[web] Implement TextStyle.shadows (flutter/engine#13769)

* Add shadows to Engine classes
* add text shadow test
* update golden locks file, update ui.ParagraphStyle, fix issues
* Change maxDiffRate for mac clients

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

@@ -18,6 +18,7 @@ class EngineParagraph implements ui.Paragraph {
     @required ui.TextAlign textAlign,
     @required ui.TextDirection textDirection,
     @required ui.Paint background,
+    @required List<ui.Shadow> shadows,
   })  : assert((plainText == null && paint == null) ||
             (plainText != null && paint != null)),
         _paragraphElement = paragraphElement,
@@ -26,7 +27,8 @@ class EngineParagraph implements ui.Paragraph {
         _textAlign = textAlign,
         _textDirection = textDirection,
         _paint = paint,
-        _background = background;
+        _background = background,
+        _shadows = shadows;
 
   final html.HtmlElement _paragraphElement;
   final ParagraphGeometricStyle _geometricStyle;
@@ -35,6 +37,7 @@ class EngineParagraph implements ui.Paragraph {
   final ui.TextAlign _textAlign;
   final ui.TextDirection _textDirection;
   final ui.Paint _background;
+  final List<ui.Shadow> _shadows;
 
   @visibleForTesting
   String get plainText => _plainText;
@@ -287,7 +290,8 @@ class EngineParagraph implements ui.Paragraph {
       return ui.TextRange(start: textPosition.offset, end: textPosition.offset);
     }
 
-    final int start = WordBreaker.prevBreakIndex(_plainText, textPosition.offset);
+    final int start =
+        WordBreaker.prevBreakIndex(_plainText, textPosition.offset);
     final int end = WordBreaker.nextBreakIndex(_plainText, textPosition.offset);
     return ui.TextRange(start: start, end: end);
   }
@@ -321,6 +325,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
     ui.StrutStyle strutStyle,
     String ellipsis,
     ui.Locale locale,
+    List<ui.Shadow> shadows,
   })  : _textAlign = textAlign,
         _textDirection = textDirection,
         _fontWeight = fontWeight,
@@ -332,7 +337,8 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
         // TODO(b/128317744): add support for strut style.
         _strutStyle = strutStyle,
         _ellipsis = ellipsis,
-        _locale = locale;
+        _locale = locale,
+        _shadows = shadows;
 
   final ui.TextAlign _textAlign;
   final ui.TextDirection _textDirection;
@@ -345,6 +351,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
   final EngineStrutStyle _strutStyle;
   final String _ellipsis;
   final ui.Locale _locale;
+  final List<ui.Shadow> _shadows;
 
   String get _effectiveFontFamily {
     if (assertionsEnabled) {
@@ -413,6 +420,7 @@ class EngineParagraphStyle implements ui.ParagraphStyle {
           'height: ${_height != null ? "${_height.toStringAsFixed(1)}x" : "unspecified"}, '
           'ellipsis: ${_ellipsis != null ? "\"$_ellipsis\"" : "unspecified"}, '
           'locale: ${_locale ?? "unspecified"}'
+          'shadows: ${_shadows ?? "unspecified"}'
           ')';
     } else {
       return super.toString();
@@ -798,6 +806,7 @@ class EngineParagraphBuilder implements ui.ParagraphBuilder {
     ui.Locale locale = _paragraphStyle._locale;
     ui.Paint background;
     ui.Paint foreground;
+    List<ui.Shadow> shadows;
 
     int i = 0;
 
@@ -852,6 +861,9 @@ class EngineParagraphBuilder implements ui.ParagraphBuilder {
       if (style._foreground != null) {
         foreground = style._foreground;
       }
+      if (style._shadows != null) {
+        shadows = style._shadows;
+      }
       i++;
     }
 
@@ -871,6 +883,7 @@ class EngineParagraphBuilder implements ui.ParagraphBuilder {
       locale: locale,
       background: background,
       foreground: foreground,
+      shadows: shadows,
     );
 
     ui.Paint paint;
@@ -900,6 +913,7 @@ class EngineParagraphBuilder implements ui.ParagraphBuilder {
           wordSpacing: wordSpacing,
           decoration: _textDecorationToCssString(decoration, decorationStyle),
           ellipsis: _paragraphStyle._ellipsis,
+          shadows: shadows,
         ),
         plainText: '',
         paint: paint,
@@ -953,6 +967,7 @@ class EngineParagraphBuilder implements ui.ParagraphBuilder {
         wordSpacing: wordSpacing,
         decoration: _textDecorationToCssString(decoration, decorationStyle),
         ellipsis: _paragraphStyle._ellipsis,
+        shadows: shadows,
       ),
       plainText: plainText,
       paint: paint,
@@ -996,6 +1011,7 @@ class EngineParagraphBuilder implements ui.ParagraphBuilder {
         lineHeight: _paragraphStyle._height,
         maxLines: _paragraphStyle._maxLines,
         ellipsis: _paragraphStyle._ellipsis,
+        shadows: _paragraphStyle._shadows,
       ),
       plainText: null,
       paint: null,
@@ -1082,6 +1098,9 @@ void _applyParagraphStyleToElement({
     if (style._effectiveFontFamily != null) {
       cssStyle.fontFamily = canonicalizeFontFamily(style._effectiveFontFamily);
     }
+    if (style._shadows != null) {
+      cssStyle.textShadow = _shadowListToCss(style._shadows);
+    }
   } else {
     if (style._textAlign != previousStyle._textAlign) {
       cssStyle.textAlign = textAlignToCssValue(
@@ -1108,6 +1127,9 @@ void _applyParagraphStyleToElement({
     if (style._fontFamily != previousStyle._fontFamily) {
       cssStyle.fontFamily = canonicalizeFontFamily(style._fontFamily);
     }
+    if (style._shadows != previousStyle._shadows) {
+      cssStyle.textShadow = _shadowListToCss(style._shadows);
+    }
   }
 }
 
@@ -1150,7 +1172,8 @@ void _applyTextStyleToElement({
       }
     } else {
       if (style._effectiveFontFamily != null) {
-        cssStyle.fontFamily = canonicalizeFontFamily(style._effectiveFontFamily);
+        cssStyle.fontFamily =
+            canonicalizeFontFamily(style._effectiveFontFamily);
       }
     }
     if (style._letterSpacing != null) {
@@ -1162,6 +1185,9 @@ void _applyTextStyleToElement({
     if (style._decoration != null) {
       updateDecoration = true;
     }
+    if (style._shadows != null) {
+      cssStyle.textShadow = _shadowListToCss(style._shadows);
+    }
   } else {
     if (style._color != previousStyle._color ||
         style._foreground != previousStyle._foreground) {
@@ -1197,6 +1223,9 @@ void _applyTextStyleToElement({
         style._decorationColor != previousStyle._decorationColor) {
       updateDecoration = true;
     }
+    if (style._shadows != previousStyle._shadows) {
+      cssStyle.textShadow = _shadowListToCss(style._shadows);
+    }
   }
 
   if (updateDecoration) {
@@ -1214,6 +1243,27 @@ void _applyTextStyleToElement({
   }
 }
 
+String _shadowListToCss(List<ui.Shadow> shadows) {
+  if (shadows.isEmpty) {
+    return '';
+  }
+  // CSS text-shadow is a comma separated list of shadows.
+  // <offsetx> <offsety> <blur-radius> <color>.
+  // Shadows are applied front-to-back with first shadow on top.
+  // Color is optional. offsetx,y are required. blur-radius is optional as well
+  // and defaults to 0.
+  StringBuffer sb = new StringBuffer();
+  for (int i = 0, len = shadows.length; i < len; i++) {
+    if (i != 0) {
+      sb.write(',');
+    }
+    ui.Shadow shadow = shadows[i];
+    sb.write('${shadow.offset.dx}px ${shadow.offset.dy}px '
+        '${shadow.blurRadius}px ${shadow.color.toCssString()}');
+  }
+  return sb.toString();
+}
+
 /// Applies background color properties in text style to paragraph or span
 /// elements.
 void _applyTextBackgroundToElement({

engine/src/flutter/lib/web_ui/lib/src/engine/text/ruler.dart

@@ -17,6 +17,7 @@ class ParagraphGeometricStyle {
     this.wordSpacing,
     this.decoration,
     this.ellipsis,
+    this.shadows,
   });
 
   final ui.FontWeight fontWeight;
@@ -29,6 +30,7 @@ class ParagraphGeometricStyle {
   final double wordSpacing;
   final String decoration;
   final String ellipsis;
+  final List<ui.Shadow> shadows;
 
   // Since all fields above are primitives, cache hashcode since ruler lookups
   // use this style as key.
@@ -109,7 +111,8 @@ class ParagraphGeometricStyle {
         letterSpacing == typedOther.letterSpacing &&
         wordSpacing == typedOther.wordSpacing &&
         decoration == typedOther.decoration &&
-        ellipsis == typedOther.ellipsis;
+        ellipsis == typedOther.ellipsis &&
+        shadows == typedOther.shadows;
   }
 
   @override
@@ -124,8 +127,12 @@ class ParagraphGeometricStyle {
         wordSpacing,
         decoration,
         ellipsis,
+        _hashShadows(shadows),
       );
 
+  int _hashShadows(List<ui.Shadow> shadows) =>
+      (shadows == null ? '' : _shadowListToCss(shadows)).hashCode;
+
   @override
   String toString() {
     if (assertionsEnabled) {
@@ -137,6 +144,7 @@ class ParagraphGeometricStyle {
           ' wordSpacing: $wordSpacing,'
           ' decoration: $decoration,'
           ' ellipsis: $ellipsis,'
+          ' shadows: $shadows,'
           ')';
     } else {
       return super.toString();
@@ -241,6 +249,10 @@ class TextDimensions {
     if (style.lineHeight != null) {
       _element.style.lineHeight = style.lineHeight.toString();
     }
+    final List<ui.Shadow> shadowList = style.shadows;
+    if (shadowList != null) {
+      _element.style.textShadow = _shadowListToCss(shadowList);
+    }
     _invalidateBoundsCache();
   }
 
@@ -765,7 +777,7 @@ class ParagraphRuler {
       return null;
     }
     final List<MeasurementResult> constraintCache =
-    _measurementCache[plainText];
+        _measurementCache[plainText];
     if (constraintCache == null) {
       return null;
     }

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

@@ -918,7 +918,7 @@ class TextRange {
   const TextRange({
     this.start,
     this.end,
-  }) : assert(start != null && start >= -1),
+  })  : assert(start != null && start >= -1),
         assert(end != null && end >= -1);
 
   /// A text range that starts and ends at offset.
@@ -971,20 +971,17 @@ class TextRange {
 
   @override
   bool operator ==(dynamic other) {
-    if (identical(this, other))
-      return true;
-    if (other is! TextRange)
-      return false;
+    if (identical(this, other)) return true;
+    if (other is! TextRange) return false;
     final TextRange typedOther = other;
-    return typedOther.start == start
-        && typedOther.end == end;
+    return typedOther.start == start && typedOther.end == end;
   }
 
   @override
   int get hashCode => hashValues(
-    start.hashCode,
-    end.hashCode,
-  );
+        start.hashCode,
+        end.hashCode,
+      );
 
   @override
   String toString() => 'TextRange(start: $start, end: $end)';

engine/src/flutter/lib/web_ui/test/golden_tests/engine/scuba.dart

@@ -39,18 +39,18 @@ class EngineScubaTester {
     return EngineScubaTester(viewportSize);
   }
 
-  Future<void> diffScreenshot(String fileName) async {
-    await matchGoldenFile('$fileName.png', region: ui.Rect.fromLTWH(0, 0, viewportSize.width, viewportSize.height));
+  Future<void> diffScreenshot(String fileName, {double maxDiffRate}) async {
+    await matchGoldenFile('$fileName.png',
+        region: ui.Rect.fromLTWH(0, 0, viewportSize.width, viewportSize.height),
+        maxDiffRate: maxDiffRate);
   }
 
   /// Prepares the DOM and inserts all the necessary nodes, then invokes scuba's
   /// screenshot diffing.
   ///
   /// It also cleans up the DOM after itself.
-  Future<void> diffCanvasScreenshot(
-    EngineCanvas canvas,
-    String fileName,
-  ) async {
+  Future<void> diffCanvasScreenshot(EngineCanvas canvas, String fileName,
+      {double maxDiffRate}) async {
     // Wrap in <flt-scene> so that our CSS selectors kick in.
     final html.Element sceneElement = html.Element.tag('flt-scene');
     try {
@@ -60,7 +60,7 @@ class EngineScubaTester {
       if (TextMeasurementService.enableExperimentalCanvasImplementation) {
         screenshotName += '+canvas_measurement';
       }
-      await diffScreenshot(screenshotName);
+      await diffScreenshot(screenshotName, maxDiffRate: maxDiffRate);
     } finally {
       // The page is reused across tests, so remove the element after taking the
       // Scuba screenshot.
@@ -72,7 +72,8 @@ class EngineScubaTester {
 typedef CanvasTest = FutureOr<void> Function(EngineCanvas canvas);
 
 /// Runs the given test [body] with each type of canvas.
-void testEachCanvas(String description, CanvasTest body) {
+void testEachCanvas(String description, CanvasTest body,
+    {double maxDiffRate, bool bSkipHoudini = false}) {
   const ui.Rect bounds = ui.Rect.fromLTWH(0, 0, 600, 800);
   test('$description (bitmap)', () {
     try {
@@ -100,14 +101,16 @@ void testEachCanvas(String description, CanvasTest body) {
       TextMeasurementService.clearCache();
     }
   });
-  test('$description (houdini)', () {
-    try {
-      TextMeasurementService.initialize(rulerCacheCapacity: 2);
-      return body(HoudiniCanvas(bounds));
-    } finally {
-      TextMeasurementService.clearCache();
-    }
-  });
+  if (!bSkipHoudini) {
+    test('$description (houdini)', () {
+      try {
+        TextMeasurementService.initialize(rulerCacheCapacity: 2);
+        return body(HoudiniCanvas(bounds));
+      } finally {
+        TextMeasurementService.clearCache();
+      }
+    });
+  }
 }
 
 final ui.TextStyle _defaultTextStyle = ui.TextStyle(

engine/src/flutter/lib/web_ui/test/golden_tests/engine/text_style_golden_test.dart

@@ -158,8 +158,64 @@ void main() async {
     );
   }
 
+  void drawTextWithShadow(EngineCanvas canvas) {
+    // Single-line text.
+    canvas.drawParagraph(
+      paragraph(
+        'Hello World',
+        maxWidth: 600,
+        textStyle: TextStyle(
+          color: const Color.fromRGBO(0, 0, 0, 1.0),
+          background: Paint()..color = const Color.fromRGBO(255, 50, 50, 1.0),
+          fontFamily: 'Arial',
+          fontSize: 30,
+          shadows: <Shadow>[
+            Shadow(
+              blurRadius: 0,
+              color: const Color.fromRGBO(255, 0, 255, 1.0),
+              offset: Offset(10, 5),
+            ),
+          ],
+        ),
+      ),
+      Offset.zero,
+    );
+
+    // Multi-line text.
+    canvas.drawParagraph(
+      paragraph(
+        'Multi line Hello World paragraph',
+        maxWidth: 200,
+        textStyle: TextStyle(
+          color: const Color.fromRGBO(0, 0, 0, 1.0),
+          background: Paint()..color = const Color.fromRGBO(50, 50, 255, 1.0),
+          fontFamily: 'Arial',
+          fontSize: 30,
+          shadows: <Shadow>[
+            Shadow(
+              blurRadius: 0,
+              color: const Color.fromRGBO(255, 0, 255, 1.0),
+              offset: Offset(10, 5),
+            ),
+            Shadow(
+              blurRadius: 0,
+              color: const Color.fromRGBO(0, 255, 255, 1.0),
+              offset: Offset(-10, -5),
+            ),
+          ],
+        ),
+      ),
+      const Offset(0, 40),
+    );
+  }
+
   testEachCanvas('draws text with a background', (EngineCanvas canvas) {
     drawTextWithBackground(canvas);
     return scuba.diffCanvasScreenshot(canvas, 'text_background');
   });
+
+  testEachCanvas('draws text with a shadow', (EngineCanvas canvas) {
+    drawTextWithShadow(canvas);
+    return scuba.diffCanvasScreenshot(canvas, 'text_shadow', maxDiffRate: 0.2);
+  }, bSkipHoudini: true);
 }