MovingWindow: Proper fix for 651538e attempt, without altering Moving…

…Window which has side-effects. Clicking on a window with the ImGuiWIndowFlags_NoMove flags takes an ActiveId so we can't hover something else. (ref #1381, #1337)

imgui.cpp

@@ -2378,10 +2378,10 @@ void ImGui::NewFrame()
     g.FramerateSecPerFrameIdx = (g.FramerateSecPerFrameIdx + 1) % IM_ARRAYSIZE(g.FramerateSecPerFrame);
     g.IO.Framerate = 1.0f / (g.FramerateSecPerFrameAccum / (float)IM_ARRAYSIZE(g.FramerateSecPerFrame));
 
-    // Handle user moving window with mouse (at the beginning of the frame to avoid input lag or sheering). Only valid for root windows.
+    // Handle user moving window with mouse (at the beginning of the frame to avoid input lag or sheering).
     if (g.MovingWindowMoveId && g.MovingWindowMoveId == g.ActiveId)
     {
-        KeepAliveID(g.MovingWindowMoveId);
+        KeepAliveID(g.ActiveId);
         IM_ASSERT(g.MovingWindow && g.MovingWindow->RootWindow);
         IM_ASSERT(g.MovingWindow->MoveId == g.MovingWindowMoveId);
         if (g.IO.MouseDown[0])
@@ -2401,6 +2401,13 @@ void ImGui::NewFrame()
     }
     else
     {
+        // When clicking/dragging from a window that has the _NoMove flag, we still set the ActiveId in order to prevent hovering others.
+        if (g.ActiveIdWindow && g.ActiveIdWindow->MoveId == g.ActiveId)
+        {
+            KeepAliveID(g.ActiveId);
+            if (!g.IO.MouseDown[0])
+                ClearActiveID();
+        }
         g.MovingWindow = NULL;
         g.MovingWindowMoveId = 0;
     }
@@ -2934,13 +2941,14 @@ void ImGui::EndFrame()
             {
                 if (g.HoveredRootWindow != NULL)
                 {
+                    // Set ActiveId even if the _NoMove flag is set, without it dragging away from a window with _NoMove would activate hover on other windows.
                     FocusWindow(g.HoveredWindow);
+                    SetActiveID(g.HoveredWindow->MoveId, g.HoveredWindow);
+                    g.ActiveIdClickOffset = g.IO.MousePos - g.HoveredRootWindow->Pos;
                     if (!(g.HoveredWindow->Flags & ImGuiWindowFlags_NoMove) && !(g.HoveredRootWindow->Flags & ImGuiWindowFlags_NoMove))
                     {
                         g.MovingWindow = g.HoveredWindow;
                         g.MovingWindowMoveId = g.MovingWindow->MoveId;
-                        SetActiveID(g.MovingWindowMoveId, g.HoveredRootWindow);
-                        g.ActiveIdClickOffset = g.IO.MousePos - g.MovingWindow->RootWindow->Pos;
                     }
                 }
                 else if (g.NavWindow != NULL && GetFrontMostModalRootWindow() == NULL)