Multi-Select: Box-Select+Tables: fixed Column return value when UnClipRect is active. (#7994, #8250)

Amend 6ce4b44 + bbd0af7. This probably should be redesigned to be more generic, e.g. move UnclipRect concept outside of Boxselect.

imgui_internal.h

@@ -3544,6 +3544,7 @@ namespace ImGui
     IMGUI_API void          TableUpdateLayout(ImGuiTable* table);
     IMGUI_API void          TableUpdateBorders(ImGuiTable* table);
     IMGUI_API void          TableUpdateColumnsWeightFromWidth(ImGuiTable* table);
+    IMGUI_API void          TableApplyExternalUnclipRect(ImGuiTable* table, ImRect& rect);
     IMGUI_API void          TableDrawBorders(ImGuiTable* table);
     IMGUI_API void          TableDrawDefaultContextMenu(ImGuiTable* table, ImGuiTableFlags flags_for_section_to_display);
     IMGUI_API bool          TableBeginContextMenuPopup(ImGuiTable* table);

imgui_tables.cpp

@@ -1152,7 +1152,6 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
         column->ClipRect.Min.y = work_rect.Min.y;
         column->ClipRect.Max.x = column->MaxX; //column->WorkMaxX;
         column->ClipRect.Max.y = FLT_MAX;
-        ImRect clip_rect_unclipped = column->ClipRect;
         column->ClipRect.ClipWithFull(host_clip_rect);
 
         // Mark column as Clipped (not in sight)
@@ -1170,9 +1169,6 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
 
         // Mark column as requesting output from user. Note that fixed + non-resizable sets are auto-fitting at all times and therefore always request output.
         column->IsRequestOutput = is_visible || column->AutoFitQueue != 0 || column->CannotSkipItemsQueue != 0;
-        ImGuiBoxSelectState* bs = &g.BoxSelectState;
-        if (!column->IsRequestOutput && bs->UnclipMode && bs->UnclipRect.Overlaps(clip_rect_unclipped))
-            column->IsRequestOutput = true;
 
         // Mark column as SkipItems (ignoring all items/layout)
         // (table->HostSkipItems is a copy of inner_window->SkipItems before we cleared it above in Part 2)
@@ -1319,14 +1315,30 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
         table->InnerWindow->DecoInnerSizeY1 = table_instance->LastFrozenHeight;
     table_instance->LastFrozenHeight = 0.0f;
 
-    // Initial state
     ImGuiWindow* inner_window = table->InnerWindow;
+    ImGuiBoxSelectState* bs = &g.BoxSelectState;
+    if (bs->Window == inner_window && bs->UnclipMode)
+        TableApplyExternalUnclipRect(table, bs->UnclipRect);
+
+    // Initial state
     if (table->Flags & ImGuiTableFlags_NoClip)
         table->DrawSplitter->SetCurrentChannel(inner_window->DrawList, TABLE_DRAW_CHANNEL_NOCLIP);
     else
         inner_window->DrawList->PushClipRect(inner_window->InnerClipRect.Min, inner_window->InnerClipRect.Max, false); // FIXME: use table->InnerClipRect?
 }
 
+// When starting a BeginMultiSelect() after table has been layout we update IsRequestOutput fields.
+void ImGui::TableApplyExternalUnclipRect(ImGuiTable* table, ImRect& rect)
+{
+    for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
+    {
+        ImGuiTableColumn* column = &table->Columns[column_n];
+        if (!column->IsRequestOutput)
+            if (rect.Overlaps(ImRect(column->MinX, table->WorkRect.Min.y, column->MaxX, FLT_MAX)))
+                column->IsRequestOutput = true;
+    }
+}
+
 // Process hit-testing on resizing borders. Actual size change will be applied in EndTable()
 // - Set table->HoveredColumnBorder with a short delay/timer to reduce visual feedback noise.
 void ImGui::TableUpdateBorders(ImGuiTable* table)

imgui_widgets.cpp

@@ -7848,6 +7848,8 @@ bool ImGui::BeginBoxSelect(const ImRect& scope_rect, ImGuiWindow* window, ImGuiI
         bs->UnclipRect = bs->BoxSelectRectPrev; // FIXME-OPT: UnclipRect X coordinates could be intersection of Prev and Curr rect on X axis.
         bs->UnclipRect.Add(bs->BoxSelectRectCurr);
     }
+    if (bs->UnclipMode && g.CurrentTable != NULL)
+        TableApplyExternalUnclipRect(g.CurrentTable, bs->UnclipRect);
 
 #ifdef IMGUI_DEBUG_BOXSELECT
     if (ms_flags & ImGuiMultiSelectFlags_BoxSelect2d)