Method WindowSelectViewport

engine/3rdparty/imgui/imgui.cpp:12854–12986

FIXME-VIEWPORT: This is all super messy and ought to be clarified or rewritten.

// FIXME-VIEWPORT: This is all super messy and ought to be clarified or rewritten.
static void ImGui::WindowSelectViewport(ImGuiWindow* window)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindowFlags flags = window->Flags;
    window->ViewportAllowPlatformMonitorExtend = -1;

    // Restore main viewport if multi-viewport is not supported by the backend
    ImGuiViewportP* main_viewport = (ImGuiViewportP*)(void*)GetMainViewport();
    if (!(g.ConfigFlagsCurrFrame & ImGuiConfigFlags_ViewportsEnable))
    {
        SetWindowViewport(window, main_viewport);
        return;
    }
    window->ViewportOwned = false;

    // Appearing popups reset their viewport so they can inherit again
    if ((flags & (ImGuiWindowFlags_Popup | ImGuiWindowFlags_Tooltip)) && window->Appearing)
    {
        window->Viewport = NULL;
        window->ViewportId = 0;
    }

    if ((g.NextWindowData.Flags & ImGuiNextWindowDataFlags_HasViewport) == 0)
    {
        // By default inherit from parent window
        if (window->Viewport == NULL && window->ParentWindow && (!window->ParentWindow->IsFallbackWindow || window->ParentWindow->WasActive))
            window->Viewport = window->ParentWindow->Viewport;

        // Attempt to restore saved viewport id (= window that hasn't been activated yet), try to restore the viewport based on saved 'window->ViewportPos' restored from .ini file
        if (window->Viewport == NULL && window->ViewportId != 0)
        {
            window->Viewport = (ImGuiViewportP*)FindViewportByID(window->ViewportId);
            if (window->Viewport == NULL && window->ViewportPos.x != FLT_MAX && window->ViewportPos.y != FLT_MAX)
                window->Viewport = AddUpdateViewport(window, window->ID, window->ViewportPos, window->Size, ImGuiViewportFlags_None);
        }
    }

    bool lock_viewport = false;
    if (g.NextWindowData.Flags & ImGuiNextWindowDataFlags_HasViewport)
    {
        // Code explicitly request a viewport
        window->Viewport = (ImGuiViewportP*)FindViewportByID(g.NextWindowData.ViewportId);
        window->ViewportId = g.NextWindowData.ViewportId; // Store ID even if Viewport isn't resolved yet.
        lock_viewport = true;
    }
    else if ((flags & ImGuiWindowFlags_ChildWindow) || (flags & ImGuiWindowFlags_ChildMenu))
    {
        // Always inherit viewport from parent window
        if (window->DockNode && window->DockNode->HostWindow)
            IM_ASSERT(window->DockNode->HostWindow->Viewport == window->ParentWindow->Viewport);
        window->Viewport = window->ParentWindow->Viewport;
    }
    else if (window->DockNode && window->DockNode->HostWindow)
    {
        // This covers the "always inherit viewport from parent window" case for when a window reattach to a node that was just created mid-frame
        window->Viewport = window->DockNode->HostWindow->Viewport;
    }
    else if (flags & ImGuiWindowFlags_Tooltip)