Fixed display of TitleBgActive color on window before a Modal window + modal window availability for navigation (#323)

imgui.cpp

@@ -4412,11 +4412,11 @@ bool ImGui::Begin(const char* name, bool* p_open, const ImVec2& size_on_first_us
         if (!(g.CurrentWindowStack[root_idx]->Flags & ImGuiWindowFlags_ChildWindow))
             break;
     for (root_non_popup_idx = root_idx; root_non_popup_idx > 0; root_non_popup_idx--)
-        if (!(g.CurrentWindowStack[root_non_popup_idx]->Flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Popup)))
+        if (!(g.CurrentWindowStack[root_non_popup_idx]->Flags & (ImGuiWindowFlags_ChildWindow | ImGuiWindowFlags_Popup)) || (g.CurrentWindowStack[root_non_popup_idx]->Flags & ImGuiWindowFlags_Modal))
             break;
     window->ParentWindow = parent_window;
     window->RootWindow = g.CurrentWindowStack[root_idx];
-    window->RootNonPopupWindow = g.CurrentWindowStack[root_non_popup_idx];      // Used e.g. to keep displaying TitleBgActive color when menu is active, and for NavWindowing
+    window->RootNonPopupWindow = g.CurrentWindowStack[root_non_popup_idx];      // Used to display TitleBgActive color and for selecting which window to use for NavWindowing
 
     // When reusing window again multiple times a frame, just append content (don't need to setup again)
     if (first_begin_of_the_frame)

imgui_internal.h

@@ -708,7 +708,7 @@ struct IMGUI_API ImGuiWindow
     float                   FontWindowScale;                    // Scale multiplier per-window
     ImDrawList*             DrawList;
     ImGuiWindow*            RootWindow;                         // If we are a child window, this is pointing to the first non-child parent window. Else point to ourself.
-    ImGuiWindow*            RootNonPopupWindow;                 // If we are a child window, this is pointing to the first non-child non-popup parent window. Else point to ourself.
+    ImGuiWindow*            RootNonPopupWindow;                 // Used to display TitleBgActive color and for selecting which window to use for NavWindowing
     ImGuiWindow*            ParentWindow;                       // Immediate parent in the window stack *regardless* of whether this window is a child window or not)
 
     // Navigation / Focus