[two_dimensional_scrollables] Fix pinned cells hit test

[beroso]

This fixes a bug where TableView trailing pinned cells lose hit tests to underlying cells.
That glitch makes one of the main use cases unworkable (action columns at the right edge of the data grid).

Fix flutter/flutter#186876

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[gemini-code-assist]

Code Review

This pull request modifies RenderTableViewport to ensure hit testing correctly accounts for pinned areas by intersecting cell rectangles with section-specific clip rectangles. It introduces a _sectionClipRectFor method to calculate these bounds and adds regression tests to verify hit-test precedence for pinned cells. Review feedback suggests optimizing hit testing by using dual contains checks to avoid unnecessary object allocations and caching viewportDimension in _sectionClipRectFor to improve readability and performance.

[gemini-code-assist]

To avoid unnecessary object allocation during hit testing, you can replace the intersect call with a combined contains check. Rect.intersect creates a new Rect object, which is not needed here since you only need to verify if the position is within both rectangles. This is a common optimization in hit testing paths to reduce pressure on the garbage collector.

      if (cellRect.contains(position) &&
          _sectionClipRectFor(cellParentData.tableVicinity).contains(position)) {

[beroso]

Done!

[gemini-code-assist]

In _sectionClipRectFor, viewportDimension is accessed many times across different branches. Consider caching it in a local variable (e.g., final Size viewportSize = viewportDimension;) at the start of the method to improve readability and avoid redundant property accesses.

[beroso]

Done!

[Piinks]

Hey @beroso thanks so much for the fix!
It looks like there may be an edge case this does not account for. The implementation of _sectionClipRectFor calculates clip boundaries without factoring in the viewport alignment offsets (_hAlignmentOffset and _vAlignmentOffset).

When the table is smaller than the viewport and configured with a custom alignment (e.g., alignment: Alignment.center), cells and clip rects are shifted by the alignment offsets. For hit testing, cells are shifted (via their paintOffset), but _sectionClipRectFor returns an un-shifted clip rect. This means hit testing on pinned cells in aligned tables fails, as the tap position falls outside of the un-shifted clip rect.

I wrote a regression test to include and verify:

Details

Add the new regression test verifying hit-testing on aligned pinned columns:

    testWidgets('Tapping on a pinned column in an aligned table (with _hAlignmentOffset) registers correctly', (
      WidgetTester tester,
    ) async {
      TableVicinity? lastTapped;

      await tester.pumpWidget(
        MaterialApp(
          home: Scaffold(
            body: SizedBox(
              height: 400,
              width: 400,
              child: TableView.builder(
                cacheExtent: 0.0,
                columnCount: 3,
                rowCount: 1,
                pinnedColumnCount: 1,
                alignment: Alignment.center,
                columnBuilder: (_) => const TableSpan(extent: FixedTableSpanExtent(100)),
                rowBuilder: (_) => const TableSpan(extent: FixedTableSpanExtent(100)),
                cellBuilder: (_, TableVicinity vicinity) {
                  return TableViewCell(
                    child: GestureDetector(
                      behavior: HitTestBehavior.opaque,
                      onTap: () => lastTapped = vicinity,
                      child: const SizedBox.expand(),
                    ),
                  );
                },
              ),
            ),
          ),
        ),
      );

      // Pinned column 0 is at x = 50..150 due to Alignment.center. Tap at (100, 200).
      await tester.tapAt(const Offset(100, 200));
      await tester.pumpAndSettle();

      expect(
        lastTapped,
        TableVicinity.zero,
        reason: 'Tapping at x=100 (inside aligned pinned column 0) should register a tap on column 0.',
      );
    });

[beroso]

Hi @Piinks thanks for the feedback!
Landed a fix about the viewport alignment offsets and add some regression tests, including yours.