Lightbox style dialogs in MFC App

Answer 1

I think you just need to create a window and set the transparency. There is an MFC CGlassDialog sample on CodeProject that might help you. There is also an article on how to do this with the Win32 APIs.

Answer 2

Here's what I did* based on Brian's links
First create a dialog resource with the properties:

• border FALSE
• 3D look FALSE
• client edge FALSE
• Popup style
• static edge FALSE
• Transparent TRUE
• Title bar FALSE

and you should end up with a dialog window with no frame or anything, just a grey box. override the Create function to look like this:

BOOL LightBoxDlg::Create(UINT nIDTemplate, CWnd* pParentWnd)
{

    if(!CDialog::Create(nIDTemplate, pParentWnd))
     return false;
    RECT rect;
    RECT size;

    GetParent()->GetWindowRect(&rect);
    size.top = 0;
    size.left = 0;
    size.right = rect.right - rect.left;
    size.bottom = rect.bottom - rect.top;
    SetWindowPos(m_pParentWnd,rect.left,rect.top,size.right,size.bottom,NULL);

    HWND hWnd=m_hWnd;  
    SetWindowLong (hWnd , GWL_EXSTYLE ,GetWindowLong (hWnd , GWL_EXSTYLE ) | WS_EX_LAYERED ) ;
    typedef DWORD (WINAPI *PSLWA)(HWND, DWORD, BYTE, DWORD);
    PSLWA pSetLayeredWindowAttributes;
    HMODULE hDLL = LoadLibrary (_T("user32"));
    pSetLayeredWindowAttributes = 
     (PSLWA) GetProcAddress(hDLL,"SetLayeredWindowAttributes");
    if (pSetLayeredWindowAttributes != NULL) 
    {
     /*
     * Second parameter RGB(255,255,255) sets the colorkey 
     * to white LWA_COLORKEY flag indicates that color key 
     * is valid LWA_ALPHA indicates that ALphablend parameter 
     * is valid - here 100 is used
     */
     pSetLayeredWindowAttributes (hWnd, 
      RGB(255,255,255), 100, LWA_COLORKEY|LWA_ALPHA);
    }


    return true;
}

then create a small black bitmap in an image editor (say 48x48) and import it as a bitmap resource (in this example IDB_BITMAP1)
override the WM_ERASEBKGND message with:

BOOL LightBoxDlg::OnEraseBkgnd(CDC* pDC)
{

    BOOL bRet = CDialog::OnEraseBkgnd(pDC);

    RECT rect;
    RECT size;
    m_pParentWnd->GetWindowRect(&rect);
    size.top = 0;
    size.left = 0;
    size.right = rect.right - rect.left;
    size.bottom = rect.bottom - rect.top;

    CBitmap cbmp;
    cbmp.LoadBitmapW(IDB_BITMAP1);
    BITMAP bmp;
    cbmp.GetBitmap(&bmp);
    CDC memDc;
    memDc.CreateCompatibleDC(pDC);
    memDc.SelectObject(&cbmp);
    pDC->StretchBlt(0,0,size.right,size.bottom,&memDc,0,0,bmp.bmWidth,bmp.bmHeight,SRCCOPY);

    return bRet;
}

Instantiate it in the DoModal of the desired dialog, Create it like a Modal Dialog i.e. on the stack(or heap if desired), call it's Create manually, show it then create your actual modal dialog over the top of it:

INT_PTR CAboutDlg::DoModal()
{
    LightBoxDlg Dlg(m_pParentWnd);//make sure to pass in the parent of the new dialog
    Dlg.Create(LightBoxDlg::IDD);
    Dlg.ShowWindow(SW_SHOW);

    BOOL ret = CDialog::DoModal();

    Dlg.ShowWindow(SW_HIDE);
    return ret;
}

and this results in something exactly like my mock up above

*there are still places for improvment, like doing it without making a dialog box to begin with and some other general tidyups.