Engine/LibTxt/dart:ui impl of TextHeightBehavior

lib/ui/text.dart

@@ -429,6 +429,94 @@ enum TextDecorationStyle {
   wavy
 }
 
+/// {@template flutter.dart:ui.textHeightBehavior}
+/// Defines how the paragraph will apply [TextStyle.height] to the ascent of the
+/// first line and descent of the last line.
+///
+/// Each boolean value represents whether the [TextStyle.height] modifier will
+/// be applied to the corresponding metric. By default, all properties are true,
+/// and [TextStyle.height] is applied as normal. When set to false, the font's
+/// default ascent will be used.
+/// {@endtemplate}
+class TextHeightBehavior {
+
+  /// Creates a new TextHeightBehavior object.
+  ///
+  ///  * applyHeightToFirstAscent: When true, the [TextStyle.height] modifier
+  ///    will be applied to the ascent of the first line. When false, the font's
+  ///    default ascent will be used.
+  ///  * applyHeightToLastDescent: When true, the [TextStyle.height] modifier
+  ///    will be applied to the descent of the last line. When false, the font's
+  ///    default descent will be used.
+  ///
+  /// All properties default to true (height modifications applied as normal).
+  const TextHeightBehavior({
+    this.applyHeightToFirstAscent = true,
+    this.applyHeightToLastDescent = true,
+  });
+
+  /// Creates a new TextHeightBehavior object from an encoded form.
+  ///
+  /// See [encode] for the creation of the encoded form.
+  const TextHeightBehavior.fromEncoded(int encoded) : applyHeightToFirstAscent = (encoded & 0x1) == 0,
+                                                      applyHeightToLastDescent = (encoded & 0x2) == 0;
+
+
+  /// Whether to apply the [TextStyle.height] modifier to the ascent of the first
+  /// line in the paragraph.
+  ///
+  /// When true, the [TextStyle.height] modifier will be applied to to the ascent
+  /// of the first line. When false, the font's default ascent will be used and
+  /// the [TextStyle.height] will have no effect on the ascent of the first line.
+  ///
+  /// This property only has effect if a non-null [TextStyle.height] is specified.
+  ///
+  /// Defaults to true (height modifications applied as normal).
+  final bool applyHeightToFirstAscent;
+
+  /// Whether to apply the [TextStyle.height] modifier to the descent of the last
+  /// line in the paragraph.
+  ///
+  /// When true, the [TextStyle.height] modifier will be applied to to the descent
+  /// of the last line. When false, the font's default descent will be used and
+  /// the [TextStyle.height] will have no effect on the descent of the last line.
+  ///
+  /// This property only has effect if a non-null [TextStyle.height] is specified.
+  ///
+  /// Defaults to true (height modifications applied as normal).
+  final bool applyHeightToLastDescent;
+
+  /// Returns an encoded int representation of this object.
+  int encode() {
+    return (applyHeightToFirstAscent ? 0 : 1 << 0) | (applyHeightToLastDescent ? 0 : 1 << 1);
+  }
+
+  @override
+  bool operator ==(dynamic other) {
+    if (other.runtimeType != runtimeType)
+      return false;
+    return other is TextHeightBehavior
+        && other.applyHeightToFirstAscent == applyHeightToFirstAscent
+        && other.applyHeightToLastDescent == applyHeightToLastDescent;
+  }
+
+  @override
+  int get hashCode {
+    return hashValues(
+      applyHeightToFirstAscent,
+      applyHeightToLastDescent,
+    );
+  }
+
+  @override
+  String toString() {
+    return 'TextHeightBehavior('
+             'applyHeightToFirstAscent: $applyHeightToFirstAscent, '
+             'applyHeightToLastDescent: $applyHeightToLastDescent'
+           ')';
+  }
+}
+
 /// 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
@@ -746,20 +834,23 @@ class TextStyle {
 //
 //  - Element 5: The value of |maxLines|.
 //
+//  - Element 6: The encoded value of |textHeightBehavior|.
+//
 Int32List _encodeParagraphStyle(
   TextAlign textAlign,
   TextDirection textDirection,
   int maxLines,
   String fontFamily,
   double fontSize,
   double height,
+  TextHeightBehavior textHeightBehavior,
   FontWeight fontWeight,
   FontStyle fontStyle,
   StrutStyle strutStyle,
   String ellipsis,
   Locale locale,
 ) {
-  final Int32List result = Int32List(6); // also update paragraph_builder.cc
+  final Int32List result = Int32List(7); // also update paragraph_builder.cc
   if (textAlign != null) {
     result[0] |= 1 << 1;
     result[1] = textAlign.index;
@@ -780,28 +871,32 @@ Int32List _encodeParagraphStyle(
     result[0] |= 1 << 5;
     result[5] = maxLines;
   }
-  if (fontFamily != null) {
+  if (textHeightBehavior != null) {
     result[0] |= 1 << 6;
+    result[6] = textHeightBehavior.encode();
+  }
+  if (fontFamily != null) {
+    result[0] |= 1 << 7;
     // Passed separately to native.
   }
   if (fontSize != null) {
-    result[0] |= 1 << 7;
+    result[0] |= 1 << 8;
     // Passed separately to native.
   }
   if (height != null) {
-    result[0] |= 1 << 8;
+    result[0] |= 1 << 9;
     // Passed separately to native.
   }
   if (strutStyle != null) {
-    result[0] |= 1 << 9;
+    result[0] |= 1 << 10;
     // Passed separately to native.
   }
   if (ellipsis != null) {
-    result[0] |= 1 << 10;
+    result[0] |= 1 << 11;
     // Passed separately to native.
   }
   if (locale != null) {
-    result[0] |= 1 << 11;
+    result[0] |= 1 << 12;
     // Passed separately to native.
   }
   return result;
@@ -842,6 +937,9 @@ class ParagraphStyle {
   ///   the line height to take the height as defined by the font, which may not
   ///   be exactly the height of the `fontSize`.
   ///
+  /// * `textHeightBehavior`: Specifies how the `height` multiplier is
+  ///   applied to ascent of the first line and the descent of the last line.
+  ///
   /// * `fontWeight`: The typeface thickness to use when painting the text
   ///   (e.g., bold).
   ///
@@ -869,6 +967,7 @@ class ParagraphStyle {
     String fontFamily,
     double fontSize,
     double height,
+    TextHeightBehavior textHeightBehavior,
     FontWeight fontWeight,
     FontStyle fontStyle,
     StrutStyle strutStyle,
@@ -881,6 +980,7 @@ class ParagraphStyle {
          fontFamily,
          fontSize,
          height,
+         textHeightBehavior,
          fontWeight,
          fontStyle,
          strutStyle,
@@ -929,11 +1029,14 @@ class ParagraphStyle {
              'fontWeight: ${    _encoded[0] & 0x008 == 0x008 ? FontWeight.values[_encoded[3]]    : "unspecified"}, '
              'fontStyle: ${     _encoded[0] & 0x010 == 0x010 ? FontStyle.values[_encoded[4]]     : "unspecified"}, '
              'maxLines: ${      _encoded[0] & 0x020 == 0x020 ? _encoded[5]                       : "unspecified"}, '
-             'fontFamily: ${    _encoded[0] & 0x040 == 0x040 ? _fontFamily                       : "unspecified"}, '
-             'fontSize: ${      _encoded[0] & 0x080 == 0x080 ? _fontSize                         : "unspecified"}, '
-             'height: ${        _encoded[0] & 0x100 == 0x100 ? "${_height}x"                     : "unspecified"}, '
-             'ellipsis: ${      _encoded[0] & 0x200 == 0x200 ? "\"$_ellipsis\""                  : "unspecified"}, '
-             'locale: ${        _encoded[0] & 0x400 == 0x400 ? _locale                           : "unspecified"}'
+             'textHeightBehavior: ${
+                                _encoded[0] & 0x040 == 0x040 ?
+                                  TextHeightBehavior.fromEncoded(_encoded[6]).toString() : "unspecified"}, '
+             'fontFamily: ${    _encoded[0] & 0x080 == 0x080 ? _fontFamily                       : "unspecified"}, '
+             'fontSize: ${      _encoded[0] & 0x100 == 0x100 ? _fontSize                         : "unspecified"}, '
+             'height: ${        _encoded[0] & 0x200 == 0x200 ? "${_height}x"                     : "unspecified"}, '
+             'ellipsis: ${      _encoded[0] & 0x400 == 0x400 ? "\"$_ellipsis\""                  : "unspecified"}, '
+             'locale: ${        _encoded[0] & 0x800 == 0x800 ? _locale                           : "unspecified"}'
            ')';
   }
 }

lib/ui/text/paragraph_builder.cc

@@ -75,12 +75,13 @@ const int psTextDirectionIndex = 2;
 const int psFontWeightIndex = 3;
 const int psFontStyleIndex = 4;
 const int psMaxLinesIndex = 5;
-const int psFontFamilyIndex = 6;
-const int psFontSizeIndex = 7;
-const int psHeightIndex = 8;
-const int psStrutStyleIndex = 9;
-const int psEllipsisIndex = 10;
-const int psLocaleIndex = 11;
+const int psTextHeightBehaviorIndex = 6;
+const int psFontFamilyIndex = 7;
+const int psFontSizeIndex = 8;
+const int psHeightIndex = 9;
+const int psStrutStyleIndex = 10;
+const int psEllipsisIndex = 11;
+const int psLocaleIndex = 12;
 
 const int psTextAlignMask = 1 << psTextAlignIndex;
 const int psTextDirectionMask = 1 << psTextDirectionIndex;
@@ -90,6 +91,7 @@ const int psMaxLinesMask = 1 << psMaxLinesIndex;
 const int psFontFamilyMask = 1 << psFontFamilyIndex;
 const int psFontSizeMask = 1 << psFontSizeIndex;
 const int psHeightMask = 1 << psHeightIndex;
+const int psTextHeightBehaviorMask = 1 << psTextHeightBehaviorIndex;
 const int psStrutStyleMask = 1 << psStrutStyleIndex;
 const int psEllipsisMask = 1 << psEllipsisIndex;
 const int psLocaleMask = 1 << psLocaleIndex;
@@ -265,6 +267,10 @@ ParagraphBuilder::ParagraphBuilder(
     style.has_height_override = true;
   }
 
+  if (mask & psTextHeightBehaviorMask) {
+    style.text_height_behavior = encoded[psTextHeightBehaviorIndex];
+  }
+
   if (mask & psStrutStyleMask) {
     decodeStrut(strutData, strutFontFamilies, style);
   }

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

@@ -25,6 +25,7 @@ class SkParagraphStyle implements ui.ParagraphStyle {
     String fontFamily,
     double fontSize,
     double height,
+    ui.TextHeightBehavior textHeightBehavior,
     ui.FontWeight fontWeight,
     ui.FontStyle fontStyle,
     ui.StrutStyle strutStyle,
@@ -38,6 +39,7 @@ class SkParagraphStyle implements ui.ParagraphStyle {
       fontFamily,
       fontSize,
       height,
+      textHeightBehavior,
       fontWeight,
       fontStyle,
       ellipsis,
@@ -85,6 +87,7 @@ class SkParagraphStyle implements ui.ParagraphStyle {
     String fontFamily,
     double fontSize,
     double height,
+    ui.TextHeightBehavior textHeightBehavior,
     ui.FontWeight fontWeight,
     ui.FontStyle fontStyle,
     String ellipsis,
@@ -129,6 +132,10 @@ class SkParagraphStyle implements ui.ParagraphStyle {
       skParagraphStyle['heightMultiplier'] = height;
     }
 
+    if (textHeightBehavior != null) {
+      skParagraphStyle['textHeightBehavior'] = textHeightBehavior.encode();
+    }
+
     if (maxLines != null) {
       skParagraphStyle['maxLines'] = maxLines;
     }

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

@@ -457,6 +457,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
     String fontFamily,
     double fontSize,
     double height,
+    ui.TextHeightBehavior textHeightBehavior,
     ui.FontWeight fontWeight,
     ui.FontStyle fontStyle,
     ui.StrutStyle strutStyle,
@@ -470,6 +471,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
         _fontFamily = fontFamily,
         _fontSize = fontSize,
         _height = height,
+        _textHeightBehavior = textHeightBehavior,
         // TODO(b/128317744): add support for strut style.
         _strutStyle = strutStyle,
         _ellipsis = ellipsis,
@@ -483,6 +485,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
   final String _fontFamily;
   final double _fontSize;
   final double _height;
+  final ui.TextHeightBehavior _textHeightBehavior;
   final EngineStrutStyle _strutStyle;
   final String _ellipsis;
   final ui.Locale _locale;
@@ -536,6 +539,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
         _fontFamily == typedOther._fontFamily ||
         _fontSize == typedOther._fontSize ||
         _height == typedOther._height ||
+        _textHeightBehavior == typedOther._textHeightBehavior ||
         _ellipsis == typedOther._ellipsis ||
         _locale == typedOther._locale;
   }
@@ -556,6 +560,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
           'fontFamily: ${_fontFamily ?? "unspecified"}, '
           'fontSize: ${_fontSize != null ? _fontSize.toStringAsFixed(1) : "unspecified"}, '
           'height: ${_height != null ? "${_height.toStringAsFixed(1)}x" : "unspecified"}, '
+          'textHeightBehavior: ${_textHeightBehavior ?? "unspecified"}, '
           'ellipsis: ${_ellipsis != null ? "\"$_ellipsis\"" : "unspecified"}, '
           'locale: ${_locale ?? "unspecified"}'
           ')';