画线一闪而过，求解释

Question

用LineTo()和MoveTo() 画线，结果一闪而过，初始划过OpenGL
这是我的OnDraw()  求大侠帮我看看
void CMineView::OnDraw(CDC* pDC)                          //OnDraw()
{
CMineDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
  ::glClearColor(1.0f,1.0f,1.0f,0.0f);
::glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
     
         ::glFlush();
         ::SwapBuffers(m_pDC->GetSafeHdc());
         pDC->MoveTo(40, 40);
         pDC->LineTo(900,400);
}

Answer 1

void CMineView::OnDraw(CDC* pDC) //OnDraw()
{
/*
CMineDoc* pDoc = GetDocument();
ASSERT_VALID(pDoc);
  ::glClearColor(1.0f,1.0f,1.0f,0.0f);
::glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
    
  ::glFlush();
  ::SwapBuffers(m_pDC->GetSafeHdc());
*/
  pDC->MoveTo(40, 40);
  pDC->LineTo(900,400);
}

Answer 2

 pDC->MoveTo(40, 40);
 pDC->LineTo(900,400);
这两句应该没问题，我用它可以画出来的，你找找是不是别的原因吧~

Answer 3

 ::glFlush();
  ::SwapBuffers(m_pDC->GetSafeHdc());
这两句是不是应该放最下边