Method FindBlockingModal

src/external/imgui/imgui.cpp:6312–6333

When a modal popup is open, newly created windows that want focus (i.e. are not popups and do not specify ImGuiWindowFlags_NoFocusOnAppearing) should be positioned behind that modal window, unless the window was created inside the modal begin-stack. In case of multiple stacked modals newly created window honors begin stack order and does not go below its own modal parent. - WindowA // F

// - FindBlockingModal(NULL) == NULL is generally equivalent to GetTopMostPopupModal() == NULL.
//   Only difference is here we check for ->Active/WasActive but it may be unecessary.
ImGuiWindow* ImGui::FindBlockingModal(ImGuiWindow* window)
{
    ImGuiContext& g = *GImGui;
    if (g.OpenPopupStack.Size <= 0)
        return NULL;

    // Find a modal that has common parent with specified window. Specified window should be positioned behind that modal.
    for (ImGuiPopupData& popup_data : g.OpenPopupStack)
    {
        ImGuiWindow* popup_window = popup_data.Window;
        if (popup_window == NULL || !(popup_window->Flags & ImGuiWindowFlags_Modal))
            continue;
        if (!popup_window->Active && !popup_window->WasActive)      // Check WasActive, because this code may run before popup renders on current frame, also check Active to handle newly created windows.
            continue;
        if (window == NULL)                                         // FindBlockingModal(NULL) test for if FocusWindow(NULL) is naturally possible via a mouse click.
            return popup_window;
        if (IsWindowWithinBeginStackOf(window, popup_window))       // Window may be over modal
            continue;
        return popup_window;                                        // Place window right below first block modal
    }
    return NULL;
}

// Push a new Dear ImGui window to add widgets to.
// - A default window called "Debug" is automatically stacked at the beginning of every frame so you can use widgets without explicitly calling a Begin/End pair.