Can't copy the background of my simple control

From:

Maik Wiege <mswiege-nospan-@gmx.de>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 01 May 2006 21:17:57 +0200

Message-ID:

<44565eea$0$22101$9b622d9e@news.freenet.de>

Hello!
I made a simple control that should simply paint a dragable circle on
the screen, but I cant get the surrounding of the circle to become the
correct background of the parent. Here is what I've done:
I crated a MainFrame, View project (for Windows Mobile, but that should
be the same for win32) with the wizard. In the ChildView derived from CWnd:
int CChildView::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
     if (CWnd::OnCreate(lpCreateStruct) == -1)
         return -1;
     svd = new CSimpleCircleDrawer();
     svd->Create(NULL,_T(""),WS_VISIBLE | WS_CHILD,
         CRect(10,10,30,30), this, 1234);
     return 0;
}
void CChildView::OnPaint()
{
     CPaintDC dc(this); // device context for painting
     CRect rect;
     GetClientRect(rect);
     CBrush brush(RGB(50, 50, 250));
     dc.FillRect(rect, &brush);
}

And my CSimpleCircleDrawer class:

BEGIN_MESSAGE_MAP(CSimpleCircleDrawer, CWnd)
     ON_WM_PAINT()
     ON_WM_LBUTTONDOWN()
     ON_WM_LBUTTONUP()
     ON_WM_MOUSEMOVE()
END_MESSAGE_MAP()

void CSimpleCircleDrawer::OnPaint()
{
     CPaintDC dc(this); // device context for painting

     //Get the parents background
     CWnd* pParent = GetParent();
     CRect rect;
     GetClientRect(&rect);
     ClientToScreen(&rect);
     pParent->ScreenToClient(&rect);
     CDC *pDC = pParent->GetDC();
     CDC memdc;
     memdc.CreateCompatibleDC(pDC);
     CBitmap m_Bmp;
     CBitmap *pOldbmp = memdc.SelectObject(&m_Bmp);
     memdc.BitBlt(0,0,rect.Width(),rect.Height(),pDC,rect.left,
        rect.top,SRCCOPY);
     pParent->ReleaseDC(pDC);

     // copy the bitmap to the memdc
     memdc.CreateCompatibleDC(&dc);
     CBitmap memBmp;
     memBmp.CreateCompatibleBitmap(&dc,rect.Width(),rect.Height());
     memdc.SelectObject(&memBmp);

     //paint the background bitmap on the memory DC
     dc.SelectObject(&m_Bmp);
     memdc.BitBlt(0,0,rect.Width(),rect.Height(),&dc,0,0,SRCCOPY);
     dc.SelectObject(pOldbmp);

     // now draw a simple circle
     dc.Ellipse(0,0,20,20);
}

void CSimpleCircleDrawer::OnLButtonDown(UINT nFlags, CPoint point)
{
     SetCapture();
     m_bCaptured = TRUE;
     m_nDragOffset = point;

     CWnd::OnLButtonDown(nFlags, point);
}

void CSimpleCircleDrawer::OnLButtonUp(UINT nFlags, CPoint point)
{
     ReleaseCapture();
     m_bCaptured = FALSE;
     CWnd::OnLButtonUp(nFlags, point);
}

void CSimpleCircleDrawer::OnMouseMove(UINT nFlags, CPoint point)
{
     CWnd* pParent = GetParent();

     //Retrieve the old postion (in parent client coordinates)
     CRect oldPos;
     GetClientRect(&oldPos);
     ClientToScreen(oldPos);
     pParent->ScreenToClient(&oldPos);

     //Work out the new position (in parent client coordinates)
     CRect newPos(point.x - m_nDragOffset.x, point.y - m_nDragOffset.y,
           point.x - m_nDragOffset.x + m_nWidth,
           point.y - m_nDragOffset.y + m_nHeight);
     ClientToScreen(&newPos);
     pParent->ScreenToClient(&newPos);

     //Only move the vertex if it is inside the client rect of the
parent
     CRect clientRect;
     pParent->GetClientRect(&clientRect);
     if (newPos.left >= clientRect.left && newPos.top >=
           clientRect.top && newPos.right < clientRect.right &&
           newPos.bottom < clientRect.bottom)
     {
          // update the drawing
          MoveWindow(newPos, FALSE);
          pParent->InvalidateRect(oldPos, FALSE);
          Invalidate(TRUE);
     }
     CWnd::OnMouseMove(nFlags, point);
}

So what is wrong here? The circle is painted fine and I can drag it
around, but the surrounding of the circle is not painted blue as it
should because the parent is blue.

Thanks for any help
  Maik