Docking: Preserve existing docked nodes when setting the ImGuiDockNodeFlags_NoDockingInCentralNode flag. (#2423, #2109)

imgui.cpp

@@ -12873,7 +12873,7 @@ void ImGui::SetWindowDock(ImGuiWindow* window, ImGuiID dock_id, ImGuiCond cond)
 
 // 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.
-void ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags dockspace_flags, const ImGuiWindowClass* window_class)
+void ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags flags, const ImGuiWindowClass* window_class)
 {
     ImGuiContext* ctx = GImGui;
     ImGuiContext& g = *ctx;
@@ -12881,18 +12881,19 @@ void ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags doc
     if (!(g.IO.ConfigFlags & ImGuiConfigFlags_DockingEnable))
         return;
 
+    IM_ASSERT((flags & ImGuiDockNodeFlags_Dockspace) == 0);
     ImGuiDockNode* node = DockContextFindNodeByID(ctx, id);
     if (!node)
     {
         node = DockContextAddNode(ctx, id);
         node->IsCentralNode = true;
     }
-    node->Flags = dockspace_flags;
+    node->Flags = 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 && !(dockspace_flags & ImGuiDockNodeFlags_KeepAliveOnly))
+    if (node->LastFrameActive == g.FrameCount && !(flags & ImGuiDockNodeFlags_KeepAliveOnly))
     {
         IM_ASSERT(node->IsDockSpace() == false && "Cannot call DockSpace() twice a frame with the same ID");
         node->Flags |= ImGuiDockNodeFlags_Dockspace;
@@ -12901,7 +12902,7 @@ void ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags doc
     node->Flags |= ImGuiDockNodeFlags_Dockspace;
 
     // Keep alive mode, this is allow windows docked into this node so stay docked even if they are not visible
-    if (dockspace_flags & ImGuiDockNodeFlags_KeepAliveOnly)
+    if (flags & ImGuiDockNodeFlags_KeepAliveOnly)
     {
         node->LastFrameAlive = g.FrameCount;
         return;
@@ -13421,12 +13422,14 @@ void ImGui::BeginDocked(ImGuiWindow* window, bool* p_open)
         g.NextWindowData.PosUndock = false;
     }
 
+#if 0
     // Undock if the ImGuiDockNodeFlags_NoDockingInCentralNode got set
     if (node->IsCentralNode && (node->Flags & ImGuiDockNodeFlags_NoDockingInCentralNode))
     {
         DockContextProcessUndockWindow(ctx, window);
         return;
     }
+#endif
 
     // Undock if our dockspace node disappeared
     // Note how we are testing for LastFrameAlive and NOT LastFrameActive. A DockSpace node can be maintained alive while being inactive with ImGuiDockNodeFlags_KeepAliveOnly.

imgui.h

@@ -594,7 +594,7 @@ namespace ImGui
     // To dock windows: hold SHIFT anywhere while moving windows (if io.ConfigDockingWithShift == true) or drag windows from their title bar (if io.ConfigDockingWithShift = false)
     // Use DockSpace() to create an explicit dock node _within_ an existing window. See Docking demo for details.
     IMGUI_API void          DockSpace(ImGuiID id, const ImVec2& size = ImVec2(0, 0), ImGuiDockNodeFlags flags = 0, const ImGuiWindowClass* window_class = NULL);
-    IMGUI_API ImGuiID       DockSpaceOverViewport(ImGuiViewport* viewport = NULL, ImGuiDockNodeFlags dockspace_flags = 0, const ImGuiWindowClass* window_class = NULL);
+    IMGUI_API ImGuiID       DockSpaceOverViewport(ImGuiViewport* viewport = NULL, ImGuiDockNodeFlags flags = 0, const ImGuiWindowClass* window_class = NULL);
     IMGUI_API void          SetNextWindowDockID(ImGuiID dock_id, ImGuiCond cond = 0);           // set next window dock id (FIXME-DOCK)
     IMGUI_API void          SetNextWindowClass(const ImGuiWindowClass* window_class);           // set next window class (rare/advanced uses: provide hints to the platform back-end via altered viewport flags and parent/child info)
     IMGUI_API ImGuiID       GetWindowDockID();
@@ -882,9 +882,9 @@ enum ImGuiDockNodeFlags_
 {
     ImGuiDockNodeFlags_None                         = 0,
     ImGuiDockNodeFlags_KeepAliveOnly                = 1 << 0,   // Don't display the dockspace node but keep it alive. Windows docked into this dockspace node won't be undocked.
-    ImGuiDockNodeFlags_NoSplit                      = 1 << 1,   // Disable splitting the node into smaller nodes. Useful e.g. when embedding dockspaces into a main root one (the root one may have splitting disabled to reduce confusion)
+    ImGuiDockNodeFlags_NoSplit                      = 1 << 1,   // Disable splitting the node into smaller nodes. Useful e.g. when embedding dockspaces into a main root one (the root one may have splitting disabled to reduce confusion). Note: when turned off, existing splits will be preserved.
     //ImGuiDockNodeFlags_NoCentralNode              = 1 << 2,   // Disable Central Node (the node which can stay empty)
-    ImGuiDockNodeFlags_NoDockingInCentralNode       = 1 << 3,   // Disable docking inside the Central Node, which will be always kept empty.
+    ImGuiDockNodeFlags_NoDockingInCentralNode       = 1 << 3,   // Disable docking inside the Central Node, which will be always kept empty. Note: when turned off, existing docked nodes will be preserved.
     //ImGuiDockNodeFlags_NoLayoutChanges            = 1 << 4,   // Disable adding/removing nodes interactively. Useful with programatically setup dockspaces.
     ImGuiDockNodeFlags_NoResize                     = 1 << 5,   // Disable resizing child nodes using the splitter/separators. Useful with programatically setup dockspaces. 
     ImGuiDockNodeFlags_PassthruDockspace            = 1 << 6,   // Enable passthru dockspace: 1) DockSpace() will render a ImGuiCol_WindowBg background covering everything excepted the Central Node when empty. Meaning the host window should probably use SetNextWindowBgAlpha(0.0f) prior to Begin() when using this. 2) When Central Node is empty: let inputs pass-through + won't display a DockingEmptyBg background.