[web] Respect maxLines when calculating boxes for a range

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

@@ -374,6 +374,10 @@ class EngineParagraph implements ui.Paragraph {
     }
 
     final List<EngineLineMetrics> lines = _measurementResult.lines;
+    if (start >= lines.last.endIndex) {
+      return <ui.TextBox>[];
+    }
+
     final EngineLineMetrics startLine = _getLineForIndex(start);
     EngineLineMetrics endLine = _getLineForIndex(end);
 
@@ -535,8 +539,7 @@ class EngineParagraph implements ui.Paragraph {
   EngineLineMetrics _getLineForIndex(int index) {
     assert(_hasLineMetrics);
     final List<EngineLineMetrics> lines = _measurementResult.lines;
-    assert(index >= lines.first.startIndex);
-    assert(index <= lines.last.endIndex);
+    assert(index >= 0);
 
     for (int i = 0; i < lines.length; i++) {
       final EngineLineMetrics line = lines[i];
@@ -545,7 +548,6 @@ class EngineParagraph implements ui.Paragraph {
       }
     }
 
-    assert(index == lines.last.endIndex);
     return lines.last;
   }
 

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

@@ -733,14 +733,30 @@ class ParagraphRuler {
     final List<html.Rectangle<num>> clientRects = rangeSpan.getClientRects();
     final List<ui.TextBox> boxes = <ui.TextBox>[];
 
+    final double maxLinesLimit = style.maxLines == null
+        ? double.infinity
+        : style.maxLines * lineHeightDimensions.height;
+
+    html.Rectangle<num> previousRect;
     for (html.Rectangle<num> rect in clientRects) {
+      // If [rect] is an empty box on the same line as the previous box, don't
+      // include it in the result.
+      if (rect.top == previousRect?.top && rect.left == rect.right) {
+        continue;
+      }
+      // As soon as we go beyond [maxLines], stop adding boxes.
+      if (rect.top >= maxLinesLimit) {
+        break;
+      }
+
       boxes.add(ui.TextBox.fromLTRBD(
         rect.left + alignOffset,
         rect.top,
         rect.right + alignOffset,
         rect.bottom,
         textDirection,
       ));
+      previousRect = rect;
     }
 
     // Cleanup after measuring the boxes.

lib/web_ui/test/paragraph_test.dart

@@ -441,12 +441,6 @@ void main() async {
     final Paragraph paragraph = builder.build();
     paragraph.layout(const ParagraphConstraints(width: 100));
 
-    // In the dom-based measurement (except Firefox), there will be some
-    // discrepancies around line ends.
-    final isDiscrepancyExpected =
-      !TextMeasurementService.enableExperimentalCanvasImplementation &&
-          browserEngine != BrowserEngine.firefox;
-
     // First line: "abcd\n"
 
     // At the beginning of the first line.
@@ -497,8 +491,6 @@ void main() async {
       paragraph.getBoxesForRange(2, 5),
       <TextBox>[
         TextBox.fromLTRBD(20.0, 0.0, 40.0, 10.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
       ],
     );
 
@@ -533,8 +525,6 @@ void main() async {
       paragraph.getBoxesForRange(10, 13),
       <TextBox>[
         TextBox.fromLTRBD(50.0, 10.0, 70.0, 20.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(70.0, 10.0, 70.0, 20.0, TextDirection.ltr),
       ],
     );
 
@@ -573,8 +563,6 @@ void main() async {
       paragraph.getBoxesForRange(2, 8),
       <TextBox>[
         TextBox.fromLTRBD(20.0, 0.0, 40.0, 10.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
         TextBox.fromLTRBD(0.0, 10.0, 30.0, 20.0, TextDirection.ltr),
       ],
     );
@@ -593,11 +581,7 @@ void main() async {
       paragraph.getBoxesForRange(3, 14),
       <TextBox>[
         TextBox.fromLTRBD(30.0, 0.0, 40.0, 10.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
         TextBox.fromLTRBD(0.0, 10.0, 70.0, 20.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(70.0, 10.0, 70.0, 20.0, TextDirection.ltr),
         TextBox.fromLTRBD(0.0, 20.0, 10.0, 30.0, TextDirection.ltr),
       ],
     );
@@ -607,11 +591,7 @@ void main() async {
       paragraph.getBoxesForRange(0, 13),
       <TextBox>[
         TextBox.fromLTRBD(0.0, 0.0, 40.0, 10.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
         TextBox.fromLTRBD(0.0, 10.0, 70.0, 20.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(70.0, 10.0, 70.0, 20.0, TextDirection.ltr),
       ],
     );
 
@@ -620,16 +600,186 @@ void main() async {
       paragraph.getBoxesForRange(0, 15),
       <TextBox>[
         TextBox.fromLTRBD(0.0, 0.0, 40.0, 10.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
         TextBox.fromLTRBD(0.0, 10.0, 70.0, 20.0, TextDirection.ltr),
-        if (isDiscrepancyExpected)
-          TextBox.fromLTRBD(70.0, 10.0, 70.0, 20.0, TextDirection.ltr),
         TextBox.fromLTRBD(0.0, 20.0, 20.0, 30.0, TextDirection.ltr),
       ],
     );
   });
 
+  testEachMeasurement('getBoxesForRange with maxLines', () {
+    final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(
+      fontFamily: 'Ahem',
+      fontStyle: FontStyle.normal,
+      fontWeight: FontWeight.normal,
+      fontSize: 10,
+      textDirection: TextDirection.ltr,
+      maxLines: 2,
+    ));
+    builder.addText('abcd\n');
+    builder.addText('abcdefg\n');
+    builder.addText('ab');
+    final Paragraph paragraph = builder.build();
+    paragraph.layout(const ParagraphConstraints(width: 100));
+
+    // First line: "abcd\n"
+
+    // At the beginning of the first line.
+    expect(
+      paragraph.getBoxesForRange(0, 0),
+      <TextBox>[],
+    );
+    // At the end of the first line.
+    expect(
+      paragraph.getBoxesForRange(4, 4),
+      <TextBox>[],
+    );
+    // Between "b" and "c" in the first line.
+    expect(
+      paragraph.getBoxesForRange(2, 2),
+      <TextBox>[],
+    );
+    // The range "ab" in the first line.
+    expect(
+      paragraph.getBoxesForRange(0, 2),
+      <TextBox>[
+        TextBox.fromLTRBD(0.0, 0.0, 20.0, 10.0, TextDirection.ltr),
+      ],
+    );
+    // The range "bc" in the first line.
+    expect(
+      paragraph.getBoxesForRange(1, 3),
+      <TextBox>[
+        TextBox.fromLTRBD(10.0, 0.0, 30.0, 10.0, TextDirection.ltr),
+      ],
+    );
+    // The range "d" in the first line.
+    expect(
+      paragraph.getBoxesForRange(3, 4),
+      <TextBox>[
+        TextBox.fromLTRBD(30.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+      ],
+    );
+    // The range "\n" in the first line.
+    expect(
+      paragraph.getBoxesForRange(4, 5),
+      <TextBox>[
+        TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+      ],
+    );
+    // The range "cd\n" in the first line.
+    expect(
+      paragraph.getBoxesForRange(2, 5),
+      <TextBox>[
+        TextBox.fromLTRBD(20.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+      ],
+    );
+
+    // Second line: "abcdefg\n"
+
+    // At the beginning of the second line.
+    expect(
+      paragraph.getBoxesForRange(5, 5),
+      <TextBox>[],
+    );
+    // At the end of the second line.
+    expect(
+      paragraph.getBoxesForRange(12, 12),
+      <TextBox>[],
+    );
+    // The range "efg" in the second line.
+    expect(
+      paragraph.getBoxesForRange(9, 12),
+      <TextBox>[
+        TextBox.fromLTRBD(40.0, 10.0, 70.0, 20.0, TextDirection.ltr),
+      ],
+    );
+    // The range "bcde" in the second line.
+    expect(
+      paragraph.getBoxesForRange(6, 10),
+      <TextBox>[
+        TextBox.fromLTRBD(10.0, 10.0, 50.0, 20.0, TextDirection.ltr),
+      ],
+    );
+    // The range "fg\n" in the second line.
+    expect(
+      paragraph.getBoxesForRange(10, 13),
+      <TextBox>[
+        TextBox.fromLTRBD(50.0, 10.0, 70.0, 20.0, TextDirection.ltr),
+      ],
+    );
+
+    // Last (third) line: "ab"
+
+    // At the beginning of the last line.
+    expect(
+      paragraph.getBoxesForRange(13, 13),
+      <TextBox>[],
+    );
+    // At the end of the last line.
+    expect(
+      paragraph.getBoxesForRange(15, 15),
+      <TextBox>[],
+    );
+    // The range "a" in the last line.
+    expect(
+      paragraph.getBoxesForRange(14, 15),
+      <TextBox>[],
+    );
+    // The range "ab" in the last line.
+    expect(
+      paragraph.getBoxesForRange(13, 15),
+      <TextBox>[],
+    );
+
+
+    // Combine multiple lines
+
+    // The range "cd\nabc".
+    expect(
+      paragraph.getBoxesForRange(2, 8),
+      <TextBox>[
+        TextBox.fromLTRBD(20.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+        TextBox.fromLTRBD(0.0, 10.0, 30.0, 20.0, TextDirection.ltr),
+      ],
+    );
+
+    // The range "\nabcd".
+    expect(
+      paragraph.getBoxesForRange(4, 9),
+      <TextBox>[
+        TextBox.fromLTRBD(40.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+        TextBox.fromLTRBD(0.0, 10.0, 40.0, 20.0, TextDirection.ltr),
+      ],
+    );
+
+    // The range "d\nabcdefg\na".
+    expect(
+      paragraph.getBoxesForRange(3, 14),
+      <TextBox>[
+        TextBox.fromLTRBD(30.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+        TextBox.fromLTRBD(0.0, 10.0, 70.0, 20.0, TextDirection.ltr),
+      ],
+    );
+
+    // The range "abcd\nabcdefg\n".
+    expect(
+      paragraph.getBoxesForRange(0, 13),
+      <TextBox>[
+        TextBox.fromLTRBD(0.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+        TextBox.fromLTRBD(0.0, 10.0, 70.0, 20.0, TextDirection.ltr),
+      ],
+    );
+
+    // The range "abcd\nabcdefg\nab".
+    expect(
+      paragraph.getBoxesForRange(0, 15),
+      <TextBox>[
+        TextBox.fromLTRBD(0.0, 0.0, 40.0, 10.0, TextDirection.ltr),
+        TextBox.fromLTRBD(0.0, 10.0, 70.0, 20.0, TextDirection.ltr),
+      ],
+    );
+  });
+
   test('longestLine', () {
     // [Paragraph.longestLine] is only supported by canvas-based measurement.
     TextMeasurementService.enableExperimentalCanvasImplementation = true;