[ADJUSTMENT] - Prefer to expand pixel snapping sizes rather than shrink, because shrinking intrinsically sized things can force a very different result on the other axis.

lib/src/flutter/flutter_pixel_alignment.dart

@@ -290,17 +290,157 @@ class RenderPixelSnapFlex extends RenderFlex {
         );
       }
 
-      if (child.size.width != child.size.width.floorToDouble() ||
-          child.size.height != child.size.height.floorToDouble()) {
+      if (!child.size.isInteger) {
         // This child doesn't have an integer width/height - run layout again,
-        // forcing the nearest smaller size.
-        child.layout(
-          BoxConstraints.tightFor(
-            width: child.size.width.floorToDouble(),
-            height: child.size.height.floorToDouble(),
-          ),
-        );
+        // forcing either slightly bigger or slightly smaller.
+        //
+        // There are a couple details that are sometimes important when changing
+        // the size to an integer value.
+        //
+        // First, we must always be mindful of text with intrinsic sizing. Any
+        // reduction in bounds to intrinsically sized text will force a relayout with
+        // some kind of wrapping, because the text reported exactly the bounds for
+        // its current layout. Thus, we want to prefer expanding size rather than
+        // contracting size. But we need to do our best to handle size contraction,
+        // too, in case we're dealing with a hard width or height constraint.
+        //
+        // Second, Columns and Rows are often intrinsically sized, too, in both
+        // dimensions. That said, Columns are often given space to expand/contract
+        // vertically, and Rows are often given space to expand/contract horizontally.
+        // For this reason, we treat Columns and Rows differently for re-sizing - we
+        // try to fit the cross-axis first, and then the main-axis second.
+        if (direction == Axis.vertical) {
+          _resizeChildForColumn(child);
+        } else {
+          _resizeChildForRow(child);
+        }
       }
     }
   }
+
+  void _resizeChildForColumn(RenderBox child) {
+    if (child.size.isInteger) {
+      return;
+    }
+
+    // This is a column. Start by working on the cross-axis, which is more likely
+    // to be bounded than the main-axis.
+    final widest = constraints.biggest.width;
+    late final int newWidth;
+    late final bool didShrinkWidth;
+    if (!child.size.widthIsInteger) {
+      if (child.size.width <= widest) {
+        // We prefer to increase size rather than decrease size, because text
+        // wrapping becomes a problem when shrinking intrinsic size. We can fit
+        // a bigger width, so use that.
+        newWidth = child.size.width.ceil();
+        didShrinkWidth = false;
+      } else {
+        // We prefer wider over narrower, but we can't fit any wider. Shrink instead.
+        newWidth = child.size.width.floor();
+        didShrinkWidth = true;
+      }
+    } else {
+      newWidth = child.size.width.toInt();
+      didShrinkWidth = false;
+    }
+
+    if (didShrinkWidth) {
+      // Shrinking the width has a non-trivial chance of significantly impacting the
+      // height, so run layout again with the new width and then deal with the height.
+      child.layout(BoxConstraints.tightFor(width: newWidth.toDouble()), parentUsesSize: true);
+    }
+
+    // Now do the main-axis.
+    final tallest = constraints.biggest.height;
+    late final int newHeight;
+    if (!child.size.heightIsInteger) {
+      if (child.size.height <= tallest) {
+        newHeight = child.size.height.ceil();
+      } else {
+        newHeight = child.size.height.floor();
+      }
+    } else {
+      newHeight = child.size.height.toInt();
+    }
+
+    // Note: This layout process can fail if a situation arises in which both the
+    // width and height need to contract, or if contracting the width produces a
+    // much taller height that violates constraints. If this happens to you, please
+    // file an issue on GitHub for flutter_test_goldens and provide us with the exact
+    // situation that's breaking for you.
+    child.layout(
+      BoxConstraints.tightFor(
+        width: newWidth.toDouble(),
+        height: newHeight.toDouble(),
+      ),
+    );
+  }
+
+  void _resizeChildForRow(RenderBox child) {
+    if (child.size.isInteger) {
+      return;
+    }
+
+    // This is a row. Start by working on the cross-axis, which is more likely
+    // to be bounded than the main-axis.
+    final tallest = constraints.biggest.height;
+    late final int newHeight;
+    late final bool didShrinkHeight;
+    if (!child.size.heightIsInteger) {
+      if (child.size.height <= tallest) {
+        // We prefer to increase size rather than decrease size, because text
+        // wrapping (and other layouts) becomes a problem when shrinking intrinsic
+        // size. We can fit a bigger height, so use that.
+        newHeight = child.size.height.ceil();
+        didShrinkHeight = false;
+      } else {
+        // We prefer taller over shorter, but we can't fit any taller. Shrink instead.
+        newHeight = child.size.height.floor();
+        didShrinkHeight = true;
+      }
+    } else {
+      newHeight = child.size.height.toInt();
+      didShrinkHeight = false;
+    }
+
+    if (didShrinkHeight) {
+      // Shrinking the height has a non-trivial chance of significantly impacting the
+      // width, so run layout again with the new height and then deal with the width.
+      child.layout(BoxConstraints.tightFor(height: newHeight.toDouble()), parentUsesSize: true);
+    }
+
+    // Now do the main-axis.
+    final widest = constraints.biggest.width;
+    late final int newWidth;
+    if (!child.size.widthIsInteger) {
+      if (child.size.width <= widest) {
+        newWidth = child.size.width.ceil();
+      } else {
+        newWidth = child.size.width.floor();
+      }
+    } else {
+      newWidth = child.size.width.toInt();
+    }
+
+    // Note: This layout process can fail if a situation arises in which both the
+    // width and height need to contract, or if contracting the width produces a
+    // much taller height that violates constraints. If this happens to you, please
+    // file an issue on GitHub for flutter_test_goldens and provide us with the exact
+    // situation that's breaking for you.
+    child.layout(
+      BoxConstraints.tightFor(
+        width: newWidth.toDouble(),
+        height: newHeight.toDouble(),
+      ),
+    );
+  }
+}
+
+extension on Size {
+  bool get isInteger => widthIsInteger && heightIsInteger;
+
+  bool get widthIsInteger => width == width.floorToDouble();
+
+  bool get heightIsInteger => height == height.floorToDouble();
 }

test/flutter/pixel_snapping_test.dart

@@ -99,11 +99,11 @@ void main() {
 
       // Ensure a whole-pixel offset.
       expect(tester.getTopLeft(find.byKey(item1Key)), Offset(7, 38));
-      expect(tester.getSize(find.byKey(item1Key)), Size(23, 23));
+      expect(tester.getSize(find.byKey(item1Key)), Size(24, 24));
       expect(tester.getTopLeft(find.byKey(item2Key)), Offset(38, 38));
-      expect(tester.getSize(find.byKey(item2Key)), Size(23, 23));
+      expect(tester.getSize(find.byKey(item2Key)), Size(24, 24));
       expect(tester.getTopLeft(find.byKey(item3Key)), Offset(69, 38));
-      expect(tester.getSize(find.byKey(item3Key)), Size(23, 23));
+      expect(tester.getSize(find.byKey(item3Key)), Size(24, 24));
     });
 
     testWidgets("PixelSnapColumn", (tester) async {
@@ -133,11 +133,11 @@ void main() {
 
       // Ensure a whole-pixel offset.
       expect(tester.getTopLeft(find.byKey(item1Key)), Offset(38, 7));
-      expect(tester.getSize(find.byKey(item1Key)), Size(23, 23));
+      expect(tester.getSize(find.byKey(item1Key)), Size(24, 24));
       expect(tester.getTopLeft(find.byKey(item2Key)), Offset(38, 38));
-      expect(tester.getSize(find.byKey(item2Key)), Size(23, 23));
+      expect(tester.getSize(find.byKey(item2Key)), Size(24, 24));
       expect(tester.getTopLeft(find.byKey(item3Key)), Offset(38, 69));
-      expect(tester.getSize(find.byKey(item3Key)), Size(23, 23));
+      expect(tester.getSize(find.byKey(item3Key)), Size(24, 24));
     });
   });
 }