The trick is to override the OnEraseBkgnd handler. Here's one way of doing it:

CBitmap bitmapBkgnd;
bitmapBkgnd.Attach (LoadBitmap (AfxGetInstanceHandle(), 
                    MAKEINTRESOURCE(m_iBitmapId)));

BOOL CTestbed2Dlg::OnEraseBkgnd(CDC* pDC) 
{
   CRect rect;

   GetClientRect(&rect);
   CDC dc;
   dc.CreateCompatibleDC(pDC);
   CBitmap* pOldBitmap = dc.SelectObject(&bitmapBkgnd);

   int iBitmapWidth, iBitmapHeight ;
   int ixOrg, iyOrg;
   BITMAP bm;

   bitmapBkgnd.GetObject(sizeof(BITMAP),&bm);
   iBitmapWidth = bm.bmWidth;
   iBitmapHeight = bm.bmHeight;

   // If our bitmap is smaller than the background and tiling is
   // supported, tile it. Otherwise watch the efficiency - don't
   // spend time setting up loops you won't need.

   if (iBitmapWidth >= rect.Width() &&
       iBitmapHeight >= rect.Height() )
   {
      pDC->BitBlt (rect.left, 
                   rect.top,
                   rect.Width(),
                   rect.Height(),
                   &dc,
                   0, 0, SRCCOPY);
   }
   else
   {
      for (iyOrg = 0; iyOrg < rect.Height(); iyOrg += iBitmapHeight)
      {
         for (ixOrg = 0; 
              ixOrg < rect.Width();
              ixOrg += iBitmapWidth)
         {
            pDC->BitBlt (ixOrg,  
                         iyOrg,
                         rect.Width(),
                         rect.Height(),
                         &dc,
                         0, 0, SRCCOPY);
         }
      }
   }
   dc.SelectObject(pOldBitmap);
   return TRUE;
}

If you have static text items and want them to have the bitmap as their background, see Tip #37.

Note that the WM_ERASEBKGND message won't appear in the VC6 ClassWizard by default, because ClassWizard hides it from you if you're stuck using this old compiler. To create the handler, you'll have to learn how to stop this hiding... which is a useful thing to know anyway. If you go to the last right-hand tab (Class Info I think) on ClassWizard, at the bottom of the tab you'll see a "filter" combo which is set to "Dialog". Change this to "Window" and then go back to the Message Map tab. You'll now see a lot more messages to choose from.

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