Support overriding font leading in TextStyle and LibTxt (flutter#6927)

Author: GaryQian

lib/ui/text.dart

@@ -256,6 +256,7 @@ Int32List _encodeTextStyle(
   double letterSpacing,
   double wordSpacing,
   double height,
+  double leading,
   Locale locale,
   Paint background,
   Paint foreground,
@@ -310,22 +311,26 @@ Int32List _encodeTextStyle(
     result[0] |= 1 << 12;
     // Passed separately to native.
   }
-  if (locale != null) {
+  if (leading != null) {
     result[0] |= 1 << 13;
     // Passed separately to native.
   }
-  if (background != null) {
+  if (locale != null) {
     result[0] |= 1 << 14;
     // Passed separately to native.
   }
-  if (foreground != null) {
+  if (background != null) {
     result[0] |= 1 << 15;
     // Passed separately to native.
   }
-  if (shadows != null) {
+  if (foreground != null) {
     result[0] |= 1 << 16;
     // Passed separately to native.
   }
+  if (shadows != null) {
+    result[0] |= 1 << 17;
+    // Passed separately to native.
+  }
   return result;
 }
 
@@ -344,7 +349,8 @@ class TextStyle {
   /// * `letterSpacing`: The amount of space (in logical pixels) to add between each letter.
   /// * `wordSpacing`: The amount of space (in logical pixels) to add at each sequence of white-space (i.e. between each word).
   /// * `textBaseline`: The common baseline that should be aligned between this text span and its parent text span, or, for the root text spans, with the line box.
-  /// * `height`: The height of this text span, as a multiple of the font size.
+  /// * `height`: The height of this text span, as a multiple of the sum of font size and leading.
+  /// * `leading`: Custom leading to use instead of the font-provided leading as a multiple of font size. When null, default font leading will be used. Leading is the additional spacing between lines.
   /// * `locale`: The locale used to select region-specific glyphs.
   /// * `background`: The paint drawn as a background for the text.
   /// * `foreground`: The paint used to draw the text. If this is specified, `color` must be null.
@@ -361,6 +367,7 @@ class TextStyle {
     double letterSpacing,
     double wordSpacing,
     double height,
+    double leading,
     Locale locale,
     Paint background,
     Paint foreground,
@@ -382,6 +389,7 @@ class TextStyle {
          letterSpacing,
          wordSpacing,
          height,
+         leading,
          locale,
          background,
          foreground,
@@ -392,6 +400,7 @@ class TextStyle {
        _letterSpacing = letterSpacing,
        _wordSpacing = wordSpacing,
        _height = height,
+       _leading = leading,
        _locale = locale,
        _background = background,
        _foreground = foreground,
@@ -403,6 +412,7 @@ class TextStyle {
   final double _letterSpacing;
   final double _wordSpacing;
   final double _height;
+  final double _leading;
   final Locale _locale;
   final Paint _background;
   final Paint _foreground;
@@ -420,6 +430,7 @@ class TextStyle {
         _letterSpacing != typedOther._letterSpacing ||
         _wordSpacing != typedOther._wordSpacing ||
         _height != typedOther._height ||
+        _leading != typedOther._leading ||
         _locale != typedOther._locale ||
         _background != typedOther._background ||
         _foreground != typedOther._foreground)
@@ -434,7 +445,7 @@ class TextStyle {
   }
 
   @override
-  int get hashCode => hashValues(hashList(_encoded), _fontFamily, _fontSize, _letterSpacing, _wordSpacing, _height, _locale, _background, _foreground);
+  int get hashCode => hashValues(hashList(_encoded), _fontFamily, _fontSize, _letterSpacing, _wordSpacing, _height, _leading, _locale, _background, _foreground);
 
   @override
   String toString() {
@@ -451,10 +462,11 @@ class TextStyle {
              '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"}'
+             'leading: ${        _encoded[0] & 0x02000 == 0x02000 ? "${_leading}x"                           : "unspecified"}, '
+             'locale: ${         _encoded[0] & 0x04000 == 0x04000 ? _locale                                 : "unspecified"}, '
+             'background: ${     _encoded[0] & 0x08000 == 0x08000 ? _background                             : "unspecified"}, '
+             'foreground: ${     _encoded[0] & 0x10000 == 0x10000 ? _foreground                             : "unspecified"}, '
+             'shadows: ${        _encoded[0] & 0x20000 == 0x20000 ? _shadows                                : "unspecified"}'
            ')';
   }
 }
@@ -1135,8 +1147,8 @@ 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, 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';
+  void pushStyle(TextStyle style) => _pushStyle(style._encoded, style._fontFamily, style._fontSize, style._letterSpacing, style._wordSpacing, style._height, style._leading, _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, double leading, 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

@@ -41,10 +41,11 @@ const int tsFontSizeIndex = 9;
 const int tsLetterSpacingIndex = 10;
 const int tsWordSpacingIndex = 11;
 const int tsHeightIndex = 12;
-const int tsLocaleIndex = 13;
-const int tsBackgroundIndex = 14;
-const int tsForegroundIndex = 15;
-const int tsTextShadowsIndex = 16;
+const int tsLeadingIndex = 13;
+const int tsLocaleIndex = 14;
+const int tsBackgroundIndex = 15;
+const int tsForegroundIndex = 16;
+const int tsTextShadowsIndex = 17;
 
 const int tsColorMask = 1 << tsColorIndex;
 const int tsTextDecorationMask = 1 << tsTextDecorationIndex;
@@ -58,6 +59,7 @@ const int tsFontSizeMask = 1 << tsFontSizeIndex;
 const int tsLetterSpacingMask = 1 << tsLetterSpacingIndex;
 const int tsWordSpacingMask = 1 << tsWordSpacingIndex;
 const int tsHeightMask = 1 << tsHeightIndex;
+const int tsLeadingMask = 1 << tsLeadingIndex;
 const int tsLocaleMask = 1 << tsLocaleIndex;
 const int tsBackgroundMask = 1 << tsBackgroundIndex;
 const int tsForegroundMask = 1 << tsForegroundIndex;
@@ -207,6 +209,7 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
                                  double letterSpacing,
                                  double wordSpacing,
                                  double height,
+                                 double leading,
                                  const std::string& locale,
                                  Dart_Handle background_objects,
                                  Dart_Handle background_data,
@@ -269,6 +272,11 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
     style.height = height;
   }
 
+  if (mask & tsLeadingMask) {
+    style.use_custom_leading = true;
+    style.leading = leading;
+  }
+
   if (mask & tsLocaleMask) {
     style.locale = locale;
   }

lib/ui/text/paragraph_builder.h

@@ -40,6 +40,7 @@ class ParagraphBuilder : public RefCountedDartWrappable<ParagraphBuilder> {
                  double letterSpacing,
                  double wordSpacing,
                  double height,
+                 double leading,
                  const std::string& locale,
                  Dart_Handle background_objects,
                  Dart_Handle background_data,

third_party/txt/src/txt/paragraph.cc

@@ -761,10 +761,13 @@ void Paragraph::Layout(double width, bool force) {
       // TODO(garyq): Multipling in the style.height on the first line is
       // probably wrong. Figure out how paragraph and line heights are supposed
       // to work and fix it.
-      double line_spacing =
-          (line_number == 0)
-              ? -metrics.fAscent * style.height
-              : (-metrics.fAscent + metrics.fLeading) * style.height;
+      double leading =
+          style.use_custom_leading
+              ? (metrics.fDescent - metrics.fAscent) * style.leading
+              : metrics.fLeading;
+      double line_spacing = (line_number == 0)
+                                ? -metrics.fAscent * style.height
+                                : (-metrics.fAscent + leading) * style.height;
       if (line_spacing > max_line_spacing) {
         max_line_spacing = line_spacing;
         if (line_number == 0) {

third_party/txt/src/txt/paragraph.h

@@ -214,7 +214,10 @@ class Paragraph {
   FRIEND_TEST(ParagraphTest, DecorationsParagraph);
   FRIEND_TEST(ParagraphTest, ItalicsParagraph);
   FRIEND_TEST(ParagraphTest, ChineseParagraph);
-  FRIEND_TEST(ParagraphTest, DISABLED_ArabicParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicLeadingOverrideParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicLeadingOverrideTallParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicLeadingOverrideNegativeParagraph);
   FRIEND_TEST(ParagraphTest, SpacingParagraph);
   FRIEND_TEST(ParagraphTest, LongWordParagraph);
   FRIEND_TEST(ParagraphTest, KernScaleParagraph);

third_party/txt/src/txt/styled_runs.h

@@ -73,7 +73,10 @@ class StyledRuns {
   FRIEND_TEST(ParagraphTest, DecorationsParagraph);
   FRIEND_TEST(ParagraphTest, ItalicsParagraph);
   FRIEND_TEST(ParagraphTest, ChineseParagraph);
-  FRIEND_TEST(ParagraphTest, DISABLED_ArabicParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicLeadingOverrideParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicLeadingOverrideTallParagraph);
+  FRIEND_TEST(ParagraphTest, ArabicLeadingOverrideNegativeParagraph);
   FRIEND_TEST(ParagraphTest, LongWordParagraph);
   FRIEND_TEST(ParagraphTest, KernParagraph);
   FRIEND_TEST(ParagraphTest, HyphenBreakParagraph);

third_party/txt/src/txt/text_style.cc

@@ -47,6 +47,10 @@ bool TextStyle::equals(const TextStyle& other) const {
     return false;
   if (height != other.height)
     return false;
+  if (use_custom_leading != other.use_custom_leading)
+    return false;
+  if (use_custom_leading && leading != other.leading)
+    return false;
   if (locale != other.locale)
     return false;
   if (foreground != other.foreground)

third_party/txt/src/txt/text_style.h

@@ -48,6 +48,8 @@ class TextStyle {
   double letter_spacing = 0.0;
   double word_spacing = 0.0;
   double height = 1.0;
+  double leading = 0;
+  bool use_custom_leading = false;
   std::string locale;
   bool has_background = false;
   SkPaint background;