Docking: Removed seemingly unnecessary test in TabItemEx() for undocking tab leading to window move. Added ImGuiDockNode::IsFloatingNode() helper to clarify code intent in various places.

imgui.cpp

@@ -11216,7 +11216,7 @@ void ImGui::DockContextUpdateDocking(ImGuiContext* ctx)
     // We can have NULL pointers when we delete nodes, but because ID are recycled this should amortize nicely (and our node count will never be very high)
     for (int n = 0; n < dc->Nodes.Data.Size; n++)
         if (ImGuiDockNode* node = (ImGuiDockNode*)dc->Nodes.Data[n].val_p)
-            if (node->IsRootNode() && !node->IsDockSpace())
+            if (node->IsFloatingNode())
                 DockNodeUpdate(node);
 }
 
@@ -11702,7 +11702,7 @@ static void ImGui::DockNodeAddWindow(ImGuiDockNode* node, ImGuiWindow* window, b
 
     // When reactivating a node with one or two loose window, the window pos/size/viewport are authoritative over the node storage.
     // In particular it is important we init the viewport from the first window so we don't create two viewports and drop one.
-    if (node->HostWindow == NULL && !node->IsDockSpace() && node->IsRootNode())
+    if (node->HostWindow == NULL && node->IsFloatingNode())
     {
         if (node->AuthorityForPos == ImGuiDataAuthority_Auto)
             node->AuthorityForPos = ImGuiDataAuthority_Window;
@@ -12026,7 +12026,7 @@ static void ImGui::DockNodeUpdate(ImGuiDockNode* node)
         DockNodeRemoveTabBar(node);
 
     // Early out for hidden root dock nodes (when all DockId references are in inactive windows, or there is only 1 floating window holding on the DockId)
-    if (node->Windows.Size <= 1 && node->IsRootNode() && node->IsLeafNode() && !node->IsDockSpace() && !g.IO.ConfigDockingTabBarOnSingleWindows)
+    if (node->Windows.Size <= 1 && node->IsFloatingNode() && node->IsLeafNode() && !g.IO.ConfigDockingTabBarOnSingleWindows)
     {
         if (node->Windows.Size == 1)
         {
@@ -13219,6 +13219,7 @@ ImGuiDockNode* ImGui::DockNodeTreeFindNodeByPos(ImGuiDockNode* node, ImVec2 pos)
 // Docking: Public Functions (SetWindowDock, DockSpace, DockSpaceOverViewport)
 //-----------------------------------------------------------------------------
 
+// [Internal] Called via SetNextWindowDockID()
 void ImGui::SetWindowDock(ImGuiWindow* window, ImGuiID dock_id, ImGuiCond cond)
 {
     // Test condition (NB: bit 0 is always true) and clear flags for next time
@@ -14156,7 +14157,7 @@ static void ImGui::DockSettingsHandler_WriteAll(ImGuiContext* ctx, ImGuiSettings
         if (ImGuiDockNode* node = DockContextFindNodeByID(ctx, node_settings->ID))
         {
             buf->appendf("%*s", ImMax(2, (line_start_pos + 92) - buf->size()), "");        // Align everything
-            if (node->IsDockSpace && node->HostWindow && node->HostWindow->ParentWindow)
+            if (node->IsDockSpace() && node->HostWindow && node->HostWindow->ParentWindow)
                 buf->appendf(" ; in '%s'", node->HostWindow->ParentWindow->Name);
             int contains_window = 0;
             for (int window_n = 0; window_n < ctx->SettingsWindows.Size; window_n++)

imgui.h

@@ -1612,7 +1612,7 @@ struct ImGuiWindowClass
     ImGuiID             ParentViewportId;           // Hint for the platform back-end. If non-zero, the platform back-end can create a parent<>child relationship between the platform windows. Not conforming back-ends are free to e.g. parent every viewport to the main viewport or not.
     ImGuiViewportFlags  ViewportFlagsOverrideMask;  // Viewport flags to override when a window of this class owns a viewport. This allows you to enforce OS decoration or task bar icon, override the defaults on a per-window basis.
     ImGuiViewportFlags  ViewportFlagsOverrideValue; // Viewport flags values to override when a window of this class owns a viewport.
-    bool                DockingAllowUnclassed;      // true = can be docked/merged with an unclassed window
+    bool                DockingAllowUnclassed;      // Set to true to allow windows of this class to be docked/merged with an unclassed window.
 
     ImGuiWindowClass()  { ClassId = 0; ParentViewportId = 0; ViewportFlagsOverrideMask = ViewportFlagsOverrideValue = 0x00; DockingAllowUnclassed = true; }
 };

imgui_internal.h

@@ -963,6 +963,7 @@ struct ImGuiDockNode
     ~ImGuiDockNode();
     bool                    IsRootNode() const      { return ParentNode == NULL; }
     bool                    IsDockSpace() const     { return (LocalFlags & ImGuiDockNodeFlags_DockSpace) != 0; }
+    bool                    IsFloatingNode() const  { return ParentNode == NULL && (LocalFlags & ImGuiDockNodeFlags_DockSpace) == 0; }
     bool                    IsCentralNode() const   { return (LocalFlags & ImGuiDockNodeFlags_CentralNode) != 0; }
     bool                    IsHiddenTabBar() const  { return (LocalFlags & ImGuiDockNodeFlags_HiddenTabBar) != 0; } // Hidden tab bar can be shown back by clicking the small triangle
     bool                    IsNoTabBar() const      { return (LocalFlags & ImGuiDockNodeFlags_NoTabBar) != 0; }     // Never show a tab bar

imgui_widgets.cpp

@@ -6979,10 +6979,8 @@ bool    ImGui::TabItemEx(ImGuiTabBar* tab_bar, const char* label, bool* p_open,
         SetItemAllowOverlap();
 
     // Drag and drop a single floating window node moves it
-    // FIXME-DOCK: In theory we shouldn't test for the ConfigDockingNodifySingleWindows flag here.
-    // When our single window node and OnlyNodeWithWindows are working properly we may remove this check here.
     ImGuiDockNode* node = docked_window ? docked_window->DockNode : NULL;
-    const bool single_floating_window_node = node && node->IsRootNode() && !node->IsDockSpace() && node->Windows.Size == 1 && g.IO.ConfigDockingTabBarOnSingleWindows;
+    const bool single_floating_window_node = node && node->IsFloatingNode() && (node->Windows.Size == 1);
     if (held && single_floating_window_node && IsMouseDragging(0, 0.0f))
     {
         // Move