Docking: Made spacing between dock nodes not a dropping gap.

docs/CHANGELOG.txt

@@ -262,6 +262,8 @@ Docking+Viewports Branch:
 - Docking: Fixed regression introduced in v1.87 when docked window content not rendered
   while switching between with CTRL+Tab. [@rokups]
 - Docking: Fixed amending into an existing tab bar from rendering invisible items. (#5515)
+- Docking: Made spacing between dock nodes not a dropping gap. When hovering it only
+  outer-docking drop markers are visible.
 - Docking+Viewports: Fixed undocking window node causing parent viewports to become unresponsive
   in certain situation (e.g. hidden tab bar). (#5503) [@rokups]
 - Backends: SDL: Fixed building backend under non-OSX Apple targets (e.g. iPhone). (#5665)

imgui.cpp

@@ -16600,7 +16600,8 @@ ImGuiDockNode* ImGui::DockNodeTreeFindVisibleNodeByPos(ImGuiDockNode* node, ImVe
     if (ImGuiDockNode* hovered_node = DockNodeTreeFindVisibleNodeByPos(node->ChildNodes[1], pos))
         return hovered_node;
 
-    return NULL;
+    // This means we are hovering over the splitter/spacing of a parent node
+    return node;
 }
 
 //-----------------------------------------------------------------------------
@@ -17469,17 +17470,19 @@ void ImGui::BeginDockableDragDropTarget(ImGuiWindow* window)
         const bool do_preview = payload->IsPreview() || payload->IsDelivery();
         if (do_preview && (node != NULL || dock_into_floating_window))
         {
+            // If we have a non-leaf node it means we are hovering the border of a parent node, in which case only outer markers will appear.
             ImGuiDockPreviewData split_inner;
             ImGuiDockPreviewData split_outer;
             ImGuiDockPreviewData* split_data = &split_inner;
-            if (node && (node->ParentNode || node->IsCentralNode()))
+            if (node && (node->ParentNode || node->IsCentralNode() || !node->IsLeafNode()))
                 if (ImGuiDockNode* root_node = DockNodeGetRootNode(node))
                 {
                     DockNodePreviewDockSetup(window, root_node, payload_window, NULL, &split_outer, is_explicit_target, true);
                     if (split_outer.IsSplitDirExplicit)
                         split_data = &split_outer;
                 }
-            DockNodePreviewDockSetup(window, node, payload_window, NULL, &split_inner, is_explicit_target, false);
+            if (!node || node->IsLeafNode())
+                DockNodePreviewDockSetup(window, node, payload_window, NULL, &split_inner, is_explicit_target, false);
             if (split_data == &split_outer)
                 split_inner.IsDropAllowed = false;
 
@@ -18614,7 +18617,7 @@ void ImGui::DebugNodeDockNode(ImGuiDockNode* node, const char* label)
     if (node->Windows.Size > 0)
         open = TreeNodeEx((void*)(intptr_t)node->ID, tree_node_flags, "%s 0x%04X%s: %d windows (vis: '%s')", label, node->ID, node->IsVisible ? "" : " (hidden)", node->Windows.Size, node->VisibleWindow ? node->VisibleWindow->Name : "NULL");
     else
-        open = TreeNodeEx((void*)(intptr_t)node->ID, tree_node_flags, "%s 0x%04X%s: %s split (vis: '%s')", label, node->ID, node->IsVisible ? "" : " (hidden)", (node->SplitAxis == ImGuiAxis_X) ? "horizontal" : (node->SplitAxis == ImGuiAxis_Y) ? "vertical" : "n/a", node->VisibleWindow ? node->VisibleWindow->Name : "NULL");
+        open = TreeNodeEx((void*)(intptr_t)node->ID, tree_node_flags, "%s 0x%04X%s: %s (vis: '%s')", label, node->ID, node->IsVisible ? "" : " (hidden)", (node->SplitAxis == ImGuiAxis_X) ? "horizontal split" : (node->SplitAxis == ImGuiAxis_Y) ? "vertical split" : "empty", node->VisibleWindow ? node->VisibleWindow->Name : "NULL");
     if (!is_alive) { PopStyleColor(); }
     if (is_active && IsItemHovered())
         if (ImGuiWindow* window = node->HostWindow ? node->HostWindow : node->VisibleWindow)