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Static control using WS_EX_TRANSPARENT style not repainted

I am trying to create a control that implements an alpha blend per pixel when drawing a 32bit bitmap.

I extended CWnd and used static control in the resource editor. I managed to draw the alpha channel correctly, but still the static control keeps drawing the gray background.

I overwritten OnEraseBkgnd to prevent the background from being drawn, but it didn't work. I was finally able to do this using WS_EX_TRANSPARENT.

Now my problem is that my control is over another control. The first time the dialog is colored everything works fine ... but if I click the "parent" control (ie the one under my control), my control did not receive the WM_PAINT message. Therefore, it is no longer colored.

If I hide the app and enlarge it again, the controls are colored again.

Please can someone give a hint? I'm going crazy with this control!

Thank.

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3 answers


If you were handling the WM_ERASEBKGND and WM_PAINT messages , then you would have to cover all the drawing options without resorting to using WS_EX_TRANSPARENT .

Are you sure your code is not passing these messages for processing by default ?



Another option could be a static member subclass to make sure your code is the only one handling these two messages.

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BEGIN_MESSAGE_MAP(CTransparentStatic, CStatic)
    ON_WM_ERASEBKGND()
    ON_WM_CTLCOLOR_REFLECT()
END_MESSAGE_MAP()

BOOL CTransparentStatic::OnEraseBkgnd(CDC* /*pDC*/)
{
    // Prevent from default background erasing.
    return FALSE;
}

BOOL CTransparentStatic::PreCreateWindow(CREATESTRUCT& cs)
{
    cs.dwExStyle |= WS_EX_TRANSPARENT;
    return CStatic::PreCreateWindow(cs);
}

HBRUSH CTransparentStatic::CtlColor(CDC* pDC, UINT /*nCtlColor*/)
{
    pDC->SetBkMode(TRANSPARENT);
    return reinterpret_cast<HBRUSH>(GetStockObject(NULL_BRUSH));
}

void CTransparentStatic::PreSubclassWindow()
{
    CStatic::PreSubclassWindow();

    const LONG_PTR exStyle = GetWindowLongPtr(m_hWnd, GWL_EXSTYLE);
    SetWindowLongPtr(m_hWnd, GWL_EXSTYLE, exStyle | WS_EX_TRANSPARENT);
}


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http://unick-soft.ru/Articles.cgi?id=12 - sorry for Russian, but there is an example. The example contains a hyperlink "To an example you can download" in the bottom article after the sample code. Learn Russian :)

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