Remove rounding from TextPainter (#127099)

To opt-in, run the tests with: `SKPARAGRAPH_REMOVE_ROUNDING_HACK=1 flutter test --dart-define=SKPARAGRAPH_REMOVE_ROUNDING_HACK=1 `

Migration plans:
1. Turn the flags on in CI, migrate customer tests if needed
1. Migrate internal customers
2. Remove the flag from skparagraph. Remove the framework flag with a manual engine roll.

Also fixes https://github.com/flutter/flutter/issues/52038

packages/flutter/lib/src/painting/text_painter.dart

@@ -271,9 +271,13 @@ class _TextLayout {
   // object when it's no logner needed.
   ui.Paragraph _paragraph;
 
+  /// Whether to enable the rounding in _applyFloatingPointHack and SkParagraph.
+  static const bool _shouldApplyFloatingPointHack = !bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK');
+
   // TODO(LongCatIsLooong): https://github.com/flutter/flutter/issues/31707
   // remove this hack as well as the flooring in `layout`.
-  static double _applyFloatingPointHack(double layoutValue) => layoutValue.ceilToDouble();
+  @pragma('vm:prefer-inline')
+  static double _applyFloatingPointHack(double layoutValue) => _shouldApplyFloatingPointHack ? layoutValue.ceilToDouble() : layoutValue;
 
   /// Whether this layout has been invalidated and disposed.
   ///

packages/flutter/lib/src/painting/text_style.dart

@@ -595,14 +595,19 @@ class TextStyle with Diagnosticable {
   // in the [fontFamilyFallback] getter.
   final String? _package;
 
-  /// The size of glyphs (in logical pixels) to use when painting the text.
+  /// The size of fonts (in logical pixels) to use when painting the text.
+  ///
+  /// The value specified matches the dimension of the
+  /// [em square](https://fonts.google.com/knowledge/glossary/em) of the
+  /// underlying font, and more often then not isn't exactly the height or the
+  /// width of glyphs in the font.
   ///
   /// During painting, the [fontSize] is multiplied by the current
   /// `textScaleFactor` to let users make it easier to read text by increasing
   /// its size.
   ///
-  /// [getParagraphStyle] will default to 14 logical pixels if the font size
-  /// isn't specified here.
+  /// The [getParagraphStyle] method defaults to 14 logical pixels if [fontSize]
+  /// is set to null.
   final double? fontSize;
 
   /// The typeface thickness to use when painting the text (e.g., bold).

packages/flutter/test/cupertino/route_test.dart

@@ -161,7 +161,8 @@ void main() {
     // Also shows the previous page's title next to the back button.
     expect(find.widgetWithText(CupertinoButton, 'An iPod'), findsOneWidget);
     // 3 paddings + 1 test font character at font size 34.0.
-    expect(tester.getTopLeft(find.text('An iPod')).dx, 8.0 + 4.0 + 34.0 + 6.0);
+    // The epsilon is needed since the text theme has a negative letter spacing thus.
+    expect(tester.getTopLeft(find.text('An iPod')).dx, moreOrLessEquals(8.0 + 4.0 + 34.0 + 6.0, epsilon: 0.5));
   });
 
   testWidgets('Previous title is correct on first transition frame', (WidgetTester tester) async {
@@ -267,7 +268,8 @@ void main() {
     // from An iPod to Back (since An Internet communicator is too long to
     // fit in the back button).
     expect(find.widgetWithText(CupertinoButton, 'Back'), findsOneWidget);
-    expect(tester.getTopLeft(find.text('Back')).dx, 8.0 + 4.0 + 34.0 + 6.0);
+    // The epsilon is needed since the text theme has a negative letter spacing thus.
+    expect(tester.getTopLeft(find.text('Back')).dx, moreOrLessEquals(8.0 + 4.0 + 34.0 + 6.0, epsilon: 0.5));
   });
 
   testWidgets('Back swipe dismiss interrupted by route push', (WidgetTester tester) async {

packages/flutter/test/material/app_bar_test.dart

@@ -4726,7 +4726,7 @@ void main() {
             child: CustomScrollView(
               slivers: <Widget>[
                 const SliverAppBar.large(
-                  title: Text(title),
+                  title: Text(title, maxLines: 1),
                 ),
                 SliverToBoxAdapter(
                   child: Container(
@@ -4771,7 +4771,7 @@ void main() {
             child: CustomScrollView(
               slivers: <Widget>[
                 const SliverAppBar.medium(
-                  title: Text(title),
+                  title: Text(title, maxLines: 1),
                 ),
                 SliverToBoxAdapter(
                   child: Container(
@@ -4820,7 +4820,7 @@ void main() {
             child: CustomScrollView(
               slivers: <Widget>[
                 const SliverAppBar.large(
-                  title: Text(title),
+                  title: Text(title, maxLines: 1),
                 ),
                 SliverToBoxAdapter(
                   child: Container(

packages/flutter/test/material/badge_test.dart

@@ -50,7 +50,10 @@ void main() {
     expect(tester.getTopLeft(find.text('0')), const Offset(16, -4));
 
     final RenderBox box = tester.renderObject(find.byType(Badge));
-    expect(box, paints..rrect(rrect: RRect.fromLTRBR(12, -4, 32, 12, const Radius.circular(8)), color: theme.colorScheme.error));
+    final RRect rrect = const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? RRect.fromLTRBR(12, -4, 31.5, 12, const Radius.circular(8))
+      : RRect.fromLTRBR(12, -4, 32, 12, const Radius.circular(8));
+    expect(box, paints..rrect(rrect: rrect, color: theme.colorScheme.error));
   });
 
   testWidgets('Large Badge defaults with RTL', (WidgetTester tester) async {
@@ -89,7 +92,10 @@ void main() {
     expect(tester.getTopLeft(find.text('0')), const Offset(0, -4));
 
     final RenderBox box = tester.renderObject(find.byType(Badge));
-    expect(box, paints..rrect(rrect: RRect.fromLTRBR(-4, -4, 16, 12, const Radius.circular(8)), color: theme.colorScheme.error));
+    final RRect rrect = const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? RRect.fromLTRBR(-4, -4, 15.5, 12, const Radius.circular(8))
+      : RRect.fromLTRBR(-4, -4, 16, 12, const Radius.circular(8));
+    expect(box, paints..rrect(rrect: rrect, color: theme.colorScheme.error));
   });
 
   // Essentially the same as 'Large Badge defaults'
@@ -143,7 +149,10 @@ void main() {
     // T = alignment.top
     // R = L + '0'.width + padding.width
     // B = T + largeSize, R = largeSize/2
-    expect(box, paints..rrect(rrect: RRect.fromLTRBR(12, -4, 32, 12, const Radius.circular(8)), color: theme.colorScheme.error));
+    final RRect rrect = const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? RRect.fromLTRBR(12, -4, 31.5, 12, const Radius.circular(8))
+      : RRect.fromLTRBR(12, -4, 32, 12, const Radius.circular(8));
+    expect(box, paints..rrect(rrect: rrect, color: theme.colorScheme.error));
 
     await tester.pumpWidget(buildFrame(1000));
     expect(find.text('999+'), findsOneWidget);

packages/flutter/test/material/flexible_space_bar_test.dart

@@ -465,18 +465,16 @@ void main() {
       ),
     );
 
+    final double textWidth = const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? width
+      : (width / 1.5).floorToDouble() * 1.5;
     // The title is scaled and transformed to be 1.5 times bigger, when the
     // FlexibleSpaceBar is fully expanded, thus we expect the width to be
     // 1.5 times smaller than the full width. The height of the text is the same
     // as the font size, with 10 dps bottom margin.
     expect(
       tester.getRect(find.byType(Text)),
-      Rect.fromLTRB(
-        0,
-        height - titleFontSize - 10,
-        (width / 1.5).floorToDouble() * 1.5,
-        height,
-      ),
+      rectMoreOrLessEquals(Rect.fromLTRB(0, height - titleFontSize - 10, textWidth, height), epsilon: 0.0001),
     );
   });
 
@@ -537,18 +535,16 @@ void main() {
     // bottom edge.
     const double bottomMargin = titleFontSize * (expandedTitleScale - 1);
 
+    final double textWidth = const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? collapsedWidth
+      : (collapsedWidth / 3).floorToDouble() * 3;
     // The title is scaled and transformed to be 3 times bigger, when the
     // FlexibleSpaceBar is fully expanded, thus we expect the width to be
     // 3 times smaller than the full width. The height of the text is the same
     // as the font size, with 40 dps bottom margin to maintain its bottom position.
     expect(
       tester.getRect(title),
-      Rect.fromLTRB(
-        0,
-        height - titleFontSize - bottomMargin,
-        (collapsedWidth / 3).floorToDouble() * 3,
-        height,
-      ),
+      rectMoreOrLessEquals(Rect.fromLTRB(0, height - titleFontSize - bottomMargin, textWidth, height), epsilon: 0.0001),
     );
   });
 

packages/flutter/test/material/input_decorator_test.dart

@@ -5697,8 +5697,11 @@ void main() {
           return false;
         }
         final Rect clipRect = arguments[0] as Rect;
-        // 133.3 is approximately 100 / 0.75 (_kFinalLabelScale)
-        expect(clipRect, rectMoreOrLessEquals(const Rect.fromLTWH(0, 0, 133.0, 16.0)));
+        // _kFinalLabelScale = 0.75
+        const double width = bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+          ? 100 / 0.75
+          : 133.0;
+        expect(clipRect, rectMoreOrLessEquals(const Rect.fromLTWH(0, 0, width, 16.0), epsilon: 1e-5));
         return true;
       }),
     );

packages/flutter/test/material/navigation_rail_test.dart

@@ -583,7 +583,7 @@ void main() {
     // Padding at the top of the rail.
     const double topPadding = 8.0;
     // Width of a destination.
-    const double destinationWidth = 126.0;
+    const double destinationWidth = bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? 125.5 : 126.0;
     // Height of a destination indicator with icon.
     const double destinationHeight = 32.0;
     // Space between the indicator and label.
@@ -858,7 +858,7 @@ void main() {
     // Padding at the top of the rail.
     const double topPadding = 8.0;
     // Width of a destination.
-    const double destinationWidth = 126.0;
+    const double destinationWidth = bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? 125.5 : 126.0;
     // Height of a destination indicator with icon.
     const double destinationHeight = 32.0;
     // Space between the indicator and label.

packages/flutter/test/material/outlined_button_test.dart

@@ -1045,7 +1045,7 @@ void main() {
         child: Directionality(
           textDirection: TextDirection.ltr,
           child: MediaQuery(
-            data: const MediaQueryData(textScaleFactor: 1.3),
+            data: const MediaQueryData(textScaleFactor: 1.25),
             child: Center(
               child: OutlinedButton(
                 style: const ButtonStyle(
@@ -1064,7 +1064,10 @@ void main() {
     );
 
     expect(tester.getSize(find.byType(OutlinedButton)), equals(const Size(88.0, 48.0)));
-    expect(tester.getSize(find.byType(Text)), const Size(55.0, 18.0));
+    expect(tester.getSize(find.byType(Text)), const Size(
+      bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? 52.5 : 53.0,
+      18.0,
+    ));
 
     // Set text scale large enough to expand text and button.
     await tester.pumpWidget(

packages/flutter/test/material/tab_bar_theme_test.dart

@@ -607,8 +607,8 @@ void main() {
         ..line(
           color: theme.colorScheme.primary,
           strokeWidth: indicatorWeight,
-          p1: const Offset(65.5, indicatorY),
-          p2: const Offset(134.5, indicatorY),
+          p1: const Offset(bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? 65.75 : 65.5, indicatorY),
+          p2: const Offset(bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? 134.25 : 134.5, indicatorY),
         ),
     );
   });

packages/flutter/test/material/tabs_test.dart

@@ -473,19 +473,31 @@ void main() {
 
     const double indicatorWeight = 3.0;
 
+
+    final RRect rrect = const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? RRect.fromLTRBAndCorners(
+          64.75,
+          tabBarBox.size.height - indicatorWeight,
+          135.25,
+          tabBarBox.size.height,
+          topLeft: const Radius.circular(3.0),
+          topRight: const Radius.circular(3.0),
+        )
+      : RRect.fromLTRBAndCorners(
+          64.5,
+          tabBarBox.size.height - indicatorWeight,
+          135.5,
+          tabBarBox.size.height,
+          topLeft: const Radius.circular(3.0),
+          topRight: const Radius.circular(3.0),
+        );
+
     expect(
       tabBarBox,
       paints
         ..rrect(
           color: theme.colorScheme.primary,
-          rrect: RRect.fromLTRBAndCorners(
-            64.5,
-            tabBarBox.size.height - indicatorWeight,
-            135.5,
-            tabBarBox.size.height,
-            topLeft: const Radius.circular(3.0),
-            topRight: const Radius.circular(3.0),
-          ),
+          rrect: rrect,
     ));
   });
 

packages/flutter/test/material/text_button_test.dart

@@ -608,7 +608,7 @@ void main() {
         child: Directionality(
           textDirection: TextDirection.ltr,
           child: MediaQuery(
-            data: const MediaQueryData(textScaleFactor: 1.3),
+            data: const MediaQueryData(textScaleFactor: 1.25),
             child: Center(
               child: TextButton(
                 onPressed: () { },
@@ -620,8 +620,14 @@ void main() {
       ),
     );
 
-    expect(tester.getSize(find.byType(TextButton)), const Size(71.0, 48.0));
-    expect(tester.getSize(find.byType(Text)), const Size(55.0, 18.0));
+    const Size textButtonSize = bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? Size(68.5, 48.0)
+      : Size(69.0, 48.0);
+    const Size textSize = bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+      ? Size(52.5, 18.0)
+      : Size(53.0, 18.0);
+    expect(tester.getSize(find.byType(TextButton)), textButtonSize);
+    expect(tester.getSize(find.byType(Text)), textSize);
 
     // Set text scale large enough to expand text and button.
     await tester.pumpWidget(

packages/flutter/test/material/time_picker_test.dart

@@ -744,7 +744,9 @@ void main() {
         switch (materialType) {
           case MaterialType.material2:
             expect(tester.getTopLeft(find.text(selectTimeString)), equals(const Offset(154, 155)));
-            expect(tester.getBottomRight(find.text(selectTimeString)), equals(const Offset(281, 165)));
+            expect(tester.getBottomRight(find.text(selectTimeString)), equals(
+              const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? const Offset(280.5, 165) : const Offset(281, 165),
+            ));
             expect(tester.getBottomRight(find.text(okString)).dx, 644);
             expect(tester.getBottomLeft(find.text(okString)).dx, 616);
             expect(tester.getBottomRight(find.text(cancelString)).dx, 582);
@@ -764,7 +766,9 @@ void main() {
 
         switch (materialType) {
           case MaterialType.material2:
-            expect(tester.getTopLeft(find.text(selectTimeString)), equals(const Offset(519, 155)));
+            expect(tester.getTopLeft(find.text(selectTimeString)), equals(
+              const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK') ? const Offset(519.5, 155) : const Offset(519, 155),
+            ));
             expect(tester.getBottomRight(find.text(selectTimeString)), equals(const Offset(646, 165)));
             expect(tester.getBottomLeft(find.text(okString)).dx, 156);
             expect(tester.getBottomRight(find.text(okString)).dx, 184);

packages/flutter/test/painting/system_fonts_test.dart

@@ -180,11 +180,11 @@ void main() {
     );
     // Metrics should be refreshed
     // ignore: avoid_dynamic_calls
-    expect(state.numberLabelWidth - 46.0 < precisionErrorTolerance, isTrue);
+    expect(state.numberLabelWidth, lessThan(46.0 + precisionErrorTolerance));
     // ignore: avoid_dynamic_calls
-    expect(state.numberLabelHeight - 23.0 < precisionErrorTolerance, isTrue);
+    expect(state.numberLabelHeight, lessThan(23.0 + precisionErrorTolerance));
     // ignore: avoid_dynamic_calls
-    expect(state.numberLabelBaseline - 18.400070190429688 < precisionErrorTolerance, isTrue);
+    expect(state.numberLabelBaseline, lessThan(18.400070190429688 + precisionErrorTolerance));
     final Element element = tester.element(find.byType(CupertinoTimerPicker));
     expect(element.dirty, isTrue);
   }, skip: isBrowser);  // TODO(yjbanov): cupertino does not work on the Web yet: https://github.com/flutter/flutter/issues/41920

packages/flutter/test/painting/text_painter_test.dart

@@ -1507,6 +1507,27 @@ void main() {
 
     painter.dispose();
   });
+
+  test('TextPainter line breaking does not round to integers', () {
+    if (! const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')) {
+      return;
+    }
+    const double fontSize = 1.25;
+    const String text = '12345';
+    assert((fontSize * text.length).truncate() != fontSize * text.length);
+    final TextPainter painter = TextPainter(
+      textDirection: TextDirection.ltr,
+      text: const TextSpan(text: text, style: TextStyle(fontSize: fontSize)),
+    )..layout(maxWidth: text.length * fontSize);
+
+    expect(painter.maxIntrinsicWidth, text.length * fontSize);
+    switch (painter.computeLineMetrics()) {
+      case [ui.LineMetrics(width: final double width)]:
+        expect(width, text.length * fontSize);
+      case final List<ui.LineMetrics> metrics:
+        expect(metrics, hasLength(1));
+    }
+  }, skip: kIsWeb && !isCanvasKit); // [intended] Browsers seem to always round font/glyph metrics.
 }
 
 class MockCanvas extends Fake implements Canvas {