush);
// memdc.SetBkColor(RGB(255,255,0));
memdc.MoveTo(0,0);
memdc.LineTo(250,250);
memdc.Ellipse(-200,-200,200,200);
dc.BitBlt(-200,-200,400,400,&memdc,-200,-200,SRCCOPY);

}

[ljhhh0123]

已经解决,将画刷设为NULL_BRUSH.