[two_dimensional_scrollables] Fix layout offset of merged pinned cells (flutter#6178)

Fixes flutter/flutter#143526

This fixes the layout offset computation when there are merged cells within pinned rows and/or columns in TableView.

Author: Piinks

packages/two_dimensional_scrollables/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.1.1
+
+* Fixes a layout issue when pinned cells are merged.
+
 ## 0.1.0
 
 * [Breaking change] Adds support for merged cells in the TableView.

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

@@ -801,15 +801,41 @@ class RenderTableViewport extends RenderTwoDimensionalViewport {
             //       | <--------- extent of merged cell ---------> |
 
             // Compute height and layout offset for merged rows.
-            mergedRowOffset = -verticalOffset.pixels +
+            final bool rowIsInPinnedColumn = _lastPinnedColumn != null &&
+                vicinity.column <= _lastPinnedColumn!;
+            final bool rowIsPinned =
+                _lastPinnedRow != null && firstRow <= _lastPinnedRow!;
+            final double baseRowOffset =
+                switch ((rowIsInPinnedColumn, rowIsPinned)) {
+              // Both row and column are pinned at this cell, or just pinned row.
+              (true, true) || (false, true) => 0.0,
+              // Cell is within a pinned column
+              (true, false) => _pinnedRowsExtent - verticalOffset.pixels,
+              // Cell is within a pinned row, or no pinned portion.
+              (false, false) => -verticalOffset.pixels,
+            };
+            mergedRowOffset = baseRowOffset +
                 _rowMetrics[firstRow]!.leadingOffset +
                 _rowMetrics[firstRow]!.configuration.padding.leading;
             mergedRowHeight = _rowMetrics[lastRow]!.trailingOffset -
                 _rowMetrics[firstRow]!.leadingOffset -
                 _rowMetrics[lastRow]!.configuration.padding.trailing -
                 _rowMetrics[firstRow]!.configuration.padding.leading;
             // Compute width and layout offset for merged columns.
-            mergedColumnOffset = -horizontalOffset.pixels +
+            final bool columnIsInPinnedRow =
+                _lastPinnedRow != null && vicinity.row <= _lastPinnedRow!;
+            final bool columnIsPinned =
+                _lastPinnedColumn != null && firstColumn <= _lastPinnedColumn!;
+            final double baseColumnOffset =
+                switch ((columnIsInPinnedRow, columnIsPinned)) {
+              // Both row and column are pinned at this cell, or just pinned column.
+              (true, true) || (false, true) => 0.0,
+              // Cell is within a pinned row.
+              (true, false) => _pinnedColumnsExtent - horizontalOffset.pixels,
+              // No pinned portion.
+              (false, false) => -horizontalOffset.pixels,
+            };
+            mergedColumnOffset = baseColumnOffset +
                 _columnMetrics[firstColumn]!.leadingOffset +
                 _columnMetrics[firstColumn]!.configuration.padding.leading;
             mergedColumnWidth = _columnMetrics[lastColumn]!.trailingOffset -

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: 0.1.0
+version: 0.1.1
 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+