Internals: ParentWindow is now NULL for non-child windows and means what everyone expects.

imgui.cpp

@@ -4338,7 +4338,7 @@ 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 ? (!g.CurrentWindowStack.empty() ? g.CurrentWindowStack.back() : NULL) : window->ParentWindow;
+    ImGuiWindow* parent_window = first_begin_of_the_frame ? ((flags & ImGuiWindowFlags_ChildWindow) && !g.CurrentWindowStack.empty() ? g.CurrentWindowStack.back() : NULL) : window->ParentWindow;
     IM_ASSERT(parent_window != NULL || !(flags & ImGuiWindowFlags_ChildWindow));
 
     // Add to stack
@@ -4409,8 +4409,8 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     {
         // Initialize
         window->ParentWindow = parent_window;
-        window->RootWindow = !(flags & ImGuiWindowFlags_ChildWindow) ? window : parent_window->RootWindow;
-        window->RootNonPopupWindow = !(flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Popup)) || (flags & ImGuiWindowFlags_Modal) ? window : parent_window->RootNonPopupWindow; // Used to display TitleBgActive color and for selecting which window to use for NavWindowing
+        window->RootWindow = ((flags & ImGuiWindowFlags_ChildWindow) && parent_window) ? parent_window->RootWindow : window;
+        window->RootNonPopupWindow = !(flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Popup)) || (flags & ImGuiWindowFlags_Modal) || (parent_window == NULL) ? window : parent_window->RootNonPopupWindow; // Used to display TitleBgActive color and for selecting which window to use for NavWindowing
         //window->RootNavWindow = window;
         //while (window->RootNavWindow->Flags & ImGuiWindowFlags_NavFlattened)
         //    window->RootNavWindow = window->RootNavWindow->ParentWindow;
@@ -4556,11 +4556,12 @@ 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];
             ImRect rect_to_avoid;
-            if (parent_window->DC.MenuBarAppending)
-                rect_to_avoid = ImRect(-FLT_MAX, parent_window->Pos.y + parent_window->TitleBarHeight(), FLT_MAX, parent_window->Pos.y + parent_window->TitleBarHeight() + parent_window->MenuBarHeight());
+            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());
             else
-                rect_to_avoid = ImRect(parent_window->Pos.x + horizontal_overlap, -FLT_MAX, parent_window->Pos.x + parent_window->Size.x - horizontal_overlap - parent_window->ScrollbarSizes.x, FLT_MAX);
+                rect_to_avoid = ImRect(parent_menu->Pos.x + horizontal_overlap, -FLT_MAX, parent_menu->Pos.x + parent_menu->Size.x - horizontal_overlap - parent_menu->ScrollbarSizes.x, FLT_MAX);
             window->PosFloat = FindBestWindowPosForPopup(window->PosFloat, window->Size, &window->AutoPosLastDirection, rect_to_avoid);
         }
         else if ((flags & ImGuiWindowFlags_Popup) != 0 && !window_pos_set_by_api && window_just_appearing_after_hidden_for_resize)

imgui_internal.h

@@ -746,7 +746,7 @@ struct IMGUI_API ImGuiWindow
     ImGuiStorage            StateStorage;
     float                   FontWindowScale;                    // Scale multiplier per-window
     ImDrawList*             DrawList;
-    ImGuiWindow*            ParentWindow;                       // Immediate parent in the window stack *regardless* of whether this window is a child window or not)
+    ImGuiWindow*            ParentWindow;                       // If we are a child window, this is pointing to our parent.
     ImGuiWindow*            RootWindow;                         // Generally point to ourself. If we are a child window, this is pointing to the first non-child parent window.
     ImGuiWindow*            RootNonPopupWindow;                 // Generally point to ourself. Used to display TitleBgActive color and for selecting which window to use for NavWindowing