[web] Fix alignment issue in rich paragraphs

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

@@ -20,6 +20,7 @@ class CanvasParagraph implements EngineParagraph {
     required this.paragraphStyle,
     required this.plainText,
     required this.placeholderCount,
+    required this.drawOnCanvas,
   });
 
   /// The flat list of spans that make up this paragraph.
@@ -34,14 +35,17 @@ class CanvasParagraph implements EngineParagraph {
   /// The number of placeholders in this paragraph.
   final int placeholderCount;
 
+  @override
+  final bool drawOnCanvas;
+
   @override
   double get width => _layoutService.width;
 
   @override
   double get height => _layoutService.height;
 
   @override
-  double get longestLine => _layoutService.longestLine;
+  double get longestLine => _layoutService.longestLine?.width ?? 0.0;
 
   @override
   double get minIntrinsicWidth => _layoutService.minIntrinsicWidth;
@@ -124,6 +128,14 @@ class CanvasParagraph implements EngineParagraph {
     return domElement.clone(true) as html.HtmlElement;
   }
 
+  double _getParagraphAlignOffset() {
+    final EngineLineMetrics? longestLine = _layoutService.longestLine;
+    if (longestLine != null) {
+      return longestLine.left;
+    }
+    return 0.0;
+  }
+
   html.HtmlElement _createDomElement() {
     final html.HtmlElement rootElement =
         domRenderer.createElement('p') as html.HtmlElement;
@@ -137,6 +149,11 @@ class CanvasParagraph implements EngineParagraph {
       // to insert our own <BR> breaks based on layout results.
       ..whiteSpace = 'pre';
 
+    final double alignOffset = _getParagraphAlignOffset();
+    if (alignOffset != 0.0) {
+      cssStyle.marginLeft = '${alignOffset}px';
+    }
+
     if (paragraphStyle._maxLines != null || paragraphStyle._ellipsis != null) {
       cssStyle
         ..overflowY = 'hidden'
@@ -199,15 +216,6 @@ class CanvasParagraph implements EngineParagraph {
     return _layoutService.getBoxesForPlaceholders();
   }
 
-  // TODO(mdebbar): Check for child spans if any has styles that can't be drawn
-  // on a canvas. e.g:
-  // - decoration
-  // - word-spacing
-  // - shadows (may be possible? https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/shadowBlur)
-  // - font features
-  @override
-  final bool drawOnCanvas = true;
-
   @override
   List<ui.TextBox> getBoxesForRange(
     int start,
@@ -599,13 +607,29 @@ class CanvasParagraphBuilder implements ui.ParagraphBuilder {
     }
   }
 
+  bool _drawOnCanvas = true;
+
   @override
   void addText(String text) {
     final EngineTextStyle style = _currentStyleNode.resolveStyle();
     final int start = _plainTextBuffer.length;
     _plainTextBuffer.write(text);
     final int end = _plainTextBuffer.length;
 
+    if (_drawOnCanvas) {
+      final ui.TextDecoration? decoration = style._decoration;
+      if (decoration != null && decoration != ui.TextDecoration.none) {
+        _drawOnCanvas = false;
+      }
+    }
+
+    if (_drawOnCanvas) {
+      final List<ui.FontFeature>? fontFeatures = style._fontFeatures;
+      if (fontFeatures != null && fontFeatures.isNotEmpty) {
+        _drawOnCanvas = false;
+      }
+    }
+
     _spans.add(FlatTextSpan(style: style, start: start, end: end));
   }
 
@@ -616,6 +640,7 @@ class CanvasParagraphBuilder implements ui.ParagraphBuilder {
       paragraphStyle: _paragraphStyle,
       plainText: _plainTextBuffer.toString(),
       placeholderCount: _placeholderCount,
+      drawOnCanvas: _drawOnCanvas,
     );
   }
 }

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

@@ -23,7 +23,7 @@ class TextLayoutService {
 
   double height = 0.0;
 
-  double longestLine = 0.0;
+  EngineLineMetrics? longestLine;
 
   double minIntrinsicWidth = 0.0;
 
@@ -65,7 +65,7 @@ class TextLayoutService {
     // Reset results from previous layout.
     width = constraints.width;
     height = 0.0;
-    longestLine = 0.0;
+    longestLine = null;
     minIntrinsicWidth = 0.0;
     maxIntrinsicWidth = 0.0;
     didExceedMaxLines = false;
@@ -187,8 +187,9 @@ class TextLayoutService {
         alphabeticBaseline = line.baseline;
         ideographicBaseline = alphabeticBaseline * _baselineRatioHack;
       }
-      if (longestLine < line.width) {
-        longestLine = line.width;
+      final double longestLineWidth = longestLine?.width ?? 0.0;
+      if (longestLineWidth < line.width) {
+        longestLine = line;
       }
     }
 

lib/web_ui/test/golden_tests/engine/canvas_paragraph/general_test.dart

@@ -112,6 +112,47 @@ void testMain() async {
     return takeScreenshot(canvas, bounds, 'canvas_paragraph_align');
   });
 
+  test('respects alignment in DOM mode', () {
+    final canvas = DomCanvas(domRenderer.createElement('flt-picture'));
+
+    Offset offset = Offset.zero;
+    CanvasParagraph paragraph;
+
+    void build(CanvasParagraphBuilder builder) {
+      builder.pushStyle(EngineTextStyle.only(color: black));
+      builder.addText('Lorem ');
+      builder.pushStyle(EngineTextStyle.only(color: blue));
+      builder.addText('ipsum ');
+      builder.pushStyle(EngineTextStyle.only(color: green));
+      builder.addText('dolor ');
+      builder.pushStyle(EngineTextStyle.only(color: red));
+      builder.addText('sit');
+    }
+
+    paragraph = rich(
+      ParagraphStyle(fontFamily: 'Roboto', textAlign: TextAlign.left),
+      build,
+    )..layout(constrain(100.0));
+    canvas.drawParagraph(paragraph, offset);
+    offset = offset.translate(0, paragraph.height + 10);
+
+    paragraph = rich(
+      ParagraphStyle(fontFamily: 'Roboto', textAlign: TextAlign.center),
+      build,
+    )..layout(constrain(100.0));
+    canvas.drawParagraph(paragraph, offset);
+    offset = offset.translate(0, paragraph.height + 10);
+
+    paragraph = rich(
+      ParagraphStyle(fontFamily: 'Roboto', textAlign: TextAlign.right),
+      build,
+    )..layout(constrain(100.0));
+    canvas.drawParagraph(paragraph, offset);
+    offset = offset.translate(0, paragraph.height + 10);
+
+    return takeScreenshot(canvas, bounds, 'canvas_paragraph_align_dom');
+  });
+
   test('paints spans with varying heights/baselines', () {
     final canvas = BitmapCanvas(bounds, RenderStrategy());
 
@@ -165,4 +206,37 @@ void testMain() async {
 
     return takeScreenshot(canvas, bounds, 'canvas_paragraph_letter_spacing');
   });
+
+  test('draws text decorations', () {
+    final canvas = BitmapCanvas(bounds, RenderStrategy());
+    final List<TextDecorationStyle> decorationStyles = <TextDecorationStyle>[
+      TextDecorationStyle.solid,
+      TextDecorationStyle.double,
+      TextDecorationStyle.dotted,
+      TextDecorationStyle.dashed,
+      TextDecorationStyle.wavy,
+    ];
+
+    final CanvasParagraph paragraph = rich(
+      ParagraphStyle(fontFamily: 'Roboto'),
+      (builder) {
+        for (TextDecorationStyle decorationStyle in decorationStyles) {
+          builder.pushStyle(EngineTextStyle.only(
+            color: const Color.fromRGBO(50, 50, 255, 1.0),
+            decoration: TextDecoration.underline,
+            decorationStyle: decorationStyle,
+            decorationColor: red,
+            fontFamily: 'Roboto',
+            fontSize: 30,
+          ));
+          builder.addText('Hello World');
+          builder.pop();
+          builder.addText(' ');
+        }
+      },
+    )..layout(constrain(double.infinity));
+
+    canvas.drawParagraph(paragraph, Offset.zero);
+    return takeScreenshot(canvas, bounds, 'canvas_paragraph_decoration');
+  });
 }

lib/web_ui/test/golden_tests/engine/canvas_paragraph/placeholders_test.dart

@@ -95,4 +95,40 @@ void testMain() async {
 
     return takeScreenshot(canvas, bounds, 'canvas_paragraph_placeholders_align');
   });
+
+  test('draws paragraphs with placeholders and text align in DOM mode', () {
+    final canvas = DomCanvas(domRenderer.createElement('flt-picture'));
+
+    const List<TextAlign> aligns = <TextAlign>[
+      TextAlign.left,
+      TextAlign.center,
+      TextAlign.right,
+    ];
+
+    Offset offset = Offset.zero;
+    for (TextAlign align in aligns) {
+      final CanvasParagraph paragraph = rich(
+        ParagraphStyle(fontFamily: 'Roboto', fontSize: 14.0, textAlign: align),
+        (builder) {
+          builder.pushStyle(TextStyle(color: black));
+          builder.addText('Lorem');
+          builder.addPlaceholder(80.0, 50.0, PlaceholderAlignment.bottom);
+          builder.pushStyle(TextStyle(color: blue));
+          builder.addText('ipsum.');
+        },
+      )..layout(constrain(200.0));
+
+      // Draw the paragraph.
+      canvas.drawParagraph(paragraph, offset);
+
+      // Then fill the placeholders.
+      final TextBox placeholderBox = paragraph.getBoxesForPlaceholders().single;
+      final SurfacePaint redPaint = Paint()..color = red;
+      canvas.drawRect(placeholderBox.toRect().shift(offset), redPaint.paintData);
+
+      offset = offset.translate(0.0, paragraph.height + 30.0);
+    }
+
+    return takeScreenshot(canvas, bounds, 'canvas_paragraph_placeholders_align_dom');
+  });
 }