Docking: Added internal DockBuilderGetCentralNode(). Fixed being unable to undock whole node from dock button in DockSpace with a central node. (#2109)

imgui.cpp

@@ -10350,7 +10350,7 @@ ImGuiDockNode::ImGuiDockNode(ImGuiID id)
     SplitAxis = ImGuiAxis_None;
 
     HostWindow = VisibleWindow = NULL;
-    OnlyNodeWithWindows = NULL;
+    CentralNode = OnlyNodeWithWindows = NULL;
     LastFrameAlive = LastFrameActive = -1;
     LastFocusedNodeID = 0;
     SelectedTabID = 0;
@@ -10674,7 +10674,7 @@ static void ImGui::DockNodeUpdate(ImGuiDockNode* node)
     IM_ASSERT(node->LastFrameActive != g.FrameCount);
     node->LastFrameAlive = g.FrameCount;
 
-    ImGuiDockNode* central_node = NULL;
+    node->CentralNode = node->OnlyNodeWithWindows = NULL;
     if (node->IsRootNode())
     {
         DockNodeUpdateVisibleFlagAndInactiveChilds(node);
@@ -10682,10 +10682,10 @@ static void ImGui::DockNodeUpdate(ImGuiDockNode* node)
         // Find if there's only a single visible window in the hierarchy (in which case we need to display a regular title bar -> FIXME-DOCK: that last part is not done yet!)
         ImGuiDockNodeUpdateScanResults results;
         DockNodeUpdateScanRec(node, &results);
-        node->OnlyNodeWithWindows = (results.CountNodesWithWindows == 1 ? results.FirstNodeWithWindows : NULL);
+        node->CentralNode = results.CentralNode;
+        node->OnlyNodeWithWindows = (results.CountNodesWithWindows == 1) ? results.FirstNodeWithWindows : NULL;
         if (node->LastFocusedNodeID == 0 && results.FirstNodeWithWindows != NULL)
             node->LastFocusedNodeID = results.FirstNodeWithWindows->ID;
-        central_node = results.CentralNode;
 
         // Copy the dock family from of our window so it can be used for proper dock filtering.
         // When node has mixed windows, prioritize the family with the most constraint (CompatibleWithNeutral = false) as the reference to copy.
@@ -10825,7 +10825,8 @@ static void ImGui::DockNodeUpdate(ImGuiDockNode* node)
     }
 
     // Register a hit-test hole in the window unless we are currently dragging a window that is compatible with our dockspace
-    bool central_node_hole = node->IsRootNode() && host_window && (node->Flags & ImGuiDockNodeFlags_PassthruDockspace) != 0 && central_node != NULL && central_node->IsEmpty();
+    const ImGuiDockNode* central_node = node->CentralNode;
+    const bool central_node_hole = node->IsRootNode() && host_window && (node->Flags & ImGuiDockNodeFlags_PassthruDockspace) != 0 && central_node != NULL && central_node->IsEmpty();
     bool central_node_hole_register_hit_test_hole = central_node_hole;
     if (central_node_hole)
         if (const ImGuiPayload* payload = ImGui::GetDragDropPayload())

imgui_internal.h

@@ -769,7 +769,8 @@ struct ImGuiDockNode
 
     ImGuiWindow*            HostWindow;
     ImGuiWindow*            VisibleWindow;
-    ImGuiDockNode*          OnlyNodeWithWindows;        // [Root node only] Set when there is a single visible node within the hierarchy
+    ImGuiDockNode*          CentralNode;                // [Root node only] Pointer to central node.
+    ImGuiDockNode*          OnlyNodeWithWindows;        // [Root node only] Set when there is a single visible node within the hierarchy.
     int                     LastFrameAlive;             // Last frame number the node was updated or kept alive explicitly with DockSpace() + ImGuiDockNodeFlags_KeepAliveOnly
     int                     LastFrameActive;            // Last frame number the node was updated.
     ImGuiID                 LastFocusedNodeID;          // [Root node only] Which of our child node (any ancestor in the hierarchy) was last focused.
@@ -1505,6 +1506,7 @@ namespace ImGui
     // Docking - Builder function needs to be generally called before the DockSpace() node is submitted.
     IMGUI_API void          DockBuilderDockWindow(const char* window_name, ImGuiID node_id);
     IMGUI_API ImGuiDockNode*DockBuilderGetNode(ImGuiID node_id);                    // Warning: DO NOT HOLD ON ImGuiDockNode* pointer, will be invalided by any split/merge/remove operation.
+    inline ImGuiDockNode*   DockBuilderGetCentralNode(ImGuiID node_id)              { ImGuiDockNode* node = DockBuilderGetNode(node_id); if (!node) return NULL; return DockNodeGetRootNode(node)->CentralNode; }
     IMGUI_API void          DockBuilderAddNode(ImGuiID node_id, ImVec2 ref_size, ImGuiDockNodeFlags flags = 0);
     IMGUI_API void          DockBuilderRemoveNode(ImGuiID node_id);                 // Remove node and all its child, undock all windows
     IMGUI_API void          DockBuilderRemoveNodeDockedWindows(ImGuiID node_id, bool clear_persistent_docking_references = true);

imgui_widgets.cpp

@@ -671,6 +671,7 @@ bool ImGui::CloseButton(ImGuiID id, const ImVec2& pos, float radius)
     return pressed;
 }
 
+// The Collapse button also functions as a Dock Menu button.
 bool ImGui::CollapseButton(ImGuiID id, const ImVec2& pos, ImGuiDockNode* dock_node)
 {
     ImGuiContext& g = *GImGui;
@@ -695,7 +696,14 @@ bool ImGui::CollapseButton(ImGuiID id, const ImVec2& pos, ImGuiDockNode* dock_no
     // Switch to moving the window after mouse is moved beyond the initial drag threshold
     if (IsItemActive() && IsMouseDragging(0))
     {
-        if (dock_node != NULL && DockNodeGetRootNode(dock_node)->OnlyNodeWithWindows != dock_node)
+        bool can_extract_dock_node = false;
+        if (dock_node != NULL)
+        {
+            ImGuiDockNode* root_node = DockNodeGetRootNode(dock_node);
+            if (root_node->OnlyNodeWithWindows != dock_node || (root_node->CentralNode != NULL))
+                can_extract_dock_node = true;
+        }
+        if (can_extract_dock_node)
         {
             float threshold_base = g.FontSize;
             float threshold_x = (threshold_base * 2.2f);