Integrate Strut: Add StrutStyle, expose Strut API, wire up strut with dart:ui,...

Integrate Strut: Add StrutStyle, expose Strut API, wire up strut with dart:ui, Roll engine 31a7f4d..e7eb1c8 (7 commits) (#26332)

Includes a breaking change to dart:ui ParagraphStyle where lineHeight is renamed to height for consistency with TextStyle.

bin/internal/engine.version

-15f2b92cce916982b7dd8ce658bbf2a465c06ba4
+e7eb1c8bf65531195fc76ba96c8fc8478ac5f554

bin/internal/goldens.version

-46a3d26acbb1b0d72b6b02c30f03b9dbda7d5bdf
+cbd3fa445868962b7e910e498791755c988e9890

packages/flutter/lib/painting.dart

@@ -51,6 +51,7 @@ export 'src/painting/paint_utilities.dart';
 export 'src/painting/rounded_rectangle_border.dart';
 export 'src/painting/shape_decoration.dart';
 export 'src/painting/stadium_border.dart';
+export 'src/painting/strut_style.dart';
 export 'src/painting/superellipse_shape.dart';
 export 'src/painting/text_painter.dart';
 export 'src/painting/text_span.dart';

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

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/foundation.dart';
+
+import 'basic_types.dart';
+
+/// Defines the strut, which sets the minimum height a line can be
+/// relative to the baseline. Strut applies to all lines in the pararaph.
+///
+/// Strut is a feature that allows minimum line heights to be set. The effect is as
+/// if a zero width space was included at the beginning of each line in the
+/// paragraph. This imaginary space is 'shaped' according the properties defined
+/// in this class.
+///
+/// No lines may be shorter than the strut. The ascent and descent of the strut
+/// are calculated, and any laid out text that has a shorter ascent or descent than
+/// the strut's ascent or descent will take the ascent and descent of the strut.
+/// Text with ascents or descents larger than the strut's ascent or descent will lay
+/// out as normal and extend past the strut.
+///
+/// Strut is defined independently from any text content or [TextStyle]s.
+///
+/// The vertical components of strut are as follows:
+///
+///  * `leading * fontSize / 2` or half the font leading if `leading` is undefined (half leading)
+///  * `ascent * height`
+///  * `descent * height`
+///  * `leading * fontSize / 2` or half the font leading if `leading` is undefined (half leading)
+///
+/// The sum of these four values is the total height of the line.
+///
+/// The `ascent + descent` is equivalent to the [fontSize]. Ascent is the font's
+/// spacing above the baseline without leading and descent is the spacing below the
+/// baseline without leading. Leading is split evenly between the top and bottom.
+/// The values for `ascent` and `descent` are provided by the font named by
+/// [fontFamily]. If no [fontFamily] or [fontFamilyFallback] is provided, then the
+/// platform's default family will be used.
+///
+/// Each line's spacing above the baseline will be at least as tall as the half
+/// leading plus ascent. Each line's spacing below the baseline will be at least as
+/// tall as the half leading plus descent.
+///
+/// ### Fields and their default values.
+
+// ///////////////////////////////////////////////////////////////////////////
+// The defaults are noted here for convenience. The actual place where they //
+// are defined is in the engine paragraph_style.h of LibTxt. The values here//
+// should be updated should it change in the engine. The engine specifies   //
+// the defaults in order to reduce the amount of data we pass to native as  //
+// strut will usually be unspecified.                                       //
+// ///////////////////////////////////////////////////////////////////////////
+
+///
+/// Omitted or null properties will take the default values specified below:
+///
+///  * [fontFamily]: the name of the font to use when calcualting the strut (e.g., Roboto).
+///    No glyphs from the font will be drawn and the font will be used purely for metrics.
+///
+///  * [fontFamilyFallback]: an ordered list of font family names that will be searched for when
+///    the font in [fontFamily] cannot be found. When all specified font families have been
+///    exhausted an no match was found, the default platform font will be used.
+///
+///  * [fontSize]: the size of the ascent plus descent in logical pixels. This is also
+///    used as the basis of the custom leading caluclation. This value cannot
+///    be negative.
+///    Default is 14 logical pixels.
+///
+///  * [height]: the multiple of [fontSize] to multiply the ascent and descent by.
+///    The [height] will impact the spacing above and below the baseline differently
+///    depending on the ratios between the font's ascent and descent. This property is
+///    separate from the leading multiplier, which is controlled through [leading].
+///    Default is 1.0.
+///
+///  * [leading]: the custom leading to apply to the strut as a multiple of [fontSize].
+///    Leading is additional spacing between lines. Half of the leading is added
+///    to the top and the other half to the bottom of the line height. This differs
+///    from [height] since the spacing is equally distributed above and below the
+///    baseline.
+///    Default is `null`, which will use the font-specified leading.
+///
+///  * [fontWeight]: the typeface thickness to use when calculating the strut (e.g., bold).
+///    Default is [FontWeight.w400].
+///
+///  * [fontStyle]: the typeface variant to use when calculating the strut (e.g., italic).
+///    Default is [FontStyle.normal].
+///
+///  * [forceStrutHeight]: when true, all lines will be laid out with the height of the
+///    strut. All line and run-specific metrics will be ignored/overridden and only strut
+///    metrics will be used instead. This property guarantees uniform line spacing, however
+///    text in adjacent lines may overlap. This property should be enabled with caution as
+///    it bypasses a large portion of the vertical layout system.
+///    The default value is false.
+///
+/// ### Examples
+///
+/// {@tool sample}
+/// In this simple case, the text will be rendered at font size 10, however, the vertical
+/// height of each line will be the strut height (Roboto in font size 30 * 1.5) as the text
+/// itself is shorter than the strut.
+///
+/// ```dart
+/// const Text(
+///   'Hello, world!\nSecond line!',
+///   style: TextStyle(
+///     fontSize: 10,
+///     fontFamily: 'Raleway',
+///   ),
+///   strutStyle: StrutStyle(
+///     fontFamily: 'Roboto',
+///     fontSize: 30,
+///     height: 1.5,
+///   ),
+/// ),
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// Here, strut is used to absorb the additional line height in the second line.
+/// The strut [height] was defined as 1.5 (the default font size is 14), which
+/// caused all lines to be laid out taller than without strut. This extra space was
+/// able to accomodate the larger font size of `Second line!` without causing the line
+/// height to change for the second line only. All lines in this example are thus the
+/// same height (`14 * 1.5`).
+///
+/// ```dart
+/// const Text.rich(
+///   TextSpan(
+///     text: 'First line!\n',
+///     style: TextStyle(
+///       fontSize: 14,
+///       fontFamily: 'Roboto'
+///     ),
+///     children: <TextSpan>[
+///       TextSpan(
+///         text: 'Second line!\n',
+///         style: TextStyle(
+///           fontSize: 16,
+///           fontFamily: 'Roboto',
+///         ),
+///       ),
+///       TextSpan(
+///         text: 'Third line!\n',
+///         style: TextStyle(
+///           fontSize: 14,
+///           fontFamily: 'Roboto',
+///         ),
+///       ),
+///     ],
+///   ),
+///   strutStyle: StrutStyle(
+///     fontFamily: 'Roboto',
+///     height: 1.5,
+///   ),
+/// ),
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// Here, strut is used to enable strange and overlapping text to achieve unique
+/// effects. The `M`s in lines 2 and 3 are able to extend above their lines and
+/// fill empty space in lines above. The [forceStrutHeight] is enabled and functions
+/// as a 'grid' for the glyphs to draw on.
+///
+/// ![The result of the example below.](https://flutter.github.io/assets-for-api-docs/assets/painting/strut_force_example.png)
+///
+/// ```dart
+/// const Text.rich(
+///   TextSpan(
+///     text: '---------         ---------\n',
+///     style: TextStyle(
+///       fontSize: 14,
+///       fontFamily: 'Roboto',
+///     ),
+///     children: <TextSpan>[
+///       TextSpan(
+///         text: '^^^M^^^\n',
+///         style: TextStyle(
+///           fontSize: 30,
+///           fontFamily: 'Roboto',
+///         ),
+///       ),
+///       TextSpan(
+///         text: 'M------M\n',
+///         style: TextStyle(
+///           fontSize: 30,
+///           fontFamily: 'Roboto',
+///         ),
+///       ),
+///     ],
+///   ),
+///   strutStyle: StrutStyle(
+///     fontFamily: 'Roboto',
+///     fontSize: 14,
+///     height: 1,
+///     forceStrutHeight: true,
+///   ),
+/// ),
+/// ```
+/// {@end-tool}
+///
+/// {@tool sample}
+/// This example uses forceStrutHeight to create a 'drop cap' for the 'T' in 'The'.
+/// By locking the line heights to the metrics of the 14pt serif font, we are able
+/// to lay out a large 37pt 'T' on the second line to take up space on both the first
+/// and second lines.
+///
+/// ![The result of the example below.](https://flutter.github.io/assets-for-api-docs/assets/painting/strut_force_example_2.png)
+///
+/// ```dart
+/// Text.rich(
+///   TextSpan(
+///     text: '       he candle flickered\n',
+///     style: TextStyle(
+///       fontSize: 14,
+///       fontFamily: 'Serif'
+///     ),
+///     children: <TextSpan>[
+///       TextSpan(
+///         text: 'T',
+///         style: TextStyle(
+///           fontSize: 37,
+///           fontFamily: 'Serif'
+///         ),
+///       ),
+///       TextSpan(
+///         text: 'in the moonlight as\n',
+///         style: TextStyle(
+///           fontSize: 14,
+///           fontFamily: 'Serif'
+///         ),
+///       ),
+///       TextSpan(
+///         text: 'Dash the bird fluttered\n',
+///         style: TextStyle(
+///           fontSize: 14,
+///           fontFamily: 'Serif'
+///         ),
+///       ),
+///       TextSpan(
+///         text: 'off into the distance.',
+///         style: TextStyle(
+///           fontSize: 14,
+///           fontFamily: 'Serif'
+///         ),
+///       ),
+///     ],
+///   ),
+///   strutStyle: StrutStyle(
+///     fontFamily: 'Serif',
+///     fontSize: 14,
+///     forceStrutHeight: true,
+///   ),
+/// ),
+/// ```
+/// {@end-tool}
+///
+@immutable
+class StrutStyle extends Diagnosticable {
+  /// Creates a strut style.
+  ///
+  /// The `package` argument must be non-null if the font family is defined in a
+  /// package. It is combined with the `fontFamily` argument to set the
+  /// [fontFamily] property.
+  const StrutStyle({
+    String fontFamily,
+    List<String> fontFamilyFallback,
+    this.fontSize,
+    this.height,
+    this.leading,
+    this.fontWeight,
+    this.fontStyle,
+    this.forceStrutHeight,
+    this.debugLabel,
+    String package,
+  }) : fontFamily = package == null ? fontFamily : 'packages/$package/$fontFamily',
+       _fontFamilyFallback = fontFamilyFallback,
+       _package = package,
+       assert(fontSize == null || fontSize > 0),
+       assert(leading == null || leading >= 0),
+       assert(package == null || (package != null && (fontFamily != null || fontFamilyFallback != null)));
+
+  /// The name of the font to use when calcualting the strut (e.g., Roboto). If the
+  /// font is defined in a package, this will be prefixed with
+  /// 'packages/package_name/' (e.g. 'packages/cool_fonts/Roboto'). The
+  /// prefixing is done by the constructor when the `package` argument is
+  /// provided.
+  ///
+  /// The value provided in [fontFamily] will act as the preferred/first font
+  /// family that will be searched for, followed in order by the font families
+  /// in [fontFamilyFallback]. If all font families are exhausted and no match
+  /// was found, the default platform font family will be used instead. Unlike
+  /// [TextStyle.fontFamilyFallback], the font does not need to contain the
+  /// desired glyphs to match.
+  final String fontFamily;
+
+  /// The ordered list of font families to fall back on when a higher priority
+  /// font family cannot be found.
+  ///
+  /// The value provided in [fontFamily] will act as the preferred/first font
+  /// family that will be searched for, followed in order by the font families
+  /// in [fontFamilyFallback]. If all font families are exhausted and no match
+  /// was found, the default platform font family will be used instead. Unlike
+  /// [TextStyle.fontFamilyFallback], the font does not need to contain the
+  /// desired glyphs to match.
+  ///
+  /// When [fontFamily] is null or not provided, the first value in [fontFamilyFallback]
+  /// acts as the preferred/first font family. When neither is provided, then
+  /// the default platform font will be used. Providing and empty list or null
+  /// for this property is the same as omitting it.
+  ///
+  /// If the font is defined in a package, each font family in the list will be
+  /// prefixed with 'packages/package_name/' (e.g. 'packages/cool_fonts/Roboto').
+  /// The package name should be provided by the `package` argument in the
+  /// constructor.
+  List<String> get fontFamilyFallback {
+    if (_package != null && _fontFamilyFallback != null)
+      return _fontFamilyFallback.map((String family) => 'packages/$_package/$family').toList();
+    return _fontFamilyFallback;
+  }
+  final List<String> _fontFamilyFallback;
+
+  // This is stored in order to prefix the fontFamilies in _fontFamilyFallback
+  // in the [fontFamilyFallback] getter.
+  final String _package;
+
+  /// The size of text (in logical pixels) to use when obtaining metrics from the font.
+  ///
+  /// The [fontSize] is used to get the base set of metrics that are then used to calculated
+  /// the metrics of strut. The height and leading are expressed as a multiple of
+  /// [fontSize].
+  ///
+  /// The default fontSize is 14 logical pixels.
+  final double fontSize;
+
+  /// The multiple of [fontSize] to multiply the ascent and descent by where `ascent + descent = fontSize`.
+  ///
+  /// Ascent is the spacing above the baseline and descent is the spacing below the baseline.
+  ///
+  /// The [height] will impact the spacing above and below the baseline differently
+  /// depending on the ratios between the font's ascent and descent. This property is
+  /// separate from the leading multiplier, which is controlled through [leading].
+  ///
+  /// The default height is 1.0.
+  final double height;
+
+  /// The typeface thickness to use when calculating the strut (e.g., bold).
+  ///
+  /// The default fontWeight is [FontWeight.w400].
+  final FontWeight fontWeight;
+
+  /// The typeface variant to use when calculating the strut (e.g., italics).
+  ///
+  /// The default fontStyle is [FontStyle.normal].
+  final FontStyle fontStyle;
+
+  /// The custom leading to apply to the strut as a multiple of [fontSize].
+  ///
+  /// Leading is additional spacing between lines. Half of the leading is added
+  /// to the top and the other half to the bottom of the line. This differs
+  /// from [height] since the spacing is equally distributed above and below the
+  /// baseline.
+  ///
+  /// The default leading is null, which will use the font-specified leading.
+  final double leading;
+
+  /// Whether the strut height should be forced.
+  ///
+  /// When true, all lines will be laid out with the height of the
+  /// strut. All line and run-specific metrics will be ignored/overridden and only strut
+  /// metrics will be used instead. This property guarantees uniform line spacing, however
+  /// text in adjacent lines may overlap.
+  ///
+  /// This property should be enabled with caution as
+  /// it bypasses a large portion of the vertical layout system.
+  ///
+  /// This is equivalent to setting [TextStyle.height] to zero for all [TextStyle]s
+  /// in the paragraph. Since the height of each line is calculated as a max of the
+  /// metrics of each run of text, zero height [TextStyle]s cause the minimums
+  /// defined by strut to always manifest, resulting in all lines having the height
+  /// of the strut.
+  ///
+  /// The default is false.
+  final bool forceStrutHeight;
+
+  /// A human-readable description of this strut style.
+  ///
+  /// This property is maintained only in debug builds.
+  ///
+  /// This property is not considered when comparing strut styles using `==` or
+  /// [compareTo], and it does not affect [hashCode].
+  final String debugLabel;
+
+  /// Describe the difference between this style and another, in terms of how
+  /// much damage it will make to the rendering.
+  ///
+  /// See also:
+  ///
+  ///  * [TextSpan.compareTo], which does the same thing for entire [TextSpan]s.
+  RenderComparison compareTo(StrutStyle other) {
+    if (identical(this, other))
+      return RenderComparison.identical;
+    if (fontFamily != other.fontFamily ||
+        fontSize != other.fontSize ||
+        fontWeight != other.fontWeight ||
+        fontStyle != other.fontStyle ||
+        height != other.height ||
+        leading != other.leading ||
+        forceStrutHeight != other.forceStrutHeight ||
+        !listEquals(fontFamilyFallback, other.fontFamilyFallback))
+      return RenderComparison.layout;
+    return RenderComparison.identical;
+  }
+
+  @override
+  bool operator ==(dynamic other) {
+    if (identical(this, other))
+      return true;
+    if (other.runtimeType != runtimeType)
+      return false;
+    final StrutStyle typedOther = other;
+    return fontFamily == typedOther.fontFamily &&
+           fontSize == typedOther.fontSize &&
+           fontWeight == typedOther.fontWeight &&
+           fontStyle == typedOther.fontStyle &&
+           height == typedOther.height &&
+           leading == typedOther.leading &&
+           forceStrutHeight == typedOther.forceStrutHeight;
+  }
+
+  @override
+  int get hashCode {
+    return hashValues(
+      fontFamily,
+      fontSize,
+      fontWeight,
+      fontStyle,
+      height,
+      leading,
+      forceStrutHeight,
+    );
+  }
+
+  /// Adds all properties prefixing property names with the optional `prefix`.
+  @override
+  void debugFillProperties(DiagnosticPropertiesBuilder properties, { String prefix = '' }) {
+    super.debugFillProperties(properties);
+    if (debugLabel != null)
+      properties.add(MessageProperty('${prefix}debugLabel', debugLabel));
+    final List<DiagnosticsNode> styles = <DiagnosticsNode>[];
+    styles.add(StringProperty('${prefix}family', fontFamily, defaultValue: null, quoted: false));
+    styles.add(IterableProperty<String>('${prefix}familyFallback', fontFamilyFallback, defaultValue: null));
+    styles.add(DoubleProperty('${prefix}size', fontSize, defaultValue: null));
+    String weightDescription;
+    if (fontWeight != null) {
+      weightDescription = '${fontWeight.index + 1}00';
+    }
+    // TODO(jacobr): switch this to use enumProperty which will either cause the
+    // weight description to change to w600 from 600 or require existing
+    // enumProperty to handle this special case.
+    styles.add(DiagnosticsProperty<FontWeight>(
+      '${prefix}weight',
+      fontWeight,
+      description: weightDescription,
+      defaultValue: null,
+    ));
+    styles.add(EnumProperty<FontStyle>('${prefix}style', fontStyle, defaultValue: null));
+    styles.add(DoubleProperty('${prefix}height', height, unit: 'x', defaultValue: null));
+    styles.add(FlagProperty('${prefix}forceStrutHeight', value: forceStrutHeight, defaultValue: null));
+
+    final bool styleSpecified = styles.any((DiagnosticsNode n) => !n.isFiltered(DiagnosticLevel.info));
+    styles.forEach(properties.add);
+
+    if (!styleSpecified)
+      properties.add(FlagProperty('forceStrutHeight', value: forceStrutHeight, ifTrue: '$prefix<strut height forced>', ifFalse: '$prefix<strut height normal>'));
+  }
+}

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

@@ -10,6 +10,7 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/services.dart';
 
 import 'basic_types.dart';
+import 'strut_style.dart';
 import 'text_span.dart';
 
 export 'package:flutter/services.dart' show TextRange, TextSelection;
@@ -48,6 +49,7 @@ class TextPainter {
     int maxLines,
     String ellipsis,
     Locale locale,
+    StrutStyle strutStyle,
   }) : assert(text == null || text.debugAssertIsValid()),
        assert(textAlign != null),
        assert(textScaleFactor != null),
@@ -58,7 +60,8 @@ class TextPainter {
        _textScaleFactor = textScaleFactor,
        _maxLines = maxLines,
        _ellipsis = ellipsis,
-       _locale = locale;
+       _locale = locale,
+       _strutStyle = strutStyle;
 
   ui.Paragraph _paragraph;
   bool _needsLayout = true;
@@ -198,6 +201,29 @@ class TextPainter {
     _needsLayout = true;
   }
 
+  /// {@template flutter.painting.textPainter.strutStyle}
+  /// The strut style to use. Strut style defines the strut, which sets minimum
+  /// vertical layout metrics.
+  ///
+  /// Omitting or providing null will disable strut.
+  ///
+  /// Omitting or providing null for any properties of [StrutStyle] will result in
+  /// default values being used. It is highly recommended to at least specify a
+  /// [fontSize].
+  ///
+  /// See [StrutStyle] for details.
+  /// {@endtemplate}
+  StrutStyle get strutStyle => _strutStyle;
+  StrutStyle _strutStyle;
+  set strutStyle(StrutStyle value) {
+    if (_strutStyle == value)
+      return;
+    _strutStyle = value;
+    _paragraph = null;
+    _needsLayout = true;
+  }
+
+
   ui.Paragraph _layoutTemplate;
 
   ui.ParagraphStyle _createParagraphStyle([TextDirection defaultTextDirection]) {
@@ -212,6 +238,7 @@ class TextPainter {
       maxLines: _maxLines,
       ellipsis: _ellipsis,
       locale: _locale,
+      strutStyle: _strutStyle,
     ) ?? ui.ParagraphStyle(
       textAlign: textAlign,
       textDirection: textDirection ?? defaultTextDirection,

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

@@ -2,11 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'dart:ui' as ui show ParagraphStyle, TextStyle, lerpDouble, Shadow;
+import 'dart:ui' as ui show ParagraphStyle, TextStyle, StrutStyle, lerpDouble, Shadow;
 
 import 'package:flutter/foundation.dart';
 
 import 'basic_types.dart';
+import 'strut_style.dart';
 
 const String _kDefaultDebugLabel = 'unknown';
 
@@ -812,17 +813,35 @@ class TextStyle extends Diagnosticable {
       String ellipsis,
       int maxLines,
       Locale locale,
+      String fontFamily,
+      double fontSize,
+      FontWeight fontWeight,
+      FontStyle fontStyle,
+      double height,
+      StrutStyle strutStyle,
   }) {
     assert(textScaleFactor != null);
     assert(maxLines == null || maxLines > 0);
     return ui.ParagraphStyle(
       textAlign: textAlign,
       textDirection: textDirection,
-      fontWeight: fontWeight,
-      fontStyle: fontStyle,
-      fontFamily: fontFamily,
-      fontSize: (fontSize ?? _defaultFontSize) * textScaleFactor,
-      lineHeight: height,
+      // Here, we stablish the contents of this TextStyle as the paragraph's default font
+      // unless an override is passed in.
+      fontWeight: fontWeight ?? this.fontWeight,
+      fontStyle: fontStyle ?? this.fontStyle,
+      fontFamily: fontFamily ?? this.fontFamily,
+      fontSize: (fontSize ?? this.fontSize ?? _defaultFontSize) * textScaleFactor,
+      height: height ?? this.height,
+      strutStyle: strutStyle == null ? null : ui.StrutStyle(
+        fontFamily: strutStyle.fontFamily,
+        fontFamilyFallback: strutStyle.fontFamilyFallback,
+        fontSize: strutStyle.fontSize,
+        height: strutStyle.height,
+        leading: strutStyle.leading,
+        fontWeight: strutStyle.fontWeight,
+        fontStyle: strutStyle.fontStyle,
+        forceStrutHeight: strutStyle.forceStrutHeight,
+      ),
       maxLines: maxLines,
       ellipsis: ellipsis,
       locale: locale,
@@ -928,35 +947,7 @@ class TextStyle extends Diagnosticable {
     styles.add(DoubleProperty('${prefix}size', fontSize, defaultValue: null));
     String weightDescription;
     if (fontWeight != null) {
-      switch (fontWeight) {
-        case FontWeight.w100:
-          weightDescription = '100';
-          break;
-        case FontWeight.w200:
-          weightDescription = '200';
-          break;
-        case FontWeight.w300:
-          weightDescription = '300';
-          break;
-        case FontWeight.w400:
-          weightDescription = '400';
-          break;
-        case FontWeight.w500:
-          weightDescription = '500';
-          break;
-        case FontWeight.w600:
-          weightDescription = '600';
-          break;
-        case FontWeight.w700:
-          weightDescription = '700';
-          break;
-        case FontWeight.w800:
-          weightDescription = '800';
-          break;
-        case FontWeight.w900:
-          weightDescription = '900';
-          break;
-      }
+      weightDescription = '${fontWeight.index + 1}00';
     }
     // TODO(jacobr): switch this to use enumProperty which will either cause the
     // weight description to change to w600 from 600 or require existing

packages/flutter/lib/src/rendering/error.dart

@@ -95,7 +95,7 @@ class RenderErrorBox extends RenderBox {
 
   /// The paragraph style to use when painting [RenderErrorBox] objects.
   static ui.ParagraphStyle paragraphStyle = ui.ParagraphStyle(
-    lineHeight: 1.0,
+    height: 1.0,
   );
 
   @override

packages/flutter/lib/src/rendering/paragraph.dart

@@ -6,6 +6,7 @@ import 'dart:ui' as ui show Gradient, Shader, TextBox;
 
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
+import 'package:flutter/painting.dart';
 import 'package:flutter/semantics.dart';
 import 'package:flutter/services.dart';
 
@@ -45,6 +46,7 @@ class RenderParagraph extends RenderBox {
     double textScaleFactor = 1.0,
     int maxLines,
     Locale locale,
+    StrutStyle strutStyle,
   }) : assert(text != null),
        assert(text.debugAssertIsValid()),
        assert(textAlign != null),
@@ -63,6 +65,7 @@ class RenderParagraph extends RenderBox {
          maxLines: maxLines,
          ellipsis: overflow == TextOverflow.ellipsis ? _kEllipsis : null,
          locale: locale,
+         strutStyle: strutStyle,
        );
 
   final TextPainter _textPainter;
@@ -194,6 +197,17 @@ class RenderParagraph extends RenderBox {
     markNeedsLayout();
   }
 
+  /// {@macro flutter.painting.textPainter.strutStyle}
+  StrutStyle get strutStyle => _textPainter.strutStyle;
+  /// The value may be null.
+  set strutStyle(StrutStyle value) {
+    if (_textPainter.strutStyle == value)
+      return;
+    _textPainter.strutStyle = value;
+    _overflowShader = null;
+    markNeedsLayout();
+  }
+
   void _layoutText({ double minWidth = 0.0, double maxWidth = double.infinity }) {
     final bool widthMatters = softWrap || overflow == TextOverflow.ellipsis;
     _textPainter.layout(minWidth: minWidth, maxWidth: widthMatters ? maxWidth : double.infinity);

packages/flutter/lib/src/widgets/basic.dart

@@ -4599,6 +4599,7 @@ class RichText extends LeafRenderObjectWidget {
     this.textScaleFactor = 1.0,
     this.maxLines,
     this.locale,
+    this.strutStyle,
   }) : assert(text != null),
        assert(textAlign != null),
        assert(softWrap != null),
@@ -4660,6 +4661,9 @@ class RichText extends LeafRenderObjectWidget {
   /// See [RenderParagraph.locale] for more information.
   final Locale locale;
 
+  /// {@macro flutter.painting.textPainter.strutStyle}
+  final StrutStyle strutStyle;
+
   @override
   RenderParagraph createRenderObject(BuildContext context) {
     assert(textDirection != null || debugCheckHasDirectionality(context));
@@ -4670,6 +4674,7 @@ class RichText extends LeafRenderObjectWidget {
       overflow: overflow,
       textScaleFactor: textScaleFactor,
       maxLines: maxLines,
+      strutStyle: strutStyle,
       locale: locale ?? Localizations.localeOf(context, nullOk: true),
     );
   }
@@ -4685,6 +4690,7 @@ class RichText extends LeafRenderObjectWidget {
       ..overflow = overflow
       ..textScaleFactor = textScaleFactor
       ..maxLines = maxLines
+      ..strutStyle = strutStyle
       ..locale = locale ?? Localizations.localeOf(context, nullOk: true);
   }
 

packages/flutter/lib/src/widgets/text.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
+import 'package:flutter/painting.dart';
 
 import 'basic.dart';
 import 'framework.dart';
@@ -224,6 +225,7 @@ class Text extends StatelessWidget {
   const Text(this.data, {
     Key key,
     this.style,
+    this.strutStyle,
     this.textAlign,
     this.textDirection,
     this.locale,
@@ -240,6 +242,7 @@ class Text extends StatelessWidget {
   const Text.rich(this.textSpan, {
     Key key,
     this.style,
+    this.strutStyle,
     this.textAlign,
     this.textDirection,
     this.locale,
@@ -269,6 +272,9 @@ class Text extends StatelessWidget {
   /// replace the closest enclosing [DefaultTextStyle].
   final TextStyle style;
 
+  /// {@macro flutter.painting.textPainter.strutStyle}
+  final StrutStyle strutStyle;
+
   /// How the text should be aligned horizontally.
   final TextAlign textAlign;
 
@@ -356,6 +362,7 @@ class Text extends StatelessWidget {
       overflow: overflow ?? defaultTextStyle.overflow,
       textScaleFactor: textScaleFactor ?? MediaQuery.textScaleFactorOf(context),
       maxLines: maxLines ?? defaultTextStyle.maxLines,
+      strutStyle: strutStyle,
       text: TextSpan(
         style: effectiveTextStyle,
         text: data,

packages/flutter/test/material/theme_test.dart

@@ -720,7 +720,7 @@ class _TextStyleProxy implements TextStyle {
   }
 
   @override
-  ui.ParagraphStyle getParagraphStyle({TextAlign textAlign, TextDirection textDirection, double textScaleFactor = 1.0, String ellipsis, int maxLines, Locale locale}) {
+  ui.ParagraphStyle getParagraphStyle({TextAlign textAlign, TextDirection textDirection, double textScaleFactor = 1.0, String ellipsis, int maxLines, Locale locale, String fontFamily, double fontSize, FontWeight fontWeight, FontStyle fontStyle, double height, StrutStyle strutStyle}) {
     throw UnimplementedError();
   }
 

packages/flutter/test/painting/text_style_test.dart

@@ -169,22 +169,22 @@ void main() {
     expect(ts2.toString(), 'TextStyle(color: Color(0xff00ff00), decoration: unspecified, decorationColor: unspecified, decorationStyle: unspecified, fontWeight: FontWeight.w800, fontStyle: unspecified, textBaseline: unspecified, fontFamily: unspecified, fontFamilyFallback: unspecified, fontSize: 10.0, letterSpacing: unspecified, wordSpacing: unspecified, height: 100.0x, locale: unspecified, background: unspecified, foreground: unspecified, shadows: unspecified)');
 
     final ui.ParagraphStyle ps2 = s2.getParagraphStyle(textAlign: TextAlign.center);
-    expect(ps2, equals(ui.ParagraphStyle(textAlign: TextAlign.center, fontWeight: FontWeight.w800, fontSize: 10.0, lineHeight: 100.0)));
-    expect(ps2.toString(), 'ParagraphStyle(textAlign: TextAlign.center, textDirection: unspecified, fontWeight: FontWeight.w800, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 10.0, lineHeight: 100.0x, ellipsis: unspecified, locale: unspecified)');
+    expect(ps2, equals(ui.ParagraphStyle(textAlign: TextAlign.center, fontWeight: FontWeight.w800, fontSize: 10.0, height: 100.0)));
+    expect(ps2.toString(), 'ParagraphStyle(textAlign: TextAlign.center, textDirection: unspecified, fontWeight: FontWeight.w800, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 10.0, height: 100.0x, ellipsis: unspecified, locale: unspecified)');
     final ui.ParagraphStyle ps5 = s5.getParagraphStyle();
-    expect(ps5, equals(ui.ParagraphStyle(fontWeight: FontWeight.w700, fontSize: 12.0, lineHeight: 123.0)));
-    expect(ps5.toString(), 'ParagraphStyle(textAlign: unspecified, textDirection: unspecified, fontWeight: FontWeight.w700, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 12.0, lineHeight: 123.0x, ellipsis: unspecified, locale: unspecified)');
+    expect(ps5, equals(ui.ParagraphStyle(fontWeight: FontWeight.w700, fontSize: 12.0, height: 123.0)));
+    expect(ps5.toString(), 'ParagraphStyle(textAlign: unspecified, textDirection: unspecified, fontWeight: FontWeight.w700, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 12.0, height: 123.0x, ellipsis: unspecified, locale: unspecified)');
   });
 
 
   test('TextStyle with text direction', () {
     final ui.ParagraphStyle ps6 = const TextStyle().getParagraphStyle(textDirection: TextDirection.ltr);
     expect(ps6, equals(ui.ParagraphStyle(textDirection: TextDirection.ltr, fontSize: 14.0)));
-    expect(ps6.toString(), 'ParagraphStyle(textAlign: unspecified, textDirection: TextDirection.ltr, fontWeight: unspecified, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 14.0, lineHeight: unspecified, ellipsis: unspecified, locale: unspecified)');
+    expect(ps6.toString(), 'ParagraphStyle(textAlign: unspecified, textDirection: TextDirection.ltr, fontWeight: unspecified, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 14.0, height: unspecified, ellipsis: unspecified, locale: unspecified)');
 
     final ui.ParagraphStyle ps7 = const TextStyle().getParagraphStyle(textDirection: TextDirection.rtl);
     expect(ps7, equals(ui.ParagraphStyle(textDirection: TextDirection.rtl, fontSize: 14.0)));
-    expect(ps7.toString(), 'ParagraphStyle(textAlign: unspecified, textDirection: TextDirection.rtl, fontWeight: unspecified, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 14.0, lineHeight: unspecified, ellipsis: unspecified, locale: unspecified)');
+    expect(ps7.toString(), 'ParagraphStyle(textAlign: unspecified, textDirection: TextDirection.rtl, fontWeight: unspecified, fontStyle: unspecified, maxLines: unspecified, fontFamily: unspecified, fontSize: 14.0, height: unspecified, ellipsis: unspecified, locale: unspecified)');
   });
 
   test('TextStyle using package font', () {

packages/flutter/test/widgets/text_golden_test.dart

@@ -220,4 +220,221 @@ void main() {
       matchesGoldenFile('text_golden.Fade.1.png'),
     );
   }, skip: !Platform.isLinux);
+
+  testWidgets('Default Strut text', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Center(
+        child: RepaintBoundary(
+          child: Container(
+            width: 200.0,
+            height: 100.0,
+            decoration: const BoxDecoration(
+              color: Color(0xff00ff00),
+            ),
+            child: const Text('Hello\nLine 2\nLine 3',
+              textDirection: TextDirection.ltr,
+              style: TextStyle(),
+              strutStyle: StrutStyle(),
+            ),
+          ),
+        ),
+      ),
+    );
+    await expectLater(
+      find.byType(Container),
+      matchesGoldenFile('text_golden.StrutDefault.png'),
+    );
+  }, skip: !Platform.isLinux);
+
+  testWidgets('Strut text 1', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Center(
+        child: RepaintBoundary(
+          child: Container(
+            width: 200.0,
+            height: 100.0,
+            decoration: const BoxDecoration(
+              color: Color(0xff00ff00),
+            ),
+            child: const Text('Hello\nLine2\nLine3',
+              textDirection: TextDirection.ltr,
+              style: TextStyle(),
+              strutStyle: StrutStyle(
+                height: 1.5,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    await expectLater(
+      find.byType(Container),
+      matchesGoldenFile('text_golden.Strut.1.png'),
+    );
+  }, skip: !Platform.isLinux);
+
+  testWidgets('Strut text 2', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Center(
+        child: RepaintBoundary(
+          child: Container(
+            width: 200.0,
+            height: 100.0,
+            decoration: const BoxDecoration(
+              color: Color(0xff00ff00),
+            ),
+            child: const Text('Hello\nLine 2\nLine 3',
+              textDirection: TextDirection.ltr,
+              style: TextStyle(),
+              strutStyle: StrutStyle(
+                height: 1.5,
+                fontSize: 14,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    await expectLater(
+      find.byType(Container),
+      matchesGoldenFile('text_golden.Strut.2.png'),
+    );
+  }, skip: !Platform.isLinux);
+
+  testWidgets('Strut text rich', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Center(
+        child: RepaintBoundary(
+          child: Container(
+            width: 200.0,
+            height: 150.0,
+            decoration: const BoxDecoration(
+              color: Color(0xff00ff00),
+            ),
+            child: const Text.rich(
+              TextSpan(
+                text: 'Hello\n',
+                style: TextStyle(
+                  color: Colors.red,
+                  fontSize: 30
+                ),
+                children: <TextSpan>[
+                  TextSpan(
+                    text: 'Second line!\n',
+                    style: TextStyle(
+                      fontSize: 5,
+                      color: Colors.blue,
+                    ),
+                  ),
+                  TextSpan(
+                    text: 'Third line!\n',
+                    style: TextStyle(
+                      fontSize: 25,
+                      color: Colors.white,
+                    ),
+                  ),
+                ],
+              ),
+              textDirection: TextDirection.ltr,
+              strutStyle: StrutStyle(
+                fontSize: 14,
+                height: 1.1,
+                leading: 0.1,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    await expectLater(
+      find.byType(Container),
+      matchesGoldenFile('text_golden.Strut.3.png'),
+    );
+  }, skip: !Platform.isLinux);
+
+  testWidgets('Strut text font fallback', (WidgetTester tester) async {
+    // Font Fallback
+    await tester.pumpWidget(
+      Center(
+        child: RepaintBoundary(
+          child: Container(
+            width: 200.0,
+            height: 100.0,
+            decoration: const BoxDecoration(
+              color: Color(0xff00ff00),
+            ),
+            child: const Text('Hello\nLine 2\nLine 3',
+              textDirection: TextDirection.ltr,
+              style: TextStyle(),
+              strutStyle: StrutStyle(
+                fontFamily: 'FakeFont 1',
+                fontFamilyFallback: <String>[
+                  'FakeFont 2',
+                  'EvilFont 3',
+                  'Nice Font 4',
+                  'ahem'
+                ],
+                fontSize: 14,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    await expectLater(
+      find.byType(Container),
+      matchesGoldenFile('text_golden.Strut.4.png'),
+    );
+  }, skip: !Platform.isLinux);
+
+  testWidgets('Strut text rich forceStrutHeight', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      Center(
+        child: RepaintBoundary(
+          child: Container(
+            width: 200.0,
+            height: 100.0,
+            decoration: const BoxDecoration(
+              color: Color(0xff00ff00),
+            ),
+            child: const Text.rich(
+              TextSpan(
+                text: 'Hello\n',
+                style: TextStyle(
+                  color: Colors.red,
+                  fontSize: 30
+                ),
+                children: <TextSpan>[
+                  TextSpan(
+                    text: 'Second line!\n',
+                    style: TextStyle(
+                      fontSize: 9,
+                      color: Colors.blue,
+                    ),
+                  ),
+                  TextSpan(
+                    text: 'Third line!\n',
+                    style: TextStyle(
+                      fontSize: 27,
+                      color: Colors.white,
+                    ),
+                  ),
+                ],
+              ),
+              textDirection: TextDirection.ltr,
+              strutStyle: StrutStyle(
+                fontSize: 14,
+                height: 1.1,
+                forceStrutHeight: true,
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+    await expectLater(
+      find.byType(Container),
+      matchesGoldenFile('text_golden.StrutForce.1.png'),
+    );
+  }, skip: !Platform.isLinux);
 }