TextStyle level leadingDistribution

lib/ui/text/paragraph_builder.cc

@@ -39,17 +39,18 @@ const int tsTextDecorationStyleIndex = 4;
 const int tsFontWeightIndex = 5;
 const int tsFontStyleIndex = 6;
 const int tsTextBaselineIndex = 7;
-const int tsTextDecorationThicknessIndex = 8;
-const int tsFontFamilyIndex = 9;
-const int tsFontSizeIndex = 10;
-const int tsLetterSpacingIndex = 11;
-const int tsWordSpacingIndex = 12;
-const int tsHeightIndex = 13;
-const int tsLocaleIndex = 14;
-const int tsBackgroundIndex = 15;
-const int tsForegroundIndex = 16;
-const int tsTextShadowsIndex = 17;
-const int tsFontFeaturesIndex = 18;
+const int tsLeadingDistributionIndex = 8;
+const int tsTextDecorationThicknessIndex = 9;
+const int tsFontFamilyIndex = 10;
+const int tsFontSizeIndex = 11;
+const int tsLetterSpacingIndex = 12;
+const int tsWordSpacingIndex = 13;
+const int tsHeightIndex = 14;
+const int tsLocaleIndex = 15;
+const int tsBackgroundIndex = 16;
+const int tsForegroundIndex = 17;
+const int tsTextShadowsIndex = 18;
+const int tsFontFeaturesIndex = 19;
 
 const int tsColorMask = 1 << tsColorIndex;
 const int tsTextDecorationMask = 1 << tsTextDecorationIndex;
@@ -59,6 +60,7 @@ const int tsTextDecorationThicknessMask = 1 << tsTextDecorationThicknessIndex;
 const int tsFontWeightMask = 1 << tsFontWeightIndex;
 const int tsFontStyleMask = 1 << tsFontStyleIndex;
 const int tsTextBaselineMask = 1 << tsTextBaselineIndex;
+const int tsLeadingDistributionMask = 1 << tsLeadingDistributionIndex;
 const int tsFontFamilyMask = 1 << tsFontFamilyIndex;
 const int tsFontSizeMask = 1 << tsFontSizeIndex;
 const int tsLetterSpacingMask = 1 << tsLetterSpacingIndex;
@@ -118,14 +120,16 @@ const int sFontStyleIndex = 1;
 const int sFontFamilyIndex = 2;
 const int sFontSizeIndex = 3;
 const int sHeightIndex = 4;
-const int sLeadingIndex = 5;
-const int sForceStrutHeightIndex = 6;
+const int sLeadingDistributionIndex = 5;
+const int sLeadingIndex = 6;
+const int sForceStrutHeightIndex = 7;
 
 const int sFontWeightMask = 1 << sFontWeightIndex;
 const int sFontStyleMask = 1 << sFontStyleIndex;
 const int sFontFamilyMask = 1 << sFontFamilyIndex;
 const int sFontSizeMask = 1 << sFontSizeIndex;
 const int sHeightMask = 1 << sHeightIndex;
+const int sLeadingDistributionMask = 1 << sLeadingDistributionIndex;
 const int sLeadingMask = 1 << sLeadingIndex;
 const int sForceStrutHeightMask = 1 << sForceStrutHeightIndex;
 
@@ -210,6 +214,12 @@ void decodeStrut(Dart_Handle strut_data,
   if (mask & sHeightMask) {
     paragraph_style.strut_height = float_data[float_count++];
     paragraph_style.strut_has_height_override = true;
+
+    // LeadingDistribution does not affect layout if height is not set.
+    if (mask & sLeadingDistributionMask) {
+      paragraph_style.strut_half_leading = uint8_data[byte_count];
+      paragraph_style.strut_has_leading_distribution_override = true;
+    }
   }
   if (mask & sLeadingMask) {
     paragraph_style.strut_leading = float_data[float_count++];
@@ -373,7 +383,7 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
                                  Dart_Handle foreground_data,
                                  Dart_Handle shadows_data,
                                  Dart_Handle font_features_data) {
-  FML_DCHECK(encoded.num_elements() == 8);
+  FML_DCHECK(encoded.num_elements() == 9);
 
   int32_t mask = encoded[0];
 
@@ -410,6 +420,11 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
     // property wasn't wired up either.
   }
 
+  style.has_leading_distribution_override = mask & tsLeadingDistributionMask;
+  if (mask & tsLeadingDistributionMask) {
+    style.half_leading = encoded[tsLeadingDistributionIndex];
+  }
+
   if (mask & (tsFontWeightMask | tsFontStyleMask | tsFontSizeMask |
               tsLetterSpacingMask | tsWordSpacingMask)) {
     if (mask & tsFontWeightMask) {

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

@@ -1211,6 +1211,8 @@ class EngineStrutStyle implements ui.StrutStyle {
     List<String>? fontFamilyFallback,
     double? fontSize,
     double? height,
+    //TODO(LongCatIsLooong): implement leadingDistribution.
+    ui.TextLeadingDistribution? leadingDistribution,
     double? leading,
     ui.FontWeight? fontWeight,
     ui.FontStyle? fontStyle,
@@ -1219,6 +1221,7 @@ class EngineStrutStyle implements ui.StrutStyle {
         _fontFamilyFallback = fontFamilyFallback,
         _fontSize = fontSize,
         _height = height,
+        _leadingDistribution = leadingDistribution,
         _leading = leading,
         _fontWeight = fontWeight,
         _fontStyle = fontStyle,
@@ -1232,6 +1235,7 @@ class EngineStrutStyle implements ui.StrutStyle {
   final ui.FontWeight? _fontWeight;
   final ui.FontStyle? _fontStyle;
   final bool? _forceStrutHeight;
+  final ui.TextLeadingDistribution? _leadingDistribution;
 
   @override
   bool operator ==(Object other) {
@@ -1246,6 +1250,7 @@ class EngineStrutStyle implements ui.StrutStyle {
         && other._fontSize == _fontSize
         && other._height == _height
         && other._leading == _leading
+        && other._leadingDistribution == _leadingDistribution
         && other._fontWeight == _fontWeight
         && other._fontStyle == _fontStyle
         && other._forceStrutHeight == _forceStrutHeight
@@ -1259,6 +1264,7 @@ class EngineStrutStyle implements ui.StrutStyle {
         _fontSize,
         _height,
         _leading,
+        _leadingDistribution,
         _fontWeight,
         _fontStyle,
         _forceStrutHeight,

lib/web_ui/lib/src/ui/text.dart

@@ -204,18 +204,29 @@ enum TextDecorationStyle {
   wavy
 }
 
+enum TextLeadingDistribution {
+  proportional,
+  even,
+}
+
 class TextHeightBehavior {
   const TextHeightBehavior({
     this.applyHeightToFirstAscent = true,
     this.applyHeightToLastDescent = true,
+    this.leadingDistribution = TextLeadingDistribution.proportional,
   });
-  const TextHeightBehavior.fromEncoded(int encoded)
-      : applyHeightToFirstAscent = (encoded & 0x1) == 0,
-        applyHeightToLastDescent = (encoded & 0x2) == 0;
+  TextHeightBehavior.fromEncoded(int encoded)
+    : applyHeightToFirstAscent = (encoded & 0x1) == 0,
+      applyHeightToLastDescent = (encoded & 0x2) == 0,
+      leadingDistribution = TextLeadingDistribution.values[encoded >> 2];
   final bool applyHeightToFirstAscent;
   final bool applyHeightToLastDescent;
+  final TextLeadingDistribution leadingDistribution;
+
   int encode() {
-    return (applyHeightToFirstAscent ? 0 : 1 << 0) | (applyHeightToLastDescent ? 0 : 1 << 1);
+    return (applyHeightToFirstAscent ? 0 : 1 << 0)
+         | (applyHeightToLastDescent ? 0 : 1 << 1)
+         | (leadingDistribution.index << 2);
   }
 
   @override
@@ -224,7 +235,8 @@ class TextHeightBehavior {
      return false;
     return other is TextHeightBehavior
         && other.applyHeightToFirstAscent == applyHeightToFirstAscent
-        && other.applyHeightToLastDescent == applyHeightToLastDescent;
+        && other.applyHeightToLastDescent == applyHeightToLastDescent
+        && other.leadingDistribution == leadingDistribution;
   }
 
   @override
@@ -239,7 +251,8 @@ class TextHeightBehavior {
   String toString() {
     return 'TextHeightBehavior('
              'applyHeightToFirstAscent: $applyHeightToFirstAscent, '
-             'applyHeightToLastDescent: $applyHeightToLastDescent'
+             'applyHeightToLastDescent: $applyHeightToLastDescent, '
+             'leadingDistribution: $leadingDistribution'
            ')';
   }
 }
@@ -260,6 +273,7 @@ abstract class TextStyle {
     double? letterSpacing,
     double? wordSpacing,
     double? height,
+    TextLeadingDistribution? leadingDistribution,
     Locale? locale,
     Paint? background,
     Paint? foreground,
@@ -370,6 +384,7 @@ abstract class StrutStyle {
     List<String>? fontFamilyFallback,
     double? fontSize,
     double? height,
+    TextLeadingDistribution? leadingDistribution,
     double? leading,
     FontWeight? fontWeight,
     FontStyle? fontStyle,

testing/dart/text_test.dart

@@ -42,6 +42,37 @@ void main() {
     });
   });
 
+  group('TextStyle', () {
+    final TextStyle ts0 = TextStyle(fontWeight: FontWeight.w700, fontSize: 12.0, height: 123.0);
+    final TextStyle ts1 = TextStyle(color: const Color(0xFF00FF00), fontWeight: FontWeight.w800, fontSize: 10.0, height: 100.0);
+    final TextStyle ts2 = TextStyle(fontFamily: 'test');
+    final TextStyle ts3 = TextStyle(fontFamily: 'foo', fontFamilyFallback: <String>['Roboto', 'test']);
+    final TextStyle ts4 = TextStyle(leadingDistribution: TextLeadingDistribution.even);
+
+    test('toString works', () {
+      expect(
+        ts0.toString(),
+        equals('TextStyle(color: unspecified, decoration: unspecified, decorationColor: unspecified, decorationStyle: unspecified, decorationThickness: unspecified, fontWeight: FontWeight.w700, fontStyle: unspecified, textBaseline: unspecified, fontFamily: unspecified, fontFamilyFallback: unspecified, fontSize: 12.0, letterSpacing: unspecified, wordSpacing: unspecified, height: 123.0x, leadingDistribution: unspecified, locale: unspecified, background: unspecified, foreground: unspecified, shadows: unspecified, fontFeatures: unspecified)'),
+      );
+      expect(
+        ts1.toString(),
+        equals('TextStyle(color: Color(0xff00ff00), decoration: unspecified, decorationColor: unspecified, decorationStyle: unspecified, decorationThickness: unspecified, fontWeight: FontWeight.w800, fontStyle: unspecified, textBaseline: unspecified, fontFamily: unspecified, fontFamilyFallback: unspecified, fontSize: 10.0, letterSpacing: unspecified, wordSpacing: unspecified, height: 100.0x, leadingDistribution: unspecified, locale: unspecified, background: unspecified, foreground: unspecified, shadows: unspecified, fontFeatures: unspecified)'),
+      );
+      expect(
+        ts2.toString(),
+        equals('TextStyle(color: unspecified, decoration: unspecified, decorationColor: unspecified, decorationStyle: unspecified, decorationThickness: unspecified, fontWeight: unspecified, fontStyle: unspecified, textBaseline: unspecified, fontFamily: test, fontFamilyFallback: unspecified, fontSize: unspecified, letterSpacing: unspecified, wordSpacing: unspecified, height: unspecified, leadingDistribution: unspecified, locale: unspecified, background: unspecified, foreground: unspecified, shadows: unspecified, fontFeatures: unspecified)'),
+      );
+      expect(
+        ts3.toString(),
+        equals('TextStyle(color: unspecified, decoration: unspecified, decorationColor: unspecified, decorationStyle: unspecified, decorationThickness: unspecified, fontWeight: unspecified, fontStyle: unspecified, textBaseline: unspecified, fontFamily: foo, fontFamilyFallback: [Roboto, test], fontSize: unspecified, letterSpacing: unspecified, wordSpacing: unspecified, height: unspecified, leadingDistribution: unspecified, locale: unspecified, background: unspecified, foreground: unspecified, shadows: unspecified, fontFeatures: unspecified)'),
+      );
+      expect(
+        ts4.toString(),
+        equals('TextStyle(color: unspecified, decoration: unspecified, decorationColor: unspecified, decorationStyle: unspecified, decorationThickness: unspecified, fontWeight: unspecified, fontStyle: unspecified, textBaseline: unspecified, fontFamily: unspecified, fontFamilyFallback: unspecified, fontSize: unspecified, letterSpacing: unspecified, wordSpacing: unspecified, height: unspecified, leadingDistribution: TextLeadingDistribution.even, locale: unspecified, background: unspecified, foreground: unspecified, shadows: unspecified, fontFeatures: unspecified)'),
+      );
+    });
+  });
+
   group('TextHeightBehavior', () {
     const TextHeightBehavior behavior0 = TextHeightBehavior();
     const TextHeightBehavior behavior1 = TextHeightBehavior(
@@ -54,6 +85,10 @@ void main() {
     const TextHeightBehavior behavior3 = TextHeightBehavior(
       applyHeightToLastDescent: false
     );
+    const TextHeightBehavior behavior4 = TextHeightBehavior(
+      applyHeightToLastDescent: false,
+      leadingDistribution: TextLeadingDistribution.even,
+    );
 
     test('default constructor works', () {
       expect(behavior0.applyHeightToFirstAscent, equals(true));
@@ -67,27 +102,33 @@ void main() {
 
       expect(behavior3.applyHeightToFirstAscent, equals(true));
       expect(behavior3.applyHeightToLastDescent, equals(false));
+
+      expect(behavior4.applyHeightToLastDescent, equals(false));
+      expect(behavior4.leadingDistribution, equals(TextLeadingDistribution.even));
     });
 
     test('encode works', () {
       expect(behavior0.encode(), equals(0));
       expect(behavior1.encode(), equals(3));
       expect(behavior2.encode(), equals(1));
       expect(behavior3.encode(), equals(2));
+      expect(behavior4.encode(), equals(6));
     });
 
     test('decode works', () {
-      expect(const TextHeightBehavior.fromEncoded(0), equals(behavior0));
-      expect(const TextHeightBehavior.fromEncoded(3), equals(behavior1));
-      expect(const TextHeightBehavior.fromEncoded(1), equals(behavior2));
-      expect(const TextHeightBehavior.fromEncoded(2), equals(behavior3));
+      expect(TextHeightBehavior.fromEncoded(0), equals(behavior0));
+      expect(TextHeightBehavior.fromEncoded(3), equals(behavior1));
+      expect(TextHeightBehavior.fromEncoded(1), equals(behavior2));
+      expect(TextHeightBehavior.fromEncoded(2), equals(behavior3));
+      expect(TextHeightBehavior.fromEncoded(6), equals(behavior4));
     });
 
     test('toString works', () {
-      expect(behavior0.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: true, applyHeightToLastDescent: true)'));
-      expect(behavior1.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: false, applyHeightToLastDescent: false)'));
-      expect(behavior2.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: false, applyHeightToLastDescent: true)'));
-      expect(behavior3.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: true, applyHeightToLastDescent: false)'));
+      expect(behavior0.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: true, applyHeightToLastDescent: true, leadingDistribution: TextLeadingDistribution.proportional)'));
+      expect(behavior1.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: false, applyHeightToLastDescent: false, leadingDistribution: TextLeadingDistribution.proportional)'));
+      expect(behavior2.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: false, applyHeightToLastDescent: true, leadingDistribution: TextLeadingDistribution.proportional)'));
+      expect(behavior3.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: true, applyHeightToLastDescent: false, leadingDistribution: TextLeadingDistribution.proportional)'));
+      expect(behavior4.toString(), equals('TextHeightBehavior(applyHeightToFirstAscent: true, applyHeightToLastDescent: false, leadingDistribution: TextLeadingDistribution.even)'));
     });
   });
 

third_party/txt/src/txt/paragraph_style.h

@@ -41,10 +41,18 @@ enum class TextDirection {
   ltr,
 };
 
-// Allows disabling height adjustments to first line's ascent and the
-// last line's descent. If disabled, the line will use the default font
-// metric provided ascent/descent and ParagraphStyle.height will not take
-// effect.
+// Adjusts the leading over and under text.
+//
+// kDisableFirstAscent and kDisableLastDescent allow disabling height
+// adjustments to first line's ascent and the last line's descent. If disabled,
+// the line will use the default font metric provided ascent/descent and
+// ParagraphStyle.height or TextStyle.height will not take effect.
+//
+// kEvenLeading determines how the leading is distributed over and under the
+// text. When true, half of the leading is added to the top of the text and the
+// other half is added to the bottom of the text. Otherwise, instead of
+// distributing the space evenly, it's distributed proportionally to the font's
+// ascent/descent ratio.
 //
 // The default behavior is kAll where height adjustments are enabled for all
 // lines.
@@ -58,6 +66,7 @@ enum TextHeightBehavior {
   kDisableFirstAscent = 0x1,
   kDisableLastDescent = 0x2,
   kDisableAll = 0x1 | 0x2,
+  kEvenLeading = 0x1 << 2,
 };
 
 class ParagraphStyle {
@@ -69,8 +78,8 @@ class ParagraphStyle {
   std::string font_family = "";
   double font_size = 14;
   double height = 1;
-  size_t text_height_behavior = TextHeightBehavior::kAll;
   bool has_height_override = false;
+  size_t text_height_behavior = TextHeightBehavior::kAll;
 
   // Strut properties. strut_enabled must be set to true for the rest of the
   // properties to take effect.
@@ -82,6 +91,8 @@ class ParagraphStyle {
   double strut_font_size = 14;
   double strut_height = 1;
   bool strut_has_height_override = false;
+  bool strut_half_leading = false;
+  bool strut_has_leading_distribution_override = false;
   double strut_leading = -1;  // Negative to use font's default leading. [0,inf)
                               // to use custom leading as a ratio of font size.
   bool force_strut_height = false;