Begin: WIP consistent Begin/End behavior, ListBoxHeader() fix.

docs/FAQ.md

@@ -429,8 +429,10 @@ provide similar or better string helpers.
 ### Q: How can I display custom shapes? (using low-level ImDrawList API)
 
 - You can use the low-level `ImDrawList` api to render shapes within a window.
+
 ```cpp
-ImGui::Begin("My shapes");
+if (!ImGui::Begin("My shapes"))
+    return;
 
 ImDrawList* draw_list = ImGui::GetWindowDrawList();
 

docs/README.md

@@ -52,7 +52,8 @@ Result:
 Code:
 ```cpp
 // Create a window called "My First Tool", with a menu bar.
-ImGui::Begin("My First Tool", &my_tool_active, ImGuiWindowFlags_MenuBar);
+if (!ImGui::Begin("My First Tool", &my_tool_active, ImGuiWindowFlags_MenuBar))
+    return;
 if (ImGui::BeginMenuBar())
 {
     if (ImGui::BeginMenu("File"))

examples/example_win32_directx11/main.cpp

@@ -122,17 +122,21 @@ int main(int, char**)
         ImGui_ImplWin32_NewFrame();
         ImGui::NewFrame();
 
+#if 1
+        // Enable Debugging
+        io.ConfigDebugBeginReturnValue = io.KeyShift;
+#endif
+
         // 1. Show the big demo window (Most of the sample code is in ImGui::ShowDemoWindow()! You can browse its code to learn more about Dear ImGui!).
         if (show_demo_window)
             ImGui::ShowDemoWindow(&show_demo_window);
 
         // 2. Show a simple window that we create ourselves. We use a Begin/End pair to created a named window.
+        if (ImGui::Begin("Hello, world!"))                          // Create a window called "Hello, world!" and append into it.
         {
             static float f = 0.0f;
             static int counter = 0;
 
-            ImGui::Begin("Hello, world!");                          // Create a window called "Hello, world!" and append into it.
-
             ImGui::Text("This is some useful text.");               // Display some text (you can use a format strings too)
             ImGui::Checkbox("Demo Window", &show_demo_window);      // Edit bools storing our window open/close state
             ImGui::Checkbox("Another Window", &show_another_window);
@@ -150,9 +154,9 @@ int main(int, char**)
         }
 
         // 3. Show another simple window.
-        if (show_another_window)
+        // Passing a pointer to our bool variable in the Begin() call: the window will have a closing button that will clear the bool when clicked.
+        if (show_another_window && ImGui::Begin("Another Window", &show_another_window))
         {
-            ImGui::Begin("Another Window", &show_another_window);   // Pass a pointer to our bool variable (the window will have a closing button that will clear the bool when clicked)
             ImGui::Text("Hello from another window!");
             if (ImGui::Button("Close Me"))
                 show_another_window = false;

imgui.cpp

@@ -1083,6 +1083,9 @@ ImGuiIO::ImGuiIO()
     ConfigWindowsMoveFromTitleBarOnly = false;
     ConfigMemoryCompactTimer = 60.0f;
 
+    // Debug options
+    ConfigDebugBeginReturnValue = false;
+
     // Platform Functions
     BackendPlatformName = BackendRendererName = NULL;
     BackendPlatformUserData = BackendRendererUserData = BackendLanguageUserData = NULL;
@@ -4107,13 +4110,29 @@ void ImGui::NewFrame()
     UpdateDebugToolItemPicker();
 
     // Create implicit/fallback window - which we will only render it if the user has added something to it.
-    // We don't use "Debug" to avoid colliding with user trying to create a "Debug" window with custom flags.
+    // - We don't use "Debug" to avoid colliding with user trying to create a "Debug" window with custom flags.
-    // This fallback is particularly important as it avoid ImGui:: calls from crashing.
+    // - This fallback is particularly important as it avoid ImGui:: calls from crashing.
+    // - The fallback window exceptionally doesn't call End() automatically if Begin() returns false (this is intended).
     g.WithinFrameScopeWithImplicitWindow = true;
     SetNextWindowSize(ImVec2(400, 400), ImGuiCond_FirstUseEver);
-    Begin("Debug##Default");
+    bool ret = Begin("Debug##Default");
+    IM_UNUSED(ret);
+    IM_ASSERT(ret);
     IM_ASSERT(g.CurrentWindow->IsFallbackWindow == true);
 
+    // [DEBUG] When io.ConfigDebugBeginReturnValue is set, we make Begin() return false at different level of the window stack to validate Begin()/End() behavior in user code.
+    if (g.IO.ConfigDebugBeginReturnValue)
+    {
+        g.DebugBeginReturnValueCullDepth = (g.DebugBeginReturnValueCullDepth == -1) ? 0 : ((g.DebugBeginReturnValueCullDepth + ((g.FrameCount % 4) == 0 ? 1 : 0)) % 10);
+        char buf[64];
+        ImFormatString(buf, IM_ARRAYSIZE(buf), "Cull depth %d", g.DebugBeginReturnValueCullDepth);
+        GetForegroundDrawList()->AddText(ImVec2(0, 0), IM_COL32(255, 255, 0, 255), buf);
+    }
+    else
+    {
+        g.DebugBeginReturnValueCullDepth = -1;
+    }
+
     CallContextHooks(&g, ImGuiContextHookType_NewFramePost);
 }
 
@@ -4134,13 +4153,15 @@ void ImGui::UpdateDebugToolItemPicker()
             g.DebugItemPickerActive = false;
         }
         ImGui::SetNextWindowBgAlpha(0.60f);
-        ImGui::BeginTooltip();
+        if (ImGui::BeginTooltip())
+        {
             ImGui::Text("HoveredId: 0x%08X", hovered_id);
             ImGui::Text("Press ESC to abort picking.");
             ImGui::TextColored(GetStyleColorVec4(hovered_id ? ImGuiCol_Text : ImGuiCol_TextDisabled), "Click to break in debugger!");
             ImGui::EndTooltip();
         }
     }
+}
 
 void ImGui::Initialize(ImGuiContext* context)
 {
@@ -5120,15 +5141,10 @@ bool ImGui::BeginChildEx(const char* name, ImGuiID id, const ImVec2& size_arg, b
     bool ret = Begin(title, NULL, flags);
     g.Style.ChildBorderSize = backup_border_size;
 
-    ImGuiWindow* child_window = g.CurrentWindow;
+    ImGuiWindow* child_window = g.LastBeginWindow; // FIXME-NEWBEGIN
     child_window->ChildId = id;
     child_window->AutoFitChildAxises = (ImS8)auto_fit_axises;
 
-    // Set the cursor to handle case where the user called SetNextWindowPos()+BeginChild() manually.
-    // While this is not really documented/defined, it seems that the expected thing to do.
-    if (child_window->BeginCount == 1)
-        parent_window->DC.CursorPos = child_window->Pos;
-
     // Process navigation-in immediately so NavInit can run on first frame
     if (g.NavActivateId == id && !(flags & ImGuiWindowFlags_NavFlattened) && (child_window->DC.NavLayerActiveMask != 0 || child_window->DC.NavHasScroll))
     {
@@ -5160,6 +5176,11 @@ void ImGui::EndChild()
     IM_ASSERT(g.WithinEndChild == false);
     IM_ASSERT(window->Flags & ImGuiWindowFlags_ChildWindow);   // Mismatched BeginChild()/EndChild() calls
 
+    // Set the cursor to handle case where the user called SetNextWindowPos()+BeginChild() manually.
+    // While this is not really documented/defined, it seems that the expected thing to do.
+    if (window->BeginCount == 1)
+        window->ParentWindow->DC.CursorPos = window->Pos;
+
     g.WithinEndChild = true;
     if (window->BeginCount > 1)
     {
@@ -5981,6 +6002,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     // We intentionally set g.CurrentWindow to NULL to prevent usage until when the viewport is set, then will call SetCurrentWindow()
     g.CurrentWindowStack.push_back(window);
     g.CurrentWindow = window;
+    g.LastBeginWindow = window;
     window->DC.StackSizesOnBegin.SetToCurrentState();
     g.CurrentWindow = NULL;
 
@@ -6740,7 +6762,24 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
         window->SkipItems = skip_items;
     }
 
-    return !window->SkipItems;
+    // FIXME-OPT
+    bool debug_skip = (g.DebugBeginReturnValueCullDepth == g.CurrentWindowStack.Size) && (window->Flags & ImGuiWindowFlags_DockNodeHost) == 0;
+    if (window->SkipItems || debug_skip)
+    {
+        // The implicit fallback is NOT automatically ended as an exception to the rule,
+        // allowing it to always be able to receive commands without crashing.
+        if (window->IsFallbackWindow)
+            return true;
+
+        if (window->Flags & ImGuiWindowFlags_Popup)
+            EndPopup();
+        else if (window->Flags & ImGuiWindowFlags_ChildWindow)
+            EndChild();
+        else
+            End();
+        return false;
+    }
+    return true;
 }
 
 void ImGui::End()
@@ -6751,6 +6790,34 @@ void ImGui::End()
     // Error checking: verify that user hasn't called End() too many times!
     if (g.CurrentWindowStack.Size <= 1 && g.WithinFrameScopeWithImplicitWindow)
     {
+        // - IMPORTANT: SINCE 1.XX (XXXX 2020): Only call a matching End() if Begin() returned true!.
+        // - IMPORTANT: BEFORE 1.XX (XXXX 2020): The return value of Begin() was inconsistent with most other BeginXXX()
+        //   functions, and would require the user to always call End() even if Begin() returned false.
+
+        // - When transitioning a codebase from < 1.XX to >= 1.XX, code needs to be refactored the following way:
+        //   Before ------------------------------------> After
+        //      ImGui::Begin("Hello");                       if (ImGui::Begin("Hello"))
+        //      ImGui::Button("OK");                         {
+        //      ImGui::End();                                    ImGui::Button("OK");
+        //                                                       ImGui::End();
+        //                                                   }
+        //
+        //   Before ------------------------------------> After
+        //      if (ImGui::Begin("Hello"))                   if (ImGui::Begin("Hello"))
+        //      {                                            {
+        //          ImGui::Button("OK");                         ImGui::Button("OK");
+        //      }                                                ImGui::End();
+        //      ImGui::End();                                }
+        //       
+        //   Before ------------------------------------> After
+        //      if (!ImGui::Begin("Hello"))                  if (!ImGui::Begin("Hello"))
+        //      {                                                return;
+        //          ImGui::End();                            ImGui::Button("OK");
+        //          return;                                  ImGui::End();
+        //      }
+        //      ImGui::Button("OK");
+        //      ImGui::End();
+
         IM_ASSERT_USER_ERROR(g.CurrentWindowStack.Size > 1, "Calling End() too many times!");
         return;
     }
@@ -8475,12 +8542,12 @@ void ImGui::SetScrollHereY(float center_y_ratio)
 // [SECTION] TOOLTIPS
 //-----------------------------------------------------------------------------
 
-void ImGui::BeginTooltip()
+bool ImGui::BeginTooltip()
 {
-    BeginTooltipEx(ImGuiWindowFlags_None, ImGuiTooltipFlags_None);
+    return BeginTooltipEx(ImGuiWindowFlags_None, ImGuiTooltipFlags_None);
 }
 
-void ImGui::BeginTooltipEx(ImGuiWindowFlags extra_flags, ImGuiTooltipFlags tooltip_flags)
+bool ImGui::BeginTooltipEx(ImGuiWindowFlags extra_flags, ImGuiTooltipFlags tooltip_flags)
 {
     ImGuiContext& g = *GImGui;
 
@@ -8509,7 +8576,11 @@ void ImGui::BeginTooltipEx(ImGuiWindowFlags extra_flags, ImGuiTooltipFlags toolt
                 ImFormatString(window_name, IM_ARRAYSIZE(window_name), "##Tooltip_%02d", ++g.TooltipOverrideCount);
             }
     ImGuiWindowFlags flags = ImGuiWindowFlags_Tooltip | ImGuiWindowFlags_NoInputs | ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoDocking;
-    Begin(window_name, NULL, flags | extra_flags);
+    bool ret = Begin(window_name, NULL, flags | extra_flags);
+    // FIXME-NEWBEGIN: adding a bool to API...
+    //IM_UNUSED(ret);
+    //IM_ASSERT(ret);
+    return ret;
 }
 
 void ImGui::EndTooltip()
@@ -8520,7 +8591,8 @@ void ImGui::EndTooltip()
 
 void ImGui::SetTooltipV(const char* fmt, va_list args)
 {
-    BeginTooltipEx(0, ImGuiTooltipFlags_OverridePreviousTooltip);
+    if (!BeginTooltipEx(0, ImGuiTooltipFlags_OverridePreviousTooltip))
+        return;
     TextV(fmt, args);
     EndTooltip();
 }
@@ -8765,11 +8837,9 @@ bool ImGui::BeginPopupEx(ImGuiID id, ImGuiWindowFlags flags)
     else
         ImFormatString(name, IM_ARRAYSIZE(name), "##Popup_%08x", id); // Not recycling, so we can close/open during the same frame
 
+    // NB: Begin can return false when the popup is completely clipped (e.g. zero size display)
     flags |= ImGuiWindowFlags_Popup | ImGuiWindowFlags_NoDocking;
     bool is_open = Begin(name, NULL, flags);
-    if (!is_open) // NB: Begin can return false when the popup is completely clipped (e.g. zero size display)
-        EndPopup();
-
     return is_open;
 }
 
@@ -8811,9 +8881,11 @@ bool ImGui::BeginPopupModal(const char* name, bool* p_open, ImGuiWindowFlags fla
     const bool is_open = Begin(name, p_open, flags);
     if (!is_open || (p_open && !*p_open)) // NB: is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
     {
-        EndPopup();
         if (is_open)
+        {
+            EndPopup();
             ClosePopupToLevel(g.BeginPopupStack.Size, true);
+        }
         return false;
     }
     return is_open;
@@ -10188,7 +10260,10 @@ void ImGui::NavUpdateWindowingOverlay()
     SetNextWindowSizeConstraints(ImVec2(viewport->Size.x * 0.20f, viewport->Size.y * 0.20f), ImVec2(FLT_MAX, FLT_MAX));
     SetNextWindowPos(viewport->Pos + viewport->Size * 0.5f, ImGuiCond_Always, ImVec2(0.5f, 0.5f));
     PushStyleVar(ImGuiStyleVar_WindowPadding, g.Style.WindowPadding * 2.0f);
-    Begin("###NavWindowingList", NULL, ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoFocusOnAppearing | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoInputs | ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoSavedSettings);
+    bool ret = Begin("###NavWindowingList", NULL, ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoFocusOnAppearing | ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoMove | ImGuiWindowFlags_NoInputs | ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoSavedSettings);
+    PopStyleVar();
+    if (!ret)
+        return;
     for (int n = g.WindowsFocusOrder.Size - 1; n >= 0; n--)
     {
         ImGuiWindow* window = g.WindowsFocusOrder[n];
@@ -10200,7 +10275,6 @@ void ImGui::NavUpdateWindowingOverlay()
         Selectable(label, g.NavWindowingTarget == window);
     }
     End();
-    PopStyleVar();
 }
 
 
@@ -10312,7 +10386,9 @@ bool ImGui::BeginDragDropSource(ImGuiDragDropFlags flags)
         {
             // Target can request the Source to not display its tooltip (we use a dedicated flag to make this request explicit)
             // We unfortunately can't just modify the source flags and skip the call to BeginTooltip, as caller may be emitting contents.
-            BeginTooltip();
+            bool ret = BeginTooltip(); // FIXME-NEWBEGIN: problematic
+            IM_UNUSED(ret);
+            IM_ASSERT(ret);
             if (g.DragDropAcceptIdPrev && (g.DragDropAcceptFlags & ImGuiDragDropFlags_AcceptNoPreviewTooltip))
             {
                 ImGuiWindow* tooltip_window = g.CurrentWindow;
@@ -13201,8 +13277,10 @@ static void ImGui::DockNodeUpdate(ImGuiDockNode* node)
             window_flags |= ImGuiWindowFlags_NoTitleBar;
 
             PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0, 0));
-            Begin(window_label, NULL, window_flags);
+            bool ret = Begin(window_label, NULL, window_flags);
             PopStyleVar();
+            IM_UNUSED(ret);
+            IM_ASSERT(ret); // FIXME-NEWBEGIN
             beginned_into_host_window = true;
 
             node->HostWindow = host_window = g.CurrentWindow;
@@ -13385,7 +13463,8 @@ bool ImGui::DockNodeBeginAmendTabBar(ImGuiDockNode* node)
         return false;
     if (node->SharedFlags & ImGuiDockNodeFlags_KeepAliveOnly)
         return false;
-    Begin(node->HostWindow->Name);
+    if (!Begin(node->HostWindow->Name))
+        return false;
     PushOverrideID(node->ID);
     bool ret = BeginTabBarEx(node->TabBar, node->TabBar->BarRect, node->TabBar->Flags, node);
     IM_ASSERT(ret);
@@ -14472,10 +14551,12 @@ void ImGui::DockSpace(ImGuiID id, const ImVec2& size_arg, ImGuiDockNodeFlags fla
     if (node->Windows.Size > 0 || node->IsSplitNode())
         PushStyleColor(ImGuiCol_ChildBg, IM_COL32(0, 0, 0, 0));
     PushStyleVar(ImGuiStyleVar_ChildBorderSize, 0.0f);
-    Begin(title, NULL, window_flags);
+    bool ret = Begin(title, NULL, window_flags);
     PopStyleVar();
     if (node->Windows.Size > 0 || node->IsSplitNode())
         PopStyleColor();
+    if (!ret)
+        return; // FIXME-NEWBEGIN
 
     ImGuiWindow* host_window = g.CurrentWindow;
     host_window->DockNodeAsHost = node;
@@ -14526,12 +14607,16 @@ ImGuiID ImGui::DockSpaceOverViewport(ImGuiViewport* viewport, ImGuiDockNodeFlags
     PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
     PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
     PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));
-    Begin(label, NULL, host_window_flags);
+    bool ret = Begin(label, NULL, host_window_flags);
     PopStyleVar(3);
-
     ImGuiID dockspace_id = GetID("DockSpace");
+
+    // FIXME-NEWBEGIN: KeepAlive if not visible?
+    if (ret)
+    {
         DockSpace(dockspace_id, ImVec2(0.0f, 0.0f), dockspace_flags, window_class);
         End();
+    }
 
     return dockspace_id;
 }
@@ -15667,9 +15752,8 @@ static void RenderViewportsThumbnails()
 static void MetricsHelpMarker(const char* desc)
 {
     ImGui::TextDisabled("(?)");
-    if (ImGui::IsItemHovered())
+    if (ImGui::IsItemHovered() && ImGui::BeginTooltip())
     {
-        ImGui::BeginTooltip();
         ImGui::PushTextWrapPos(ImGui::GetFontSize() * 35.0f);
         ImGui::TextUnformatted(desc);
         ImGui::PopTextWrapPos();
@@ -15680,10 +15764,7 @@ static void MetricsHelpMarker(const char* desc)
 void ImGui::ShowMetricsWindow(bool* p_open)
 {
     if (!Begin("Dear ImGui Metrics/Debugger", p_open))
-    {
-        End();
         return;
-    }
 
     ImGuiContext& g = *GImGui;
     ImGuiIO& io = g.IO;

imgui.h

@@ -68,6 +68,9 @@ Index of this file:
 #define IMGUI_HAS_VIEWPORT          1 // Viewport WIP branch
 #define IMGUI_HAS_DOCK              1 // Docking WIP branch
 
+// Features
+#define IMGUI_HAS_NEWBEGIN          1
+
 // Define attributes of all API symbols declarations (e.g. for DLL under Windows)
 // IMGUI_API is used for core imgui functions, IMGUI_IMPL_API is used for the default backends files (imgui_impl_xxx.h)
 // Using dear imgui via a shared library is not recommended, because we don't guarantee backward nor forward ABI compatibility (also function call overhead, as dear imgui is a call-heavy API)
@@ -101,6 +104,16 @@ Index of this file:
 #define IM_FMTLIST(FMT)
 #endif
 
+#if (__cplusplus >= 201703)
+#define IM_NODISCARD                [[nodiscard]]
+#elif defined(__GNUC__) && (__GNUC__ >= 4)
+#define IM_NODISCARD                __attribute__ ((warn_unused_result))
+#elif defined(_MSC_VER) && (_MSC_VER >= 1700)
+#define IM_NODISCARD                _Check_return_
+#else
+#define IM_NODISCARD
+#endif
+
 // Warnings
 #if defined(__clang__)
 #pragma clang diagnostic push
@@ -297,24 +310,23 @@ namespace ImGui
     // - You may append multiple times to the same window during the same frame by calling Begin()/End() pairs multiple times.
     //   Some information such as 'flags' or 'p_open' will only be considered by the first call to Begin().
     // - Begin() return 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 End() for each Begin() call, regardless of its return value!
+    //   anything to the window.
-    //   [Important: due to legacy reason, this is inconsistent with most other functions such as BeginMenu/EndMenu,
+    // - IMPORTANT: SINCE 1.XX (XXXX 2020): Only call a matching End() if Begin() returned true!.
-    //    BeginPopup/EndPopup, etc. where the EndXXX call should only be called if the corresponding BeginXXX function
+    // - IMPORTANT: BEFORE 1.XX (XXXX 2020): The return value of Begin() was inconsistent with most other BeginXXX()
-    //    returned true. Begin and BeginChild are the only odd ones out. Will be fixed in a future update.]
+    //   functions, and would require the user to always call End() even if Begin() returned false.
     // - Note that the bottom of window stack always contains a window called "Debug".
-    IMGUI_API bool          Begin(const char* name, bool* p_open = NULL, ImGuiWindowFlags flags = 0);
+    IM_NODISCARD IMGUI_API bool Begin(const char* name, bool* p_open = NULL, ImGuiWindowFlags flags = 0);
     IMGUI_API void          End();
 
     // Child Windows
     // - 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.
+    // - IMPORTANT: SINCE 1.XX (XXXX 2020): Only call a matching EndChild() if BeginChild() returned true!.
-    //   [Important: due to legacy reason, this is inconsistent with most other functions such as BeginMenu/EndMenu,
+    // - IMPORTANT: BEFORE 1.XX (XXXX 2020): The return value of BeginChild() was inconsistent with most other BeginXXX()
-    //    BeginPopup/EndPopup, etc. where the EndXXX call should only be called if the corresponding BeginXXX function
+    //   functions, and would require the user to always call EndChild() even if BeginChild() returned false. This has been changed.
-    //    returned true. Begin and BeginChild are the only odd ones out. Will be fixed in a future update.]
+    IM_NODISCARD IMGUI_API bool          BeginChild(const char* str_id, const ImVec2& size = ImVec2(0, 0), bool border = false, ImGuiWindowFlags flags = 0);
-    IMGUI_API bool          BeginChild(const char* str_id, const ImVec2& size = ImVec2(0, 0), bool border = false, ImGuiWindowFlags flags = 0);
+    IM_NODISCARD IMGUI_API bool          BeginChild(ImGuiID 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();
 
     // Windows Utilities
@@ -622,7 +634,7 @@ namespace ImGui
 
     // Tooltips
     // - Tooltip are windows following the mouse which do not take focus away.
-    IMGUI_API void          BeginTooltip();                                                     // begin/append a tooltip window. to create full-featured tooltip (with any kind of items).
+    IMGUI_API bool          BeginTooltip();                                                     // begin/append a tooltip window. to create full-featured tooltip (with any kind of items).
     IMGUI_API void          EndTooltip();
     IMGUI_API void          SetTooltip(const char* fmt, ...) IM_FMTARGS(1);                     // set a text-only tooltip, typically use with ImGui::IsItemHovered(). override any previous call to SetTooltip().
     IMGUI_API void          SetTooltipV(const char* fmt, va_list args) IM_FMTLIST(1);
@@ -822,7 +834,7 @@ namespace ImGui
     IMGUI_API void          SetStateStorage(ImGuiStorage* storage);                             // replace current window storage with our own (if you want to manipulate it yourself, typically clear subsection of it)
     IMGUI_API ImGuiStorage* GetStateStorage();
     IMGUI_API void          CalcListClipping(int items_count, float items_height, int* out_items_display_start, int* out_items_display_end);    // calculate coarse clipping for large list of evenly sized items. Prefer using the ImGuiListClipper higher-level helper if you can.
-    IMGUI_API bool          BeginChildFrame(ImGuiID id, const ImVec2& size, ImGuiWindowFlags flags = 0); // helper to create a child window / scrolling region that looks like a normal widget frame
+    IM_NODISCARD IMGUI_API bool          BeginChildFrame(ImGuiID id, const ImVec2& size, ImGuiWindowFlags flags = 0); // helper to create a child window / scrolling region that looks like a normal widget frame
     IMGUI_API void          EndChildFrame();                                                    // always call EndChildFrame() regardless of BeginChildFrame() return values (which indicates a collapsed/clipped window)
 
     // Text Utilities
@@ -1821,6 +1833,9 @@ struct ImGuiIO
     bool        ConfigWindowsMoveFromTitleBarOnly; // = false       // [BETA] Set to true to only allow moving windows when clicked+dragged from the title bar. Windows without a title bar are not affected.
     float       ConfigMemoryCompactTimer;       // = 60.0f          // [BETA] Free transient windows/tables memory buffers when unused for given amount of time. Set to -1.0f to disable.
 
+    // Debug options
+    bool        ConfigDebugBeginReturnValue;    // = false          // When set, some calls to Begin() will return false to facilitate testing and transitioning to 1.78 Begin()/End() pairing behavior. Will cycle through each unique window depth then repeat. Suggested use: add "io.ConfigDebugBeginReturnValue = io.KeyShift" in your main loop then occasionally press SHIFT. Windows should be flickering. Your code will assert in End() if calling End() incorrectly.
+
     //------------------------------------------------------------------
     // Platform Functions
     // (the imgui_impl_xxxx backend files are setting those up for you)

imgui_demo.cpp

@@ -179,9 +179,8 @@ static void ShowExampleMenuFile();
 static void HelpMarker(const char* desc)
 {
     ImGui::TextDisabled("(?)");
-    if (ImGui::IsItemHovered())
+    if (ImGui::IsItemHovered() && ImGui::BeginTooltip())
     {
-        ImGui::BeginTooltip();
         ImGui::PushTextWrapPos(ImGui::GetFontSize() * 35.0f);
         ImGui::TextUnformatted(desc);
         ImGui::PopTextWrapPos();
@@ -300,10 +299,12 @@ void ImGui::ShowDemoWindow(bool* p_open)
     if (show_app_about)         { ImGui::ShowAboutWindow(&show_app_about); }
     if (show_app_style_editor)
     {
-        ImGui::Begin("Dear ImGui Style Editor", &show_app_style_editor);
+        if (ImGui::Begin("Dear ImGui Style Editor", &show_app_style_editor))
+        {
             ImGui::ShowStyleEditor();
             ImGui::End();
         }
+    }
 
     // Demonstrate the various window flags. Typically you would just use the default!
     static bool no_titlebar = false;
@@ -339,11 +340,7 @@ void ImGui::ShowDemoWindow(bool* p_open)
 
     // Main body of the Demo window starts here.
     if (!ImGui::Begin("Dear ImGui Demo", p_open, window_flags))
-    {
-        // Early out if the window is collapsed, as an optimization.
-        ImGui::End();
         return;
-    }
 
     // Most "big" widgets share a common width settings by default. See 'Demo->Layout->Widgets Width' for details.
 
@@ -623,9 +620,8 @@ static void ShowDemoWindowWidgets()
 
         ImGui::SameLine();
         ImGui::Text("- or me");
-        if (ImGui::IsItemHovered())
+        if (ImGui::IsItemHovered() && ImGui::BeginTooltip())
         {
-            ImGui::BeginTooltip();
             ImGui::Text("I am a fancy tooltip");
             static float arr[] = { 0.6f, 0.1f, 1.0f, 0.5f, 0.92f, 0.1f, 0.2f };
             ImGui::PlotLines("Curve", arr, IM_ARRAYSIZE(arr));
@@ -1008,9 +1004,8 @@ static void ShowDemoWindowWidgets()
             ImVec4 tint_col = ImVec4(1.0f, 1.0f, 1.0f, 1.0f);   // No tint
             ImVec4 border_col = ImVec4(1.0f, 1.0f, 1.0f, 0.5f); // 50% opaque white
             ImGui::Image(my_tex_id, ImVec2(my_tex_w, my_tex_h), uv_min, uv_max, tint_col, border_col);
-            if (ImGui::IsItemHovered())
+            if (ImGui::IsItemHovered() && ImGui::BeginTooltip())
             {
-                ImGui::BeginTooltip();
                 float region_sz = 32.0f;
                 float region_x = io.MousePos.x - pos.x - region_sz * 0.5f;
                 float region_y = io.MousePos.y - pos.y - region_sz * 0.5f;
@@ -2109,9 +2104,12 @@ static void ShowDemoWindowWidgets()
 
         static bool embed_all_inside_a_child_window = false;
         ImGui::Checkbox("Embed everything inside a child window (for additional testing)", &embed_all_inside_a_child_window);
+        bool visible = true;
         if (embed_all_inside_a_child_window)
-            ImGui::BeginChild("outer_child", ImVec2(0, ImGui::GetFontSize() * 20.0f), true);
+            visible = ImGui::BeginChild("outer_child", ImVec2(0, ImGui::GetFontSize() * 20.0f), true);
 
+        if (visible)
+        {
             // Testing IsWindowFocused() function with its various flags.
             // Note that the ImGuiFocusedFlags_XXX flags can be combined.
             ImGui::BulletText(
@@ -2146,11 +2144,14 @@ static void ShowDemoWindowWidgets()
                 ImGui::IsWindowHovered(ImGuiHoveredFlags_RootWindow),
                 ImGui::IsWindowHovered(ImGuiHoveredFlags_AnyWindow));
 
-        ImGui::BeginChild("child", ImVec2(0, 50), true);
+            if (ImGui::BeginChild("child", ImVec2(0, 50), true))
+            {
                 ImGui::Text("This is another child window for testing the _ChildWindows flag.");
                 ImGui::EndChild();
+            }
             if (embed_all_inside_a_child_window)
                 ImGui::EndChild();
+        }
 
         static char unused_str[] = "This widget is only here to be able to tab-out of the widgets above.";
         ImGui::InputText("unused", unused_str, IM_ARRAYSIZE(unused_str), ImGuiInputTextFlags_ReadOnly);
@@ -2159,12 +2160,11 @@ static void ShowDemoWindowWidgets()
         // This is useful in particular if you want to create a context menu associated to the title bar of a window.
         // This will also work when docked into a Tab (the Tab replace the Title Bar and guarantee the same properties).
         static bool test_window = false;
-        ImGui::Checkbox("Hovered/Active tests after Begin() for title bar testing", &test_window);
-        if (test_window)
-        {
         // FIXME-DOCK: This window cannot be docked within the ImGui Demo window, this will cause a feedback loop and get them stuck.
         // Could we fix this through an ImGuiWindowClass feature? Or an API call to tag our parent as "don't skip items"?
-            ImGui::Begin("Title bar Hovered/Active tests", &test_window);
+        ImGui::Checkbox("Hovered/Active tests after Begin() for title bar testing", &test_window);
+        if (test_window && ImGui::Begin("Title bar Hovered/Active tests", &test_window))
+        {
             if (ImGui::BeginPopupContextItem()) // <-- This is using IsItemHovered()
             {
                 if (ImGui::MenuItem("Close")) { test_window = false; }
@@ -2199,11 +2199,13 @@ static void ShowDemoWindowLayout()
             ImGuiWindowFlags window_flags = ImGuiWindowFlags_HorizontalScrollbar;
             if (disable_mouse_wheel)
                 window_flags |= ImGuiWindowFlags_NoScrollWithMouse;
-            ImGui::BeginChild("ChildL", ImVec2(ImGui::GetWindowContentRegionWidth() * 0.5f, 260), false, window_flags);
+            if (ImGui::BeginChild("ChildL", ImVec2(ImGui::GetWindowContentRegionWidth() * 0.5f, 260), false, window_flags))
+            {
                 for (int i = 0; i < 100; i++)
                     ImGui::Text("%04d: scrollable region", i);
                 ImGui::EndChild();
             }
+        }
 
         ImGui::SameLine();
 
@@ -2215,7 +2217,10 @@ static void ShowDemoWindowLayout()
             if (!disable_menu)
                 window_flags |= ImGuiWindowFlags_MenuBar;
             ImGui::PushStyleVar(ImGuiStyleVar_ChildRounding, 5.0f);
-            ImGui::BeginChild("ChildR", ImVec2(0, 260), true, window_flags);
+            bool visible = ImGui::BeginChild("ChildR", ImVec2(0, 260), true, window_flags);
+            ImGui::PopStyleVar();
+            if (visible)
+            {
                 if (!disable_menu && ImGui::BeginMenuBar())
                 {
                     if (ImGui::BeginMenu("Menu"))
@@ -2237,7 +2242,7 @@ static void ShowDemoWindowLayout()
                     ImGui::EndTable();
                 }
                 ImGui::EndChild();
-            ImGui::PopStyleVar();
+            }
         }
 
         ImGui::Separator();
@@ -2256,14 +2261,17 @@ static void ShowDemoWindowLayout()
 
             ImGui::SetCursorPosX(ImGui::GetCursorPosX() + (float)offset_x);
             ImGui::PushStyleColor(ImGuiCol_ChildBg, IM_COL32(255, 0, 0, 100));
-            ImGui::BeginChild("Red", ImVec2(200, 100), true, ImGuiWindowFlags_None);
+            bool visible = ImGui::BeginChild("Red", ImVec2(200, 100), true, ImGuiWindowFlags_None);
+            ImGui::PopStyleColor();
+            if (visible)
+            {
                 for (int n = 0; n < 50; n++)
                     ImGui::Text("Some test %d", n);
                 ImGui::EndChild();
+            }
             bool child_is_hovered = ImGui::IsItemHovered();
             ImVec2 child_rect_min = ImGui::GetItemRectMin();
             ImVec2 child_rect_max = ImGui::GetItemRectMax();
-            ImGui::PopStyleColor();
             ImGui::Text("Hovered: %d", child_is_hovered);
             ImGui::Text("Rect of child window is: (%.0f,%.0f) (%.0f,%.0f)", child_rect_min.x, child_rect_min.y, child_rect_max.x, child_rect_max.y);
         }
@@ -2780,7 +2788,8 @@ static void ShowDemoWindowLayout()
 
             const ImGuiWindowFlags child_flags = enable_extra_decorations ? ImGuiWindowFlags_MenuBar : 0;
             const ImGuiID child_id = ImGui::GetID((void*)(intptr_t)i);
-            const bool child_is_visible = ImGui::BeginChild(child_id, ImVec2(child_w, 200.0f), true, child_flags);
+            if (ImGui::BeginChild(child_id, ImVec2(child_w, 200.0f), true, child_flags))
+            {
                 if (ImGui::BeginMenuBar())
                 {
                     ImGui::TextUnformatted("abc");
@@ -2790,8 +2799,6 @@ static void ShowDemoWindowLayout()
                     ImGui::SetScrollY(scroll_to_off_px);
                 if (scroll_to_pos)
                     ImGui::SetScrollFromPosY(ImGui::GetCursorStartPos().y + scroll_to_pos_px, i * 0.25f);
-            if (child_is_visible) // Avoid calling SetScrollHereY when running with culled items
-            {
                 for (int item = 0; item < 100; item++)
                 {
                     if (enable_track && item == track_item)
@@ -2804,11 +2811,15 @@ static void ShowDemoWindowLayout()
                         ImGui::Text("Item %d", item);
                     }
                 }
-            }
                 float scroll_y = ImGui::GetScrollY();
                 float scroll_max_y = ImGui::GetScrollMaxY();
                 ImGui::EndChild();
                 ImGui::Text("%.0f/%.0f", scroll_y, scroll_max_y);
+            }
+            else
+            {
+                ImGui::Text("N/A");
+            }
             ImGui::EndGroup();
         }
         ImGui::PopID();
@@ -2826,13 +2837,14 @@ static void ShowDemoWindowLayout()
             float child_height = ImGui::GetTextLineHeight() + style.ScrollbarSize + style.WindowPadding.y * 2.0f;
             ImGuiWindowFlags child_flags = ImGuiWindowFlags_HorizontalScrollbar | (enable_extra_decorations ? ImGuiWindowFlags_AlwaysVerticalScrollbar : 0);
             ImGuiID child_id = ImGui::GetID((void*)(intptr_t)i);
-            bool child_is_visible = ImGui::BeginChild(child_id, ImVec2(-100, child_height), true, child_flags);
+            float scroll_x = 0.0f;
+            float scroll_max_x = 0.0f;
+            if (ImGui::BeginChild(child_id, ImVec2(-100, child_height), true, child_flags))
+            {
                 if (scroll_to_off)
                     ImGui::SetScrollX(scroll_to_off_px);
                 if (scroll_to_pos)
                     ImGui::SetScrollFromPosX(ImGui::GetCursorStartPos().x + scroll_to_pos_px, i * 0.25f);
-            if (child_is_visible) // Avoid calling SetScrollHereY when running with culled items
-            {
                 for (int item = 0; item < 100; item++)
                 {
                     if (enable_track && item == track_item)
@@ -2846,10 +2858,10 @@ static void ShowDemoWindowLayout()
                     }
                     ImGui::SameLine();
                 }
-            }
+                scroll_x = ImGui::GetScrollX();
-            float scroll_x = ImGui::GetScrollX();
+                scroll_max_x = ImGui::GetScrollMaxX();
-            float scroll_max_x = ImGui::GetScrollMaxX();
                 ImGui::EndChild();
+            }
             ImGui::SameLine();
             const char* names[] = { "Left", "25%", "Center", "75%", "Right" };
             ImGui::Text("%s\n%.0f/%.0f", names[i], scroll_x, scroll_max_x);
@@ -2866,7 +2878,10 @@ static void ShowDemoWindowLayout()
         ImGui::PushStyleVar(ImGuiStyleVar_FrameRounding, 3.0f);
         ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(2.0f, 1.0f));
         ImVec2 scrolling_child_size = ImVec2(0, ImGui::GetFrameHeightWithSpacing() * 7 + 30);
-        ImGui::BeginChild("scrolling", scrolling_child_size, true, ImGuiWindowFlags_HorizontalScrollbar);
+        float scroll_x = 0.0f;
+        float scroll_max_x = 0.0f;
+        if (ImGui::BeginChild("scrolling", scrolling_child_size, true, ImGuiWindowFlags_HorizontalScrollbar))
+        {
             for (int line = 0; line < lines; line++)
             {
                 // Display random stuff. For the sake of this trivial demo we are using basic Button() + SameLine()
@@ -2890,9 +2905,10 @@ static void ShowDemoWindowLayout()
                     ImGui::PopID();
                 }
             }
-        float scroll_x = ImGui::GetScrollX();
+            scroll_x = ImGui::GetScrollX();
-        float scroll_max_x = ImGui::GetScrollMaxX();
+            scroll_max_x = ImGui::GetScrollMaxX();
             ImGui::EndChild();
+        }
         ImGui::PopStyleVar(2);
         float scroll_x_delta = 0.0f;
         ImGui::SmallButton("<<");
@@ -2909,10 +2925,13 @@ static void ShowDemoWindowLayout()
         {
             // Demonstrate a trick: you can use Begin to set yourself in the context of another window
             // (here we are already out of your child window)
-            ImGui::BeginChild("scrolling");
+            // FIXME-NEWBEGIN: Becomes more awkward
+            if (ImGui::BeginChild("scrolling"))
+            {
                 ImGui::SetScrollX(ImGui::GetScrollX() + scroll_x_delta);
                 ImGui::EndChild();
             }
+        }
         ImGui::Spacing();
 
         static bool show_horizontal_contents_size_demo_window = false;
@@ -2931,7 +2950,8 @@ static void ShowDemoWindowLayout()
             static float contents_size_x = 300.0f;
             if (explicit_content_size)
                 ImGui::SetNextWindowContentSize(ImVec2(contents_size_x, 0.0f));
-            ImGui::Begin("Horizontal contents size demo window", &show_horizontal_contents_size_demo_window, show_h_scrollbar ? ImGuiWindowFlags_HorizontalScrollbar : 0);
+            if (ImGui::Begin("Horizontal contents size demo window", &show_horizontal_contents_size_demo_window, show_h_scrollbar ? ImGuiWindowFlags_HorizontalScrollbar : 0))
+            {
                 ImGui::PushStyleVar(ImGuiStyleVar_ItemSpacing, ImVec2(2, 0));
                 ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(2, 0));
                 HelpMarker("Test of different widgets react and impact the work rectangle growing when horizontal scrolling is enabled.\n\nUse 'Metrics->Tools->Show windows rectangles' to visualize rectangles.");
@@ -3009,11 +3029,12 @@ static void ShowDemoWindowLayout()
                 }
                 if (show_child)
                 {
-                ImGui::BeginChild("child", ImVec2(0, 0), true);
+                    if (ImGui::BeginChild("child", ImVec2(0, 0), true))
                         ImGui::EndChild();
                 }
                 ImGui::End();
             }
+        }
 
         ImGui::TreePop();
     }
@@ -5147,10 +5168,10 @@ static void ShowDemoWindowColumns()
     {
         ImGui::SetNextWindowContentSize(ImVec2(1500.0f, 0.0f));
         ImVec2 child_size = ImVec2(0, ImGui::GetFontSize() * 20.0f);
-        ImGui::BeginChild("##ScrollingRegion", child_size, false, ImGuiWindowFlags_HorizontalScrollbar);
+        if (ImGui::BeginChild("##ScrollingRegion", child_size, false, ImGuiWindowFlags_HorizontalScrollbar))
-        ImGui::Columns(10);
+        {
-
             // Also demonstrate using clipper for large vertical lists
+            ImGui::Columns(10);
             int ITEMS_COUNT = 2000;
             ImGuiListClipper clipper;
             clipper.Begin(ITEMS_COUNT);
@@ -5165,6 +5186,7 @@ static void ShowDemoWindowColumns()
             }
             ImGui::Columns(1);
             ImGui::EndChild();
+        }
         ImGui::TreePop();
     }
 
@@ -5388,10 +5410,8 @@ static void ShowDemoWindowMisc()
 void ImGui::ShowAboutWindow(bool* p_open)
 {
     if (!ImGui::Begin("About Dear ImGui", p_open, ImGuiWindowFlags_AlwaysAutoResize))
-    {
-        ImGui::End();
         return;
-    }
+
     ImGui::Text("Dear ImGui %s", ImGui::GetVersion());
     ImGui::Separator();
     ImGui::Text("By Omar Cornut and all Dear ImGui contributors.");
@@ -5399,14 +5419,13 @@ void ImGui::ShowAboutWindow(bool* p_open)
 
     static bool show_config_info = false;
     ImGui::Checkbox("Config/Build Information", &show_config_info);
-    if (show_config_info)
+
-    {
     ImGuiIO& io = ImGui::GetIO();
     ImGuiStyle& style = ImGui::GetStyle();
-
+    const bool copy_to_clipboard = show_config_info && ImGui::Button("Copy to clipboard");
-        bool copy_to_clipboard = ImGui::Button("Copy to clipboard");
+    const ImVec2 child_size = ImVec2(0, ImGui::GetTextLineHeightWithSpacing() * 18);
-        ImVec2 child_size = ImVec2(0, ImGui::GetTextLineHeightWithSpacing() * 18);
+    if (show_config_info && ImGui::BeginChildFrame(ImGui::GetID("cfg_infos"), child_size, ImGuiWindowFlags_NoMove))
-        ImGui::BeginChildFrame(ImGui::GetID("cfg_infos"), child_size, ImGuiWindowFlags_NoMove);
+    {
         if (copy_to_clipboard)
         {
             ImGui::LogToClipboard();
@@ -5660,9 +5679,8 @@ static void NodeFont(ImFont* font)
                 draw_list->AddRect(cell_p1, cell_p2, glyph ? IM_COL32(255, 255, 255, 100) : IM_COL32(255, 255, 255, 50));
                 if (glyph)
                     font->RenderChar(draw_list, cell_size, cell_p1, glyph_col, (ImWchar)(base + n));
-                if (glyph && ImGui::IsMouseHoveringRect(cell_p1, cell_p2))
+                if (glyph && ImGui::IsMouseHoveringRect(cell_p1, cell_p2) && ImGui::BeginTooltip())
                 {
-                    ImGui::BeginTooltip();
                     ImGui::Text("Codepoint: U+%04X", base + n);
                     ImGui::Separator();
                     ImGui::Text("Visible: %d", glyph->Visible);
@@ -5804,7 +5822,8 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
                 "Left-click on color square to open color picker,\n"
                 "Right-click to open edit options menu.");
 
-            ImGui::BeginChild("##colors", ImVec2(0, 0), true, ImGuiWindowFlags_AlwaysVerticalScrollbar | ImGuiWindowFlags_AlwaysHorizontalScrollbar | ImGuiWindowFlags_NavFlattened);
+            if (ImGui::BeginChild("##colors", ImVec2(0, 0), true, ImGuiWindowFlags_AlwaysVerticalScrollbar | ImGuiWindowFlags_AlwaysHorizontalScrollbar | ImGuiWindowFlags_NavFlattened))
+            {
                 ImGui::PushItemWidth(-160);
                 for (int i = 0; i < ImGuiCol_COUNT; i++)
                 {
@@ -5827,6 +5846,7 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
                 }
                 ImGui::PopItemWidth();
                 ImGui::EndChild();
+            }
 
             ImGui::EndTabItem();
         }
@@ -5890,7 +5910,8 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
             if (ImGui::IsItemActive())
             {
                 ImGui::SetNextWindowPos(ImGui::GetCursorScreenPos());
-                ImGui::BeginTooltip();
+                if (ImGui::BeginTooltip())
+                {
                     ImVec2 p = ImGui::GetCursorScreenPos();
                     ImDrawList* draw_list = ImGui::GetWindowDrawList();
                     float RAD_MIN = 10.0f, RAD_MAX = 80.0f;
@@ -5904,6 +5925,7 @@ void ImGui::ShowStyleEditor(ImGuiStyle* ref)
                     ImGui::Dummy(ImVec2(off_x, RAD_MAX * 2.0f));
                     ImGui::EndTooltip();
                 }
+            }
             ImGui::SameLine();
             HelpMarker("When drawing circle primitives with \"num_segments == 0\" tesselation will be calculated automatically.");
 
@@ -5986,10 +6008,12 @@ static void ShowExampleMenuFile()
     {
         static bool enabled = true;
         ImGui::MenuItem("Enabled", "", &enabled);
-        ImGui::BeginChild("child", ImVec2(0, 60), true);
+        if (ImGui::BeginChild("child", ImVec2(0, 60), true))
+        {
             for (int i = 0; i < 10; i++)
                 ImGui::Text("Scrolling Text %d", i);
             ImGui::EndChild();
+        }
         static float f = 0.5f;
         static int n = 0;
         ImGui::SliderFloat("Value", &f, 0.0f, 1.0f);
@@ -6099,10 +6123,7 @@ struct ExampleAppConsole
     {
         ImGui::SetNextWindowSize(ImVec2(520, 600), ImGuiCond_FirstUseEver);
         if (!ImGui::Begin(title, p_open))
-        {
-            ImGui::End();
             return;
-        }
 
         // As a specific feature guaranteed by the library, after calling Begin() the last Item represent the title bar.
         // So e.g. IsItemHovered() will return true when hovering the title bar.
@@ -6148,7 +6169,8 @@ struct ExampleAppConsole
 
         // Reserve enough left-over height for 1 separator + 1 input text
         const float footer_height_to_reserve = ImGui::GetStyle().ItemSpacing.y + ImGui::GetFrameHeightWithSpacing();
-        ImGui::BeginChild("ScrollingRegion", ImVec2(0, -footer_height_to_reserve), false, ImGuiWindowFlags_HorizontalScrollbar);
+        if (ImGui::BeginChild("ScrollingRegion", ImVec2(0, -footer_height_to_reserve), false, ImGuiWindowFlags_HorizontalScrollbar))
+        {
             if (ImGui::BeginPopupContextWindow())
             {
                 if (ImGui::Selectable("Clear")) ClearLog();
@@ -6209,6 +6231,7 @@ struct ExampleAppConsole
 
             ImGui::PopStyleVar();
             ImGui::EndChild();
+        }
         ImGui::Separator();
 
         // Command-line
@@ -6432,10 +6455,7 @@ struct ExampleAppLog
     void    Draw(const char* title, bool* p_open = NULL)
     {
         if (!ImGui::Begin(title, p_open))
-        {
-            ImGui::End();
             return;
-        }
 
         // Options menu
         if (ImGui::BeginPopup("Options"))
@@ -6455,8 +6475,8 @@ struct ExampleAppLog
         Filter.Draw("Filter", -100.0f);
 
         ImGui::Separator();
-        ImGui::BeginChild("scrolling", ImVec2(0, 0), false, ImGuiWindowFlags_HorizontalScrollbar);
+        if (ImGui::BeginChild("scrolling", ImVec2(0, 0), false, ImGuiWindowFlags_HorizontalScrollbar))
-
+        {
             if (clear)
                 Clear();
             if (copy)
@@ -6513,6 +6533,7 @@ struct ExampleAppLog
                 ImGui::SetScrollHereY(1.0f);
 
             ImGui::EndChild();
+        }
         ImGui::End();
     }
 };
@@ -6526,7 +6547,8 @@ static void ShowExampleAppLog(bool* p_open)
     // We take advantage of a rarely used feature: multiple calls to Begin()/End() are appending to the _same_ window.
     // Most of the contents of the window will be added by the log.Draw() call.
     ImGui::SetNextWindowSize(ImVec2(500, 400), ImGuiCond_FirstUseEver);
-    ImGui::Begin("Example: Log", p_open);
+    if (ImGui::Begin("Example: Log", p_open))
+    {
         if (ImGui::SmallButton("[Debug] Add 5 entries"))
         {
             static int counter = 0;
@@ -6542,6 +6564,7 @@ static void ShowExampleAppLog(bool* p_open)
             }
         }
         ImGui::End();
+    }
 
     // Actually call in the regular Log helper (which will Begin() into the same window as we just did)
     log.Draw("Example: Log", p_open);
@@ -6555,8 +6578,8 @@ static void ShowExampleAppLog(bool* p_open)
 static void ShowExampleAppLayout(bool* p_open)
 {
     ImGui::SetNextWindowSize(ImVec2(500, 440), ImGuiCond_FirstUseEver);
-    if (ImGui::Begin("Example: Simple layout", p_open, ImGuiWindowFlags_MenuBar))
+    if (!ImGui::Begin("Example: Simple layout", p_open, ImGuiWindowFlags_MenuBar))
-    {
+        return;
     if (ImGui::BeginMenuBar())
     {
         if (ImGui::BeginMenu("File"))
@@ -6570,7 +6593,8 @@ static void ShowExampleAppLayout(bool* p_open)
     // Left
     static int selected = 0;
     {
-            ImGui::BeginChild("left pane", ImVec2(150, 0), true);
+        if (ImGui::BeginChild("left pane", ImVec2(150, 0), true))
+        {
             for (int i = 0; i < 100; i++)
             {
                 char label[128];
@@ -6580,12 +6604,14 @@ static void ShowExampleAppLayout(bool* p_open)
             }
             ImGui::EndChild();
         }
+    }
     ImGui::SameLine();
 
     // Right
     {
         ImGui::BeginGroup();
-            ImGui::BeginChild("item view", ImVec2(0, -ImGui::GetFrameHeightWithSpacing())); // Leave room for 1 line below us
+        if (ImGui::BeginChild("item view", ImVec2(0, -ImGui::GetFrameHeightWithSpacing()))) // Leave room for 1 line below us
+        {
             ImGui::Text("MyObject: %d", selected);
             ImGui::Separator();
             if (ImGui::BeginTabBar("##Tabs", ImGuiTabBarFlags_None))
@@ -6603,12 +6629,12 @@ static void ShowExampleAppLayout(bool* p_open)
                 ImGui::EndTabBar();
             }
             ImGui::EndChild();
+        }
         if (ImGui::Button("Revert")) {}
         ImGui::SameLine();
         if (ImGui::Button("Save")) {}
         ImGui::EndGroup();
     }
-    }
     ImGui::End();
 }
 
@@ -6668,10 +6694,7 @@ static void ShowExampleAppPropertyEditor(bool* p_open)
 {
     ImGui::SetNextWindowSize(ImVec2(430, 450), ImGuiCond_FirstUseEver);
     if (!ImGui::Begin("Example: Property editor", p_open))
-    {
-        ImGui::End();
         return;
-    }
 
     HelpMarker(
         "This example shows how you may implement a property editor using two columns.\n"
@@ -6703,10 +6726,7 @@ static void ShowExampleAppLongText(bool* p_open)
 {
     ImGui::SetNextWindowSize(ImVec2(520, 600), ImGuiCond_FirstUseEver);
     if (!ImGui::Begin("Example: Long text display", p_open))
-    {
-        ImGui::End();
         return;
-    }
 
     static int test_type = 0;
     static ImGuiTextBuffer log;
@@ -6725,7 +6745,9 @@ static void ShowExampleAppLongText(bool* p_open)
             log.appendf("%i The quick brown fox jumps over the lazy dog\n", lines + i);
         lines += 1000;
     }
-    ImGui::BeginChild("Log");
+
+    if (ImGui::BeginChild("Log"))
+    {
         switch (test_type)
         {
         case 0:
@@ -6753,6 +6775,7 @@ static void ShowExampleAppLongText(bool* p_open)
             break;
         }
         ImGui::EndChild();
+    }
     ImGui::End();
 }
 
@@ -6764,10 +6787,7 @@ static void ShowExampleAppLongText(bool* p_open)
 static void ShowExampleAppAutoResize(bool* p_open)
 {
     if (!ImGui::Begin("Example: Auto-resizing window", p_open, ImGuiWindowFlags_AlwaysAutoResize))
-    {
-        ImGui::End();
         return;
-    }
 
     static int lines = 10;
     ImGui::TextUnformatted(
@@ -6817,10 +6837,12 @@ static void ShowExampleAppConstrainedResize(bool* p_open)
     if (type == 6) ImGui::SetNextWindowSizeConstraints(ImVec2(0, 0),     ImVec2(FLT_MAX, FLT_MAX), CustomConstraints::Step, (void*)(intptr_t)100); // Fixed Step
 
     ImGuiWindowFlags flags = auto_resize ? ImGuiWindowFlags_AlwaysAutoResize : 0;
-    if (ImGui::Begin("Example: Constrained Resize", p_open, flags))
+    if (!ImGui::Begin("Example: Constrained Resize", p_open, flags))
-    {
+        return;
+
     if (ImGui::IsWindowDocked())
         ImGui::Text("Warning: Sizing Constraints won't work if the window is docked!");
+
     if (ImGui::Button("200x200")) { ImGui::SetWindowSize(ImVec2(200, 200)); } ImGui::SameLine();
     if (ImGui::Button("500x500")) { ImGui::SetWindowSize(ImVec2(500, 500)); } ImGui::SameLine();
     if (ImGui::Button("800x200")) { ImGui::SetWindowSize(ImVec2(800, 200)); }
@@ -6831,7 +6853,6 @@ static void ShowExampleAppConstrainedResize(bool* p_open)
     ImGui::Checkbox("Auto-resize", &auto_resize);
     for (int i = 0; i < display_lines; i++)
         ImGui::Text("%*sHello, sailor! Making this line long enough for the example.", i * 4, "");
-    }
     ImGui::End();
 }
 
@@ -6860,8 +6881,9 @@ static void ShowExampleAppSimpleOverlay(bool* p_open)
         ImGui::SetNextWindowViewport(viewport->ID);
     }
     ImGui::SetNextWindowBgAlpha(0.35f); // Transparent background
-    if (ImGui::Begin("Example: Simple overlay", p_open, window_flags))
+    if (!ImGui::Begin("Example: Simple overlay", p_open, window_flags))
-    {
+        return;
+
     ImGui::Text("Simple overlay\n" "in the corner of the screen.\n" "(right-click to change position)");
     ImGui::Separator();
     if (ImGui::IsMousePosValid())
@@ -6878,7 +6900,6 @@ static void ShowExampleAppSimpleOverlay(bool* p_open)
         if (p_open && ImGui::MenuItem("Close")) *p_open = false;
         ImGui::EndPopup();
     }
-    }
     ImGui::End();
 }
 
@@ -6896,23 +6917,29 @@ static void ShowExampleAppWindowTitles(bool*)
 
     // Using "##" to display same title but have unique identifier.
     ImGui::SetNextWindowPos(ImVec2(100, 100), ImGuiCond_FirstUseEver);
-    ImGui::Begin("Same title as another window##1");
+    if (ImGui::Begin("Same title as another window##1"))
+    {
         ImGui::Text("This is window 1.\nMy title is the same as window 2, but my identifier is unique.");
         ImGui::End();
+    }
 
     ImGui::SetNextWindowPos(ImVec2(100, 200), ImGuiCond_FirstUseEver);
-    ImGui::Begin("Same title as another window##2");
+    if (ImGui::Begin("Same title as another window##2"))
+    {
         ImGui::Text("This is window 2.\nMy title is the same as window 1, but my identifier is unique.");
         ImGui::End();
+    }
 
     // Using "###" to display a changing title but keep a static identifier "AnimatedTitle"
     char buf[128];
     sprintf(buf, "Animated title %c %d###AnimatedTitle", "|/-\\"[(int)(ImGui::GetTime() / 0.25f) & 3], ImGui::GetFrameCount());
     ImGui::SetNextWindowPos(ImVec2(100, 300), ImGuiCond_FirstUseEver);
-    ImGui::Begin(buf);
+    if (ImGui::Begin(buf))
+    {
         ImGui::Text("This window has a changing title.");
         ImGui::End();
     }
+}
 
 //-----------------------------------------------------------------------------
 // [SECTION] Example App: Custom Rendering using ImDrawList API / ShowExampleAppCustomRendering()
@@ -6922,10 +6949,7 @@ static void ShowExampleAppWindowTitles(bool*)
 static void ShowExampleAppCustomRendering(bool* p_open)
 {
     if (!ImGui::Begin("Example: Custom rendering", p_open))
-    {
-        ImGui::End();
         return;
-    }
 
     // Tip: If you do a lot of custom rendering, you probably want to use your own geometrical types and benefit of
     // overloaded operators, etc. Define IM_VEC2_CLASS_EXTRA in imconfig.h to create implicit conversions between your
@@ -7201,12 +7225,14 @@ void ShowExampleAppDockSpace(bool* p_open)
     // any change of dockspace/settings would lead to windows being stuck in limbo and never being visible.
     if (!opt_padding)
         ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0.0f, 0.0f));
-    ImGui::Begin("DockSpace Demo", p_open, window_flags);
+    bool ret = ImGui::Begin("DockSpace Demo", p_open, window_flags);
+
     if (!opt_padding)
         ImGui::PopStyleVar();
-
     if (opt_fullscreen)
         ImGui::PopStyleVar(2);
+    if (!ret)
+        return; // FIXME-NEWBEGIN: KeepAlive?
 
     // DockSpace
     ImGuiIO& io = ImGui::GetIO();
@@ -7376,11 +7402,8 @@ void ShowExampleAppDocuments(bool* p_open)
     // Another solution may be to make the "Example: Documents" window use the ImGuiWindowFlags_NoDocking.
 
     bool window_contents_visible = ImGui::Begin("Example: Documents", p_open, ImGuiWindowFlags_MenuBar);
-    if (!window_contents_visible && opt_target != Target_DockSpaceAndWindow)
+    if (!window_contents_visible && opt_target != Target_DockSpaceAndWindow) // FIXME-NEWBEGIN
-    {
-        ImGui::End();
         return;
-    }
 
     // Menu
     if (ImGui::BeginMenuBar())

imgui_internal.h

@@ -1438,6 +1438,7 @@ struct ImGuiContext
     ImGuiWindow*            HoveredWindowUnderMovingWindow;     // Hovered window ignoring MovingWindow. Only set if MovingWindow is set.
     ImGuiDockNode*          HoveredDockNode;                    // Hovered dock node.
     ImGuiWindow*            MovingWindow;                       // Track the window we clicked on (in order to preserve focus). The actual window that is moved is generally MovingWindow->RootWindow.
+    ImGuiWindow*            LastBeginWindow;                    // Track the last window we called Begin() on, this is used to easily access it even if Begin() returned false.
     ImGuiWindow*            WheelingWindow;                     // Track the window we started mouse-wheeling on. Until a timer elapse or mouse has moved, generally keep scrolling the same window even if during the course of scrolling the mouse ends up hovering a child window.
     ImVec2                  WheelingWindowRefMousePos;
     float                   WheelingWindowTimer;
@@ -1640,6 +1641,7 @@ struct ImGuiContext
     // Debug Tools
     bool                    DebugItemPickerActive;              // Item picker is active (started with DebugStartItemPicker())
     ImGuiID                 DebugItemPickerBreakId;             // Will call IM_DEBUG_BREAK() when encountering this id
+    int                     DebugBeginReturnValueCullDepth;     // Cycle between 0..9 then wrap around.
     ImGuiMetricsConfig      DebugMetricsConfig;
 
     // Misc
@@ -1675,6 +1677,7 @@ struct ImGuiContext
         HoveredWindowUnderMovingWindow = NULL;
         HoveredDockNode = NULL;
         MovingWindow = NULL;
+        LastBeginWindow = NULL;
         WheelingWindow = NULL;
         WheelingWindowTimer = 0.0f;
 
@@ -1793,6 +1796,7 @@ struct ImGuiContext
 
         DebugItemPickerActive = false;
         DebugItemPickerBreakId = 0;
+        DebugBeginReturnValueCullDepth = -1;
 
         memset(FramerateSecPerFrame, 0, sizeof(FramerateSecPerFrame));
         FramerateSecPerFrameIdx = 0;
@@ -2445,7 +2449,7 @@ namespace ImGui
     IMGUI_API void          ClosePopupsOverWindow(ImGuiWindow* ref_window, bool restore_focus_to_window_under_popup);
     IMGUI_API bool          IsPopupOpen(ImGuiID id, ImGuiPopupFlags popup_flags);
     IMGUI_API bool          BeginPopupEx(ImGuiID id, ImGuiWindowFlags extra_flags);
-    IMGUI_API void          BeginTooltipEx(ImGuiWindowFlags extra_flags, ImGuiTooltipFlags tooltip_flags);
+    IMGUI_API bool          BeginTooltipEx(ImGuiWindowFlags extra_flags, ImGuiTooltipFlags tooltip_flags);
     IMGUI_API ImGuiWindow*  GetTopMostPopupModal();
     IMGUI_API ImVec2        FindBestWindowPosForPopup(ImGuiWindow* window);
     IMGUI_API ImVec2        FindBestWindowPosForPopupEx(const ImVec2& ref_pos, const ImVec2& size, ImGuiDir* last_dir, const ImRect& r_outer, const ImRect& r_avoid, ImGuiPopupPositionPolicy policy);

imgui_widgets.cpp

@@ -1627,7 +1627,6 @@ bool ImGui::BeginCombo(const char* label, const char* preview_value, ImGuiComboF
     PopStyleVar();
     if (!ret)
     {
-        EndPopup();
         IM_ASSERT(0);   // This should never happen as we tested for IsPopupOpen() above
         return false;
     }
@@ -3838,7 +3837,6 @@ bool ImGui::InputTextEx(const char* label, const char* hint, char* buf, int buf_
         PopStyleColor();
         if (!child_visible)
         {
-            EndChild();
             EndGroup();
             return false;
         }
@@ -5355,7 +5353,8 @@ void ImGui::ColorTooltip(const char* text, const float* col, ImGuiColorEditFlags
 {
     ImGuiContext& g = *GImGui;
 
-    BeginTooltipEx(0, ImGuiTooltipFlags_OverridePreviousTooltip);
+    if (!BeginTooltipEx(0, ImGuiTooltipFlags_OverridePreviousTooltip))
+        return;
     const char* text_end = text ? FindRenderedTextEnd(text, NULL) : text;
     if (text_end > text)
     {
@@ -6133,8 +6132,11 @@ bool ImGui::ListBoxHeader(const char* label, const ImVec2& size_arg)
     if (label_size.x > 0)
         RenderText(ImVec2(frame_bb.Max.x + style.ItemInnerSpacing.x, frame_bb.Min.y + style.FramePadding.y), label);
 
-    BeginChildFrame(id, frame_bb.GetSize());
+    // FIXME-NEWBEGIN: Use to be return true so we'll trigger more issues.
-    return true;
+    bool ret = BeginChildFrame(id, frame_bb.GetSize());
+    if (!ret)
+        EndGroup();
+    return ret;
 }
 
 // FIXME: In principle this function should be called EndListBox(). We should rename it after re-evaluating if we want to keep the same signature.
@@ -6568,10 +6570,7 @@ bool ImGui::BeginMainMenuBar()
 
     g.NextWindowData.MenuBarOffsetMinVal = ImVec2(0.0f, 0.0f);
     if (!is_open)
-    {
-        End();
         return false;
-    }
     return true; //-V1020
 }
 

misc/freetype/README.md

@@ -104,7 +104,8 @@ struct FreeTypeTest
     // Call to draw interface
     void ShowFreetypeOptionsWindow()
     {
-        ImGui::Begin("FreeType Options");
+        if (!ImGui::Begin("FreeType Options"))
+            return;
         ImGui::ShowFontSelector("Fonts");
         WantRebuild |= ImGui::RadioButton("FreeType", (int*)&BuildMode, FontBuildMode_FreeType);
         ImGui::SameLine();