Windows, Viewport: fixed an issue where interrupting a viewport move with e.g. a ClearActiveID() call would leave the dragged viewport with the ImGuiViewportFlags_NoInputs flag.

Amend 6b7766817, 36055213c5, #5324.
Next would be good to amend the ImGuiViewportFlags_NoInputs clear to match the set logic.

docs/CHANGELOG.txt

@@ -62,6 +62,13 @@ Other Changes:
 - Backends: Vulkan: Fixed texture update corruption introduced in 1.92.0,
   affecting some drivers/setups. (#8801, #8755, #8840) [@Retro52, @Miolith]
 
+Docking+Viewports Branch:
+
+- Windows, Viewport: fixed an issue where interrupting a viewport move with
+  e.g. a ClearActiveID() call would leave the dragged viewport with the
+  normally temporary ImGuiViewportFlags_NoInputs flag, preventing further
+  interactions with the viewport. (#5324) (thanks @mdelaharpe)
+
 
 -----------------------------------------------------------------------
  VERSION 1.92.1 (Released 2025-07-09)

imgui.cpp

@@ -4606,15 +4606,6 @@ void ImGui::SetActiveID(ImGuiID id, ImGuiWindow* window)
     // Clear previous active id
     if (g.ActiveId != 0)
     {
-        // While most behaved code would make an effort to not steal active id during window move/drag operations,
-        // we at least need to be resilient to it. Canceling the move is rather aggressive and users of 'master' branch
-        // may prefer the weird ill-defined half working situation ('docking' did assert), so may need to rework that.
-        if (g.MovingWindow != NULL && g.ActiveId == g.MovingWindow->MoveId)
-        {
-            IMGUI_DEBUG_LOG_ACTIVEID("SetActiveID() cancel MovingWindow\n");
-            g.MovingWindow = NULL;
-        }
-
         // Store deactivate data
         ImGuiDeactivatedItemData* deactivated_data = &g.DeactivatedItemData;
         deactivated_data->ID = g.ActiveId;
@@ -4627,6 +4618,15 @@ void ImGui::SetActiveID(ImGuiID id, ImGuiWindow* window)
         // One common scenario leading to this is: pressing Key ->NavMoveRequestApplyResult() -> ClearActiveID()
         if (g.InputTextState.ID == g.ActiveId)
             InputTextDeactivateHook(g.ActiveId);
+
+        // While most behaved code would make an effort to not steal active id during window move/drag operations,
+        // we at least need to be resilient to it. Canceling the move is rather aggressive and users of 'master' branch
+        // may prefer the weird ill-defined half working situation ('docking' did assert), so may need to rework that.
+        if (g.MovingWindow != NULL && g.ActiveId == g.MovingWindow->MoveId)
+        {
+            IMGUI_DEBUG_LOG_ACTIVEID("SetActiveID() cancel MovingWindow\n");
+            StopMouseMovingWindow();
+        }
     }
 
     // Set active id
@@ -5207,6 +5207,34 @@ void ImGui::StartMouseMovingWindowOrNode(ImGuiWindow* window, ImGuiDockNode* nod
         StartMouseMovingWindow(window);
 }
 
+// This is not 100% symetric with StartMouseMovingWindow().
+// We do NOT clear ActiveID, because:
+// - It would lead to rather confusing recursive code paths. Caller can call ClearActiveID() if desired.
+// - Some code intentionally cancel moving but keep the ActiveID to lock inputs (e.g. code path taken when clicking a disabled item).
+void ImGui::StopMouseMovingWindow()
+{
+    ImGuiContext& g = *GImGui;
+    ImGuiWindow* window = g.MovingWindow;
+
+    // Ref commits 6b7766817, 36055213c for some partial history on checking if viewport != NULL.
+    if (window && window->Viewport)
+    {
+        // Try to merge the window back into the main viewport.
+        // This works because MouseViewport should be != MovingWindow->Viewport on release (as per code in UpdateViewports)
+        if (g.ConfigFlagsCurrFrame & ImGuiConfigFlags_ViewportsEnable)
+            UpdateTryMergeWindowIntoHostViewport(window, g.MouseViewport);
+
+        // Restore the mouse viewport so that we don't hover the viewport _under_ the moved window during the frame we released the mouse button.
+        if (!IsDragDropPayloadBeingAccepted())
+            g.MouseViewport = window->Viewport;
+
+        // Clear the NoInputs window flag set by the Viewport system in AddUpdateViewport()
+        window->Viewport->Flags &= ~ImGuiViewportFlags_NoInputs;
+    }
+
+    g.MovingWindow = NULL;
+}
+
 // Handle mouse moving window
 // Note: moving window with the navigation keys (Square + d-pad / CTRL+TAB + Arrows) are processed in NavUpdateWindowing()
 // FIXME: We don't have strong guarantee that g.MovingWindow stay synced with g.ActiveId == g.MovingWindow->MoveId.
@@ -5224,8 +5252,8 @@ void ImGui::UpdateMouseMovingWindowNewFrame()
         ImGuiWindow* moving_window = g.MovingWindow->RootWindowDockTree;
 
         // When a window stop being submitted while being dragged, it may will its viewport until next Begin()
-        const bool window_disappared = (!moving_window->WasActive && !moving_window->Active);
-        if (g.IO.MouseDown[0] && IsMousePosValid(&g.IO.MousePos) && !window_disappared)
+        const bool window_disappeared = (!moving_window->WasActive && !moving_window->Active);
+        if (g.IO.MouseDown[0] && IsMousePosValid(&g.IO.MousePos) && !window_disappeared)
         {
             ImVec2 pos = g.IO.MousePos - g.ActiveIdClickOffset;
             if (moving_window->Pos.x != pos.x || moving_window->Pos.y != pos.y)
@@ -5241,23 +5269,7 @@ void ImGui::UpdateMouseMovingWindowNewFrame()
         }
         else
         {
-            if (!window_disappared)
-            {
-                // Try to merge the window back into the main viewport.
-                // This works because MouseViewport should be != MovingWindow->Viewport on release (as per code in UpdateViewports)
-                if (g.ConfigFlagsCurrFrame & ImGuiConfigFlags_ViewportsEnable)
-                    UpdateTryMergeWindowIntoHostViewport(moving_window, g.MouseViewport);
-
-                // Restore the mouse viewport so that we don't hover the viewport _under_ the moved window during the frame we released the mouse button.
-                if (moving_window->Viewport && !IsDragDropPayloadBeingAccepted())
-                    g.MouseViewport = moving_window->Viewport;
-
-                // Clear the NoInput window flag set by the Viewport system
-                if (moving_window->Viewport)
-                    moving_window->Viewport->Flags &= ~ImGuiViewportFlags_NoInputs;
-            }
-
-            g.MovingWindow = NULL;
+            StopMouseMovingWindow();
             ClearActiveID();
         }
     }
@@ -5299,6 +5311,9 @@ void ImGui::UpdateMouseMovingWindowEndFrame()
         {
             StartMouseMovingWindow(g.HoveredWindow); //-V595
 
+            // FIXME: In principal we might be able to call StopMouseMovingWindow() below.
+            // Please note how StartMouseMovingWindow() and StopMouseMovingWindow() and not entirely symetrical, at the later doesn't clear ActiveId.
+
             // Cancel moving if clicked outside of title bar
             if (g.IO.ConfigWindowsMoveFromTitleBarOnly)
                 if (!(root_window->Flags & ImGuiWindowFlags_NoTitleBar) || root_window->DockIsActive)

imgui_internal.h

@@ -3382,6 +3382,7 @@ namespace ImGui
     IMGUI_API void          FindHoveredWindowEx(const ImVec2& pos, bool find_first_and_in_any_viewport, ImGuiWindow** out_hovered_window, ImGuiWindow** out_hovered_window_under_moving_window);
     IMGUI_API void          StartMouseMovingWindow(ImGuiWindow* window);
     IMGUI_API void          StartMouseMovingWindowOrNode(ImGuiWindow* window, ImGuiDockNode* node, bool undock);
+    IMGUI_API void          StopMouseMovingWindow();
     IMGUI_API void          UpdateMouseMovingWindowNewFrame();
     IMGUI_API void          UpdateMouseMovingWindowEndFrame();