Tables: Fixed auto-width columns when using synced-instances of same table. (#7218)

docs/CHANGELOG.txt

@@ -60,6 +60,8 @@ Other changes:
 - Windows: BeginChild(): Resizing logic for child windows evaluates whether per-axis clamping
   should be applied based on parent scrollbars, not child scrollbars. (#7440, #1710) [@cfillion]
   Adjust those resizing limits to match window padding rather than inner clipping rectangle.
+- Tables: Fixed auto-width columns when using synced-instances of same table, width of
+  one instance would bleed into next one instead of sharing their widths. (#7218)
 - Tables: Angled headers: fixed border hit box extending beyond when used within
   non-scrollable tables. (#7416) [@cfillion]
 - Tables: Angled headers: fixed borders not moving back up after TableAngleHeadersRow()

imgui_demo.cpp

@@ -5478,6 +5478,7 @@ static void ShowDemoWindowTables()
         HelpMarker("Multiple tables with the same identifier will share their settings, width, visibility, order etc.");
 
         static ImGuiTableFlags flags = ImGuiTableFlags_Resizable | ImGuiTableFlags_Reorderable | ImGuiTableFlags_Hideable | ImGuiTableFlags_Borders | ImGuiTableFlags_SizingFixedFit | ImGuiTableFlags_NoSavedSettings;
+        ImGui::CheckboxFlags("ImGuiTableFlags_Resizable", &flags, ImGuiTableFlags_Resizable);
         ImGui::CheckboxFlags("ImGuiTableFlags_ScrollY", &flags, ImGuiTableFlags_ScrollY);
         ImGui::CheckboxFlags("ImGuiTableFlags_SizingFixedFit", &flags, ImGuiTableFlags_SizingFixedFit);
         ImGui::CheckboxFlags("ImGuiTableFlags_HighlightHoveredColumn", &flags, ImGuiTableFlags_HighlightHoveredColumn);

imgui_tables.cpp

@@ -1068,6 +1068,7 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
         // - ClipRect.Max.x: using WorkMaxX instead of MaxX (aka including padding) makes things more consistent when resizing down, tho slightly detrimental to visibility in very-small column.
         // - ClipRect.Max.x: using MaxX makes it easier for header to receive hover highlight with no discontinuity and display sorting arrow.
         // - FIXME-TABLE: We want equal width columns to have equal (ClipRect.Max.x - WorkMinX) width, which means ClipRect.max.x cannot stray off host_clip_rect.Max.x else right-most column may appear shorter.
+        const float previous_instance_work_min_x = column->WorkMinX;
         column->WorkMinX = column->MinX + table->CellPaddingX + table->CellSpacingX1;
         column->WorkMaxX = column->MaxX - table->CellPaddingX - table->CellSpacingX2; // Expected max
         column->ItemWidth = ImTrunc(column->WidthGiven * 0.65f);
@@ -1120,8 +1121,22 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
         //    column->WorkMinX = ImLerp(column->WorkMinX, ImMax(column->StartX, column->MaxX - column->ContentWidthRowsUnfrozen), 0.5f);
 
         // Reset content width variables
-        column->ContentMaxXFrozen = column->ContentMaxXUnfrozen = column->WorkMinX;
-        column->ContentMaxXHeadersUsed = column->ContentMaxXHeadersIdeal = column->WorkMinX;
+        if (table->InstanceCurrent == 0)
+        {
+            column->ContentMaxXFrozen = column->WorkMinX;
+            column->ContentMaxXUnfrozen = column->WorkMinX;
+            column->ContentMaxXHeadersUsed = column->WorkMinX;
+            column->ContentMaxXHeadersIdeal = column->WorkMinX;
+        }
+        else
+        {
+            // As we store an absolute value to make per-cell updates faster, we need to offset values used for width computation.
+            const float offset_from_previous_instance = column->WorkMinX - previous_instance_work_min_x;
+            column->ContentMaxXFrozen += offset_from_previous_instance;
+            column->ContentMaxXUnfrozen += offset_from_previous_instance;
+            column->ContentMaxXHeadersUsed += offset_from_previous_instance;
+            column->ContentMaxXHeadersIdeal += offset_from_previous_instance;
+        }
 
         // Don't decrement auto-fit counters until container window got a chance to submit its items
         if (table->HostSkipItems == false)