Question

Is it possible to create a label with a transparent background within a window using only WinAPI commands?

I am trying to add an image to a Dialog window that will serve as a background image and then display text upon that image. Everything I have tried so far shows the text label on top of the background image with a grey rectangle drawn around it.

This is an example of my code so far (showing the entire message handler for the dialog):

INT_PTR CALLBACK OfferWindowProc(HWND hDlg, UINT message, WPARAM wParam, LPARAM lParam)
{       
    HWND hWndBackground;
    HWND hWndLabel;
    HBRUSH hLabelBackColour = NULL;
      HFONT hfFont;
      HWND hWndTitleLabel;
    HDC hdcStatic = NULL;

    UNREFERENCED_PARAMETER(lParam);
    switch (message)
    {
    case WM_INITDIALOG:             

        //Load the background image
        HANDLE hBitmap;
        hBitmap = LoadImage(NULL, L"C:\\Users\\DavidHall\\Documents\\bg.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
        if (hBitmap != NULL)
        {
            hWndBackground = CreateWindow(L"STATIC", L"image box", WS_CHILD | WS_VISIBLE | SS_BITMAP, 0, 0, 100, 100, hDlg, (HMENU) 2000, NULL, NULL);          
            SendMessage(hWndBackground, STM_SETIMAGE, IMAGE_BITMAP, LPARAM(hBitmap));
        }           

        // Create the label using CreateWindowEx
        hfFont = CreateFont(20, 0, 0, 0, fontWeight, FALSE, FALSE, FALSE, DEFAULT_CHARSET, OUT_DEFAULT_PRECIS, CLIP_DEFAULT_PRECIS, ANTIALIASED_QUALITY,
            DEFAULT_PITCH, L"Verdana");

        hWndTitleLabel = CreateWindowEx( WS_EX_TRANSPARENT, L"STATIC", L"", WS_CHILD | WS_VISIBLE | SS_LEFT | WS_SYSMENU , xPos, yPos, width, height, hwnd, (HMENU) id, hInst, NULL);           

        SendMessage(hWndTitleLabel, WM_SETTEXT, NULL, (LPARAM) labelText.c_str());

        SendMessage(hWndTitleLabel, WM_SETFONT, (WPARAM)hfFont, NULL);  

        return (INT_PTR)TRUE;   

    case WM_CLOSE:
        EndDialog(hDlg, LOWORD(wParam));    

        // Delete the brush - is that correct?
        DeleteObject(hLabelBackColour);
        return (INT_PTR)TRUE;

    case WM_COMMAND:
        if (LOWORD(wParam) == IDCANCEL)
        {
            EndDialog(hDlg, LOWORD(wParam));
            return (INT_PTR)TRUE;
        }
        break;
    default:
        break;
    }
    return (INT_PTR)FALSE;
}

I’ve tried various combinations of things including:

• SetLayeredWindowAttributes
• SetBkMode(hdc, TRANSPARENT)
• Handling the WM_CTLCOLORSTATIC message

Answer 1

I’ve found something that appears to be working, though since I am very new to programming in pure WinAPI this could well be very bad practice and I would have no idea!

I am handling the WM_CTLCOLORSTATIC message as shown:

case WM_CTLCOLORSTATIC:

    hdcStatic = (HDC) wParam; 
    SetTextColor(hdcStatic, RGB(0,0,0));    
    SetBkMode (hdcStatic, TRANSPARENT);

    return (LRESULT)GetStockObject(NULL_BRUSH);

This gives the effect that I’m after of my label appearing on top of my image with a transparent background.