Cache TextPainter plain text value to improve performance

packages/flutter/lib/src/painting/text_painter.dart

@@ -259,10 +259,7 @@ class TextPainter {
   /// This and [textDirection] must be non-null before you call [layout].
   ///
   /// The [InlineSpan] this provides is in the form of a tree that may contain
-  /// multiple instances of [TextSpan]s and [WidgetSpan]s. To obtain a plain text
-  /// representation of the contents of this [TextPainter], use [InlineSpan.toPlainText]
-  /// to get the full contents of all nodes in the tree. [TextSpan.text] will
-  /// only provide the contents of the first node in the tree.
+  /// multiple instances of [TextSpan]s and [WidgetSpan]s.
   InlineSpan? get text => _text;
   InlineSpan? _text;
   set text(InlineSpan? value) {
@@ -279,6 +276,7 @@ class TextPainter {
       : _text?.compareTo(value) ?? RenderComparison.layout;
 
     _text = value;
+    _cachedPlainText = null;
 
     if (comparison.index >= RenderComparison.layout.index) {
       markNeedsLayout();
@@ -290,6 +288,15 @@ class TextPainter {
     // Neither relayout or repaint is needed.
   }
 
+  /// Returns a plain text version of the text to paint.
+  ///
+  /// This uses [InlineSpan.toPlainText] to get the full contents of all nodes in the tree.
+  String get plainText {
+    _cachedPlainText ??= _text!.toPlainText(includeSemanticsLabels: false);
+    return _cachedPlainText!;
+  }
+  String? _cachedPlainText;
+
   /// How the text should be aligned horizontally.
   ///
   /// After this is set, you must call [layout] before the next call to [paint].
@@ -802,11 +809,11 @@ class TextPainter {
   // Get the Rect of the cursor (in logical pixels) based off the near edge
   // of the character upstream from the given string offset.
   Rect? _getRectFromUpstream(int offset, Rect caretPrototype) {
-    final String flattenedText = _text!.toPlainText(includeSemanticsLabels: false);
-    final int? prevCodeUnit = _text!.codeUnitAt(max(0, offset - 1));
-    if (prevCodeUnit == null) {
+    final int plainTextLength = plainText.length;
+    if (plainTextLength == 0 || offset > plainTextLength) {
       return null;
     }
+    final int prevCodeUnit = plainText.codeUnitAt(max(0, offset - 1));
 
     // If the upstream character is a newline, cursor is at start of next line
     const int NEWLINE_CODE_UNIT = 10;
@@ -827,7 +834,7 @@ class TextPainter {
         if (!needsSearch && prevCodeUnit == NEWLINE_CODE_UNIT) {
           break; // Only perform one iteration if no search is required.
         }
-        if (prevRuneOffset < -flattenedText.length) {
+        if (prevRuneOffset < -plainTextLength) {
           break; // Stop iterating when beyond the max length of the text.
         }
         // Multiply by two to log(n) time cover the entire text span. This allows
@@ -854,12 +861,13 @@ class TextPainter {
   // Get the Rect of the cursor (in logical pixels) based off the near edge
   // of the character downstream from the given string offset.
   Rect? _getRectFromDownstream(int offset, Rect caretPrototype) {
-    final String flattenedText = _text!.toPlainText(includeSemanticsLabels: false);
-    // We cap the offset at the final index of the _text.
-    final int? nextCodeUnit = _text!.codeUnitAt(min(offset, flattenedText.length - 1));
-    if (nextCodeUnit == null) {
+    final int plainTextLength = plainText.length;
+    if (plainTextLength == 0 || offset < 0) {
       return null;
     }
+    // We cap the offset at the final index of plain text.
+    final int nextCodeUnit = plainText.codeUnitAt(min(offset, plainTextLength - 1));
+
     // Check for multi-code-unit glyphs such as emojis or zero width joiner
     final bool needsSearch = _isUtf16Surrogate(nextCodeUnit) || nextCodeUnit == _zwjUtf16 || _isUnicodeDirectionality(nextCodeUnit);
     int graphemeClusterLength = needsSearch ? 2 : 1;
@@ -876,7 +884,7 @@ class TextPainter {
         if (!needsSearch) {
           break; // Only perform one iteration if no search is required.
         }
-        if (nextRuneOffset >= flattenedText.length << 1) {
+        if (nextRuneOffset >= plainTextLength << 1) {
           break; // Stop iterating when beyond the max length of the text.
         }
         // Multiply by two to log(n) time cover the entire text span. This allows

packages/flutter/lib/src/rendering/editable.dart

@@ -658,7 +658,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     final TextRange line = _textPainter.getLineBoundary(position);
     // If text is obscured, the entire string should be treated as one line.
     if (obscureText) {
-      return TextSelection(baseOffset: 0, extentOffset: _plainText.length);
+      return TextSelection(baseOffset: 0, extentOffset: plainText.length);
     }
     return TextSelection(baseOffset: line.start, extentOffset: line.end);
   }
@@ -727,12 +727,12 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
 
   void _setSelection(TextSelection nextSelection, SelectionChangedCause cause) {
     if (nextSelection.isValid) {
-      // The nextSelection is calculated based on _plainText, which can be out
+      // The nextSelection is calculated based on plainText, which can be out
       // of sync with the textSelectionDelegate.textEditingValue by one frame.
       // This is due to the render editable and editable text handle pointer
       // event separately. If the editable text changes the text during the
       // event handler, the render editable will use the outdated text stored in
-      // the _plainText when handling the pointer event.
+      // the plainText when handling the pointer event.
       //
       // If this happens, we need to make sure the new selection is still valid.
       final int textLength = textSelectionDelegate.textEditingValue.text.length;
@@ -774,15 +774,8 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     _textLayoutLastMinWidth = null;
   }
 
-  String? _cachedPlainText;
-  // Returns a plain text version of the text in the painter.
-  //
-  // Returns the obscured text when [obscureText] is true. See
-  // [obscureText] and [obscuringCharacter].
-  String get _plainText {
-    _cachedPlainText ??= _textPainter.text!.toPlainText(includeSemanticsLabels: false);
-    return _cachedPlainText!;
-  }
+  /// Returns a plain text version of the text in the painter.
+  String get plainText => _textPainter.plainText;
 
   /// The text to display.
   InlineSpan? get text => _textPainter.text;
@@ -794,7 +787,6 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
       return;
     }
     _textPainter.text = value;
-    _cachedPlainText = null;
     _cachedAttributedValue = null;
     _cachedCombinedSemanticsInfos = null;
     _extractPlaceholderSpans(value);
@@ -1293,7 +1285,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     }
     if (_cachedAttributedValue == null) {
       if (obscureText) {
-        _cachedAttributedValue = AttributedString(obscuringCharacter * _plainText.length);
+        _cachedAttributedValue = AttributedString(obscuringCharacter * plainText.length);
       } else {
         final StringBuffer buffer = StringBuffer();
         int offset = 0;
@@ -1813,7 +1805,7 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
 
     // Set the height based on the content.
     if (width == double.infinity) {
-      final String text = _plainText;
+      final String text = plainText;
       int lines = 1;
       for (int index = 0; index < text.length; index += 1) {
         // Count explicit line breaks.
@@ -2077,15 +2069,15 @@ class RenderEditable extends RenderBox with RelayoutWhenSystemFontsChangeMixin,
     }
     // If text is obscured, the entire sentence should be treated as one word.
     if (obscureText) {
-      return TextSelection(baseOffset: 0, extentOffset: _plainText.length);
+      return TextSelection(baseOffset: 0, extentOffset: plainText.length);
     // On iOS, select the previous word if there is a previous word, or select
     // to the end of the next word if there is a next word. Select nothing if
     // there is neither a previous word nor a next word.
     //
     // If the platform is Android and the text is read only, try to select the
     // previous word if there is one; otherwise, select the single whitespace at
     // the position.
-    } else if (TextLayoutMetrics.isWhitespace(_plainText.codeUnitAt(position.offset))
+    } else if (TextLayoutMetrics.isWhitespace(plainText.codeUnitAt(position.offset))
         && position.offset > 0) {
       assert(defaultTargetPlatform != null);
       final TextRange? previousWord = _getPreviousWord(word.start);

packages/flutter/lib/src/widgets/editable_text.dart

@@ -3128,7 +3128,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       return;
     }
 
-    final String text = renderEditable.text?.toPlainText(includeSemanticsLabels: false) ?? '';
+    final String text = renderEditable.plainText;
     final List<Rect> firstSelectionBoxes = renderEditable.getBoxesForSelection(const TextSelection(baseOffset: 0, extentOffset: 1));
     final Rect? firstRect = firstSelectionBoxes.isNotEmpty ? firstSelectionBoxes.first : null;
     final ScrollDirection scrollDirection = _scrollController.position.userScrollDirection;

packages/flutter/lib/src/widgets/text_selection.dart

@@ -474,8 +474,6 @@ class TextSelectionOverlay {
   }
 
   double _getStartGlyphHeight() {
-    final InlineSpan span = renderObject.text!;
-    final String prevText = span.toPlainText();
     final String currText = selectionDelegate.textEditingValue.text;
     final int firstSelectedGraphemeExtent;
     Rect? startHandleRect;
@@ -486,7 +484,7 @@ class TextSelectionOverlay {
     // widget.renderObject.getRectForComposingRange might fail. In cases where
     // the current frame is different from the previous we fall back to
     // renderObject.preferredLineHeight.
-    if (prevText == currText && _selection != null && _selection.isValid && !_selection.isCollapsed) {
+    if (renderObject.plainText == currText && _selection != null && _selection.isValid && !_selection.isCollapsed) {
       final String selectedGraphemes = _selection.textInside(currText);
       firstSelectedGraphemeExtent = selectedGraphemes.characters.first.length;
       startHandleRect = renderObject.getRectForComposingRange(TextRange(start: _selection.start, end: _selection.start + firstSelectedGraphemeExtent));
@@ -495,13 +493,11 @@ class TextSelectionOverlay {
   }
 
   double _getEndGlyphHeight() {
-    final InlineSpan span = renderObject.text!;
-    final String prevText = span.toPlainText();
     final String currText = selectionDelegate.textEditingValue.text;
     final int lastSelectedGraphemeExtent;
     Rect? endHandleRect;
     // See the explanation in _getStartGlyphHeight.
-    if (prevText == currText && _selection != null && _selection.isValid && !_selection.isCollapsed) {
+    if (renderObject.plainText == currText && _selection != null && _selection.isValid && !_selection.isCollapsed) {
       final String selectedGraphemes = _selection.textInside(currText);
       lastSelectedGraphemeExtent = selectedGraphemes.characters.last.length;
       endHandleRect = renderObject.getRectForComposingRange(TextRange(start: _selection.end - lastSelectedGraphemeExtent, end: _selection.end));