IsItemHovered(): fixed return value false positive when used after EndChild(), EndGroup() or widgets using either... (#3851, #1370)

...when the hovered location is located within a child window, e.g. InputTextMultiline().
This is intended to have no side effects, but brace yourself for the possible comeback..
This essentially makes IsItemHovered() not accept hover from child windows, but EndChild/EndGroup are forwarded.
More or less should fix/revert c76f014292 which was a revert of 344d48be3

docs/CHANGELOG.txt

@@ -52,6 +52,9 @@ Other Changes:
   area (e.g. when window is collapsed + moved in a corner) to facilitate moving the window away. (#3825)
 - Window, Nav: Fixed crash when calling SetWindowFocus(NULL) as the time a new window appears. (#3865) [@nem0]
 - Tables: Fixed unaligned accesses when using TableSetBgColor(ImGuiTableBgTarget_CellBg). (#3872)
+- IsItemHovered(): fixed return value false positive when used after EndChild(), EndGroup() or widgets using
+  either of them, when the hovered location is located within a child window, e.g. InputTextMultiline().
+  This is intended to have no side effects, but brace yourself for the possible comeback.. (#3851, #1370)
 - Added GetAllocatorFunctions() to facilitate sharing allocators accross DLL boundaries. (#3836)
 - ImFontAtlas: Added 'bool TexPixelsUseColors' output to help backend decide of underlying texture format. (#3369)
   This can currently only ever be set by the Freetype renderer.

imgui.cpp

@@ -3122,20 +3122,22 @@ bool ImGui::IsItemHovered(ImGuiHoveredFlags flags)
         return IsItemFocused();
 
     // Test for bounding box overlap, as updated as ItemAdd()
-    if (!(window->DC.LastItemStatusFlags & ImGuiItemStatusFlags_HoveredRect))
+    ImGuiItemStatusFlags status_flags = window->DC.LastItemStatusFlags;
+    if (!(status_flags & ImGuiItemStatusFlags_HoveredRect))
         return false;
     IM_ASSERT((flags & (ImGuiHoveredFlags_RootWindow | ImGuiHoveredFlags_ChildWindows)) == 0);   // Flags not supported by this function
 
     // Test if we are hovering the right window (our window could be behind another window)
-    // [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 to use IsItemHovered() after EndChild() itself.
-    // Until a solution is found I believe reverting to the test from 2017/09/27 is safe since this was the test that has been running for a long while.
-    //if (g.HoveredWindow != window)
-    //    return false;
-    if (g.HoveredRootWindow != window->RootWindow && !(flags & ImGuiHoveredFlags_AllowWhenOverlapped))
-        return false;
+    // [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
+    // to use IsItemHovered() after EndChild() itself. Until a solution is found I believe reverting to the test from 2017/09/27 is safe since this was
+    // the test that has been running for a long while.
+    if (g.HoveredWindow != window && (status_flags & ImGuiItemStatusFlags_HoveredWindow) == 0)
+        if ((flags & ImGuiHoveredFlags_AllowWhenOverlapped) == 0)
+            return false;
 
     // Test if another item is active (e.g. being dragged)
-    if (!(flags & ImGuiHoveredFlags_AllowWhenBlockedByActiveItem))
+    if ((flags & ImGuiHoveredFlags_AllowWhenBlockedByActiveItem) == 0)
         if (g.ActiveId != 0 && g.ActiveId != window->DC.LastItemId && !g.ActiveIdAllowOverlap && g.ActiveId != window->MoveId)
             return false;
 
@@ -5014,6 +5016,8 @@ void ImGui::EndChild()
             // Not navigable into
             ItemAdd(bb, 0);
         }
+        if (g.HoveredWindow == window)
+            parent_window->DC.LastItemStatusFlags |= ImGuiItemStatusFlags_HoveredWindow;
     }
     g.WithinEndChild = false;
     g.LogLinePosY = -FLT_MAX; // To enforce a carriage return
@@ -7647,6 +7651,7 @@ void ImGui::BeginGroup()
     group_data.BackupCurrLineSize = window->DC.CurrLineSize;
     group_data.BackupCurrLineTextBaseOffset = window->DC.CurrLineTextBaseOffset;
     group_data.BackupActiveIdIsAlive = g.ActiveIdIsAlive;
+    group_data.BackupHoveredIdIsAlive = g.HoveredId != 0;
     group_data.BackupActiveIdPreviousFrameIsAlive = g.ActiveIdPreviousFrameIsAlive;
     group_data.EmitItem = true;
 
@@ -7700,6 +7705,11 @@ void ImGui::EndGroup()
         window->DC.LastItemId = g.ActiveIdPreviousFrame;
     window->DC.LastItemRect = group_bb;
 
+    // Forward Hovered flag
+    const bool group_contains_curr_hovered_id = (group_data.BackupHoveredIdIsAlive == false) && g.HoveredId != 0;
+    if (group_contains_curr_hovered_id)
+        window->DC.LastItemStatusFlags |= ImGuiItemStatusFlags_HoveredWindow;
+
     // Forward Edited flag
     if (group_contains_curr_active_id && g.ActiveIdHasBeenEditedThisFrame)
         window->DC.LastItemStatusFlags |= ImGuiItemStatusFlags_Edited;

imgui_internal.h

@@ -697,12 +697,13 @@ enum ImGuiItemStatusFlags_
 {
     ImGuiItemStatusFlags_None               = 0,
     ImGuiItemStatusFlags_HoveredRect        = 1 << 0,
-    ImGuiItemStatusFlags_HasDisplayRect     = 1 << 1,
+    ImGuiItemStatusFlags_HasDisplayRect     = 1 << 1,   // LastItemDisplayRect is valid
     ImGuiItemStatusFlags_Edited             = 1 << 2,   // Value exposed by item was edited in the current frame (should match the bool return value of most widgets)
     ImGuiItemStatusFlags_ToggledSelection   = 1 << 3,   // Set when Selectable(), TreeNode() reports toggling a selection. We can't report "Selected" because reporting the change allows us to handle clipping with less issues.
     ImGuiItemStatusFlags_ToggledOpen        = 1 << 4,   // Set when TreeNode() reports toggling their open state.
     ImGuiItemStatusFlags_HasDeactivated     = 1 << 5,   // Set if the widget/group is able to provide data for the ImGuiItemStatusFlags_Deactivated flag.
-    ImGuiItemStatusFlags_Deactivated        = 1 << 6    // Only valid if ImGuiItemStatusFlags_HasDeactivated is set.
+    ImGuiItemStatusFlags_Deactivated        = 1 << 6,   // Only valid if ImGuiItemStatusFlags_HasDeactivated is set.
+    ImGuiItemStatusFlags_HoveredWindow      = 1 << 7    // Override the HoveredWindow test to allow cross-window hover testing.
 
 #ifdef IMGUI_ENABLE_TEST_ENGINE
     , // [imgui_tests only]
@@ -924,7 +925,7 @@ struct ImGuiStyleMod
 };
 
 // Stacked storage data for BeginGroup()/EndGroup()
-struct ImGuiGroupData
+struct IMGUI_API ImGuiGroupData
 {
     ImGuiID     WindowID;
     ImVec2      BackupCursorPos;
@@ -935,6 +936,7 @@ struct ImGuiGroupData
     float       BackupCurrLineTextBaseOffset;
     ImGuiID     BackupActiveIdIsAlive;
     bool        BackupActiveIdPreviousFrameIsAlive;
+    bool        BackupHoveredIdIsAlive;
     bool        EmitItem;
 };