MultiSelect: Box-Select: Further refactor to extra mode code away from multi-select function into box-select funcitons.

imgui_internal.h

@@ -1718,6 +1718,7 @@ struct ImGuiBoxSelectState
     bool                    IsActive;
     bool                    IsStarting;
     bool                    IsStartedFromVoid;  // Starting click was not from an item.
+    bool                    RequestClear;
     ImGuiKeyChord           KeyMods : 16;       // Latched key-mods for box-select logic.
     ImVec2                  StartPosRel;        // Start position in window-contents relative space (to support scrolling)
     ImVec2                  EndPosRel;          // End position in window-contents relative space
@@ -1729,7 +1730,6 @@ struct ImGuiBoxSelectState
     ImRect                  UnclipRect;         // Rectangle where ItemAdd() clipping may be temporarily disabled. Need support by multi-select supporting widgets.
     ImRect                  BoxSelectRectPrev;  // Selection rectangle in absolute coordinates (derived every frame from BoxSelectStartPosRel and MousePos)
     ImRect                  BoxSelectRectCurr;
-    ImGuiSelectionUserData  LastSubmittedItem;  // Copy of last submitted item data, used to merge output ranges.
 
     ImGuiBoxSelectState()   { memset(this, 0, sizeof(*this)); }
 };
@@ -1762,6 +1762,7 @@ struct IMGUI_API ImGuiMultiSelectTempData
     bool                    NavIdPassedBy;
     bool                    RangeSrcPassedBy;   // Set by the item that matches RangeSrcItem.
     bool                    RangeDstPassedBy;   // Set by the item that matches NavJustMovedToId when IsSetRange is set.
+    ImGuiSelectionUserData  BoxSelectLastitem;  // Copy of last submitted item data, used to merge output ranges.
 
     ImGuiMultiSelectTempData()  { Clear(); }
     void Clear()            { size_t io_sz = sizeof(IO); ClearIO(); memset((void*)(&IO + 1), 0, sizeof(*this) - io_sz); } // Zero-clear except IO as we preserve IO.Requests[] buffer allocation.
@@ -3403,6 +3404,10 @@ namespace ImGui
     IMGUI_API int           TypingSelectFindNextSingleCharMatch(ImGuiTypingSelectRequest* req, int items_count, const char* (*get_item_name_func)(void*, int), void* user_data, int nav_item_idx);
     IMGUI_API int           TypingSelectFindBestLeadingMatch(ImGuiTypingSelectRequest* req, int items_count, const char* (*get_item_name_func)(void*, int), void* user_data);
 
+    // Box-Select API
+    IMGUI_API bool          BeginBoxSelect(ImGuiWindow* window, ImGuiID box_select_id, ImGuiMultiSelectFlags ms_flags);
+    IMGUI_API void          EndBoxSelect(const ImRect& scope_rect, bool enable_scroll);
+
     // Multi-Select API
     IMGUI_API void          MultiSelectItemHeader(ImGuiID id, bool* p_selected, ImGuiButtonFlags* p_button_flags);
     IMGUI_API void          MultiSelectItemFooter(ImGuiID id, bool* p_selected, bool* p_pressed);