MultiSelect+Tables: fixed an issue where box-select would skip items while drag-scrolling in a table with outer borders. (#7970, #7821).

See "widgets_multiselect_boxselect_2" test.

docs/CHANGELOG.txt

@@ -63,6 +63,8 @@ Other changes:
      #6223, #6364, #6387, #6567, #6692, #6724, #6939, #6984, #7246, #7270, #7375, #7421, #7434,
      #7472, #7581, #7724, #7926, #7937 and probably more..)
 - Nav: pressing any keyboard key while holding Alt disable toggling nav layer on Alt release. (#4439)
+- MultiSelect+Tables: fixed an issue where box-select would skip items while drag-scrolling
+  in a table with outer borders. (#7970, #7821).
 - InputText: internal refactoring to simplify and optimize the code. The ImWchar buffer has been
   removed. Simplifications allowed to implement new optimizations for handling very large text buffers
   (e.g. in our testing, handling of a 1 MB text buffer is now 3 times faster in VS2022 Debug build).

imgui_widgets.cpp

@@ -7403,6 +7403,7 @@ static void DebugLogMultiSelectRequests(const char* function, const ImGuiMultiSe
 
 static ImRect CalcScopeRect(ImGuiMultiSelectTempData* ms, ImGuiWindow* window)
 {
+    ImGuiContext& g = *GImGui;
     if (ms->Flags & ImGuiMultiSelectFlags_ScopeRect)
     {
         // Warning: this depends on CursorMaxPos so it means to be called by EndMultiSelect() only
@@ -7410,8 +7411,12 @@ static ImRect CalcScopeRect(ImGuiMultiSelectTempData* ms, ImGuiWindow* window)
     }
     else
     {
-        // Add inner table decoration (#7821) // FIXME: Why not baking in InnerClipRect?
+        // When a table, pull HostClipRect, which allows us to predict ClipRect before first row/layout is performed. (#7970)
         ImRect scope_rect = window->InnerClipRect;
+        if (g.CurrentTable != NULL)
+            scope_rect = g.CurrentTable->HostClipRect;
+
+        // Add inner table decoration (#7821) // FIXME: Why not baking in InnerClipRect?
         scope_rect.Min = ImMin(scope_rect.Min + ImVec2(window->DecoInnerSizeX1, window->DecoInnerSizeY1), scope_rect.Max);
         return scope_rect;
     }