C / C++ / MFC

CBitmap m_bitmap_background;
BITMAP m_bmInfo_background;

m_bitmap_background.LoadBitmap(IDB_BACKGROUND); // change IDB_BACKGROUND to whatever your resource-located bitmap is called.
::GetObject(m_bitmap_background,sizeof(BITMAP),&m_bmInfo_background);

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

    CDC dcMem;
    dcMem.CreateCompatibleDC(pDC);
    
    HBITMAP* pBmpOld=(HBITMAP*)::SelectObject(dcMem.m_hDC,m_bitmap_background);

    for(int y=rect.top;y<rect.bottom;y+=m_bmInfo_background.bmHeight){
        for(int x=rect.left;x<=rect.right;x+=m_bmInfo_background.bmWidth){
            pDC->BitBlt(x,y,m_bmInfo_background.bmWidth,m_bmInfo_background.bmHeight,
                        &dcMem,0,0,SRCCOPY);
        }
    }

    ::SelectObject(dcMem.m_hDC, pBmpOld);

    return TRUE;
}

BOOL CMainFrame::OnCreateClient(LPCREATESTRUCT lpcs, CCreateContext* pContext) 
{
	if(!CMDIFrameWnd::OnCreateClient(lpcs, pContext))return FALSE;
	m_wndClient.SubclassWindow(m_hWndMDIClient);
	return TRUE;
}