Fix PushFocusScopeID() + using shared stack. Renamed GetFocusScopeID() to GetFocusedFocusScope() - the two existing functions name are very error prone.

imgui.cpp

@@ -5962,7 +5962,6 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         window->DC.NavLayerCurrent = ImGuiNavLayer_Main;
         window->DC.NavLayerActiveMask = window->DC.NavLayerActiveMaskNext;
         window->DC.NavLayerActiveMaskNext = 0x00;
-        window->DC.NavFocusScopeIdCurrent = (flags & ImGuiWindowFlags_ChildWindow) ? parent_window->DC.NavFocusScopeIdCurrent : 0; // -V595
         window->DC.NavHideHighlightOneFrame = false;
         window->DC.NavHasScroll = (window->ScrollMax.y > 0.0f);
 
@@ -6030,12 +6029,12 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         SetCurrentWindow(window);
     }
 
+    window->DC.NavFocusScopeIdCurrent = (flags & ImGuiWindowFlags_ChildWindow) ? parent_window->DC.NavFocusScopeIdCurrent : 0; // -V595
+
     PushClipRect(window->InnerClipRect.Min, window->InnerClipRect.Max, true);
 
     // Clear 'accessed' flag last thing (After PushClipRect which will set the flag. We want the flag to stay false when the default "Debug" window is unused)
-    if (first_begin_of_the_frame)
     window->WriteAccessed = false;
-
     window->BeginCount++;
     g.NextWindowData.ClearFlags();
 
@@ -6651,14 +6650,11 @@ void ImGui::ActivateItem(ImGuiID id)
     g.NavNextActivateId = id;
 }
 
-// FIXME: this is storing in same stack as IDStack, so Push/Pop mismatch will be reported there. Maybe play nice and a separate in-context stack.
 void ImGui::PushFocusScope(ImGuiID id)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
-    ImGuiID top_most_id = window->IDStack.back();
-    window->IDStack.push_back(window->DC.NavFocusScopeIdCurrent);
-    window->IDStack.push_back(top_most_id);
+    g.FocusScopeStack.push_back(window->DC.NavFocusScopeIdCurrent);
     window->DC.NavFocusScopeIdCurrent = id;
 }
 
@@ -6666,10 +6662,9 @@ void ImGui::PopFocusScope()
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
-    window->DC.NavFocusScopeIdCurrent = window->IDStack.back();
-    window->IDStack.pop_back();
-    IM_ASSERT(window->IDStack.Size > 1); // Too many PopID or PopFocusScope (or could be popping in a wrong/different window?)
-    window->IDStack.pop_back();
+    IM_ASSERT(g.FocusScopeStack.Size > 0); // Too many PopFocusScope() ?
+    window->DC.NavFocusScopeIdCurrent = g.FocusScopeStack.back();
+    g.FocusScopeStack.pop_back();
 }
 
 void ImGui::SetKeyboardFocusHere(int offset)
@@ -6768,7 +6763,7 @@ ImGuiID ImGui::GetIDWithSeed(const char* str, const char* str_end, ImGuiID seed)
 void ImGui::PopID()
 {
     ImGuiWindow* window = GImGui->CurrentWindow;
-    IM_ASSERT(window->IDStack.Size > 1); // Too many PopID or PopFocusScope (or could be popping in a wrong/different window?)
+    IM_ASSERT(window->IDStack.Size > 1); // Too many PopID(), or could be popping in a wrong/different window?
     window->IDStack.pop_back();
 }
 

imgui.h

@@ -291,7 +291,10 @@ namespace ImGui
     // - Use child windows to begin into a self-contained independent scrolling/clipping regions within a host window. Child windows can embed their own child.
     // - For each independent axis of 'size': ==0.0f: use remaining host window size / >0.0f: fixed size / <0.0f: use remaining window size minus abs(size) / Each axis can use a different mode, e.g. ImVec2(0,400).
     // - BeginChild() returns false to indicate the window is collapsed or fully clipped, so you may early out and omit submitting anything to the window.
-    //   Always call a matching EndChild() for each BeginChild() call, regardless of its return value [as with Begin: this is due to legacy reason and inconsistent with most BeginXXX functions apart from the regular Begin() which behaves like BeginChild().]
+    //   Always call a matching EndChild() for each BeginChild() call, regardless of its return value.
+    //   [Important: due to legacy reason, this is inconsistent with most other functions such as BeginMenu/EndMenu,
+    //    BeginPopup/EndPopup, etc. where the EndXXX call should only be called if the corresponding BeginXXX function
+    //    returned true. Begin and BeginChild are the only odd ones out. Will be fixed in a future update.]
     IMGUI_API bool          BeginChild(const char* str_id, const ImVec2& size = ImVec2(0, 0), bool border = false, ImGuiWindowFlags flags = 0);
     IMGUI_API bool          BeginChild(ImGuiID id, const ImVec2& size = ImVec2(0, 0), bool border = false, ImGuiWindowFlags flags = 0);
     IMGUI_API void          EndChild();

imgui_internal.h

@@ -1207,6 +1207,7 @@ struct ImGuiContext
     ImVector<ImGuiColorMod> ColorModifiers;                     // Stack for PushStyleColor()/PopStyleColor()
     ImVector<ImGuiStyleMod> StyleModifiers;                     // Stack for PushStyleVar()/PopStyleVar()
     ImVector<ImFont*>       FontStack;                          // Stack for PushFont()/PopFont()
+    ImVector<ImGuiID>       FocusScopeStack;                    // Stack for PushFocusScope()/PopFocusScope()
     ImVector<ImGuiPopupData>OpenPopupStack;                     // Which popups are open (persistent)
     ImVector<ImGuiPopupData>BeginPopupStack;                    // Which level of BeginPopup() we are in (reset every frame)
 
@@ -1910,7 +1911,8 @@ namespace ImGui
     // patterns generally need to react (e.g. clear selection) when landing on an item of the set.
     IMGUI_API void          PushFocusScope(ImGuiID id);
     IMGUI_API void          PopFocusScope();
-    inline ImGuiID          GetFocusScopeID()               { ImGuiContext& g = *GImGui; return g.NavFocusScopeId; }
+    inline ImGuiID          GetFocusedFocusScope()          { ImGuiContext& g = *GImGui; return g.NavFocusScopeId; }                            // Focus scope which is actually active
+    inline ImGuiID          GetFocusScope()                 { ImGuiContext& g = *GImGui; return g.CurrentWindow->DC.NavFocusScopeIdCurrent; }   // Focus scope we are outputting into, set by PushFocusScope()
 
     // Inputs
     // FIXME: Eventually we should aim to move e.g. IsActiveIdUsingKey() into IsKeyXXX functions.