Method DockSpace

extern/imgui/imgui.cpp:17150–17245

Create an explicit dockspace node within an existing window. Also expose dock node flags and creates a CentralNode by default. The Central Node is always displayed even when empty and shrink/extend according to the requested size of its neighbors. DockSpace() needs to be submitted _before_ any window they can host. If you use a dockspace, submit it early in your app.

// The Central Node is always displayed even when empty and shrink/extend according to the requested size of its neighbors.
// DockSpace() needs to be submitted _before_ any window they can host. If you use a dockspace, submit it early in your app.
ImGuiID ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags flags, const ImGuiWindowClass* window_class)
{
    ImGuiContext* ctx = GImGui;
    ImGuiContext& g = *ctx;
    ImGuiWindow* window = GetCurrentWindow();
    if (!(g.IO.ConfigFlags & ImGuiConfigFlags_DockingEnable))
        return 0;

    // Early out if parent window is hidden/collapsed
    // This is faster but also DockNodeUpdateTabBar() relies on TabBarLayout() running (which won't if SkipItems=true) to set NextSelectedTabId = 0). See #2960.
    // If for whichever reason this is causing problem we would need to ensure that DockNodeUpdateTabBar() ends up clearing NextSelectedTabId even if SkipItems=true.
    if (window->SkipItems)
        flags |= ImGuiDockNodeFlags_KeepAliveOnly;

    IM_ASSERT((flags & ImGuiDockNodeFlags_DockSpace) == 0);
    IM_ASSERT(id != 0);
    ImGuiDockNode* node = DockContextFindNodeByID(ctx, id);
    if (!node)
    {
        IMGUI_DEBUG_LOG_DOCKING("[docking] DockSpace: dockspace node 0x%08X created\n", id);
        node = DockContextAddNode(ctx, id);
        node->SetLocalFlags(ImGuiDockNodeFlags_CentralNode);
    }
    if (window_class && window_class->ClassId != node->WindowClass.ClassId)
        IMGUI_DEBUG_LOG_DOCKING("[docking] DockSpace: dockspace node 0x%08X: setup WindowClass 0x%08X -> 0x%08X\n", id, node->WindowClass.ClassId, window_class->ClassId);
    node->SharedFlags = flags;
    node->WindowClass = window_class ? *window_class : ImGuiWindowClass();

    // When a DockSpace transitioned form implicit to explicit this may be called a second time
    // It is possible that the node has already been claimed by a docked window which appeared before the DockSpace() node, so we overwrite IsDockSpace again.
    if (node->LastFrameActive == g.FrameCount && !(flags & ImGuiDockNodeFlags_KeepAliveOnly))
    {
        IM_ASSERT(node->IsDockSpace() == false && "Cannot call DockSpace() twice a frame with the same ID");
        node->SetLocalFlags(node->LocalFlags | ImGuiDockNodeFlags_DockSpace);
        return id;
    }
    node->SetLocalFlags(node->LocalFlags | ImGuiDockNodeFlags_DockSpace);

    // Keep alive mode, this is allow windows docked into this node so stay docked even if they are not visible
    if (flags & ImGuiDockNodeFlags_KeepAliveOnly)
    {
        node->LastFrameAlive = g.FrameCount;
        return id;
    }

    const ImVec2 content_avail = GetContentRegionAvail();
    ImVec2 size = ImFloor(size_arg);
    if (size.x <= 0.0f)
        size.x = ImMax(content_avail.x + size.x, 4.0f); // Arbitrary minimum child size (0.0f causing too much issues)
    if (size.y <= 0.0f)
        size.y = ImMax(content_avail.y + size.y, 4.0f);
    IM_ASSERT(size.x > 0.0f && size.y > 0.0f);

    node->Pos = window->DC.CursorPos;
    node->Size = node->SizeRef = size;
    SetNextWindowPos(node->Pos);
    SetNextWindowSize(node->Size);
    g.NextWindowData.PosUndock = false;