Add support for text shadows (#6385)

Text shadows can now be added to a TextStyle by providing a List<Shadow>. The dart:ui Shadow class is now the base class to flutter BoxShadow.

ci/licenses_golden/licenses_flutter

@@ -1023,6 +1023,8 @@ FILE: ../../../flutter/third_party/txt/src/txt/test_font_manager.h
 FILE: ../../../flutter/third_party/txt/src/txt/text_baseline.h
 FILE: ../../../flutter/third_party/txt/src/txt/text_decoration.cc
 FILE: ../../../flutter/third_party/txt/src/txt/text_decoration.h
+FILE: ../../../flutter/third_party/txt/src/txt/text_shadow.cc
+FILE: ../../../flutter/third_party/txt/src/txt/text_shadow.h
 FILE: ../../../flutter/third_party/txt/src/txt/text_style.cc
 FILE: ../../../flutter/third_party/txt/src/txt/text_style.h
 FILE: ../../../flutter/third_party/txt/src/txt/typeface_font_asset_provider.cc

lib/ui/painting.dart

@@ -3639,6 +3639,217 @@ class PictureRecorder extends NativeFieldWrapperClass2 {
   Picture endRecording() native 'PictureRecorder_endRecording';
 }
 
+/// A single shadow.
+///
+/// Multiple shadows are stacked together in a [TextStyle].
+class Shadow {
+  /// Construct a shadow.
+  ///
+  /// The default shadow is a black shadow with zero offset and zero blur.
+  /// Default shadows should be completely covered by the casting element,
+  /// and not be visble.
+  ///
+  /// Transparency should be adjusted through the [color] alpha.
+  ///
+  /// Shadow order matters due to compositing multiple translucent objects not
+  /// being commutative.
+  const Shadow({
+    this.color = const Color(_kColorDefault),
+    this.offset = Offset.zero,
+    this.blurRadius = 0.0,
+  }) : assert(color != null, 'Text shadow color was null.'),
+       assert(offset != null, 'Text shadow offset was null.'),
+       assert(blurRadius >= 0.0, 'Text shadow blur radius should be non-negative.');
+
+  static const int _kColorDefault = 0xFF000000;
+  // Constants for shadow encoding.
+  static const int _kBytesPerShadow = 16;
+  static const int _kColorOffset = 0 << 2;
+  static const int _kXOffset = 1 << 2;
+  static const int _kYOffset = 2 << 2;
+  static const int _kBlurOffset = 3 << 2;
+
+  /// Color that the shadow will be drawn with.
+  ///
+  /// The shadows are shapes composited directly over the base canvas, and do not
+  /// represent optical occlusion.
+  final Color color;
+
+  /// The displacement of the shadow from the casting element.
+  ///
+  /// Positive x/y offsets will shift the shadow to the right and down, while
+  /// negative offsets shift the shadow to the left and up. The offsets are
+  /// relative to the position of the element that is casting it.
+  final Offset offset;
+
+  /// The standard deviation of the Gaussian to convolve with the shadow's shape.
+  final double blurRadius;
+
+  /// Converts a blur radius in pixels to sigmas.
+  ///
+  /// See the sigma argument to [MaskFilter.blur].
+  ///
+  // See SkBlurMask::ConvertRadiusToSigma().
+  // <https://github.com/google/skia/blob/bb5b77db51d2e149ee66db284903572a5aac09be/src/effects/SkBlurMask.cpp#L23>
+  static double convertRadiusToSigma(double radius) {
+    return radius * 0.57735 + 0.5;
+  }
+
+  /// The [blurRadius] in sigmas instead of logical pixels.
+  ///
+  /// See the sigma argument to [MaskFilter.blur].
+  double get blurSigma => convertRadiusToSigma(blurRadius);
+
+  /// Create the [Paint] object that corresponds to this shadow description.
+  ///
+  /// The [offset] is not represented in the [Paint] object.
+  /// To honor this as well, the shape should be translated by [offset] before
+  /// being filled using this [Paint].
+  ///
+  /// This class does not provide a way to disable shadows to avoid inconsistencies
+  /// in shadow blur rendering, primarily as a method of reducing test flakiness.
+  /// [toPaint] should be overriden in subclasses to provide this functionality.
+  Paint toPaint() {
+    return Paint()
+      ..color = color
+      ..maskFilter = MaskFilter.blur(BlurStyle.normal, blurSigma);
+  }
+
+  /// Returns a new shadow with its [offset] and [blurRadius] scaled by the given
+  /// factor.
+  Shadow scale(double factor) {
+    return Shadow(
+      color: color,
+      offset: offset * factor,
+      blurRadius: blurRadius * factor,
+    );
+  }
+
+  /// Linearly interpolate between two shadows.
+  ///
+  /// If either shadow is null, this function linearly interpolates from a
+  /// a shadow that matches the other shadow in color but has a zero
+  /// offset and a zero blurRadius.
+  ///
+  /// {@template dart.ui.shadow.lerp}
+  /// The `t` argument represents position on the timeline, with 0.0 meaning
+  /// that the interpolation has not started, returning `a` (or something
+  /// equivalent to `a`), 1.0 meaning that the interpolation has finished,
+  /// returning `b` (or something equivalent to `b`), and values in between
+  /// meaning that the interpolation is at the relevant point on the timeline
+  /// between `a` and `b`. The interpolation can be extrapolated beyond 0.0 and
+  /// 1.0, so negative values and values greater than 1.0 are valid (and can
+  /// easily be generated by curves such as [Curves.elasticInOut]).
+  ///
+  /// Values for `t` are usually obtained from an [Animation<double>], such as
+  /// an [AnimationController].
+  /// {@endtemplate}
+  static Shadow lerp(Shadow a, Shadow b, double t) {
+    assert(t != null);
+    if (a == null && b == null)
+      return null;
+    if (a == null)
+      return b.scale(t);
+    if (b == null)
+      return a.scale(1.0 - t);
+    return Shadow(
+      color: Color.lerp(a.color, b.color, t),
+      offset: Offset.lerp(a.offset, b.offset, t),
+      blurRadius: lerpDouble(a.blurRadius, b.blurRadius, t),
+    );
+  }
+
+  /// Linearly interpolate between two lists of shadows.
+  ///
+  /// If the lists differ in length, excess items are lerped with null.
+  ///
+  /// {@macro dart.ui.shadow.lerp}
+  static List<Shadow> lerpList(List<Shadow> a, List<Shadow> b, double t) {
+    assert(t != null);
+    if (a == null && b == null)
+      return null;
+    a ??= <Shadow>[];
+    b ??= <Shadow>[];
+    final List<Shadow> result = <Shadow>[];
+    final int commonLength = math.min(a.length, b.length);
+    for (int i = 0; i < commonLength; i += 1)
+      result.add(Shadow.lerp(a[i], b[i], t));
+    for (int i = commonLength; i < a.length; i += 1)
+      result.add(a[i].scale(1.0 - t));
+    for (int i = commonLength; i < b.length; i += 1)
+      result.add(b[i].scale(t));
+    return result;
+  }
+
+  @override
+  bool operator ==(dynamic other) {
+    if (identical(this, other))
+      return true;
+    if (other is! Shadow)
+      return false;
+    final Shadow typedOther = other;
+    return color == typedOther.color &&
+           offset == typedOther.offset &&
+           blurRadius == typedOther.blurRadius;
+  }
+
+  @override
+  int get hashCode => hashValues(color, offset, blurRadius);
+
+  /// Determines if lists [a] and [b] are deep equivalent.
+  ///
+  /// Returns true if the lists are both null, or if they are both non-null, have
+  /// the same length, and contain the same Shadows in the same order. Returns
+  /// false otherwise.
+  static bool _shadowsListEquals(List<Shadow> a, List<Shadow> b) {
+    // Compare _shadows
+    if (a == null)
+      return b == null;
+    if (b == null || a.length != b.length)
+      return false;
+    for (int index = 0; index < a.length; ++index)
+      if (a[index] != b[index])
+        return false;
+    return true;
+  }
+
+  // Serialize [shadows] into ByteData. The format is a single uint_32_t at
+  // the beginning indicating the number of shadows, followed by _kBytesPerShadow
+  // bytes for each shadow.
+  static ByteData _encodeShadows(List<Shadow> shadows) {
+    if (shadows == null)
+      return ByteData(0);
+
+    final int byteCount = shadows.length * _kBytesPerShadow;
+    final ByteData shadowsData = ByteData(byteCount);
+
+    int shadowOffset = 0;
+    for (int shadowIndex = 0; shadowIndex < shadows.length; ++shadowIndex) {
+      final Shadow shadow = shadows[shadowIndex];
+      if (shadow == null)
+        continue;
+      shadowOffset = shadowIndex * _kBytesPerShadow;
+
+      shadowsData.setInt32(_kColorOffset + shadowOffset,
+        shadow.color.value ^ Shadow._kColorDefault, _kFakeHostEndian);
+
+      shadowsData.setFloat32(_kXOffset + shadowOffset,
+        shadow.offset.dx, _kFakeHostEndian);
+
+      shadowsData.setFloat32(_kYOffset + shadowOffset,
+        shadow.offset.dy, _kFakeHostEndian);
+
+      shadowsData.setFloat32(_kBlurOffset + shadowOffset,
+        shadow.blurRadius, _kFakeHostEndian);
+    }
+
+    return shadowsData;
+  }
+
+  @override
+  String toString() => 'TextShadow($color, $offset, $blurRadius)';
+}
+
 /// Generic callback signature, used by [_futurize].
 typedef _Callback<T> = void Function(T result);
 

lib/ui/text.dart

@@ -259,6 +259,7 @@ Int32List _encodeTextStyle(
   Locale locale,
   Paint background,
   Paint foreground,
+  List<Shadow> shadows
 ) {
   final Int32List result = new Int32List(8);
   if (color != null) {
@@ -321,6 +322,10 @@ Int32List _encodeTextStyle(
     result[0] |= 1 << 15;
     // Passed separately to native.
   }
+  if (shadows != null) {
+    result[0] |= 1 << 16;
+    // Passed separately to native.
+  }
   return result;
 }
 
@@ -359,6 +364,7 @@ class TextStyle {
     Locale locale,
     Paint background,
     Paint foreground,
+    List<Shadow> shadows,
   }) : assert(color == null || foreground == null,
          'Cannot provide both a color and a foreground\n'
          'The color argument is just a shorthand for "foreground: new Paint()..color = color".'
@@ -379,6 +385,7 @@ class TextStyle {
          locale,
          background,
          foreground,
+         shadows,
        ),
        _fontFamily = fontFamily ?? '',
        _fontSize = fontSize,
@@ -387,7 +394,8 @@ class TextStyle {
        _height = height,
        _locale = locale,
        _background = background,
-       _foreground = foreground;
+       _foreground = foreground,
+       _shadows = shadows;
 
   final Int32List _encoded;
   final String _fontFamily;
@@ -398,6 +406,7 @@ class TextStyle {
   final Locale _locale;
   final Paint _background;
   final Paint _foreground;
+  final List<Shadow> _shadows;
 
   @override
   bool operator ==(dynamic other) {
@@ -419,6 +428,8 @@ class TextStyle {
       if (_encoded[index] != typedOther._encoded[index])
         return false;
     }
+    if (!Shadow._shadowsListEquals(_shadows, typedOther._shadows))
+      return false;
     return true;
   }
 
@@ -428,21 +439,22 @@ class TextStyle {
   @override
   String toString() {
     return 'TextStyle('
-             'color: ${          _encoded[0] & 0x0002 == 0x0002 ? new Color(_encoded[1])                  : "unspecified"}, '
-             'decoration: ${     _encoded[0] & 0x0004 == 0x0004 ? new TextDecoration._(_encoded[2])       : "unspecified"}, '
-             'decorationColor: ${_encoded[0] & 0x0008 == 0x0008 ? new Color(_encoded[3])                  : "unspecified"}, '
-             'decorationStyle: ${_encoded[0] & 0x0010 == 0x0010 ? TextDecorationStyle.values[_encoded[4]] : "unspecified"}, '
-             'fontWeight: ${     _encoded[0] & 0x0020 == 0x0020 ? FontWeight.values[_encoded[5]]          : "unspecified"}, '
-             'fontStyle: ${      _encoded[0] & 0x0040 == 0x0040 ? FontStyle.values[_encoded[6]]           : "unspecified"}, '
-             'textBaseline: ${   _encoded[0] & 0x0080 == 0x0080 ? TextBaseline.values[_encoded[7]]        : "unspecified"}, '
-             'fontFamily: ${     _encoded[0] & 0x0100 == 0x0100 ? _fontFamily                             : "unspecified"}, '
-             'fontSize: ${       _encoded[0] & 0x0200 == 0x0200 ? _fontSize                               : "unspecified"}, '
-             'letterSpacing: ${  _encoded[0] & 0x0400 == 0x0400 ? "${_letterSpacing}x"                    : "unspecified"}, '
-             'wordSpacing: ${    _encoded[0] & 0x0800 == 0x0800 ? "${_wordSpacing}x"                      : "unspecified"}, '
-             'height: ${         _encoded[0] & 0x1000 == 0x1000 ? "${_height}x"                           : "unspecified"}, '
-             'locale: ${         _encoded[0] & 0x2000 == 0x2000 ? _locale                                 : "unspecified"}, '
-             'background: ${     _encoded[0] & 0x4000 == 0x4000 ? _background                             : "unspecified"}, '
-             'foreground: ${     _encoded[0] & 0x8000 == 0x8000 ? _foreground                             : "unspecified"}'
+             'color: ${          _encoded[0] & 0x00002 == 0x00002 ? new Color(_encoded[1])                  : "unspecified"}, '
+             'decoration: ${     _encoded[0] & 0x00004 == 0x00004 ? new TextDecoration._(_encoded[2])       : "unspecified"}, '
+             'decorationColor: ${_encoded[0] & 0x00008 == 0x00008 ? new Color(_encoded[3])                  : "unspecified"}, '
+             'decorationStyle: ${_encoded[0] & 0x00010 == 0x00010 ? TextDecorationStyle.values[_encoded[4]] : "unspecified"}, '
+             'fontWeight: ${     _encoded[0] & 0x00020 == 0x00020 ? FontWeight.values[_encoded[5]]          : "unspecified"}, '
+             'fontStyle: ${      _encoded[0] & 0x00040 == 0x00040 ? FontStyle.values[_encoded[6]]           : "unspecified"}, '
+             'textBaseline: ${   _encoded[0] & 0x00080 == 0x00080 ? TextBaseline.values[_encoded[7]]        : "unspecified"}, '
+             'fontFamily: ${     _encoded[0] & 0x00100 == 0x00100 ? _fontFamily                             : "unspecified"}, '
+             'fontSize: ${       _encoded[0] & 0x00200 == 0x00200 ? _fontSize                               : "unspecified"}, '
+             'letterSpacing: ${  _encoded[0] & 0x00400 == 0x00400 ? "${_letterSpacing}x"                    : "unspecified"}, '
+             'wordSpacing: ${    _encoded[0] & 0x00800 == 0x00800 ? "${_wordSpacing}x"                      : "unspecified"}, '
+             'height: ${         _encoded[0] & 0x01000 == 0x01000 ? "${_height}x"                           : "unspecified"}, '
+             'locale: ${         _encoded[0] & 0x02000 == 0x02000 ? _locale                                 : "unspecified"}, '
+             'background: ${     _encoded[0] & 0x04000 == 0x04000 ? _background                             : "unspecified"}, '
+             'foreground: ${     _encoded[0] & 0x08000 == 0x08000 ? _foreground                             : "unspecified"}, '
+             'shadows: ${        _encoded[0] & 0x10000 == 0x10000 ? _shadows                                : "unspecified"}'
            ')';
   }
 }
@@ -1035,6 +1047,7 @@ class Paragraph extends NativeFieldWrapperClass2 {
 /// After constructing a [Paragraph], call [Paragraph.layout] on it and then
 /// paint it with [Canvas.drawParagraph].
 class ParagraphBuilder extends NativeFieldWrapperClass2 {
+
   /// Creates a [ParagraphBuilder] object, which is used to create a
   /// [Paragraph].
   @pragma('vm:entry-point')
@@ -1044,8 +1057,8 @@ class ParagraphBuilder extends NativeFieldWrapperClass2 {
   /// Applies the given style to the added text until [pop] is called.
   ///
   /// See [pop] for details.
-  void pushStyle(TextStyle style) => _pushStyle(style._encoded, style._fontFamily, style._fontSize, style._letterSpacing, style._wordSpacing, style._height, _encodeLocale(style._locale), style._background?._objects, style._background?._data, style._foreground?._objects, style._foreground?._data);
-  void _pushStyle(Int32List encoded, String fontFamily, double fontSize, double letterSpacing, double wordSpacing, double height, String locale, List<dynamic> backgroundObjects, ByteData backgroundData, List<dynamic> foregroundObjects, ByteData foregroundData) native 'ParagraphBuilder_pushStyle';
+  void pushStyle(TextStyle style) => _pushStyle(style._encoded, style._fontFamily, style._fontSize, style._letterSpacing, style._wordSpacing, style._height, _encodeLocale(style._locale), style._background?._objects, style._background?._data, style._foreground?._objects, style._foreground?._data, Shadow._encodeShadows(style._shadows));
+  void _pushStyle(Int32List encoded, String fontFamily, double fontSize, double letterSpacing, double wordSpacing, double height, String locale, List<dynamic> backgroundObjects, ByteData backgroundData, List<dynamic> foregroundObjects, ByteData foregroundData, ByteData shadowsData) native 'ParagraphBuilder_pushStyle';
 
   static String _encodeLocale(Locale locale) => locale?.toString() ?? '';
 

lib/ui/text/paragraph_builder.cc

@@ -6,6 +6,7 @@
 
 #include "flutter/common/settings.h"
 #include "flutter/common/task_runners.h"
+#include "flutter/fml/logging.h"
 #include "flutter/fml/task_runner.h"
 #include "flutter/lib/ui/text/font_collection.h"
 #include "flutter/lib/ui/ui_dart_state.h"
@@ -16,10 +17,12 @@
 #include "flutter/third_party/txt/src/txt/text_decoration.h"
 #include "flutter/third_party/txt/src/txt/text_style.h"
 #include "third_party/icu/source/common/unicode/ustring.h"
+#include "third_party/skia/include/core/SkColor.h"
 #include "third_party/tonic/converter/dart_converter.h"
 #include "third_party/tonic/dart_args.h"
 #include "third_party/tonic/dart_binding_macros.h"
 #include "third_party/tonic/dart_library_natives.h"
+#include "third_party/tonic/typed_data/dart_byte_data.h"
 
 namespace blink {
 namespace {
@@ -41,6 +44,7 @@ const int tsHeightIndex = 12;
 const int tsLocaleIndex = 13;
 const int tsBackgroundIndex = 14;
 const int tsForegroundIndex = 15;
+const int tsTextShadowsIndex = 16;
 
 const int tsColorMask = 1 << tsColorIndex;
 const int tsTextDecorationMask = 1 << tsTextDecorationIndex;
@@ -57,6 +61,7 @@ const int tsHeightMask = 1 << tsHeightIndex;
 const int tsLocaleMask = 1 << tsLocaleIndex;
 const int tsBackgroundMask = 1 << tsBackgroundIndex;
 const int tsForegroundMask = 1 << tsForegroundIndex;
+const int tsTextShadowsMask = 1 << tsTextShadowsIndex;
 
 // ParagraphStyle
 
@@ -82,6 +87,16 @@ const int psLineHeightMask = 1 << psLineHeightIndex;
 const int psEllipsisMask = 1 << psEllipsisIndex;
 const int psLocaleMask = 1 << psLocaleIndex;
 
+// TextShadows decoding
+
+constexpr uint32_t kColorDefault = 0xFF000000;
+constexpr uint32_t kBytesPerShadow = 16;
+constexpr uint32_t kShadowPropertiesCount = 4;
+constexpr uint32_t kColorOffset = 0;
+constexpr uint32_t kXOffset = 1;
+constexpr uint32_t kYOffset = 2;
+constexpr uint32_t kBlurOffset = 3;
+
 }  // namespace
 
 static void ParagraphBuilder_constructor(Dart_NativeArguments args) {
@@ -148,13 +163,11 @@ ParagraphBuilder::ParagraphBuilder(tonic::Int32List& encoded,
   if (mask & psMaxLinesMask)
     style.max_lines = encoded[psMaxLinesIndex];
 
-  if (mask & psEllipsisMask) {
+  if (mask & psEllipsisMask)
     style.ellipsis = ellipsis;
-  }
 
-  if (mask & psLocaleMask) {
+  if (mask & psLocaleMask)
     style.locale = locale;
-  }
 
   FontCollection& font_collection =
       UIDartState::Current()->window()->client()->GetFontCollection();
@@ -164,6 +177,30 @@ ParagraphBuilder::ParagraphBuilder(tonic::Int32List& encoded,
 
 ParagraphBuilder::~ParagraphBuilder() = default;
 
+void decodeTextShadows(Dart_Handle shadows_data,
+                       std::vector<txt::TextShadow>& decoded_shadows) {
+  decoded_shadows.clear();
+
+  tonic::DartByteData byte_data(shadows_data);
+  FML_CHECK(byte_data.length_in_bytes() % kBytesPerShadow == 0);
+
+  const uint32_t* uint_data = static_cast<const uint32_t*>(byte_data.data());
+  const float* float_data = static_cast<const float*>(byte_data.data());
+
+  size_t shadow_count = byte_data.length_in_bytes() / kBytesPerShadow;
+  size_t shadow_count_offset = 0;
+  for (size_t shadow_index = 0; shadow_index < shadow_count; ++shadow_index) {
+    shadow_count_offset = shadow_index * kShadowPropertiesCount;
+    SkColor color =
+        uint_data[shadow_count_offset + kColorOffset] ^ kColorDefault;
+    decoded_shadows.emplace_back(
+        color,
+        SkPoint::Make(float_data[shadow_count_offset + kXOffset],
+                      float_data[shadow_count_offset + kYOffset]),
+        float_data[shadow_count_offset + kBlurOffset]);
+  }
+}
+
 void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
                                  const std::string& fontFamily,
                                  double fontSize,
@@ -174,7 +211,8 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
                                  Dart_Handle background_objects,
                                  Dart_Handle background_data,
                                  Dart_Handle foreground_objects,
-                                 Dart_Handle foreground_data) {
+                                 Dart_Handle foreground_data,
+                                 Dart_Handle shadows_data) {
   FML_DCHECK(encoded.num_elements() == 8);
 
   int32_t mask = encoded[0];
@@ -183,6 +221,8 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
   // explicitly given.
   txt::TextStyle style = m_paragraphBuilder->PeekStyle();
 
+  // Only change the style property from the previous value if a new explicitly
+  // set value is available
   if (mask & tsColorMask)
     style.color = encoded[tsColorIndex];
 
@@ -249,6 +289,10 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
     }
   }
 
+  if (mask & tsTextShadowsMask) {
+    decodeTextShadows(shadows_data, style.text_shadows);
+  }
+
   m_paragraphBuilder->PushStyle(style);
 }
 

lib/ui/text/paragraph_builder.h

@@ -44,7 +44,8 @@ class ParagraphBuilder : public RefCountedDartWrappable<ParagraphBuilder> {
                  Dart_Handle background_objects,
                  Dart_Handle background_data,
                  Dart_Handle foreground_objects,
-                 Dart_Handle foreground_data);
+                 Dart_Handle foreground_data,
+                 Dart_Handle shadows_data);
 
   void pop();
 

third_party/txt/BUILD.gn

@@ -89,6 +89,8 @@ source_set("txt") {
     "src/txt/text_baseline.h",
     "src/txt/text_decoration.cc",
     "src/txt/text_decoration.h",
+    "src/txt/text_shadow.cc",
+    "src/txt/text_shadow.h",
     "src/txt/text_style.cc",
     "src/txt/text_style.h",
     "src/txt/typeface_font_asset_provider.cc",

third_party/txt/src/txt/paragraph.cc

@@ -36,6 +36,7 @@
 #include "minikin/MinikinFont.h"
 #include "third_party/icu/source/common/unicode/ubidi.h"
 #include "third_party/skia/include/core/SkCanvas.h"
+#include "third_party/skia/include/core/SkMaskFilter.h"
 #include "third_party/skia/include/core/SkPaint.h"
 #include "third_party/skia/include/core/SkTextBlob.h"
 #include "third_party/skia/include/core/SkTypeface.h"
@@ -729,9 +730,9 @@ void Paragraph::Layout(double width, bool force) {
     auto update_line_metrics = [&](const SkPaint::FontMetrics& metrics,
                                    const TextStyle& style) {
       double line_spacing =
-          (line_number == 0)
-              ? -metrics.fAscent * style.height
-              : (-metrics.fAscent + metrics.fLeading) * style.height;
+          (line_number == 0) ? -metrics.fAscent * style.height
+                             : (-metrics.fAscent + metrics.fLeading) *
+                                   style.height * paragraph_style_.line_height;
       if (line_spacing > max_line_spacing) {
         max_line_spacing = line_spacing;
         if (line_number == 0) {
@@ -886,6 +887,7 @@ void Paragraph::Paint(SkCanvas* canvas, double x, double y) {
     }
     SkPoint offset = base_offset + record.offset();
     PaintBackground(canvas, record, base_offset);
+    PaintShadow(canvas, record, offset);
     canvas->drawTextBlob(record.text(), offset.x(), offset.y(), paint);
     PaintDecorations(canvas, record, base_offset);
   }
@@ -1065,6 +1067,27 @@ void Paragraph::PaintBackground(SkCanvas* canvas,
   canvas->drawRect(rect, record.style().background);
 }
 
+void Paragraph::PaintShadow(SkCanvas* canvas,
+                            const PaintRecord& record,
+                            SkPoint offset) {
+  if (record.style().text_shadows.size() == 0)
+    return;
+  for (TextShadow text_shadow : record.style().text_shadows) {
+    if (!text_shadow.hasShadow()) {
+      continue;
+    }
+
+    SkPaint paint;
+    paint.setColor(text_shadow.color);
+    if (text_shadow.blur_radius != 0.0) {
+      paint.setMaskFilter(SkMaskFilter::MakeBlur(
+          kNormal_SkBlurStyle, text_shadow.blur_radius, false));
+    }
+    canvas->drawTextBlob(record.text(), offset.x() + text_shadow.offset.x(),
+                         offset.y() + text_shadow.offset.y(), paint);
+  }
+}
+
 std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
     size_t start,
     size_t end,
@@ -1101,7 +1124,8 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(
         SkRect::MakeLTRB(left, top, right, bottom), run.direction);
   }
 
-  // Add empty rectangles representing any newline characters within the range.
+  // Add empty rectangles representing any newline characters within the
+  // range.
   for (size_t line_number = 0; line_number < line_ranges_.size();
        ++line_number) {
     const LineRange& line = line_ranges_[line_number];

third_party/txt/src/txt/paragraph.h

@@ -206,6 +206,9 @@ class Paragraph {
   FRIEND_TEST(ParagraphTest, RepeatLayoutParagraph);
   FRIEND_TEST(ParagraphTest, Ellipsize);
   FRIEND_TEST(ParagraphTest, UnderlineShiftParagraph);
+  FRIEND_TEST(ParagraphTest, SimpleShadow);
+  FRIEND_TEST(ParagraphTest, ComplexShadow);
+  FRIEND_TEST(ParagraphTest, LineHeightsParagraph);
 
   // Starting data to layout.
   std::vector<uint16_t> text_;
@@ -349,6 +352,9 @@ class Paragraph {
                        const PaintRecord& record,
                        SkPoint base_offset);
 
+  // Draws the shadows onto the canvas.
+  void PaintShadow(SkCanvas* canvas, const PaintRecord& record, SkPoint offset);
+
   // Obtain a Minikin font collection matching this text style.
   std::shared_ptr<minikin::FontCollection> GetMinikinFontCollectionForStyle(
       const TextStyle& style);

third_party/txt/src/txt/styled_runs.h

@@ -79,6 +79,9 @@ class StyledRuns {
   FRIEND_TEST(ParagraphTest, HyphenBreakParagraph);
   FRIEND_TEST(ParagraphTest, RepeatLayoutParagraph);
   FRIEND_TEST(ParagraphTest, Ellipsize);
+  FRIEND_TEST(ParagraphTest, SimpleShadow);
+  FRIEND_TEST(ParagraphTest, ComplexShadow);
+  FRIEND_TEST(ParagraphTest, LineHeightsParagraph);
 
   struct IndexedRun {
     size_t style_index = 0;

third_party/txt/src/txt/text_shadow.cc

+/*
+ * Copyright 2018 Google, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "text_shadow.h"
+#include "third_party/skia/include/core/SkColor.h"
+
+namespace txt {
+
+TextShadow::TextShadow() {}
+TextShadow::TextShadow(SkColor color, SkPoint offset, double blur_radius)
+    : color(color), offset(offset), blur_radius(blur_radius) {}
+
+bool TextShadow::operator==(const TextShadow& other) const {
+  if (color != other.color)
+    return false;
+  if (offset != other.offset)
+    return false;
+  if (blur_radius != other.blur_radius)
+    return false;
+
+  return true;
+}
+
+bool TextShadow::operator!=(const TextShadow& other) const {
+  return !(*this == other);
+}
+
+bool TextShadow::hasShadow() const {
+  if (!offset.isZero())
+    return true;
+  if (blur_radius != 0.0)
+    return true;
+
+  return false;
+}
+
+}  // namespace txt

third_party/txt/src/txt/text_shadow.h

+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef LIB_TXT_SRC_TEXT_SHADOW_H_
+#define LIB_TXT_SRC_TEXT_SHADOW_H_
+
+#include "third_party/skia/include/core/SkColor.h"
+#include "third_party/skia/include/core/SkPoint.h"
+
+namespace txt {
+
+class TextShadow {
+ public:
+  SkColor color = SK_ColorBLACK;
+  SkPoint offset;
+  double blur_radius = 0.0;
+
+  TextShadow();
+
+  TextShadow(SkColor color, SkPoint offset, double blur_radius);
+
+  bool operator==(const TextShadow& other) const;
+
+  bool operator!=(const TextShadow& other) const;
+
+  bool hasShadow() const;
+};
+
+}  // namespace txt
+
+#endif  // LIB_TXT_SRC_TEXT_SHADOW_H_

third_party/txt/src/txt/text_style.cc

@@ -51,6 +51,13 @@ bool TextStyle::equals(const TextStyle& other) const {
     return false;
   if (foreground != other.foreground)
     return false;
+  if (text_shadows.size() != other.text_shadows.size())
+    return false;
+  for (size_t shadow_index = 0; shadow_index < text_shadows.size();
+       ++shadow_index) {
+    if (text_shadows[shadow_index] != other.text_shadows[shadow_index])
+      return false;
+  }
 
   return true;
 }

third_party/txt/src/txt/text_style.h

@@ -18,11 +18,13 @@
 #define LIB_TXT_SRC_TEXT_STYLE_H_
 
 #include <string>
+#include <vector>
 
 #include "font_style.h"
 #include "font_weight.h"
 #include "text_baseline.h"
 #include "text_decoration.h"
+#include "text_shadow.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkPaint.h"
 
@@ -51,6 +53,7 @@ class TextStyle {
   SkPaint background;
   bool has_foreground = false;
   SkPaint foreground;
+  std::vector<TextShadow> text_shadows;
 
   TextStyle();
 

third_party/txt/tests/paragraph_unittests.cc

@@ -1731,4 +1731,264 @@ TEST_F(ParagraphTest, UnderlineShiftParagraph) {
   }
 }
 
+TEST_F(ParagraphTest, SimpleShadow) {
+  const char* text = "Hello World Text Dialog";
+  auto icu_text = icu::UnicodeString::fromUTF8(text);
+  std::u16string u16_text(icu_text.getBuffer(),
+                          icu_text.getBuffer() + icu_text.length());
+
+  txt::ParagraphStyle paragraph_style;
+  txt::ParagraphBuilder builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.font_family = "Roboto";
+  text_style.color = SK_ColorBLACK;
+  text_style.text_shadows.emplace_back(SK_ColorBLACK, SkPoint::Make(2.0, 2.0),
+                                       1.0);
+  builder.PushStyle(text_style);
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(GetTestCanvasWidth());
+  paragraph->Paint(GetCanvas(), 10.0, 15.0);
+
+  ASSERT_EQ(paragraph->text_.size(), std::string{text}.length());
+  for (size_t i = 0; i < u16_text.length(); i++) {
+    ASSERT_EQ(paragraph->text_[i], u16_text[i]);
+  }
+  ASSERT_EQ(paragraph->runs_.runs_.size(), 1ull);
+  ASSERT_EQ(paragraph->runs_.styles_.size(), 2ull);
+  ASSERT_TRUE(paragraph->runs_.styles_[1].equals(text_style));
+  ASSERT_EQ(paragraph->records_[0].style().color, text_style.color);
+
+  ASSERT_EQ(paragraph->records_[0].style().text_shadows.size(), 1ull);
+  ASSERT_EQ(paragraph->records_[0].style().text_shadows[0],
+            text_style.text_shadows[0]);
+
+  ASSERT_TRUE(Snapshot());
+}
+
+TEST_F(ParagraphTest, ComplexShadow) {
+  const char* text = "Text Chunk ";
+  auto icu_text = icu::UnicodeString::fromUTF8(text);
+  std::u16string u16_text(icu_text.getBuffer(),
+                          icu_text.getBuffer() + icu_text.length());
+
+  txt::ParagraphStyle paragraph_style;
+  txt::ParagraphBuilder builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.font_family = "Roboto";
+  text_style.color = SK_ColorBLACK;
+  text_style.text_shadows.emplace_back(SK_ColorBLACK, SkPoint::Make(2.0, 2.0),
+                                       1.0);
+  builder.PushStyle(text_style);
+  builder.AddText(u16_text);
+
+  text_style.text_shadows.emplace_back(SK_ColorRED, SkPoint::Make(2.0, 2.0),
+                                       5.0);
+  text_style.text_shadows.emplace_back(SK_ColorGREEN, SkPoint::Make(10.0, -5.0),
+                                       3.0);
+  builder.PushStyle(text_style);
+  builder.AddText(u16_text);
+
+  builder.Pop();
+  builder.AddText(u16_text);
+
+  text_style.text_shadows.emplace_back(SK_ColorGREEN, SkPoint::Make(0.0, -1.0),
+                                       0.0);
+  builder.PushStyle(text_style);
+  builder.AddText(u16_text);
+
+  builder.Pop();
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(GetTestCanvasWidth());
+  paragraph->Paint(GetCanvas(), 10.0, 15.0);
+
+  ASSERT_EQ(paragraph->text_.size(), std::string{text}.length() * 5);
+  for (size_t i = 0; i < u16_text.length(); i++) {
+    ASSERT_EQ(paragraph->text_[i], u16_text[i]);
+  }
+
+  ASSERT_EQ(paragraph->records_[0].style().text_shadows.size(), 1ull);
+  ASSERT_EQ(paragraph->records_[1].style().text_shadows.size(), 3ull);
+  ASSERT_EQ(paragraph->records_[2].style().text_shadows.size(), 1ull);
+  ASSERT_EQ(paragraph->records_[3].style().text_shadows.size(), 4ull);
+  ASSERT_EQ(paragraph->records_[4].style().text_shadows.size(), 1ull);
+  for (size_t i = 0; i < 1; ++i)
+    ASSERT_EQ(paragraph->records_[0].style().text_shadows[i],
+              text_style.text_shadows[i]);
+  for (size_t i = 0; i < 3; ++i)
+    ASSERT_EQ(paragraph->records_[1].style().text_shadows[i],
+              text_style.text_shadows[i]);
+  for (size_t i = 0; i < 1; ++i)
+    ASSERT_EQ(paragraph->records_[2].style().text_shadows[i],
+              text_style.text_shadows[i]);
+  for (size_t i = 0; i < 4; ++i)
+    ASSERT_EQ(paragraph->records_[3].style().text_shadows[i],
+              text_style.text_shadows[i]);
+  for (size_t i = 0; i < 1; ++i)
+    ASSERT_EQ(paragraph->records_[4].style().text_shadows[i],
+              text_style.text_shadows[i]);
+
+  ASSERT_TRUE(Snapshot());
+}
+
+TEST_F(ParagraphTest, DISABLE_ON_WINDOWS(LineHeightsParagraph)) {
+  const char* text =
+      "This is a very long sentence to test if the text will properly wrap "
+      "around and go to the next line. Sometimes, short sentence. Longer "
+      "sentences are okay too because they are nessecary. Very short. "
+      "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod "
+      "tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim "
+      "veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea "
+      "commodo consequat. Duis aute irure dolor in reprehenderit in voluptate "
+      "velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint "
+      "occaecat cupidatat non proident, sunt in culpa qui officia deserunt "
+      "mollit anim id est laborum. "
+      "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod "
+      "tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim "
+      "veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea "
+      "commodo consequat. Duis aute irure dolor in reprehenderit in voluptate "
+      "velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint "
+      "occaecat cupidatat non proident, sunt in culpa qui officia deserunt "
+      "mollit anim id est laborum.";
+  auto icu_text = icu::UnicodeString::fromUTF8(text);
+  std::u16string u16_text(icu_text.getBuffer(),
+                          icu_text.getBuffer() + icu_text.length());
+
+  txt::ParagraphStyle paragraph_style;
+  paragraph_style.max_lines = 14;
+  paragraph_style.text_align = TextAlign::left;
+  double line_height = 2.0;
+  paragraph_style.line_height = line_height;
+  txt::ParagraphBuilder builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.font_family = "Roboto";
+  text_style.font_size = 26;
+  text_style.letter_spacing = 1;
+  text_style.word_spacing = 5;
+  text_style.color = SK_ColorBLACK;
+  text_style.height = 1;
+  text_style.decoration = TextDecoration::kUnderline;
+  text_style.decoration_color = SK_ColorBLACK;
+  builder.PushStyle(text_style);
+
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(GetTestCanvasWidth() - 100);
+
+  paragraph->Paint(GetCanvas(), 0, 0);
+
+  ASSERT_TRUE(Snapshot());
+
+  ASSERT_EQ(paragraph->text_.size(), std::string{text}.length());
+  for (size_t i = 0; i < u16_text.length(); i++) {
+    ASSERT_EQ(paragraph->text_[i], u16_text[i]);
+  }
+  ASSERT_EQ(paragraph->runs_.runs_.size(), 1ull);
+  ASSERT_EQ(paragraph->runs_.styles_.size(), 2ull);
+  ASSERT_TRUE(paragraph->runs_.styles_[1].equals(text_style));
+  ASSERT_EQ(paragraph->records_.size(), paragraph_style.max_lines);
+  double expected_y = 24;
+
+  ASSERT_TRUE(paragraph->records_[0].style().equals(text_style));
+  ASSERT_DOUBLE_EQ(paragraph->records_[0].offset().y(), expected_y);
+  expected_y += 27.5 * line_height;
+  ASSERT_DOUBLE_EQ(paragraph->records_[0].offset().x(), 0);
+
+  ASSERT_TRUE(paragraph->records_[1].style().equals(text_style));
+  ASSERT_DOUBLE_EQ(paragraph->records_[1].offset().y(), expected_y);
+  expected_y += 27.5 * line_height;
+  ASSERT_DOUBLE_EQ(paragraph->records_[1].offset().x(), 0);
+
+  ASSERT_TRUE(paragraph->records_[2].style().equals(text_style));
+  ASSERT_DOUBLE_EQ(paragraph->records_[2].offset().y(), expected_y);
+  expected_y += 27.5 * line_height;
+  ASSERT_DOUBLE_EQ(paragraph->records_[2].offset().x(), 0);
+
+  ASSERT_TRUE(paragraph->records_[3].style().equals(text_style));
+  ASSERT_DOUBLE_EQ(paragraph->records_[3].offset().y(), expected_y);
+  expected_y += 27.5 * 10 * line_height;
+  ASSERT_DOUBLE_EQ(paragraph->records_[3].offset().x(), 0);
+
+  ASSERT_TRUE(paragraph->records_[13].style().equals(text_style));
+  ASSERT_DOUBLE_EQ(paragraph->records_[13].offset().y(), expected_y);
+  ASSERT_DOUBLE_EQ(paragraph->records_[13].offset().x(), 0);
+
+  ASSERT_EQ(paragraph_style.text_align,
+            paragraph->GetParagraphStyle().text_align);
+
+  // Tests for GetGlyphPositionAtCoordinate()
+  ASSERT_EQ(paragraph->GetGlyphPositionAtCoordinate(0, 0).position, 0ull);
+  ASSERT_EQ(paragraph->GetGlyphPositionAtCoordinate(1, 1).position, 0ull);
+  ASSERT_EQ(paragraph->GetGlyphPositionAtCoordinate(1, 35).position, 68ull);
+  ASSERT_EQ(paragraph->GetGlyphPositionAtCoordinate(1, 70).position, 68ull);
+  ASSERT_EQ(paragraph->GetGlyphPositionAtCoordinate(2000, 35).position, 134ull);
+
+  ASSERT_TRUE(Snapshot());
+}
+
+TEST_F(ParagraphTest, BaselineParagraph) {
+  const char* text =
+      "左線読設Byg後碁給能上目秘使約。満毎冠行来昼本可必図将発確年。今属場育"
+      "図情闘陰野高備込制詩西校客。審対江置講今固残必託地集済決維駆年策。立得";
+  auto icu_text = icu::UnicodeString::fromUTF8(text);
+  std::u16string u16_text(icu_text.getBuffer(),
+                          icu_text.getBuffer() + icu_text.length());
+
+  txt::ParagraphStyle paragraph_style;
+  paragraph_style.max_lines = 14;
+  paragraph_style.text_align = TextAlign::justify;
+  paragraph_style.line_height = 1.5;
+  txt::ParagraphBuilder builder(paragraph_style, GetTestFontCollection());
+
+  txt::TextStyle text_style;
+  text_style.color = SK_ColorBLACK;
+  text_style.font_size = 55;
+  text_style.letter_spacing = 2;
+  text_style.font_family = "Source Han Serif CN";
+  text_style.decoration_style = txt::TextDecorationStyle::kSolid;
+  text_style.decoration_color = SK_ColorBLACK;
+  builder.PushStyle(text_style);
+
+  builder.AddText(u16_text);
+
+  builder.Pop();
+
+  auto paragraph = builder.Build();
+  paragraph->Layout(GetTestCanvasWidth() - 100);
+
+  paragraph->Paint(GetCanvas(), 0, 0);
+
+  SkPaint paint;
+  paint.setStyle(SkPaint::kStroke_Style);
+  paint.setAntiAlias(true);
+  paint.setStrokeWidth(1);
+  paint.setColor(SK_ColorRED);
+  GetCanvas()->drawLine(0, paragraph->GetIdeographicBaseline(),
+                        paragraph->GetMaxWidth(),
+                        paragraph->GetIdeographicBaseline(), paint);
+
+  paint.setColor(SK_ColorGREEN);
+
+  GetCanvas()->drawLine(0, paragraph->GetAlphabeticBaseline(),
+                        paragraph->GetMaxWidth(),
+                        paragraph->GetAlphabeticBaseline(), paint);
+  ASSERT_DOUBLE_EQ(paragraph->GetIdeographicBaseline(), 79.035003662109375);
+  ASSERT_DOUBLE_EQ(paragraph->GetAlphabeticBaseline(), 63.305000305175781);
+
+  ASSERT_TRUE(Snapshot());
+}
+
 }  // namespace txt