[two_dimensional_scrollables] optimizes tableview janks with >250k rows (#10738)

### Description:
This PR optimizes the scrolling jank issue of the TableView component when the number of rows exceeds 250,000.

### Root Cause:
The _updateFirstAndLastVisibleCell method in RenderTableViewport uses linear for-loop traversal on _columnMetrics and _rowMetrics to locate the visible boundary cells: _firstNonPinnedRow, _lastNonPinnedRow, _firstNonPinnedColumn, and _lastNonPinnedColumn. When the number of rows/columns is extremely large (e.g., >250k rows), this linear traversal causes significant main-thread blocking and scrolling jank.

### Solution:
Replace the linear for-loop with binary search algorithm to find the visible boundary cells (_firstNonPinnedRow, _lastNonPinnedRow, _firstNonPinnedColumn, _lastNonPinnedColumn). Binary search reduces the time complexity from O(n) to O(log n), effectively optimizing the scrolling jank issue under large data volumes.

### Fixes: [#138271](flutter/flutter#138271)

### Video performance comparison
before:
https://github.com/user-attachments/assets/ca5b8821-4bdb-411f-bb2c-63998ac7c0d9

after:
https://github.com/user-attachments/assets/ebbf96d9-9e04-4ede-ae79-cd433885d3ab

## Pre-Review Checklist

Author: wangfeihang

packages/two_dimensional_scrollables/CHANGELOG.md

@@ -1,7 +1,8 @@
-## NEXT
+## 0.3.8
 
 * Updates minimum supported SDK version to Flutter 3.35/Dart 3.9.
 * Updates examples to use the new RadioGroup API instead of deprecated Radio parameters.
+* Optimizes tableview janks with >250k rows.
 
 ## 0.3.7
 

packages/two_dimensional_scrollables/lib/src/table_view/table.dart

@@ -728,6 +728,32 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
     return verticalOffset.applyContentDimensions(0.0, maxVerticalScrollExtent);
   }
 
+  /// Binary search to find the first index with [_Span] matching the condition.
+  /// [map]: Index-[_Span] map, [condition]: Match rule
+  /// Returns the first matched index or null if not found.
+  int? _binarySearchFirstFromMap(
+    Map<int, _Span> map,
+    bool Function(_Span) condition,
+  ) {
+    if (map.isEmpty) {
+      return null;
+    }
+    var low = 0;
+    int high = map.length - 1;
+    int? result;
+    while (low <= high) {
+      final int mid = low + ((high - low) >> 1);
+      final _Span span = map[mid]!;
+      if (condition(span)) {
+        result = mid;
+        high = mid - 1;
+      } else {
+        low = mid + 1;
+      }
+    }
+    return result;
+  }
+
   // Uses the cached metrics to update the currently visible cells. If the
   // number of rows or columns are infinite, the layout is computed lazily, so
   // this will call for an update to the metrics if we have scrolled beyond the
@@ -750,21 +776,17 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
     }
     _firstNonPinnedColumn = null;
     _lastNonPinnedColumn = null;
-    for (var column = 0; column < _columnMetrics.length; column++) {
-      if (_columnMetrics[column]!.isPinned) {
-        continue;
-      }
-      final double endOfColumn = _columnMetrics[column]!.trailingOffset;
-      if (endOfColumn >= _targetLeadingColumnPixel &&
-          _firstNonPinnedColumn == null) {
-        _firstNonPinnedColumn = column;
-      }
-      if (endOfColumn >= _targetTrailingColumnPixel &&
-          _lastNonPinnedColumn == null) {
-        _lastNonPinnedColumn = column;
-        break;
-      }
-    }
+    // Binary search replaces for-loop to reduce computation.
+    _firstNonPinnedColumn = _binarySearchFirstFromMap(
+      _columnMetrics,
+      (span) =>
+          !span.isPinned && span.trailingOffset >= _targetLeadingColumnPixel,
+    );
+    _lastNonPinnedColumn = _binarySearchFirstFromMap(
+      _columnMetrics,
+      (span) =>
+          !span.isPinned && span.trailingOffset >= _targetTrailingColumnPixel,
+    );
     if (_firstNonPinnedColumn != null) {
       _lastNonPinnedColumn ??= _columnMetrics.length - 1;
     }
@@ -786,19 +808,16 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
     }
     _firstNonPinnedRow = null;
     _lastNonPinnedRow = null;
-    for (var row = 0; row < _rowMetrics.length; row++) {
-      if (_rowMetrics[row]!.isPinned) {
-        continue;
-      }
-      final double endOfRow = _rowMetrics[row]!.trailingOffset;
-      if (endOfRow >= _targetLeadingRowPixel && _firstNonPinnedRow == null) {
-        _firstNonPinnedRow = row;
-      }
-      if (endOfRow >= _targetTrailingRowPixel && _lastNonPinnedRow == null) {
-        _lastNonPinnedRow = row;
-        break;
-      }
-    }
+    // Binary search replaces for-loop to reduce computation.
+    _firstNonPinnedRow = _binarySearchFirstFromMap(
+      _rowMetrics,
+      (span) => !span.isPinned && span.trailingOffset >= _targetLeadingRowPixel,
+    );
+    _lastNonPinnedRow = _binarySearchFirstFromMap(
+      _rowMetrics,
+      (span) =>
+          !span.isPinned && span.trailingOffset >= _targetTrailingRowPixel,
+    );
     if (_firstNonPinnedRow != null) {
       _lastNonPinnedRow ??= _rowMetrics.length - 1;
     }

packages/two_dimensional_scrollables/pubspec.yaml

@@ -1,6 +1,6 @@
 name: two_dimensional_scrollables
 description: Widgets that scroll using the two dimensional scrolling foundation.
-version: 0.3.7
+version: 0.3.8
 repository: https://github.com/flutter/packages/tree/main/packages/two_dimensional_scrollables
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+two_dimensional_scrollables%22+
 

packages/two_dimensional_scrollables/test/table_view/table_test.dart

@@ -2130,6 +2130,35 @@ void main() {
           ),
         );
       });
+
+      testWidgets('Binary search correctly finds first/last non-pinned cells', (
+        WidgetTester tester,
+      ) async {
+        Future<void> runScrollTest(Widget tableView) async {
+          await tester.pumpWidget(MaterialApp(home: tableView));
+          await tester.pumpAndSettle();
+          expect(verticalController.position.pixels, 0.0);
+          expect(horizontalController.position.pixels, 0.0);
+          expect(find.text('R0:C0'), findsOneWidget);
+          expect(find.text('R4:C5'), findsOneWidget);
+          // No columns laid out beyond column 5.
+          expect(find.text('R0:C6'), findsNothing);
+          // Change the vertical scroll offset, validate more rows were
+          verticalController.jumpTo(1000000.0);
+          await tester.pump();
+          expect(find.text('R5000:C0'), findsOneWidget);
+          expect(find.text('R5004:C0'), findsOneWidget);
+          expect(find.text('R4990:C0'), findsNothing); // Not laid out
+          expect(find.text('R5007:C0'), findsNothing); // Not laid out
+          await tester.pumpWidget(Container());
+        }
+
+        // infinite rows & columns
+        await runScrollTest(getTableView());
+
+        // finite rows & columns
+        await runScrollTest(getTableView(rowCount: 10000, columnCount: 200));
+      });
     });
   });