Method DockNodeUpdateFlagsAndCollapse

imgui_tiny_app/imgui/imgui.cpp:18843–18914

- Remove inactive windows/nodes. - Update visibility flag.

// - Remove inactive windows/nodes.
// - Update visibility flag.
static void ImGui::DockNodeUpdateFlagsAndCollapse(ImGuiDockNode* node)
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(node->ParentNode == NULL || node->ParentNode->ChildNodes[0] == node || node->ParentNode->ChildNodes[1] == node);

    // Inherit most flags
    if (node->ParentNode)
        node->SharedFlags = node->ParentNode->SharedFlags & ImGuiDockNodeFlags_SharedFlagsInheritMask_;

    // Recurse into children
    // There is the possibility that one of our child becoming empty will delete itself and moving its sibling contents into 'node'.
    // If 'node->ChildNode[0]' delete itself, then 'node->ChildNode[1]->Windows' will be moved into 'node'
    // If 'node->ChildNode[1]' delete itself, then 'node->ChildNode[0]->Windows' will be moved into 'node' and the "remove inactive windows" loop will have run twice on those windows (harmless)
    node->HasCentralNodeChild = false;
    if (node->ChildNodes[0])
        DockNodeUpdateFlagsAndCollapse(node->ChildNodes[0]);
    if (node->ChildNodes[1])
        DockNodeUpdateFlagsAndCollapse(node->ChildNodes[1]);

    // Remove inactive windows, collapse nodes
    // Merge node flags overrides stored in windows
    node->LocalFlagsInWindows = ImGuiDockNodeFlags_None;
    for (int window_n = 0; window_n < node->Windows.Size; window_n++)
    {
        ImGuiWindow* window = node->Windows[window_n];
        IM_ASSERT(window->DockNode == node);

        bool node_was_active = (node->LastFrameActive + 1 == g.FrameCount);
        bool remove = false;
        remove |= node_was_active && (window->WasActive == false); // Can't use 'window->LastFrameActive + 1 < g.FrameCount'. (see #9151)
        remove |= node_was_active && (node->WantCloseAll || node->WantCloseTabId == window->TabId) && window->HasCloseButton && !(window->Flags & ImGuiWindowFlags_UnsavedDocument);  // Submit all _expected_ closure from last frame
        remove |= (window->DockTabWantClose);
        if (remove)
        {
            window->DockTabWantClose = false;
            if (node->Windows.Size == 1 && !node->IsCentralNode())
            {
                DockNodeHideHostWindow(node);
                node->State = ImGuiDockNodeState_HostWindowHiddenBecauseSingleWindow;
                DockNodeRemoveWindow(node, window, node->ID); // Will delete the node so it'll be invalid on return
                return;
            }
            DockNodeRemoveWindow(node, window, node->ID);
            window_n--;
            continue;
        }

        // FIXME-DOCKING: Missing policies for conflict resolution, hence the "Experimental" tag on this.
        //node->LocalFlagsInWindow &= ~window->WindowClass.DockNodeFlagsOverrideClear;
        node->LocalFlagsInWindows |= window->WindowClass.DockNodeFlagsOverrideSet;
    }
    node->UpdateMergedFlags();

    // Auto-hide tab bar option
    ImGuiDockNodeFlags node_flags = node->MergedFlags;
    if (node->WantHiddenTabBarUpdate && node->Windows.Size == 1 && (node_flags & ImGuiDockNodeFlags_AutoHideTabBar) && !node->IsHiddenTabBar())
        node->WantHiddenTabBarToggle = true;
    node->WantHiddenTabBarUpdate = false;