Alternative fix for bug introduced in d845135 (#1651), fix CTRL+Tab and fallback tooltip.

imgui.cpp

@@ -3349,6 +3349,7 @@ void ImGui::NewFrame()
     // This fallback is particularly important as it avoid ImGui:: calls from crashing.
     SetNextWindowSize(ImVec2(400,400), ImGuiCond_FirstUseEver);
     Begin("Debug##Default");
+    g.FrameScopePushedImplicitWindow = true;
 
 #ifdef IMGUI_ENABLE_TEST_ENGINE
     ImGuiTestEngineHook_PostNewFrame();
@@ -3580,9 +3581,6 @@ void ImGui::EndFrame()
         return;
     IM_ASSERT(g.FrameScopeActive && "Forgot to call ImGui::NewFrame()?");
 
-    g.FrameScopeActive = false;
-    g.FrameCountEnded = g.FrameCount;
-
     // Notify OS when our Input Method Editor cursor has moved (e.g. CJK inputs using Microsoft IME)
     if (g.IO.ImeSetInputScreenPosFn && ImLengthSqr(g.PlatformImeLastPos - g.PlatformImePos) > 0.0001f)
     {
@@ -3607,11 +3605,12 @@ void ImGui::EndFrame()
     }
 
     // Hide implicit/fallback "Debug" window if it hasn't been used
+    g.FrameScopePushedImplicitWindow = false;
     if (g.CurrentWindow && !g.CurrentWindow->WriteAccessed)
         g.CurrentWindow->Active = false;
     End();
 
-    // Show CTRL+TAB list
+    // Show CTRL+TAB list window
     if (g.NavWindowingTarget)
         NavUpdateWindowingList();
 
@@ -3632,6 +3631,10 @@ void ImGui::EndFrame()
         g.DragDropWithinSourceOrTarget = false;
     }
 
+    // End frame
+    g.FrameScopeActive = false;
+    g.FrameCountEnded = g.FrameCount;
+
     // Initiate moving window
     if (g.ActiveId == 0 && g.HoveredId == 0)
     {
@@ -5283,11 +5286,12 @@ void ImGui::End()
 {
     ImGuiContext& g = *GImGui;
 
-    if (g.CurrentWindowStack.Size <= 1 && g.FrameScopeActive)
+    if (g.CurrentWindowStack.Size <= 1 && g.FrameScopePushedImplicitWindow)
     {
         IM_ASSERT(g.CurrentWindowStack.Size > 1 && "Calling End() too many times!");
         return; // FIXME-ERRORHANDLING
     }
+    IM_ASSERT(g.CurrentWindowStack.Size > 0);
 
     ImGuiWindow* window = g.CurrentWindow;
 

imgui_internal.h

@@ -694,7 +694,8 @@ struct ImGuiTabBarSortItem
 struct ImGuiContext
 {
     bool                    Initialized;
-    bool                    FrameScopeActive;                   // Set by NewFrame(), cleared by EndFrame()/Render()
+    bool                    FrameScopeActive;                   // Set by NewFrame(), cleared by EndFrame()
+    bool                    FrameScopePushedImplicitWindow;     // Set by NewFrame(), cleared by EndFrame()
     bool                    FontAtlasOwnedByContext;            // Io.Fonts-> is owned by the ImGuiContext and will be destructed along with it.
     ImGuiIO                 IO;
     ImGuiStyle              Style;
@@ -859,7 +860,7 @@ struct ImGuiContext
     ImGuiContext(ImFontAtlas* shared_font_atlas) : OverlayDrawList(NULL)
     {
         Initialized = false;
-        FrameScopeActive = false;
+        FrameScopeActive = FrameScopePushedImplicitWindow = false;
         Font = NULL;
         FontSize = FontBaseSize = 0.0f;
         FontAtlasOwnedByContext = shared_font_atlas ? false : true;