Add line boundary information to LineMetrics. (#13727)

This exposes the line boundary information a line by adding getLineBoundary to return the indices corresponding to a line around a TextPosition. The information is already calculated when calculating line metrics, so that we can enable moving the selection/cursor to the beginning/end of a line in a text field.

lib/ui/text.dart

@@ -1866,23 +1866,32 @@ class Paragraph extends NativeFieldWrapperClass2 {
   }
   List<int> _getPositionForOffset(double dx, double dy) native 'Paragraph_getPositionForOffset';
 
-  /// Returns the [start, end] of the word at the given offset. Characters not
-  /// part of a word, such as spaces, symbols, and punctuation, have word breaks
-  /// on both sides. In such cases, this method will return [offset, offset+1].
-  /// Word boundaries are defined more precisely in Unicode Standard Annex #29
-  /// http://www.unicode.org/reports/tr29/#Word_Boundaries
-  List<int> getWordBoundary(dynamic position) {
-    // TODO(gspencergoog): have this take only a TextPosition once the framework
-    // code is calling it with that.
-    if (position is TextPosition) {
-      return _getWordBoundary(position.offset);
-    } else {
-      final int offset = position;
-      return _getWordBoundary(offset);
-    }
+  /// Returns the [TextRange] of the word at the given [TextPosition].
+  ///
+  /// Characters not part of a word, such as spaces, symbols, and punctuation,
+  /// have word breaks on both sides. In such cases, this method will return
+  /// [offset, offset+1]. Word boundaries are defined more precisely in Unicode
+  /// Standard Annex #29 http://www.unicode.org/reports/tr29/#Word_Boundaries
+  TextRange getWordBoundary(TextPosition position) {
+    final List<int> boundary = _getWordBoundary(position.offset);
+    return TextRange(start: boundary[0], end: boundary[1]);
   }
   List<int> _getWordBoundary(int offset) native 'Paragraph_getWordBoundary';
 
+  /// Returns the [TextRange] of the line at the given [TextPosition].
+  ///
+  /// The newline (if any) is returned as part of the range.
+  ///
+  /// Not valid until after layout.
+  ///
+  /// This can potentially be expensive, since it needs to compute the line
+  /// metrics, so use it sparingly.
+  TextRange getLineBoundary(TextPosition position) {
+    final List<int> boundary = _getLineBoundary(position.offset);
+    return TextRange(start: boundary[0], end: boundary[1]);
+  }
+  List<int> _getLineBoundary(int offset) native 'Paragraph_getLineBoundary';
+
   // Redirecting the paint function in this way solves some dependency problems
   // in the C++ code. If we straighten out the C++ dependencies, we can remove
   // this indirection.

lib/ui/text/paragraph.cc

@@ -31,6 +31,7 @@ IMPLEMENT_WRAPPERTYPEINFO(ui, Paragraph);
   V(Paragraph, layout)                  \
   V(Paragraph, paint)                   \
   V(Paragraph, getWordBoundary)         \
+  V(Paragraph, getLineBoundary)         \
   V(Paragraph, getRectsForRange)        \
   V(Paragraph, getRectsForPlaceholders) \
   V(Paragraph, getPositionForOffset)    \
@@ -134,6 +135,23 @@ Dart_Handle Paragraph::getWordBoundary(unsigned offset) {
   return result;
 }
 
+Dart_Handle Paragraph::getLineBoundary(unsigned offset) {
+  std::vector<txt::LineMetrics> metrics = m_paragraph->GetLineMetrics();
+  int line_start = -1;
+  int line_end = -1;
+  for (txt::LineMetrics& line : metrics) {
+    if (offset >= line.start_index && offset < line.end_index) {
+      line_start = line.start_index;
+      line_end = line.end_index;
+      break;
+    }
+  }
+  Dart_Handle result = Dart_NewListOf(Dart_CoreType_Int, 2);
+  Dart_ListSetAt(result, 0, ToDart(line_start));
+  Dart_ListSetAt(result, 1, ToDart(line_end));
+  return result;
+}
+
 std::vector<LineMetrics> Paragraph::computeLineMetrics() {
   std::vector<LineMetrics> result;
   std::vector<txt::LineMetrics> metrics = m_paragraph->GetLineMetrics();

lib/ui/text/paragraph.h

@@ -49,6 +49,7 @@ class Paragraph : public RefCountedDartWrappable<Paragraph> {
   std::vector<TextBox> getRectsForPlaceholders();
   Dart_Handle getPositionForOffset(double dx, double dy);
   Dart_Handle getWordBoundary(unsigned offset);
+  Dart_Handle getLineBoundary(unsigned offset);
   std::vector<LineMetrics> computeLineMetrics();
 
   size_t GetAllocationSize() override;

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

@@ -281,27 +281,22 @@ class EngineParagraph implements ui.Paragraph {
   }
 
   @override
-  List<int> getWordBoundary(dynamic position) {
-    // TODO(gspencergoog): have this take only a TextPosition once the framework
-    // code is calling it with that.
-    if (position is ui.TextPosition) {
-      ui.TextPosition textPosition = position;
-      if (_plainText == null) {
-        return <int>[textPosition.offset, textPosition.offset];
-      }
-
-      final int start = WordBreaker.prevBreakIndex(_plainText, textPosition.offset);
-      final int end = WordBreaker.nextBreakIndex(_plainText, textPosition.offset);
-      return <int>[start, end];
-    }
-
+  ui.TextRange getWordBoundary(ui.TextPosition position) {
+    ui.TextPosition textPosition = position;
     if (_plainText == null) {
-      return <int>[position, position];
+      return ui.TextRange(start: textPosition.offset, end: textPosition.offset);
     }
 
-    final int start = WordBreaker.prevBreakIndex(_plainText, position);
-    final int end = WordBreaker.nextBreakIndex(_plainText, position);
-    return <int>[start, end];
+    final int start = WordBreaker.prevBreakIndex(_plainText, textPosition.offset);
+    final int end = WordBreaker.nextBreakIndex(_plainText, textPosition.offset);
+    return ui.TextRange(start: start, end: end);
+  }
+
+  @override
+  ui.TextRange getLineBoundary(ui.TextPosition position) {
+    // TODO(flutter_web): https://github.com/flutter/flutter/issues/39537
+    // Depends upon LineMetrics measurement.
+    return null;
   }
 
   @override

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

@@ -1237,12 +1237,23 @@ abstract class Paragraph {
   /// within the text.
   TextPosition getPositionForOffset(Offset offset);
 
-  /// Returns the [start, end] of the word at the given offset. Characters not
-  /// part of a word, such as spaces, symbols, and punctuation, have word breaks
-  /// on both sides. In such cases, this method will return [offset, offset+1].
-  /// Word boundaries are defined more precisely in Unicode Standard Annex #29
-  /// http://www.unicode.org/reports/tr29/#Word_Boundaries
-  List<int> getWordBoundary(dynamic position);
+  /// Returns the [TextRange] of the word at the given [TextPosition].
+  ///
+  /// Characters not part of a word, such as spaces, symbols, and punctuation,
+  /// have word breaks on both sides. In such cases, this method will return
+  /// [offset, offset+1]. Word boundaries are defined more precisely in Unicode
+  /// Standard Annex #29 http://www.unicode.org/reports/tr29/#Word_Boundaries
+  TextRange getWordBoundary(TextPosition  position);
+
+  /// Returns the [TextRange] of the line at the given [TextPosition].
+  ///
+  /// The newline (if any) is returned as part of the range.
+  ///
+  /// Not valid until after layout.
+  ///
+  /// This can potentially be expensive, since it needs to compute the line
+  /// metrics, so use it sparingly.
+  TextRange getLineBoundary(TextPosition position);
 
   /// Returns a list of text boxes that enclose all placeholders in the paragraph.
   ///
@@ -1252,6 +1263,13 @@ abstract class Paragraph {
   /// where positive y values indicate down.
   List<TextBox> getBoxesForPlaceholders();
 
+  /// Returns the full list of [LineMetrics] that describe in detail the various
+  /// metrics of each laid out line.
+  ///
+  /// Not valid until after layout.
+  ///
+  /// This can potentially return a large amount of data, so it is not recommended
+  /// to repeatedly call this. Instead, cache the results.
   List<LineMetrics> computeLineMetrics();
 }