Docking: Revised undocking logic to reduce accidental whole-node undocking:

Amend bb2aa5e77.
Revert to normal threshold in StartMouseMovingWindowOrNode().
Added tooltip when hovering the collapse/window menu button.

docs/CHANGELOG.txt

@@ -157,6 +157,14 @@ Docking+Viewports Branch:
 - Viewports: Fixed window inner clipping rectangle off by one when window is located on a monitor
   with negative coordinates. While it is expected that other small issues with arise from this
   situation, at the moment we are fixing the most noticeable one. (#6861, #2884) [@Vuhdo, @alektron]
+- Docking: revised undocking to reduce accidental whole-node undocking:
+  - cannot undock a whole node by dragging from empty space in tab-bar.
+  - can undock whole node by dragging from window/collapse menu button.
+  - can undock single window by dragging from its tab.
+  - can still move (but not undock) whole node or whole hierarchy when node is part of a
+    floating hierarchy.
+  - added tooltip when hovering the collapse/window menu button, to faciliate understanding
+    that whole dock node may be undocked or grabbed from here.
 - Docking: Fixed an issue leading to incorrect restoration of selected tab in dock nodes that
   don't carry the currently focused window. (#2304)
 - Docking: added ImGuiDockNodeFlags_NoUndocking. (#2999, #6823, #6780, #3492)

imgui.cpp

@@ -3657,7 +3657,8 @@ static const ImGuiLocEntry GLocalizationEntriesEnUS[] =
     { ImGuiLocKey_WindowingPopup,       "(Popup)"                               },
     { ImGuiLocKey_WindowingUntitled,    "(Untitled)"                            },
     { ImGuiLocKey_DockingHideTabBar,    "Hide tab bar###HideTabBar"             },
-    { ImGuiLocKey_DockingHoldShiftToDock, "Hold SHIFT to enable Docking window."},
+    { ImGuiLocKey_DockingHoldShiftToDock,       "Hold SHIFT to enable Docking window."  },
+    { ImGuiLocKey_DockingDragToUndockOrMoveNode,"Click and drag to move or undock whole node."    },
 };
 
 void ImGui::Initialize()
@@ -4489,26 +4490,23 @@ void ImGui::StartMouseMovingWindow(ImGuiWindow* window)
         g.MovingWindow = window;
 }
 
-// We use 'undock_floating_node == false' when dragging from title bar to allow moving groups of floating nodes without undocking them.
-// - undock_floating_node == true: when dragging from a floating node within a hierarchy, always undock the node.
-// - undock_floating_node == false: when dragging from a floating node within a hierarchy, move root window.
-void ImGui::StartMouseMovingWindowOrNode(ImGuiWindow* window, ImGuiDockNode* node, bool undock_floating_node)
+// We use 'undock == false' when dragging from title bar to allow moving groups of floating nodes without undocking them.
+void ImGui::StartMouseMovingWindowOrNode(ImGuiWindow* window, ImGuiDockNode* node, bool undock)
 {
     ImGuiContext& g = *GImGui;
     bool can_undock_node = false;
-    if (node != NULL && node->VisibleWindow && (node->VisibleWindow->Flags & ImGuiWindowFlags_NoMove) == 0 && (node->MergedFlags & ImGuiDockNodeFlags_NoUndocking) == 0)
+    if (undock && node != NULL && node->VisibleWindow && (node->VisibleWindow->Flags & ImGuiWindowFlags_NoMove) == 0 && (node->MergedFlags & ImGuiDockNodeFlags_NoUndocking) == 0)
     {
         // Can undock if:
-        // - part of a floating node hierarchy with more than one visible node (if only one is visible, we'll just move the whole hierarchy)
-        // - part of a dockspace node hierarchy (trivia: undocking from a fixed/central node will create a new node and copy windows)
+        // - part of a hierarchy with more than one visible node (if only one is visible, we'll just move the root window)
+        // - part of a dockspace node hierarchy: so we can undock the last single visible node too (trivia: undocking from a fixed/central node will create a new node and copy windows)
         ImGuiDockNode* root_node = DockNodeGetRootNode(node);
         if (root_node->OnlyNodeWithWindows != node || root_node->CentralNode != NULL)   // -V1051 PVS-Studio thinks node should be root_node and is wrong about that.
-            if (undock_floating_node || root_node->IsDockSpace())
-                can_undock_node = true;
+            can_undock_node = true;
     }
 
     const bool clicked = IsMouseClicked(0);
-    const bool dragging = IsMouseDragging(0, g.IO.MouseDragThreshold * 1.70f);
+    const bool dragging = IsMouseDragging(0);
     if (can_undock_node && dragging)
         DockContextQueueUndockNode(&g, node); // Will lead to DockNodeStartMouseMovingWindow() -> StartMouseMovingWindow() being called next frame
     else if (!can_undock_node && (clicked || dragging) && g.MovingWindow != window)
@@ -6445,7 +6443,7 @@ void ImGui::RenderWindowDecorations(ImGuiWindow* window, const ImRect& title_bar
             if (ButtonBehavior(r, unhide_id, &hovered, &held, ImGuiButtonFlags_FlattenChildren))
                 node->WantHiddenTabBarToggle = true;
             else if (held && IsMouseDragging(0))
-                StartMouseMovingWindowOrNode(window, node, true);
+                StartMouseMovingWindowOrNode(window, node, true); // Undock from tab-bar triangle = same as window/collapse menu button
 
             // FIXME-DOCK: Ideally we'd use ImGuiCol_TitleBgActive/ImGuiCol_TitleBg here, but neither is guaranteed to be visible enough at this sort of size..
             ImU32 col = GetColorU32(((held && hovered) || (node->IsFocused && !hovered)) ? ImGuiCol_ButtonActive : hovered ? ImGuiCol_ButtonHovered : ImGuiCol_Button);
@@ -16887,6 +16885,8 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
             OpenPopup("#WindowMenu");
         if (IsItemActive())
             focus_tab_id = tab_bar->SelectedTabId;
+        if (IsItemHovered(ImGuiHoveredFlags_ForTooltip | ImGuiHoveredFlags_DelayNormal) && g.HoveredIdTimer > 0.5f)
+            SetTooltip("%s", LocalizeGetMsg(ImGuiLocKey_DockingDragToUndockOrMoveNode));
     }
 
     // If multiple tabs are appearing on the same frame, sort them based on their persistent DockOrder value
@@ -17015,7 +17015,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
     ImGuiID title_bar_id = host_window->GetID("#TITLEBAR");
     if (g.HoveredId == 0 || g.HoveredId == title_bar_id || g.ActiveId == title_bar_id)
     {
-        // AllowItem mode required for appending into dock node tab bar,
+        // AllowOverlap mode required for appending into dock node tab bar,
         // otherwise dragging window will steal HoveredId and amended tabs cannot get them.
         bool held;
         KeepAliveID(title_bar_id);
@@ -17031,7 +17031,7 @@ static void ImGui::DockNodeUpdateTabBar(ImGuiDockNode* node, ImGuiWindow* host_w
 
             // Forward moving request to selected window
             if (ImGuiTabItem* tab = TabBarFindTabByID(tab_bar, tab_bar->SelectedTabId))
-                StartMouseMovingWindowOrNode(tab->Window ? tab->Window : node->HostWindow, node, false);
+                StartMouseMovingWindowOrNode(tab->Window ? tab->Window : node->HostWindow, node, false); // Undock from tab bar empty space
         }
     }
 

imgui_internal.h

@@ -1929,6 +1929,7 @@ enum ImGuiLocKey : int
     ImGuiLocKey_WindowingUntitled,
     ImGuiLocKey_DockingHideTabBar,
     ImGuiLocKey_DockingHoldShiftToDock,
+    ImGuiLocKey_DockingDragToUndockOrMoveNode,
     ImGuiLocKey_COUNT
 };
 
@@ -3162,7 +3163,7 @@ namespace ImGui
     IMGUI_API void          UpdateInputEvents(bool trickle_fast_inputs);
     IMGUI_API void          UpdateHoveredWindowAndCaptureFlags();
     IMGUI_API void          StartMouseMovingWindow(ImGuiWindow* window);
-    IMGUI_API void          StartMouseMovingWindowOrNode(ImGuiWindow* window, ImGuiDockNode* node, bool undock_floating_node);
+    IMGUI_API void          StartMouseMovingWindowOrNode(ImGuiWindow* window, ImGuiDockNode* node, bool undock);
     IMGUI_API void          UpdateMouseMovingWindowNewFrame();
     IMGUI_API void          UpdateMouseMovingWindowEndFrame();
 

imgui_widgets.cpp

@@ -862,7 +862,7 @@ 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))
-        StartMouseMovingWindowOrNode(window, dock_node, true);
+        StartMouseMovingWindowOrNode(window, dock_node, true); // Undock from window/collapse menu button
 
     return pressed;
 }