Internals: Child windows that are clipped or part of a collapsed parent are not marked as collapsed anymore, but just a separate hidden marker set. We distinguish hiding for size measurement vs hiding for other reasons. Cleaned a little the end of Begin.

imgui.cpp

@@ -2120,6 +2120,7 @@ ImGuiWindow::ImGuiWindow(ImGuiContext* context, const char* name)
     CollapseToggleWanted = false;
     SkipItems = false;
     Appearing = false;
+    Hidden = false;
     HasCloseButton = false;
     BeginOrderWithinParent = -1;
     BeginOrderWithinContext = -1;
@@ -2129,7 +2130,7 @@ ImGuiWindow::ImGuiWindow(ImGuiContext* context, const char* name)
     AutoFitOnlyGrows = false;
     AutoFitChildAxises = 0x00;
     AutoPosLastDirection = ImGuiDir_None;
-    HiddenFrames = 0;
+    HiddenFramesRegular = HiddenFramesForResize = 0;
     SetWindowPosAllowFlags = SetWindowSizeAllowFlags = SetWindowCollapsedAllowFlags = ImGuiCond_Always | ImGuiCond_Once | ImGuiCond_FirstUseEver | ImGuiCond_Appearing;
     SetWindowPosVal = SetWindowPosPivot = ImVec2(FLT_MAX, FLT_MAX);
 
@@ -3665,7 +3666,7 @@ void ImGui::UpdateMouseMovingWindow()
 
 static bool IsWindowActiveAndVisible(ImGuiWindow* window)
 {
-    return (window->HiddenFrames == 0) && (window->Active);
+    return (window->Active) && (!window->Hidden);
 }
 
 static void ImGui::UpdateMouseInputs()
@@ -4340,7 +4341,7 @@ static void AddWindowToDrawData(ImVector<ImDrawList*>* out_render_list, ImGuiWin
     for (int i = 0; i < window->DC.ChildWindows.Size; i++)
     {
         ImGuiWindow* child = window->DC.ChildWindows[i];
-        if (child->Active && child->HiddenFrames == 0) // clipped children may have been marked not active
+        if (IsWindowActiveAndVisible(child)) // clipped children may have been marked not active
             AddWindowToDrawData(out_render_list, child);
     }
 }
@@ -4924,7 +4925,7 @@ static void FindHoveredWindow()
     for (int i = g.Windows.Size - 1; i >= 0 && hovered_window == NULL; i--)
     {
         ImGuiWindow* window = g.Windows[i];
-        if (!window->Active)
+        if (!window->Active || window->Hidden)
             continue;
         if (window->Flags & ImGuiWindowFlags_NoInputs)
             continue;
@@ -5251,7 +5252,8 @@ void ImGui::BeginTooltipEx(ImGuiWindowFlags extra_flags, bool override_previous_
             if (window->Active)
             {
                 // Hide previous tooltip from being displayed. We can't easily "reset" the content of a window so we create a new one.
-                window->HiddenFrames = 1;
+                window->Hidden = true;
+                window->HiddenFramesRegular = 1;
                 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_NoNav;
@@ -6220,7 +6222,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
 
     // Update the Appearing flag
     bool window_just_activated_by_user = (window->LastFrameActive < current_frame - 1);   // Not using !WasActive because the implicit "Debug" window would always toggle off->on
-    const bool window_just_appearing_after_hidden_for_resize = (window->HiddenFrames > 0);
+    const bool window_just_appearing_after_hidden_for_resize = (window->HiddenFramesForResize > 0);
     if (flags & ImGuiWindowFlags_Popup)
     {
         ImGuiPopupRef& popup_ref = g.OpenPopupStack[g.CurrentPopupStack.Size];
@@ -6316,18 +6318,20 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
 
         // Update contents size from last frame for auto-fitting (or use explicit size)
         window->SizeContents = CalcSizeContents(window);
-        if (window->HiddenFrames > 0)
-            window->HiddenFrames--;
+        if (window->HiddenFramesRegular > 0)
+            window->HiddenFramesRegular--;
+        if (window->HiddenFramesForResize > 0)
+            window->HiddenFramesForResize--;
 
         // Hide new windows for one frame until they calculate their size
         if (window_just_created && (!window_size_x_set_by_api || !window_size_y_set_by_api))
-            window->HiddenFrames = 1;
+            window->HiddenFramesForResize = 1;
 
         // Hide popup/tooltip window when re-opening while we measure size (because we recycle the windows)
         // We reset Size/SizeContents for reappearing popups/tooltips early in this function, so further code won't be tempted to use the old size.
         if (window_just_activated_by_user && (flags & (ImGuiWindowFlags_Popup | ImGuiWindowFlags_Tooltip)) != 0)
         {
-            window->HiddenFrames = 1;
+            window->HiddenFramesForResize = 1;
             if (flags & ImGuiWindowFlags_AlwaysAutoResize)
             {
                 if (!window_size_x_set_by_api)
@@ -6432,7 +6436,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
                 window->Pos = parent_window->DC.CursorPos;
         }
 
-        const bool window_pos_with_pivot = (window->SetWindowPosVal.x != FLT_MAX && window->HiddenFrames == 0);
+        const bool window_pos_with_pivot = (window->SetWindowPosVal.x != FLT_MAX && window->HiddenFramesForResize == 0);
         if (window_pos_with_pivot)
             SetWindowPos(window, ImMax(style.DisplaySafeAreaPadding, window->SetWindowPosVal - window->SizeFull * window->SetWindowPosPivot), 0); // Position given a pivot (e.g. for centering)
         else if ((flags & ImGuiWindowFlags_ChildMenu) != 0)
@@ -6500,7 +6504,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
             PushClipRect(viewport_rect.Min, viewport_rect.Max, true);
 
         // Draw modal window background (darkens what is behind them, all viewports)
-        const bool dim_bg_for_modal = (flags & ImGuiWindowFlags_Modal) && window == GetFrontMostPopupModal() && window->HiddenFrames <= 0;
+        const bool dim_bg_for_modal = (flags & ImGuiWindowFlags_Modal) && window == GetFrontMostPopupModal() && window->HiddenFramesForResize <= 0;
         const bool dim_bg_for_window_list = g.NavWindowingTargetAnim && (window == g.NavWindowingTargetAnim->RootWindow);
         if (dim_bg_for_modal || dim_bg_for_window_list)
         {
@@ -6750,29 +6754,31 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     window->BeginCount++;
     g.NextWindowData.Clear();
 
-
     if (flags & ImGuiWindowFlags_ChildWindow)
     {
         // Child window can be out of sight and have "negative" clip windows.
         // Mark them as collapsed so commands are skipped earlier (we can't manually collapse them because they have no title bar).
         IM_ASSERT((flags & ImGuiWindowFlags_NoTitleBar) != 0);
-        window->Collapsed = parent_window && parent_window->Collapsed;
 
         if (!(flags & ImGuiWindowFlags_AlwaysAutoResize) && window->AutoFitFramesX <= 0 && window->AutoFitFramesY <= 0)
-            window->Collapsed |= (window->OuterRectClipped.Min.x >= window->OuterRectClipped.Max.x || window->OuterRectClipped.Min.y >= window->OuterRectClipped.Max.y);
+            if (window->OuterRectClipped.Min.x >= window->OuterRectClipped.Max.x || window->OuterRectClipped.Min.y >= window->OuterRectClipped.Max.y)
+                window->HiddenFramesRegular = 1;
 
-        // We also hide the window from rendering because we've already added its border to the command list.
-        // (we could perform the check earlier in the function but it is simpler at this point)
-        if (window->Collapsed)
-            window->Active = false;
+        // Completely hide along with parent or if parent is collapsed
+        if (parent_window && (parent_window->Collapsed || parent_window->Hidden))
+            window->HiddenFramesRegular = 1;
     }
 
     // Don't render if style alpha is 0.0 at the time of Begin(). This is arbitrary and inconsistent but has been there for a long while (may remove at some point)
     if (style.Alpha <= 0.0f)
-        window->Active = false;
+        window->HiddenFramesRegular = 1;
+
+    // Update the Hidden flag
+    window->Hidden = (window->HiddenFramesRegular > 0) || (window->HiddenFramesForResize);
 
     // Return false if we don't intend to display anything to allow user to perform an early out optimization
-    window->SkipItems = (window->Collapsed || !window->Active) && window->AutoFitFramesX <= 0 && window->AutoFitFramesY <= 0;
+    window->SkipItems = (window->Collapsed || !window->Active || window->Hidden) && window->AutoFitFramesX <= 0 && window->AutoFitFramesY <= 0 && window->HiddenFramesForResize <= 0;
+
     return !window->SkipItems;
 }
 
@@ -13667,7 +13673,7 @@ bool ImGui::BeginDragDropSource(ImGuiDragDropFlags flags)
             {
                 ImGuiWindow* tooltip_window = g.CurrentWindow;
                 tooltip_window->SkipItems = true;
-                tooltip_window->HiddenFrames = 1;
+                tooltip_window->HiddenFramesRegular = 1;
             }
         }
 
@@ -14073,6 +14079,7 @@ void ImGui::ShowMetricsWindow(bool* p_open)
                     (flags & ImGuiWindowFlags_NoInputs)    ? "NoInputs":"", (flags & ImGuiWindowFlags_AlwaysAutoResize) ? "AlwaysAutoResize" : "");
                 ImGui::BulletText("Scroll: (%.2f/%.2f,%.2f/%.2f)", window->Scroll.x, GetScrollMaxX(window), window->Scroll.y, GetScrollMaxY(window));
                 ImGui::BulletText("Active: %d/%d, WriteAccessed: %d, BeginOrderWithinContext: %d", window->Active, window->WasActive, window->WriteAccessed, (window->Active || window->WasActive) ? window->BeginOrderWithinContext : -1);
+                ImGui::BulletText("Appearing: %d, Hidden: %d (Reg %d Resize %d), SkipItems: %d", window->Appearing, window->Hidden, window->HiddenFramesRegular, window->HiddenFramesForResize, window->SkipItems);
                 ImGui::BulletText("NavLastIds: 0x%08X,0x%08X, NavLayerActiveMask: %X", window->NavLastIds[0], window->NavLastIds[1], window->DC.NavLayerActiveMask);
                 ImGui::BulletText("NavLastChildNavWindow: %s", window->NavLastChildNavWindow ? window->NavLastChildNavWindow->Name : "NULL");
                 if (!window->NavRectRel[0].IsInverted())

imgui_internal.h

@@ -982,6 +982,7 @@ struct IMGUI_API ImGuiWindow
     bool                    CollapseToggleWanted;
     bool                    SkipItems;                          // Set when items can safely be all clipped (e.g. window not visible or collapsed)
     bool                    Appearing;                          // Set during the frame where the window is appearing (or re-appearing)
+    bool                    Hidden;                             // Do not display (== (HiddenFramesForResize > 0) ||
     bool                    HasCloseButton;                     // Set when the window has a close button (p_open != NULL)
     int                     BeginOrderWithinParent;             // Order within immediate parent window, if we are a child window. Otherwise 0.
     int                     BeginOrderWithinContext;            // Order within entire imgui context. This is mostly used for debugging submission order related issues.
@@ -991,7 +992,8 @@ struct IMGUI_API ImGuiWindow
     bool                    AutoFitOnlyGrows;
     int                     AutoFitChildAxises;
     ImGuiDir                AutoPosLastDirection;
-    int                     HiddenFrames;
+    int                     HiddenFramesRegular;                // Hide the window for N frames
+    int                     HiddenFramesForResize;              // Hide the window for N frames while allowing items to be submitted so we can measure their size
     ImGuiCond               SetWindowPosAllowFlags;             // store acceptable condition flags for SetNextWindowPos() use.
     ImGuiCond               SetWindowSizeAllowFlags;            // store acceptable condition flags for SetNextWindowSize() use.
     ImGuiCond               SetWindowCollapsedAllowFlags;       // store acceptable condition flags for SetNextWindowCollapsed() use.