Method setWindowGroupIds

src/SFML/Window/Unix/WindowImplX11.cpp:2306–2352

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void WindowImplX11::setWindowGroupIds()
{
    using namespace WindowImplX11Impl;

    // Nothing to do if there are no windows left
    if (allWindows.empty())
        return;

    const auto display = sf::priv::openDisplay();

    // Set window group IDs for all windows
    // Setting the window group ID lets the window manager
    // know that all our windows belong to the same group
    // The window manager can use this information to treat
    // multiple windows as a group instead of individual windows
    // What effect this has in practice depends on how each window
    // manager is implemented and whether it cares about groups
    // We use the the first window in our list as the group leader
    const auto groupLeader = allWindows.front()->m_window;

    // Prepare the atom necessary to set the WM_CLIENT_LEADER property
    static const auto wmClientLeaderAtom = getAtom("WM_CLIENT_LEADER");

    for (const auto* window : allWindows)
    {
        // Update the WM_HINTS group ID
        auto hints = X11Ptr<XWMHints>(XGetWMHints(display.get(), window->m_window));
        if (hints == nullptr)
            hints.reset(XAllocWMHints());
        hints->flags |= WindowGroupHint;
        hints->window_group = groupLeader;
        XSetWMHints(display.get(), window->m_window, hints.get());

        // Set the WM_CLIENT_LEADER property
        if (wmClientLeaderAtom)
        {
            XChangeProperty(display.get(),
                            window->m_window,
                            wmClientLeaderAtom,
                            XA_WINDOW,
                            32,
                            PropModeReplace,
                            reinterpret_cast<const unsigned char*>(&groupLeader),
                            1);
        }
    }
}

} // namespace sf::priv