Various comments

As it turns out, functions like IsItemHovered() won't work on an open BeginMenu() because LastItemData is overriden by BeginPopup(). Probably an easy fix.

imgui.cpp

@@ -3584,6 +3584,7 @@ bool ImGui::IsItemHovered(ImGuiHoveredFlags flags)
             return false;
         IM_ASSERT((flags & (ImGuiHoveredFlags_AnyWindow | ImGuiHoveredFlags_RootWindow | ImGuiHoveredFlags_ChildWindows | ImGuiHoveredFlags_NoPopupHierarchy)) == 0);   // Flags not supported by this function
 
+        // Done with rectangle culling so we can perform heavier checks now
         // Test if we are hovering the right window (our window could be behind another window)
         // [2021/03/02] Reworked / reverted the revert, finally. Note we want e.g. BeginGroup/ItemAdd/EndGroup to work as well. (#3851)
         // [2017/10/16] Reverted commit 344d48be3 and testing RootWindow instead. I believe it is correct to NOT test for RootWindow but this leaves us unable
@@ -3648,6 +3649,8 @@ bool ImGui::ItemHoverable(const ImRect& bb, ImGuiID id)
         return false;
     if (!IsMouseHoveringRect(bb.Min, bb.Max))
         return false;
+
+    // Done with rectangle culling so we can perform heavier checks now.
     if (!IsWindowContentHoverable(window, ImGuiHoveredFlags_None))
     {
         g.HoveredIdDisabled = true;

imgui_internal.h

@@ -149,8 +149,8 @@ typedef int ImGuiLayoutType;            // -> enum ImGuiLayoutType_         // E
 typedef int ImGuiActivateFlags;         // -> enum ImGuiActivateFlags_      // Flags: for navigation/focus function (will be for ActivateItem() later)
 typedef int ImGuiDebugLogFlags;         // -> enum ImGuiDebugLogFlags_      // Flags: for ShowDebugLogWindow(), g.DebugLogFlags
 typedef int ImGuiInputFlags;            // -> enum ImGuiInputFlags_         // Flags: for IsKeyPressedEx()
-typedef int ImGuiItemFlags;             // -> enum ImGuiItemFlags_          // Flags: for PushItemFlag()
+typedef int ImGuiItemFlags;             // -> enum ImGuiItemFlags_          // Flags: for PushItemFlag(), g.LastItemData.InFlags
-typedef int ImGuiItemStatusFlags;       // -> enum ImGuiItemStatusFlags_    // Flags: for DC.LastItemStatusFlags
+typedef int ImGuiItemStatusFlags;       // -> enum ImGuiItemStatusFlags_    // Flags: for g.LastItemData.StatusFlags
 typedef int ImGuiOldColumnFlags;        // -> enum ImGuiOldColumnFlags_     // Flags: for BeginColumns()
 typedef int ImGuiNavHighlightFlags;     // -> enum ImGuiNavHighlightFlags_  // Flags: for RenderNavHighlight()
 typedef int ImGuiNavMoveFlags;          // -> enum ImGuiNavMoveFlags_       // Flags: for navigation requests
@@ -758,7 +758,10 @@ struct ImDrawDataBuilder
 // [SECTION] Widgets support: flags, enums, data structures
 //-----------------------------------------------------------------------------
 
-// Transient per-window flags, reset at the beginning of the frame. For child window, inherited from parent on first Begin().
+// Flags used by upcoming items
+// - input: PushItemFlag() manipulates g.CurrentItemFlags, ItemAdd() calls may add extra flags.
+// - output: stored in g.LastItemData.InFlags
+// Current window shared by all windows.
 // This is going to be exposed in imgui.h when stabilized enough.
 enum ImGuiItemFlags_
 {
@@ -774,10 +777,11 @@ enum ImGuiItemFlags_
     ImGuiItemFlags_ReadOnly                 = 1 << 7,  // false     // [ALPHA] Allow hovering interactions but underlying value is not changed.
 
     // Controlled by widget code
-    ImGuiItemFlags_Inputable                = 1 << 8,  // false     // [WIP] Auto-activate input mode when tab focused. Currently only used and supported by a few items before it becomes a generic feature.
+    ImGuiItemFlags_Inputable                = 1 << 10, // false     // [WIP] Auto-activate input mode when tab focused. Currently only used and supported by a few items before it becomes a generic feature.
 };
 
-// Storage for LastItem data
+// Status flags for an already submitted item
+// - output: stored in g.LastItemData.StatusFlags
 enum ImGuiItemStatusFlags_
 {
     ImGuiItemStatusFlags_None               = 0,
@@ -2650,7 +2654,7 @@ namespace ImGui
     IMGUI_API ImVec2        GetContentRegionMaxAbs();
     IMGUI_API void          ShrinkWidths(ImGuiShrinkWidthItem* items, int count, float width_excess);
 
-    // Parameter stacks
+    // Parameter stacks (shared)
     IMGUI_API void          PushItemFlag(ImGuiItemFlags option, bool enabled);
     IMGUI_API void          PopItemFlag();
 

imgui_widgets.cpp

@@ -7018,6 +7018,7 @@ bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
     ImVec2 label_size = CalcTextSize(label, NULL, true);
 
     // Odd hack to allow hovering across menus of a same menu-set (otherwise we wouldn't be able to hover parent without always being a Child window)
+    // This is only done for items for the menu set and not the full parent window.
     const bool menuset_is_open = IsRootOfOpenMenuSet();
     ImGuiWindow* backed_nav_window = g.NavWindow;
     if (menuset_is_open)
@@ -7156,9 +7157,10 @@ bool ImGui::BeginMenuEx(const char* label, const char* icon, bool enabled)
 
     if (menu_is_open)
     {
-        SetNextWindowPos(popup_pos, ImGuiCond_Always); // Note: this is super misleading! The value will serve as reference for FindBestWindowPosForPopup(), not actual pos.
+        // FIXME: This technically breaks functions relying on LastItemData, somehow nobody complained yet. Should backup/restore LastItemData.
+        SetNextWindowPos(popup_pos, ImGuiCond_Always);                  // Note: misleading: the value will serve as reference for FindBestWindowPosForPopup(), not actual pos.
         PushStyleVar(ImGuiStyleVar_ChildRounding, style.PopupRounding); // First level will use _PopupRounding, subsequent will use _ChildRounding
-        menu_is_open = BeginPopupEx(id, flags); // menu_is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
+        menu_is_open = BeginPopupEx(id, flags);                         // menu_is_open can be 'false' when the popup is completely clipped (e.g. zero size display)
         PopStyleVar();
     }
     else
@@ -7177,7 +7179,7 @@ bool ImGui::BeginMenu(const char* label, bool enabled)
 void ImGui::EndMenu()
 {
     // Nav: When a left move request _within our child menu_ failed, close ourselves (the _parent_ menu).
-    // A menu doesn't close itself because EndMenuBar() wants the catch the last Left<>Right inputs.
+    // A menu doesn't close itself because EndMenuBar() wants to catch the last Left<>Right inputs.
     // However, it means that with the current code, a BeginMenu() from outside another menu or a menu-bar won't be closable with the Left direction.
     // FIXME: This doesn't work if the parent BeginMenu() is not on a menu.
     ImGuiContext& g = *GImGui;
@@ -7203,6 +7205,7 @@ bool ImGui::MenuItemEx(const char* label, const char* icon, const char* shortcut
     ImVec2 pos = window->DC.CursorPos;
     ImVec2 label_size = CalcTextSize(label, NULL, true);
 
+    // See BeginMenuEx() for comments about this.
     const bool menuset_is_open = IsRootOfOpenMenuSet();
     ImGuiWindow* backed_nav_window = g.NavWindow;
     if (menuset_is_open)