Revert "[web] Correct getPositionForOffset for multi-line paragraphs (#16206)" (#16268)

This reverts commit 4ac82f6.

This caused a regression in a framework test (material/text_field_splash_test.dart)

Author: jason-simmons

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

@@ -373,10 +373,7 @@ class DomTextMeasurementService extends TextMeasurementService {
   @override
   ui.TextPosition getTextPositionForOffset(EngineParagraph paragraph,
       ui.ParagraphConstraints constraints, ui.Offset offset) {
-    assert(
-      paragraph._measurementResult.lines == null,
-      'should only be called when the faster lines-based approach is not possible',
-    );
+    assert(paragraph._plainText == null, 'should only be called for multispan');
 
     final ParagraphGeometricStyle style = paragraph._geometricStyle;
     final ParagraphRuler ruler =

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

@@ -378,53 +378,17 @@ class EngineParagraph implements ui.Paragraph {
 
   @override
   ui.TextPosition getPositionForOffset(ui.Offset offset) {
-    final List<EngineLineMetrics> lines = _measurementResult.lines;
-    if (lines == null) {
+    if (_plainText == null) {
       return getPositionForMultiSpanOffset(offset);
     }
-
-    final int lineNumber = offset.dy ~/ _measurementResult.lineHeight;
-
-    // [offset] is below all the lines.
-    if (lineNumber >= lines.length) {
-      return ui.TextPosition(
-        offset: _plainText.length,
-        affinity: ui.TextAffinity.upstream,
-      );
-    }
-
-    final EngineLineMetrics lineMetrics = lines[lineNumber];
-    final double lineLeft = lineMetrics.left;
-    final double lineRight = lineLeft + lineMetrics.width;
-
-    // [offset] is to the left of the line.
-    if (offset.dx <= lineLeft) {
-      return ui.TextPosition(
-        offset: lineMetrics.startIndex,
-        affinity: ui.TextAffinity.downstream,
-      );
-    }
-
-    // [offset] is to the right of the line.
-    if (offset.dx >= lineRight) {
-      return ui.TextPosition(
-        offset: lineMetrics.endIndex,
-        affinity: ui.TextAffinity.upstream,
-      );
-    }
-
-    // If we reach here, it means the [offset] is somewhere within the line. The
-    // code below will do a binary search to find where exactly the [offset]
-    // falls within the line.
-
     final double dx = offset.dx - _alignOffset;
     final TextMeasurementService instance = _measurementService;
 
-    int low = lineMetrics.startIndex;
-    int high = lineMetrics.endIndex;
+    int low = 0;
+    int high = _plainText.length;
     do {
       final int current = (low + high) ~/ 2;
-      final double width = instance.measureSubstringWidth(this, lineMetrics.startIndex, current);
+      final double width = instance.measureSubstringWidth(this, 0, current);
       if (width < dx) {
         low = current;
       } else if (width > dx) {
@@ -439,8 +403,8 @@ class EngineParagraph implements ui.Paragraph {
       return ui.TextPosition(offset: high, affinity: ui.TextAffinity.upstream);
     }
 
-    final double lowWidth = instance.measureSubstringWidth(this, lineMetrics.startIndex, low);
-    final double highWidth = instance.measureSubstringWidth(this, lineMetrics.startIndex, high);
+    final double lowWidth = instance.measureSubstringWidth(this, 0, low);
+    final double highWidth = instance.measureSubstringWidth(this, 0, high);
 
     if (dx - lowWidth < highWidth - dx) {
       // The offset is closer to the low index.

lib/web_ui/test/paragraph_test.dart

@@ -8,7 +8,7 @@ import 'package:ui/ui.dart';
 import 'package:test/test.dart';
 
 void testEachMeasurement(String description, VoidCallback body, {bool skip}) {
-  test('$description (dom measurement)', () async {
+  test(description, () async {
     try {
       TextMeasurementService.initialize(rulerCacheCapacity: 2);
       return body();
@@ -130,154 +130,6 @@ void main() async {
   }, // TODO(nurhan): https://github.com/flutter/flutter/issues/46638
       skip: (browserEngine == BrowserEngine.firefox));
 
-  testEachMeasurement('getPositionForOffset single-line', () {
-    final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(
-      fontFamily: 'Ahem',
-      fontStyle: FontStyle.normal,
-      fontWeight: FontWeight.normal,
-      fontSize: 10,
-      textDirection: TextDirection.ltr,
-    ));
-    builder.addText('abcd efg');
-    final Paragraph paragraph = builder.build();
-    paragraph.layout(const ParagraphConstraints(width: 1000));
-
-    // At the beginning of the line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, 5)),
-      TextPosition(offset: 0, affinity: TextAffinity.downstream),
-    );
-    // Below the line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, 12)),
-      TextPosition(offset: 8, affinity: TextAffinity.upstream),
-    );
-    // Above the line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, -5)),
-      TextPosition(offset: 0, affinity: TextAffinity.downstream),
-    );
-    // At the end of the line.
-    expect(
-      paragraph.getPositionForOffset(Offset(80, 5)),
-      TextPosition(offset: 8, affinity: TextAffinity.upstream),
-    );
-    // On the left side of "b".
-    expect(
-      paragraph.getPositionForOffset(Offset(14, 5)),
-      TextPosition(offset: 1, affinity: TextAffinity.downstream),
-    );
-    // On the right side of "b".
-    expect(
-      paragraph.getPositionForOffset(Offset(16, 5)),
-      TextPosition(offset: 2, affinity: TextAffinity.upstream),
-    );
-  });
-
-  test('getPositionForOffset multi-line', () {
-    // [Paragraph.getPositionForOffset] for multi-line text doesn't work well
-    // with dom-based measurement.
-    TextMeasurementService.enableExperimentalCanvasImplementation = true;
-    TextMeasurementService.initialize(rulerCacheCapacity: 2);
-
-    final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(
-      fontFamily: 'Ahem',
-      fontStyle: FontStyle.normal,
-      fontWeight: FontWeight.normal,
-      fontSize: 10,
-      textDirection: TextDirection.ltr,
-    ));
-    builder.addText('abcd\n');
-    builder.addText('abcdefg\n');
-    builder.addText('ab');
-    final Paragraph paragraph = builder.build();
-    paragraph.layout(const ParagraphConstraints(width: 1000));
-
-    // First line: "abcd\n"
-
-    // At the beginning of the first line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, 5)),
-      TextPosition(offset: 0, affinity: TextAffinity.downstream),
-    );
-    // Above the first line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, -5)),
-      TextPosition(offset: 0, affinity: TextAffinity.downstream),
-    );
-    // At the end of the first line.
-    expect(
-      paragraph.getPositionForOffset(Offset(50, 5)),
-      TextPosition(offset: 5, affinity: TextAffinity.upstream),
-    );
-    // On the left side of "b" in the first line.
-    expect(
-      paragraph.getPositionForOffset(Offset(14, 5)),
-      TextPosition(offset: 1, affinity: TextAffinity.downstream),
-    );
-    // On the right side of "b" in the first line.
-    expect(
-      paragraph.getPositionForOffset(Offset(16, 5)),
-      TextPosition(offset: 2, affinity: TextAffinity.upstream),
-    );
-
-
-    // Second line: "abcdefg\n"
-
-    // At the beginning of the second line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, 15)),
-      TextPosition(offset: 5, affinity: TextAffinity.downstream),
-    );
-    // At the end of the second line.
-    expect(
-      paragraph.getPositionForOffset(Offset(100, 15)),
-      TextPosition(offset: 13, affinity: TextAffinity.upstream),
-    );
-    // On the left side of "e" in the second line.
-    expect(
-      paragraph.getPositionForOffset(Offset(44, 15)),
-      TextPosition(offset: 9, affinity: TextAffinity.downstream),
-    );
-    // On the right side of "e" in the second line.
-    expect(
-      paragraph.getPositionForOffset(Offset(46, 15)),
-      TextPosition(offset: 10, affinity: TextAffinity.upstream),
-    );
-
-
-    // Last (third) line: "ab"
-
-    // At the beginning of the last line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, 25)),
-      TextPosition(offset: 13, affinity: TextAffinity.downstream),
-    );
-    // At the end of the last line.
-    expect(
-      paragraph.getPositionForOffset(Offset(40, 25)),
-      TextPosition(offset: 15, affinity: TextAffinity.upstream),
-    );
-    // Below the last line.
-    expect(
-      paragraph.getPositionForOffset(Offset(0, 32)),
-      TextPosition(offset: 15, affinity: TextAffinity.upstream),
-    );
-    // On the left side of "b" in the last line.
-    expect(
-      paragraph.getPositionForOffset(Offset(12, 25)),
-      TextPosition(offset: 14, affinity: TextAffinity.downstream),
-    );
-    // On the right side of "a" in the last line.
-    expect(
-      paragraph.getPositionForOffset(Offset(9, 25)),
-      TextPosition(offset: 14, affinity: TextAffinity.upstream),
-    );
-
-    TextMeasurementService.clearCache();
-    TextMeasurementService.enableExperimentalCanvasImplementation = false;
-  });
-
   testEachMeasurement('getBoxesForRange returns a box', () {
     final ParagraphBuilder builder = ParagraphBuilder(ParagraphStyle(
       fontFamily: 'Ahem',