Debug: move debug assertion in post-clip code to reduce overhead. (#4796

 and more).

Amend c801799

imgui.cpp

@@ -9613,6 +9613,7 @@ void ImGuiStackSizes::CompareWithContextState(ImGuiContext* ctx)
 // Advance cursor given item size for layout.
 // Register minimum needed size so it can extend the bounding box used for auto-fit calculation.
 // See comments in ItemAdd() about how/why the size provided to ItemSize() vs ItemAdd() may often different.
+// THIS IS IN THE PERFORMANCE CRITICAL PATH.
 void ImGui::ItemSize(const ImVec2& size, float text_baseline_y)
 {
     ImGuiContext& g = *GImGui;
@@ -9652,6 +9653,7 @@ void ImGui::ItemSize(const ImVec2& size, float text_baseline_y)
 // Declare item bounding box for clipping and interaction.
 // Note that the size can be different than the one provided to ItemSize(). Typically, widgets that spread over available surface
 // declare their minimum size requirement to ItemSize() and provide a larger region to ItemAdd() which is used drawing/interaction.
+// THIS IS IN THE PERFORMANCE CRITICAL PATH (UNTIL THE CLIPPING TEST AND EARLY-RETURN)
 bool ImGui::ItemAdd(const ImRect& bb, ImGuiID id, const ImRect* nav_bb_arg, ImGuiItemFlags extra_flags)
 {
     ImGuiContext& g = *GImGui;
@@ -9666,11 +9668,11 @@ bool ImGui::ItemAdd(const ImRect& bb, ImGuiID id, const ImRect* nav_bb_arg, ImGu
     g.LastItemData.StatusFlags = ImGuiItemStatusFlags_None;
     // Note: we don't copy 'g.NextItemData.SelectionUserData' to an hypothetical g.LastItemData.SelectionUserData: since the former is not cleared.
 
-    // Directional navigation processing
     if (id != 0)
     {
         KeepAliveID(id);
 
+        // Directional navigation processing
         // Runs prior to clipping early-out
         //  (a) So that NavInitRequest can be honored, for newly opened windows to select a default widget
         //  (b) So that we can scroll up/down past clipped items. This adds a small O(N) cost to regular navigation requests
@@ -9689,12 +9691,9 @@ bool ImGui::ItemAdd(const ImRect& bb, ImGuiID id, const ImRect* nav_bb_arg, ImGu
                     if (window == g.NavWindow || ((window->Flags | g.NavWindow->Flags) & ImGuiWindowFlags_NavFlattened))
                         NavProcessItem();
         }
-
-        // [DEBUG] People keep stumbling on this problem and using "" as identifier in the root of a window instead of "##something".
-        // Empty identifier are valid and useful in a small amount of cases, but 99.9% of the time you want to use "##something".
-        // READ THE FAQ: https://dearimgui.com/faq
-        IM_ASSERT(id != window->ID && "Cannot have an empty ID at the root of a window. If you need an empty label, use ## and read the FAQ about how the ID Stack works!");
     }
+
+    // Lightweight clear of SetNextItemXXX data.
     g.NextItemData.Flags = ImGuiNextItemDataFlags_None;
     g.NextItemData.ItemFlags = ImGuiItemFlags_None;
 
@@ -9704,7 +9703,7 @@ bool ImGui::ItemAdd(const ImRect& bb, ImGuiID id, const ImRect* nav_bb_arg, ImGu
 #endif
 
     // Clipping test
-    // (FIXME: This is a modified copy of IsClippedEx() so we can reuse the is_rect_visible value)
+    // (this is a modified copy of IsClippedEx() so we can reuse the is_rect_visible value)
     //const bool is_clipped = IsClippedEx(bb, id);
     //if (is_clipped)
     //    return false;
@@ -9716,12 +9715,20 @@ bool ImGui::ItemAdd(const ImRect& bb, ImGuiID id, const ImRect* nav_bb_arg, ImGu
 
     // [DEBUG]
 #ifndef IMGUI_DISABLE_DEBUG_TOOLS
-    if (id != 0 && id == g.DebugLocateId)
-        DebugLocateItemResolveWithLastItem();
-#endif
+    if (id != 0)
+    {
+        if (id == g.DebugLocateId)
+            DebugLocateItemResolveWithLastItem();
+
+        // [DEBUG] People keep stumbling on this problem and using "" as identifier in the root of a window instead of "##something".
+        // Empty identifier are valid and useful in a small amount of cases, but 99.9% of the time you want to use "##something".
+        // READ THE FAQ: https://dearimgui.com/faq
+        IM_ASSERT(id != window->ID && "Cannot have an empty ID at the root of a window. If you need an empty label, use ## and read the FAQ about how the ID Stack works!");
+    }
     //if (g.IO.KeyAlt) window->DrawList->AddRect(bb.Min, bb.Max, IM_COL32(255,255,0,120)); // [DEBUG]
     //if ((g.LastItemData.InFlags & ImGuiItemFlags_NoNav) == 0)
     //    window->DrawList->AddRect(g.LastItemData.NavRect.Min, g.LastItemData.NavRect.Max, IM_COL32(255,255,0,255)); // [DEBUG]
+#endif
 
     // We need to calculate this now to take account of the current clipping rectangle (as items like Selectable may change them)
     if (is_rect_visible)