Function AddRootWindowToDrawData

core/src/imgui/imgui.cpp:4317–4321

Layer is locked for the root window, however child windows may use a different viewport (e.g. extruding menu)

// Layer is locked for the root window, however child windows may use a different viewport (e.g. extruding menu)
static void AddRootWindowToDrawData(ImGuiWindow* window)
{
    int layer = (window->Flags & ImGuiWindowFlags_Tooltip) ? 1 : 0;
    AddWindowToDrawData(window, layer);
}

void ImDrawDataBuilder::FlattenIntoSingleLayer()
{