Allow custom foreground paint to be used for drawing text (flutter#5395)

* Allow specifying the foreground paint

* fix typo

* doc update

* call paint.reset

lib/ui/text.dart

@@ -258,6 +258,7 @@ Int32List _encodeTextStyle(
   double height,
   Locale locale,
   Paint background,
+  Paint foreground,
 ) {
   final Int32List result = new Int32List(8);
   if (color != null) {
@@ -316,14 +317,18 @@ Int32List _encodeTextStyle(
     result[0] |= 1 << 14;
     // Passed separately to native.
   }
+  if (foreground != null) {
+    result[0] |= 1 << 15;
+    // Passed separately to native.
+  }
   return result;
 }
 
 /// An opaque object that determines the size, position, and rendering of text.
 class TextStyle {
   /// Creates a new TextStyle object.
   ///
-  /// * `color`: The color to use when painting the text.
+  /// * `color`: The color to use when painting the text. If this is specified, `foreground` must be null.
   /// * `decoration`: The decorations to paint near the text (e.g., an underline).
   /// * `decorationColor`: The color in which to paint the text decorations.
   /// * `decorationStyle`: The style in which to paint the text decorations (e.g., dashed).
@@ -337,6 +342,7 @@ class TextStyle {
   /// * `height`: The height of this text span, as a multiple of the font size.
   /// * `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.
   TextStyle({
     Color color,
     TextDecoration decoration,
@@ -352,7 +358,12 @@ class TextStyle {
     double height,
     Locale locale,
     Paint background,
-  }) : _encoded = _encodeTextStyle(
+    Paint foreground,
+  }) : 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".'
+       ),
+       _encoded = _encodeTextStyle(
          color,
          decoration,
          decorationColor,
@@ -367,14 +378,16 @@ class TextStyle {
          height,
          locale,
          background,
+         foreground,
        ),
        _fontFamily = fontFamily ?? '',
        _fontSize = fontSize,
        _letterSpacing = letterSpacing,
        _wordSpacing = wordSpacing,
        _height = height,
        _locale = locale,
-       _background = background;
+       _background = background,
+       _foreground = foreground;
 
   final Int32List _encoded;
   final String _fontFamily;
@@ -384,6 +397,7 @@ class TextStyle {
   final double _height;
   final Locale _locale;
   final Paint _background;
+  final Paint _foreground;
 
   @override
   bool operator ==(dynamic other) {
@@ -398,7 +412,8 @@ class TextStyle {
         _wordSpacing != typedOther._wordSpacing ||
         _height != typedOther._height ||
         _locale != typedOther._locale ||
-        _background != typedOther._background)
+        _background != typedOther._background ||
+        _foreground != typedOther._foreground)
      return false;
     for (int index = 0; index < _encoded.length; index += 1) {
       if (_encoded[index] != typedOther._encoded[index])
@@ -408,7 +423,7 @@ class TextStyle {
   }
 
   @override
-  int get hashCode => hashValues(hashList(_encoded), _fontFamily, _fontSize, _letterSpacing, _wordSpacing, _height, _locale, _background);
+  int get hashCode => hashValues(hashList(_encoded), _fontFamily, _fontSize, _letterSpacing, _wordSpacing, _height, _locale, _background, _foreground);
 
   @override
   String toString() {
@@ -426,7 +441,8 @@ class TextStyle {
              '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"}'
+             'background: ${     _encoded[0] & 0x4000 == 0x4000 ? _background                             : "unspecified"}, '
+             'foreground: ${     _encoded[0] & 0x8000 == 0x8000 ? _foreground                             : "unspecified"}'
            ')';
   }
 }
@@ -1025,8 +1041,8 @@ 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);
-  void _pushStyle(Int32List encoded, String fontFamily, double fontSize, double letterSpacing, double wordSpacing, double height, String locale, List<dynamic> backgroundObjects, ByteData backgroundData) 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);
+  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';
 
   static String _encodeLocale(Locale locale) => locale?.toString() ?? '';
 

lib/ui/text/paragraph_builder.cc

@@ -39,6 +39,7 @@ const int tsWordSpacingIndex = 11;
 const int tsHeightIndex = 12;
 const int tsLocaleIndex = 13;
 const int tsBackgroundIndex = 14;
+const int tsForegroundIndex = 15;
 
 const int tsColorMask = 1 << tsColorIndex;
 const int tsTextDecorationMask = 1 << tsTextDecorationIndex;
@@ -54,6 +55,7 @@ const int tsWordSpacingMask = 1 << tsWordSpacingIndex;
 const int tsHeightMask = 1 << tsHeightIndex;
 const int tsLocaleMask = 1 << tsLocaleIndex;
 const int tsBackgroundMask = 1 << tsBackgroundIndex;
+const int tsForegroundMask = 1 << tsForegroundIndex;
 
 // ParagraphStyle
 
@@ -167,7 +169,9 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
                                  double height,
                                  const std::string& locale,
                                  Dart_Handle background_objects,
-                                 Dart_Handle background_data) {
+                                 Dart_Handle background_data,
+                                 Dart_Handle foreground_objects,
+                                 Dart_Handle foreground_data) {
   FXL_DCHECK(encoded.num_elements() == 8);
 
   int32_t mask = encoded[0];
@@ -235,6 +239,14 @@ void ParagraphBuilder::pushStyle(tonic::Int32List& encoded,
     }
   }
 
+  if (mask & tsForegroundMask) {
+    Paint foreground(foreground_objects, foreground_data);
+    if (foreground.paint()) {
+      style.has_foreground = true;
+      style.foreground = *foreground.paint();
+    }
+  }
+
   m_paragraphBuilder->PushStyle(style);
 }
 

lib/ui/text/paragraph_builder.h

@@ -43,7 +43,9 @@ class ParagraphBuilder : public fxl::RefCountedThreadSafe<ParagraphBuilder>,
                  double height,
                  const std::string& locale,
                  Dart_Handle background_objects,
-                 Dart_Handle background_data);
+                 Dart_Handle background_data,
+                 Dart_Handle foreground_objects,
+                 Dart_Handle foreground_data);
 
   void pop();
 

third_party/txt/src/txt/paragraph.cc

@@ -877,7 +877,12 @@ void Paragraph::Paint(SkCanvas* canvas, double x, double y) {
   canvas->translate(x, y);
   SkPaint paint;
   for (const PaintRecord& record : records_) {
-    paint.setColor(record.style().color);
+    if (record.style().has_foreground) {
+      paint = record.style().foreground;
+    } else {
+      paint.reset();
+      paint.setColor(record.style().color);
+    }
     SkPoint offset = record.offset();
     PaintBackground(canvas, record);
     canvas->drawTextBlob(record.text(), offset.x(), offset.y(), paint);
@@ -1049,8 +1054,8 @@ void Paragraph::PaintBackground(SkCanvas* canvas, const PaintRecord& record) {
     return;
 
   const SkPaint::FontMetrics& metrics = record.metrics();
-  SkRect rect(SkRect::MakeLTRB(0, metrics.fAscent,
-                               record.GetRunWidth(), metrics.fDescent));
+  SkRect rect(SkRect::MakeLTRB(0, metrics.fAscent, record.GetRunWidth(),
+                               metrics.fDescent));
   rect.offset(record.offset());
   canvas->drawRect(rect, record.style().background);
 }
@@ -1090,15 +1095,16 @@ std::vector<Paragraph::TextBox> Paragraph::GetRectsForRange(size_t start,
   }
 
   // Add empty rectangles representing any newline characters within the range.
-  for (size_t line_number = 0; line_number < line_ranges_.size(); ++line_number) {
+  for (size_t line_number = 0; line_number < line_ranges_.size();
+       ++line_number) {
     const LineRange& line = line_ranges_[line_number];
     if (line.start >= end)
       break;
     if (line.end_including_newline <= start)
       continue;
     if (line_boxes.find(line_number) == line_boxes.end()) {
-      if (line.end != line.end_including_newline &&
-          line.end >= start && line.end_including_newline <= end) {
+      if (line.end != line.end_including_newline && line.end >= start &&
+          line.end_including_newline <= end) {
         SkScalar x = line_widths_[line_number];
         SkScalar top = (line_number > 0) ? line_heights_[line_number - 1] : 0;
         SkScalar bottom = line_heights_[line_number];

third_party/txt/src/txt/text_style.cc

@@ -49,6 +49,8 @@ bool TextStyle::equals(const TextStyle& other) const {
     return false;
   if (locale != other.locale)
     return false;
+  if (foreground != other.foreground)
+    return false;
 
   return true;
 }

third_party/txt/src/txt/text_style.h

@@ -49,6 +49,8 @@ class TextStyle {
   std::string locale;
   bool has_background = false;
   SkPaint background;
+  bool has_foreground = false;
+  SkPaint foreground;
 
   TextStyle();