Tweak

imgui.cpp

@@ -4338,7 +4338,8 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         SetWindowConditionAllowFlags(window, ImGuiCond_Appearing, true);
 
     // Parent window is latched only on the first call to Begin() of the frame, so further append-calls can be done from a different window stack
-    ImGuiWindow* parent_window = first_begin_of_the_frame ? ((flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Popup)) && !g.CurrentWindowStack.empty() ? g.CurrentWindowStack.back() : NULL) : window->ParentWindow;
+    ImGuiWindow* parent_window_in_stack = g.CurrentWindowStack.empty() ? NULL : g.CurrentWindowStack.back();
+    ImGuiWindow* parent_window = first_begin_of_the_frame ? ((flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Popup)) ? parent_window_in_stack : NULL) : window->ParentWindow;
     IM_ASSERT(parent_window != NULL || !(flags & ImGuiWindowFlags_ChildWindow));
 
     // Add to stack
@@ -4559,7 +4560,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             // This is how we end up with child menus appearing (most-commonly) on the right of the parent menu.
             IM_ASSERT(window_pos_set_by_api);
             float horizontal_overlap = style.ItemSpacing.x; // We want some overlap to convey the relative depth of each popup (currently the amount of overlap it is hard-coded to style.ItemSpacing.x, may need to introduce another style value).
-            ImGuiWindow* parent_menu = g.CurrentWindowStack[g.CurrentWindowStack.Size - 2];
+            ImGuiWindow* parent_menu = parent_window_in_stack;
             ImRect rect_to_avoid;
             if (parent_menu->DC.MenuBarAppending)
                 rect_to_avoid = ImRect(-FLT_MAX, parent_menu->Pos.y + parent_menu->TitleBarHeight(), FLT_MAX, parent_menu->Pos.y + parent_menu->TitleBarHeight() + parent_menu->MenuBarHeight());