Revert "[web] Calculate align offset for each paragraph line (LineMetrics.left) (flutter#14537)" (flutter#14569)

This reverts commit 1ecfdcb.

Author: chingjun

lib/web_ui/lib/src/engine/bitmap_canvas.dart

@@ -666,7 +666,6 @@ class BitmapCanvas extends EngineCanvas with SaveStackTracking {
     double x,
     double y,
   ) {
-    x += line.left;
     final double letterSpacing = style.letterSpacing;
     if (letterSpacing == null || letterSpacing == 0.0) {
       ctx.fillText(line.text, x, y);
@@ -713,10 +712,11 @@ class BitmapCanvas extends EngineCanvas with SaveStackTracking {
       }
       _applyPaint(paragraph._paint.paintData);
 
+      final double x = offset.dx + paragraph._alignOffset;
       double y = offset.dy + paragraph.alphabeticBaseline;
       final int len = lines.length;
       for (int i = 0; i < len; i++) {
-        _drawTextLine(style, lines[i], offset.dx, y);
+        _drawTextLine(style, lines[i], x, y);
         y += paragraph._lineHeight;
       }
       _resetPaint();

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

@@ -416,19 +416,13 @@ class DomTextMeasurementService extends TextMeasurementService {
     List<EngineLineMetrics> lines;
     if (text != null) {
       final double lineWidth = maxIntrinsicWidth;
-      final double alignOffset = _calculateAlignOffsetForLine(
-        paragraph: paragraph,
-        lineWidth: lineWidth,
-        maxWidth: width,
-      );
       lines = <EngineLineMetrics>[
         EngineLineMetrics.withText(
           text,
           startIndex: 0,
           endIndex: text.length,
           hardBreak: true,
           width: lineWidth,
-          left: alignOffset,
           lineNumber: 0,
         ),
       ];
@@ -446,8 +440,6 @@ class DomTextMeasurementService extends TextMeasurementService {
       alphabeticBaseline: alphabeticBaseline,
       ideographicBaseline: ideographicBaseline,
       lines: lines,
-      textAlign: paragraph._textAlign,
-      textDirection: paragraph._textDirection,
     );
   }
 
@@ -496,8 +488,6 @@ class DomTextMeasurementService extends TextMeasurementService {
       alphabeticBaseline: alphabeticBaseline,
       ideographicBaseline: ideographicBaseline,
       lines: null,
-      textAlign: paragraph._textAlign,
-      textDirection: paragraph._textDirection,
     );
   }
 
@@ -556,7 +546,7 @@ class CanvasTextMeasurementService extends TextMeasurementService {
     // TODO(mdebbar): Check if the whole text can fit in a single-line. Then avoid all this ceremony.
     _canvasContext.font = style.cssFontString;
     final LinesCalculator linesCalculator =
-        LinesCalculator(_canvasContext, paragraph, constraints.width);
+        LinesCalculator(_canvasContext, text, style, constraints.width);
     final MinIntrinsicCalculator minIntrinsicCalculator =
         MinIntrinsicCalculator(_canvasContext, text, style);
     final MaxIntrinsicCalculator maxIntrinsicCalculator =
@@ -607,8 +597,6 @@ class CanvasTextMeasurementService extends TextMeasurementService {
       maxIntrinsicWidth: maxIntrinsicCalculator.value,
       width: constraints.width,
       lines: linesCalculator.lines,
-      textAlign: paragraph._textAlign,
-      textDirection: paragraph._textDirection,
     );
     return result;
   }
@@ -714,18 +702,16 @@ int _excludeTrailing(String text, int start, int end, CharPredicate predicate) {
 /// During the text layout phase, this class splits the lines of text so that it
 /// ends up fitting into the given width constraint.
 ///
-/// It implements the Flutter engine's behavior when it comes to handling
-/// ellipsis and max lines.
+/// It mimicks the Flutter engine's behavior when it comes to handling ellipsis
+/// and max lines.
 class LinesCalculator {
-  LinesCalculator(this._canvasContext, this._paragraph, this._maxWidth);
+  LinesCalculator(this._canvasContext, this._text, this._style, this._maxWidth);
 
   final html.CanvasRenderingContext2D _canvasContext;
-  final EngineParagraph _paragraph;
+  final String _text;
+  final ParagraphGeometricStyle _style;
   final double _maxWidth;
 
-  String get _text => _paragraph._plainText;
-  ParagraphGeometricStyle get _style => _paragraph._geometricStyle;
-
   /// The lines that have been consumed so far.
   List<EngineLineMetrics> lines = <EngineLineMetrics>[];
 
@@ -782,20 +768,12 @@ class LinesCalculator {
           start: _lineStart,
           end: chunkEndWithoutSpace,
         );
-        final double widthOfResultingLine =
-            measureSubstring(_lineStart, breakingPoint) + _ellipsisWidth;
-        final double alignOffset = _calculateAlignOffsetForLine(
-          paragraph: _paragraph,
-          lineWidth: widthOfResultingLine,
-          maxWidth: _maxWidth,
-        );
         lines.add(EngineLineMetrics.withText(
           _text.substring(_lineStart, breakingPoint) + _style.ellipsis,
           startIndex: _lineStart,
           endIndex: chunkEnd,
           hardBreak: false,
-          width: widthOfResultingLine,
-          left: alignOffset,
+          width: measureSubstring(_lineStart, breakingPoint) + _ellipsisWidth,
           lineNumber: lines.length,
         ));
       } else if (isChunkTooLong) {
@@ -848,19 +826,12 @@ class LinesCalculator {
       _whitespacePredicate,
     );
     final int lineNumber = lines.length;
-    final double lineWidth = measureSubstring(_lineStart, endWithoutSpace);
-    final double alignOffset = _calculateAlignOffsetForLine(
-      paragraph: _paragraph,
-      lineWidth: lineWidth,
-      maxWidth: _maxWidth,
-    );
     final EngineLineMetrics metrics = EngineLineMetrics.withText(
       _text.substring(_lineStart, endWithoutNewlines),
       startIndex: _lineStart,
       endIndex: lineEnd,
       hardBreak: isHardBreak,
-      width: lineWidth,
-      left: alignOffset,
+      width: measureSubstring(_lineStart, endWithoutSpace),
       lineNumber: lineNumber,
     );
     lines.add(metrics);
@@ -987,30 +958,3 @@ class MaxIntrinsicCalculator {
     _lastHardLineEnd = hardLineEnd;
   }
 }
-
-/// Calculates the offset necessary for the given line to be correctly aligned.
-double _calculateAlignOffsetForLine({
-  @required EngineParagraph paragraph,
-  @required double lineWidth,
-  @required double maxWidth,
-}) {
-  final double emptySpace = maxWidth - lineWidth;
-  // WARNING: the [paragraph] may not be laid out yet at this point. This
-  // function must not use layout metrics, such as [paragraph.height].
-  switch (paragraph._textAlign) {
-    case ui.TextAlign.center:
-      return emptySpace / 2.0;
-    case ui.TextAlign.right:
-      return emptySpace;
-    case ui.TextAlign.start:
-      return paragraph._textDirection == ui.TextDirection.rtl
-          ? emptySpace
-          : 0.0;
-    case ui.TextAlign.end:
-      return paragraph._textDirection == ui.TextDirection.rtl
-          ? 0.0
-          : emptySpace;
-    default:
-      return 0.0;
-  }
-}

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

@@ -29,13 +29,12 @@ class EngineLineMetrics implements ui.LineMetrics {
     this.unscaledAscent,
     this.height,
     @required this.width,
-    @required this.left,
+    this.left,
     this.baseline,
     @required this.lineNumber,
   })  : assert(text != null),
         assert(hardBreak != null),
         assert(width != null),
-        assert(left != null),
         assert(lineNumber != null && lineNumber >= 0);
 
   /// The textual content representing this line.

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

@@ -800,9 +800,7 @@ class ParagraphRuler {
     final int len = constraintCache.length;
     for (int i = 0; i < len; i++) {
       final MeasurementResult item = constraintCache[i];
-      if (item.constraintWidth == constraints.width &&
-          item.textAlign == paragraph._textAlign &&
-          item.textDirection == paragraph._textDirection) {
+      if (item.constraintWidth == constraints.width) {
         return item;
       }
     }
@@ -854,13 +852,7 @@ class MeasurementResult {
   /// of each laid out line.
   final List<EngineLineMetrics> lines;
 
-  /// The text align value of the paragraph.
-  final ui.TextAlign textAlign;
-
-  /// The text direction of the paragraph.
-  final ui.TextDirection textDirection;
-
-  MeasurementResult(
+  const MeasurementResult(
     this.constraintWidth, {
     @required this.isSingleLine,
     @required this.width,
@@ -872,8 +864,6 @@ class MeasurementResult {
     @required this.alphabeticBaseline,
     @required this.ideographicBaseline,
     @required this.lines,
-    @required this.textAlign,
-    @required this.textDirection,
   })  : assert(constraintWidth != null),
         assert(isSingleLine != null),
         assert(width != null),
@@ -882,7 +872,5 @@ class MeasurementResult {
         assert(minIntrinsicWidth != null),
         assert(maxIntrinsicWidth != null),
         assert(alphabeticBaseline != null),
-        assert(ideographicBaseline != null),
-        assert(textAlign != null),
-        assert(textDirection != null);
+        assert(ideographicBaseline != null);
 }