Reland #43118 "Add a flag to ParagraphBuilder for rounding hack migration" (#43647)

real diff: aedc37a

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: LongCatIsLooong

lib/ui/dart_ui.cc

@@ -78,7 +78,7 @@ typedef CanvasPath Path;
   V(Gradient::Create, 1)                                              \
   V(ImageFilter::Create, 1)                                           \
   V(ImageShader::Create, 1)                                           \
-  V(ParagraphBuilder::Create, 9)                                      \
+  V(ParagraphBuilder::Create, 10)                                     \
   V(PathMeasure::Create, 3)                                           \
   V(Path::Create, 1)                                                  \
   V(PictureRecorder::Create, 1)                                       \

lib/ui/text.dart

@@ -2798,7 +2798,7 @@ abstract class Paragraph {
   /// This only returns a valid value if asserts are enabled, and must not be
   /// used otherwise.
   bool get debugDisposed;
- }
+}
 
 @pragma('vm:entry-point')
 base class _NativeParagraph extends NativeFieldWrapperClass1 implements Paragraph {
@@ -3015,6 +3015,28 @@ abstract class ParagraphBuilder {
   /// [Paragraph].
   factory ParagraphBuilder(ParagraphStyle style) = _NativeParagraphBuilder;
 
+  /// Whether the rounding hack enabled by default in SkParagraph and TextPainter
+  /// is disabled.
+  ///
+  /// Do not rely on this getter as it exists for migration purposes only and
+  /// will soon be removed.
+  static bool get shouldDisableRoundingHack {
+    return const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+        || _roundingHackDisabledInDebugMode;
+  }
+  static bool _roundingHackDisabledInDebugMode = false;
+
+  /// Only works in debug mode. Do not call this method as it is for migration
+  /// purposes only and will soon be removed.
+  static void setDisableRoundingHack(bool disableRoundingHack) {
+    // bool.hasEnvironment does not work in internal tests so an additional flag
+    // is needed for tests.
+    assert(() {
+      _roundingHackDisabledInDebugMode = disableRoundingHack;
+      return true;
+    }());
+  }
+
   /// The number of placeholders currently in the paragraph.
   int get placeholderCount;
 
@@ -3132,11 +3154,12 @@ base class _NativeParagraphBuilder extends NativeFieldWrapperClass1 implements P
         style._fontSize ?? 0,
         style._height ?? 0,
         style._ellipsis ?? '',
-        _encodeLocale(style._locale)
+        _encodeLocale(style._locale),
+        !ParagraphBuilder.shouldDisableRoundingHack,
       );
   }
 
-  @Native<Void Function(Handle, Handle, Handle, Handle, Handle, Double, Double, Handle, Handle)>(symbol: 'ParagraphBuilder::Create')
+  @Native<Void Function(Handle, Handle, Handle, Handle, Handle, Double, Double, Handle, Handle, Bool)>(symbol: 'ParagraphBuilder::Create')
   external void _constructor(
       Int32List encoded,
       ByteData? strutData,
@@ -3145,7 +3168,8 @@ base class _NativeParagraphBuilder extends NativeFieldWrapperClass1 implements P
       double fontSize,
       double height,
       String ellipsis,
-      String locale);
+      String locale,
+      bool applyRoundingHack);
 
   @override
   int get placeholderCount => _placeholderCount;

lib/ui/text/paragraph_builder.cc

@@ -151,11 +151,12 @@ void ParagraphBuilder::Create(Dart_Handle wrapper,
                               double fontSize,
                               double height,
                               const std::u16string& ellipsis,
-                              const std::string& locale) {
+                              const std::string& locale,
+                              bool applyRoundingHack) {
   UIDartState::ThrowIfUIOperationsProhibited();
   auto res = fml::MakeRefCounted<ParagraphBuilder>(
       encoded_handle, strutData, fontFamily, strutFontFamilies, fontSize,
-      height, ellipsis, locale);
+      height, ellipsis, locale, applyRoundingHack);
   res->AssociateWithDartWrapper(wrapper);
 }
 
@@ -230,7 +231,8 @@ ParagraphBuilder::ParagraphBuilder(
     double fontSize,
     double height,
     const std::u16string& ellipsis,
-    const std::string& locale) {
+    const std::string& locale,
+    bool applyRoundingHack) {
   int32_t mask = 0;
   txt::ParagraphStyle style;
   {
@@ -291,6 +293,7 @@ ParagraphBuilder::ParagraphBuilder(
   if (mask & kPSLocaleMask) {
     style.locale = locale;
   }
+  style.apply_rounding_hack = applyRoundingHack;
 
   FontCollection& font_collection = UIDartState::Current()
                                         ->platform_configuration()

lib/ui/text/paragraph_builder.h

@@ -30,7 +30,8 @@ class ParagraphBuilder : public RefCountedDartWrappable<ParagraphBuilder> {
                      double fontSize,
                      double height,
                      const std::u16string& ellipsis,
-                     const std::string& locale);
+                     const std::string& locale,
+                     bool applyRoundingHack);
 
   ~ParagraphBuilder() override;
 
@@ -76,7 +77,8 @@ class ParagraphBuilder : public RefCountedDartWrappable<ParagraphBuilder> {
                             double fontSize,
                             double height,
                             const std::u16string& ellipsis,
-                            const std::string& locale);
+                            const std::string& locale,
+                            bool applyRoundingHack);
 
   std::unique_ptr<txt::ParagraphBuilder> m_paragraphBuilder;
 };

lib/web_ui/lib/src/engine/canvaskit/canvaskit_api.dart

@@ -2722,6 +2722,8 @@ extension SkParagraphStylePropertiesExtension on SkParagraphStyleProperties {
   @JS('replaceTabCharacters')
   external set _replaceTabCharacters(JSBoolean? bool);
   set replaceTabCharacters(bool? bool) => _replaceTabCharacters = bool?.toJS;
+
+  external set applyRoundingHack(bool applyRoundingHack);
 }
 
 @JS()

lib/web_ui/lib/src/engine/canvaskit/renderer.dart

@@ -328,6 +328,7 @@ class CanvasKitRenderer implements Renderer {
     strutStyle: strutStyle,
     ellipsis: ellipsis,
     locale: locale,
+    applyRoundingHack: !ui.ParagraphBuilder.shouldDisableRoundingHack,
   );
 
   @override

lib/web_ui/lib/src/engine/canvaskit/text.dart

@@ -33,6 +33,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
     ui.StrutStyle? strutStyle,
     String? ellipsis,
     ui.Locale? locale,
+    bool applyRoundingHack = true,
   })  : skParagraphStyle = toSkParagraphStyle(
           textAlign,
           textDirection,
@@ -46,6 +47,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
           strutStyle,
           ellipsis,
           locale,
+          applyRoundingHack,
         ),
         _fontFamily = _effectiveFontFamily(fontFamily),
         _fontSize = fontSize,
@@ -145,6 +147,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
     ui.StrutStyle? strutStyle,
     String? ellipsis,
     ui.Locale? locale,
+    bool applyRoundingHack,
   ) {
     final SkParagraphStyleProperties properties = SkParagraphStyleProperties();
 
@@ -181,6 +184,7 @@ class CkParagraphStyle implements ui.ParagraphStyle {
     properties.replaceTabCharacters = true;
     properties.textStyle = toSkTextStyleProperties(
         fontFamily, fontSize, height, fontWeight, fontStyle);
+    properties.applyRoundingHack = applyRoundingHack;
 
     return canvasKit.ParagraphStyle(properties);
   }

lib/web_ui/lib/text.dart

@@ -685,6 +685,19 @@ abstract class Paragraph {
 abstract class ParagraphBuilder {
   factory ParagraphBuilder(ParagraphStyle style) =>
     engine.renderer.createParagraphBuilder(style);
+
+  static bool get shouldDisableRoundingHack {
+    return const bool.hasEnvironment('SKPARAGRAPH_REMOVE_ROUNDING_HACK')
+        || _roundingHackDisabledInDebugMode;
+  }
+  static bool _roundingHackDisabledInDebugMode = false;
+  static void setDisableRoundingHack(bool disableRoundingHack) {
+    assert(() {
+      _roundingHackDisabledInDebugMode = disableRoundingHack;
+      return true;
+    }());
+  }
+
   void pushStyle(TextStyle style);
   void pop();
   void addText(String text);

lib/web_ui/test/canvaskit/text_test.dart

@@ -123,7 +123,51 @@ void testMain() {
         }
       });
     });
+
+    test('applyRoundingHack works', () {
+      bool assertsEnabled = false;
+      assert(() {
+        assertsEnabled = true;
+        return true;
+      }());
+      if (!assertsEnabled){
+        return;
+      }
+
+      const double fontSize = 1.25;
+      const String text = '12345';
+      assert((fontSize * text.length).truncate() != fontSize * text.length);
+      final bool roundingHackWasDisabled = ui.ParagraphBuilder.shouldDisableRoundingHack;
+      ui.ParagraphBuilder.setDisableRoundingHack(true);
+      final ui.ParagraphBuilder builder = ui.ParagraphBuilder(
+        ui.ParagraphStyle(fontSize: fontSize, fontFamily: 'FlutterTest'),
+      );
+      builder.addText(text);
+      final ui.Paragraph paragraph = builder.build()
+        ..layout(const ui.ParagraphConstraints(width: text.length * fontSize));
+
+      expect(paragraph.maxIntrinsicWidth, text.length * fontSize);
+      switch (paragraph.computeLineMetrics()) {
+        case [ui.LineMetrics(width: final double width)]:
+          expect(width, text.length * fontSize);
+        case final List<ui.LineMetrics> metrics:
+          expect(metrics, hasLength(1));
+      }
+      ui.ParagraphBuilder.setDisableRoundingHack(roundingHackWasDisabled);
+    });
+
+    test('rounding hack applied by default', () {
+      const double fontSize = 1.25;
+      const String text = '12345';
+      assert((fontSize * text.length).truncate() != fontSize * text.length);
+      expect(ui.ParagraphBuilder.shouldDisableRoundingHack, isFalse);
+      final ui.ParagraphBuilder builder = ui.ParagraphBuilder(ui.ParagraphStyle(fontSize: fontSize, fontFamily: 'FlutterTest'));
+      builder.addText(text);
+      final ui.Paragraph paragraph = builder.build()
+        ..layout(const ui.ParagraphConstraints(width: text.length * fontSize));
+      expect(paragraph.computeLineMetrics().length, greaterThan(1));
+    });
+
     // TODO(hterkelsen): https://github.com/flutter/flutter/issues/71520
   }, skip: isSafari || isFirefox);
-
 }

testing/dart/paragraph_test.dart

@@ -233,4 +233,45 @@ void main() {
       expect(callback, throwsStateError);
     }
   });
+
+  test('disableRoundingHack works in tests', () {
+    bool assertsEnabled = false;
+    assert(() {
+      assertsEnabled = true;
+      return true;
+    }());
+    if (!assertsEnabled){
+      return;
+    }
+    const double fontSize = 1.25;
+    const String text = '12345';
+    assert((fontSize * text.length).truncate() != fontSize * text.length);
+    final bool roundingHackWasDisabled = ParagraphBuilder.shouldDisableRoundingHack;
+    ParagraphBuilder.setDisableRoundingHack(true);
+    final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(fontSize: fontSize));
+    builder.addText(text);
+    final Paragraph paragraph = builder.build()
+      ..layout(const ParagraphConstraints(width: text.length * fontSize));
+
+    expect(paragraph.maxIntrinsicWidth, text.length * fontSize);
+    switch (paragraph.computeLineMetrics()) {
+      case [LineMetrics(width: final double width)]:
+        expect(width, text.length * fontSize);
+      case final List<LineMetrics> metrics:
+        expect(metrics, hasLength(1));
+    }
+    ParagraphBuilder.setDisableRoundingHack(roundingHackWasDisabled);
+  });
+
+  test('rounding hack applied by default', () {
+    const double fontSize = 1.25;
+    const String text = '12345';
+    assert((fontSize * text.length).truncate() != fontSize * text.length);
+    expect(ParagraphBuilder.shouldDisableRoundingHack, isFalse);
+    final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(fontSize: fontSize));
+    builder.addText(text);
+    final Paragraph paragraph = builder.build()
+      ..layout(const ParagraphConstraints(width: text.length * fontSize));
+    expect(paragraph.computeLineMetrics().length, greaterThan(1));
+  });
 }