Docking: added io.ConfigDockingNoDockingOver to prevent merging windows into a same tab-bar.

docs/CHANGELOG.txt

@@ -164,6 +164,8 @@ Docking+Viewports Branch:
   by docked windows. (#8983, #9064)
 - Docking: fixed crash loading certain form of invalid .ini settings (e.g. nodes 
   referring to a missing parent, duplicate nodes id). (#9070)
+- Docking: added io.ConfigDockingNoDockingOver helper config flag to prevent
+  merging windows into a same tab-bar.
 - Examples:
   - SDL2+DX11, SDL3+DX11, Win32+DX10, Win32+DX11: fixed one resource leak
     from the use of MakeWindowAssociation() in 1.92.4. (#9010, #4350) [@o-3-o]

imgui.cpp

@@ -1590,6 +1590,7 @@ ImGuiIO::ImGuiIO()
 
     // Docking options (when ImGuiConfigFlags_DockingEnable is set)
     ConfigDockingNoSplit = false;
+    ConfigDockingNoDockingOver = false;
     ConfigDockingWithShift = false;
     ConfigDockingAlwaysTabBar = false;
     ConfigDockingTransparentPayload = false;
@@ -19653,6 +19654,8 @@ static void ImGui::DockNodePreviewDockSetup(ImGuiWindow* host_window, ImGuiDockN
     data->IsCenterAvailable = true;
     if (is_outer_docking)
         data->IsCenterAvailable = false;
+    else if (g.IO.ConfigDockingNoDockingOver)
+        data->IsCenterAvailable = false;
     else if (dst_node_flags & ImGuiDockNodeFlags_NoDockingOverMe)
         data->IsCenterAvailable = false;
     else if (host_node && (dst_node_flags & ImGuiDockNodeFlags_NoDockingOverCentralNode) && host_node->IsCentralNode())

imgui.h

@@ -2493,6 +2493,7 @@ struct ImGuiIO
 
     // Docking options (when ImGuiConfigFlags_DockingEnable is set)
     bool        ConfigDockingNoSplit;           // = false          // Simplified docking mode: disable window splitting, so docking is limited to merging multiple windows together into tab-bars.
+    bool        ConfigDockingNoDockingOver;     // = false          // Simplified docking mode: disable window merging into a same tab-bar, so docking is limited to splitting windows.
     bool        ConfigDockingWithShift;         // = false          // Enable docking with holding Shift key (reduce visual noise, allows dropping in wider space)
     bool        ConfigDockingAlwaysTabBar;      // = false          // [BETA] [FIXME: This currently creates regression with auto-sizing and general overhead] Make every single floating window display within a docking node.
     bool        ConfigDockingTransparentPayload;// = false          // [BETA] Make window or viewport transparent when docking and only display docking boxes on the target viewport. Useful if rendering of multiple viewport cannot be synced. Best used with ConfigViewportsNoAutoMerge.

imgui_demo.cpp

@@ -533,6 +533,8 @@ void ImGui::ShowDemoWindow(bool* p_open)
                 ImGui::Indent();
                 ImGui::Checkbox("io.ConfigDockingNoSplit", &io.ConfigDockingNoSplit);
                 ImGui::SameLine(); HelpMarker("Simplified docking mode: disable window splitting, so docking is limited to merging multiple windows together into tab-bars.");
+                ImGui::Checkbox("io.ConfigDockingNoDockingOver", &io.ConfigDockingNoDockingOver);
+                ImGui::SameLine(); HelpMarker("Simplified docking mode: disable window merging into a same tab-bar, so docking is limited to splitting windows.");
                 ImGui::Checkbox("io.ConfigDockingWithShift", &io.ConfigDockingWithShift);
                 ImGui::SameLine(); HelpMarker("Enable docking when holding Shift only (allow to drop in wider space, reduce visual noise)");
                 ImGui::Checkbox("io.ConfigDockingAlwaysTabBar", &io.ConfigDockingAlwaysTabBar);
@@ -8313,6 +8315,7 @@ void ImGui::ShowAboutWindow(bool* p_open)
         if (io.ConfigViewportsNoDecoration)                             ImGui::Text("io.ConfigViewportsNoDecoration");
         if (io.ConfigViewportsNoDefaultParent)                          ImGui::Text("io.ConfigViewportsNoDefaultParent");
         if (io.ConfigDockingNoSplit)                                    ImGui::Text("io.ConfigDockingNoSplit");
+        if (io.ConfigDockingNoDockingOver)                              ImGui::Text("io.ConfigDockingNoDockingOver");
         if (io.ConfigDockingWithShift)                                  ImGui::Text("io.ConfigDockingWithShift");
         if (io.ConfigDockingAlwaysTabBar)                               ImGui::Text("io.ConfigDockingAlwaysTabBar");
         if (io.ConfigDockingTransparentPayload)                         ImGui::Text("io.ConfigDockingTransparentPayload");