Docking: Fix bug added in 71a58261 + Misc docking omments

imgui.cpp

@@ -3398,7 +3398,7 @@ void ImGui::UpdateMouseMovingWindowEndFrame()
     // (after we're done with all our widgets, so e.g. clicking on docking tab-bar which have set HoveredId already and not get us here!)
     if (g.IO.MouseClicked[0])
     {
-        ImGuiWindow* root_window = g.HoveredWindow->RootWindowDockStop;
+        ImGuiWindow* root_window = g.HoveredWindow ? g.HoveredWindow->RootWindowDockStop : NULL;
         if (root_window != NULL)
         {
             StartMouseMovingWindow(g.HoveredWindow);
@@ -13006,6 +13006,7 @@ bool ImGui::DockNodeCalcDropRectsAndTestMousePos(const ImRect& parent, ImGuiDir
 }
 
 // host_node may be NULL if the window doesn't have a DockNode already.
+// FIXME-DOCK: This is misnamed since it's also doing the filtering.
 static void ImGui::DockNodePreviewDockCalc(ImGuiWindow* host_window, ImGuiDockNode* host_node, ImGuiWindow* root_payload, ImGuiDockPreviewData* data, bool is_explicit_target, bool is_outer_docking)
 {
     ImGuiContext& g = *GImGui;
@@ -14253,7 +14254,7 @@ void ImGui::BeginDocked(ImGuiWindow* window, bool* p_open)
         return;
     }
 
-    // Position window
+    // Position/Size window
     SetNextWindowPos(node->Pos);
     SetNextWindowSize(node->Size);
     g.NextWindowData.PosUndock = false; // Cancel implicit undocking of SetNextWindowPos()
@@ -14346,7 +14347,8 @@ void ImGui::BeginDockableDragDropTarget(ImGuiWindow* window)
         const bool do_preview = payload->IsPreview() || payload->IsDelivery();
         if (do_preview && (node != NULL || allow_null_target_node))
         {
-            ImGuiDockPreviewData split_inner, split_outer;
+            ImGuiDockPreviewData split_inner;
+            ImGuiDockPreviewData split_outer;
             ImGuiDockPreviewData* split_data = &split_inner;
             if (node && (node->ParentNode || node->IsCentralNode()))
                 if (ImGuiDockNode* root_node = DockNodeGetRootNode(node))

imgui.h

@@ -1609,8 +1609,13 @@ struct ImGuiSizeCallbackData
     ImVec2  DesiredSize;    // Read-write.  Desired size, based on user's mouse position. Write to this field to restrain resizing.
 };
 
-// [BETA] Rarely used / very advanced uses only. Use with SetNextWindowClass() and DockSpace() functions.
-// Provide hints to the platform back-end via altered viewport flags (enable/disable OS decoration, OS task bar icons, etc.) and OS level parent/child relationships.
+// [ALPHA] Rarely used / very advanced uses only. Use with SetNextWindowClass() and DockSpace() functions.
+// Important: the content of this class is still highly WIP and likely to change and be refactored
+// before we stabilize Docking features. Please be mindful if using this.
+// Provide hints:
+// - To the platform back-end via altered viewport flags (enable/disable OS decoration, OS task bar icons, etc.) 
+// - To the platform back-end for OS level parent/child relationships of viewport.
+// - To the docking system for various options and filtering.
 struct ImGuiWindowClass
 {
     ImGuiID             ClassId;                    // User data. 0 = Default class (unclassed). Windows of different classes cannot be docked with each others.

imgui_internal.h

@@ -1912,6 +1912,7 @@ namespace ImGui
     IMGUI_API void          DockContextQueueUndockNode(ImGuiContext* ctx, ImGuiDockNode* node);
     IMGUI_API bool          DockContextCalcDropPosForDocking(ImGuiWindow* target, ImGuiDockNode* target_node, ImGuiWindow* payload, ImGuiDir split_dir, bool split_outer, ImVec2* out_pos);
     inline ImGuiDockNode*   DockNodeGetRootNode(ImGuiDockNode* node) { while (node->ParentNode) node = node->ParentNode; return node; }
+    inline ImGuiDockNode*   GetWindowDockNode() { ImGuiContext& g = *GImGui; return g.CurrentWindow->DockNode; }
     IMGUI_API bool          GetWindowAlwaysWantOwnTabBar(ImGuiWindow* window);
     IMGUI_API void          BeginDocked(ImGuiWindow* window, bool* p_open);
     IMGUI_API void          BeginDockableDragDropSource(ImGuiWindow* window);