//加载原始位图
void CMyView::OnDraw(CDC* pDC)
{
CMyDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
CDC  mdc;
CBitmap * bitmap=new CBitmap();
CBitmap* oldBitmap;
    //CClientDC *dc=(ClientDC *)GetDC();

bitmap->LoadBitmap(IDB_BITMAP2);
mdc.CreateCompatibleDC(pDC);
    oldBitmap=mdc.SelectObject(bitmap);
// pDC->BitBlt(0,0,63,63,&mdc,630,630,SRCCOPY);//原始大小
pDC->StretchBlt    (0,0,1024,768,&mdc,0,0,1024,768,SRCCOPY);  //拉伸大小
// TODO: add draw code for native data here
mdc.SelectObject(oldBitmap);      switch (nEffect)
{
     case MUKE:
          Muke(pDC);
          break;
      ..........
}
   }
//
void CMyView::Muke(CDC *pDC)
{
int red,green,blue,total;
for(int i=0;i<1024;i++)
{
for(int j=0;j<768;j++)
{
m_colPxiel[i][j]=pDC->GetPixel(i,j);
            red=m_colPxiel[i][j]&RGB(255,0,0);
green=(m_colPxiel[i][j]>>8)&RGB(255,0,0);
blue=(m_colPxiel[i][j]>>16)&RGB(255,0,0);
total=(red+green+blue)/3;
if(total<128)
{
m_colPxiel[i][j]=RGB(255,255,255);
    AfxMessageBox("hi");
}
else
{
                m_colPxiel[i][j]=RGB(0,0,0);

}
           pDC->SetPixel(i,j,m_colPxiel[i][j]);
}
}
   
}
  怎么显示黑色,但是如果在加载完位图后,直接Muke(pDC)可以实现木刻效果,为何???