From f08b33fd0c9ef438ef2a1d87447a700f01aa7168 Mon Sep 17 00:00:00 2001
From: ocornut <omar@miracleworld.net>
Date: Thu, 9 Apr 2026 22:15:32 +0200
Subject: [PATCH] Multi-Select: Box-Select: fixed an issue where items out of
 horizontal view would sometimes lead to incorrect merging of sequential
 selection requests. (#7994, #1861, #6518)

SetNextItemSelectionUserData() could use g.NextItemData.SelectionUserData if we could guarantee if would be valid when nesting multi-select blocks.
But it doesn't make much of a difference as whole ImGuiMultiSelectTempData fits in 2 cache lines.
---
 docs/CHANGELOG.txt | 4 +++-
 imgui_internal.h   | 3 ++-
 imgui_widgets.cpp  | 7 ++++---
 3 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/docs/CHANGELOG.txt b/docs/CHANGELOG.txt
index 148728e7b..cf57f093b 100644
--- a/docs/CHANGELOG.txt
+++ b/docs/CHANGELOG.txt
@@ -60,8 +60,10 @@ Other Changes:
     default ItemWidth. (#9355)
 - Multi-Select:
   - Box-Select: fixed an issue using ImGuiMultiSelectFlags_BoxSelect2d mode, where
-    items out of view wouldn't be properly selected when scrolling while mouse cursor
+    items out of view wouldn't be properly selected while scrolling while mouse cursor
     is hovering outside of selection scope. (#7994, #1861, #6518)
+  - Box-Select: fixed an issue where items out of horizontal view would sometimes lead
+    to incorrect merging of sequential selection requests. (#7994, #1861, #6518)
 - Fonts:
   - imgui_freetype: add FreeType headers & compiled version in 'About Dear ImGui' details.
 - Clipper:
diff --git a/imgui_internal.h b/imgui_internal.h
index 2a51931ef..5281c012e 100644
--- a/imgui_internal.h
+++ b/imgui_internal.h
@@ -1915,7 +1915,8 @@ struct IMGUI_API ImGuiMultiSelectTempData
     ImGuiMultiSelectFlags   Flags;
     ImVec2                  ScopeRectMin;
     ImVec2                  BackupCursorMaxPos;
-    ImGuiSelectionUserData  LastSubmittedItem;  // Copy of last submitted item data, used to merge output ranges.
+    ImGuiSelectionUserData  CurrSubmittedItem;  // Copy of last submitted item data, used to merge output ranges.
+    ImGuiSelectionUserData  PrevSubmittedItem;  // Copy of previous submitted item data, used to merge output ranges.
     ImGuiID                 BoxSelectId;
     ImGuiKeyChord           KeyMods;
     ImS8                    LoopRequestSetAll;  // -1: no operation, 0: clear all, 1: select all.
diff --git a/imgui_widgets.cpp b/imgui_widgets.cpp
index bee85438f..b929589aa 100644
--- a/imgui_widgets.cpp
+++ b/imgui_widgets.cpp
@@ -8050,7 +8050,7 @@ ImGuiMultiSelectIO* ImGui::BeginMultiSelect(ImGuiMultiSelectFlags flags, int sel
             storage->LastSelectionSize = 0;
     }
     ms->LoopRequestSetAll = request_select_all ? 1 : request_clear ? 0 : -1;
-    ms->LastSubmittedItem = ImGuiSelectionUserData_Invalid;
+    ms->PrevSubmittedItem = ImGuiSelectionUserData_Invalid;
 
     if (g.DebugLogFlags & ImGuiDebugLogFlags_EventSelection)
         DebugLogMultiSelectRequests("BeginMultiSelect", &ms->IO);
@@ -8153,6 +8153,8 @@ void ImGui::SetNextItemSelectionUserData(ImGuiSelectionUserData selection_user_d
         g.NextItemData.ItemFlags |= ImGuiItemFlags_HasSelectionUserData | ImGuiItemFlags_IsMultiSelect;
         if (ms->IO.RangeSrcItem == selection_user_data)
             ms->RangeSrcPassedBy = true;
+        ms->PrevSubmittedItem = ms->CurrSubmittedItem; // Can't rely on previous g.NextItemData.SelectionUserData because NextItemData is not restored on nested multi-select.
+        ms->CurrSubmittedItem = selection_user_data;
     }
     else
     {
@@ -8430,7 +8432,6 @@ void ImGui::MultiSelectItemFooter(ImGuiID id, bool* p_selected, bool* p_pressed)
     }
     if (storage->NavIdItem == item_data)
         ms->NavIdPassedBy = true;
-    ms->LastSubmittedItem = item_data;
 
     *p_selected = selected;
     *p_pressed = pressed;
@@ -8449,7 +8450,7 @@ void ImGui::MultiSelectAddSetRange(ImGuiMultiSelectTempData* ms, bool selected,
     if (ms->IO.Requests.Size > 0 && first_item == last_item && (ms->Flags & ImGuiMultiSelectFlags_NoRangeSelect) == 0)
     {
         ImGuiSelectionRequest* prev = &ms->IO.Requests.Data[ms->IO.Requests.Size - 1];
-        if (prev->Type == ImGuiSelectionRequestType_SetRange && prev->RangeLastItem == ms->LastSubmittedItem && prev->Selected == selected)
+        if (prev->Type == ImGuiSelectionRequestType_SetRange && prev->RangeLastItem == ms->PrevSubmittedItem && prev->Selected == selected)
         {
             prev->RangeLastItem = last_item;
             return;