blob: 478f5271872f3305b985f3e4c28edf8da97afbcf [file] [log] [blame]
// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
import 'dart:math' show min, max;
import 'dart:ui' as ui show Paragraph, ParagraphBuilder, ParagraphConstraints, ParagraphStyle, PlaceholderAlignment, LineMetrics, TextHeightBehavior, TextStyle, BoxHeightStyle, BoxWidthStyle;
import 'package:flutter/foundation.dart';
import 'package:flutter/services.dart';
import 'basic_types.dart';
import 'inline_span.dart';
import 'placeholder_span.dart';
import 'strut_style.dart';
import 'text_span.dart';
export 'package:flutter/services.dart' show TextRange, TextSelection;
// The default font size if none is specified. This should be kept in
// sync with the default values in text_style.dart, as well as the
// defaults set in the engine (eg, LibTxt's text_style.h, paragraph_style.h).
const double _kDefaultFontSize = 14.0;
/// How overflowing text should be handled.
///
/// A [TextOverflow] can be passed to [Text] and [RichText] via their
/// [Text.overflow] and [RichText.overflow] properties respectively.
enum TextOverflow {
/// Clip the overflowing text to fix its container.
clip,
/// Fade the overflowing text to transparent.
fade,
/// Use an ellipsis to indicate that the text has overflowed.
ellipsis,
/// Render overflowing text outside of its container.
visible,
}
/// Holds the [Size] and baseline required to represent the dimensions of
/// a placeholder in text.
///
/// Placeholders specify an empty space in the text layout, which is used
/// to later render arbitrary inline widgets into defined by a [WidgetSpan].
///
/// The [size] and [alignment] properties are required and cannot be null.
///
/// See also:
///
/// * [WidgetSpan], a subclass of [InlineSpan] and [PlaceholderSpan] that
/// represents an inline widget embedded within text. The space this
/// widget takes is indicated by a placeholder.
/// * [RichText], a text widget that supports text inline widgets.
@immutable
class PlaceholderDimensions {
/// Constructs a [PlaceholderDimensions] with the specified parameters.
///
/// The `size` and `alignment` are required as a placeholder's dimensions
/// require at least `size` and `alignment` to be fully defined.
const PlaceholderDimensions({
required this.size,
required this.alignment,
this.baseline,
this.baselineOffset,
}) : assert(size != null),
assert(alignment != null);
/// A constant representing an empty placeholder.
static const PlaceholderDimensions empty = PlaceholderDimensions(size: Size.zero, alignment: ui.PlaceholderAlignment.bottom);
/// Width and height dimensions of the placeholder.
final Size size;
/// How to align the placeholder with the text.
///
/// See also:
///
/// * [baseline], the baseline to align to when using
/// [dart:ui.PlaceholderAlignment.baseline],
/// [dart:ui.PlaceholderAlignment.aboveBaseline],
/// or [dart:ui.PlaceholderAlignment.belowBaseline].
/// * [baselineOffset], the distance of the alphabetic baseline from the upper
/// edge of the placeholder.
final ui.PlaceholderAlignment alignment;
/// Distance of the [baseline] from the upper edge of the placeholder.
///
/// Only used when [alignment] is [ui.PlaceholderAlignment.baseline].
final double? baselineOffset;
/// The [TextBaseline] to align to. Used with:
///
/// * [ui.PlaceholderAlignment.baseline]
/// * [ui.PlaceholderAlignment.aboveBaseline]
/// * [ui.PlaceholderAlignment.belowBaseline]
/// * [ui.PlaceholderAlignment.middle]
final TextBaseline? baseline;
@override
String toString() {
return 'PlaceholderDimensions($size, $baseline)';
}
}
/// The different ways of measuring the width of one or more lines of text.
///
/// See [Text.textWidthBasis], for example.
enum TextWidthBasis {
/// multiline text will take up the full width given by the parent. For single
/// line text, only the minimum amount of width needed to contain the text
/// will be used. A common use case for this is a standard series of
/// paragraphs.
parent,
/// The width will be exactly enough to contain the longest line and no
/// longer. A common use case for this is chat bubbles.
longestLine,
}
/// This is used to cache and pass the computed metrics regarding the
/// caret's size and position. This is preferred due to the expensive
/// nature of the calculation.
class _CaretMetrics {
const _CaretMetrics({required this.offset, this.fullHeight});
/// The offset of the top left corner of the caret from the top left
/// corner of the paragraph.
final Offset offset;
/// The full height of the glyph at the caret position.
final double? fullHeight;
}
/// An object that paints a [TextSpan] tree into a [Canvas].
///
/// To use a [TextPainter], follow these steps:
///
/// 1. Create a [TextSpan] tree and pass it to the [TextPainter]
/// constructor.
///
/// 2. Call [layout] to prepare the paragraph.
///
/// 3. Call [paint] as often as desired to paint the paragraph.
///
/// If the width of the area into which the text is being painted
/// changes, return to step 2. If the text to be painted changes,
/// return to step 1.
///
/// The default text style is white. To change the color of the text,
/// pass a [TextStyle] object to the [TextSpan] in `text`.
class TextPainter {
/// Creates a text painter that paints the given text.
///
/// The `text` and `textDirection` arguments are optional but [text] and
/// [textDirection] must be non-null before calling [layout].
///
/// The [textAlign] property must not be null.
///
/// The [maxLines] property, if non-null, must be greater than zero.
TextPainter({
InlineSpan? text,
TextAlign textAlign = TextAlign.start,
TextDirection? textDirection,
double textScaleFactor = 1.0,
int? maxLines,
String? ellipsis,
Locale? locale,
StrutStyle? strutStyle,
TextWidthBasis textWidthBasis = TextWidthBasis.parent,
ui.TextHeightBehavior? textHeightBehavior,
}) : assert(text == null || text.debugAssertIsValid()),
assert(textAlign != null),
assert(textScaleFactor != null),
assert(maxLines == null || maxLines > 0),
assert(textWidthBasis != null),
_text = text,
_textAlign = textAlign,
_textDirection = textDirection,
_textScaleFactor = textScaleFactor,
_maxLines = maxLines,
_ellipsis = ellipsis,
_locale = locale,
_strutStyle = strutStyle,
_textWidthBasis = textWidthBasis,
_textHeightBehavior = textHeightBehavior;
// _paragraph being null means the text needs layout because of style changes.
// Setting _paragraph to null invalidates all the layout cache.
//
// The TextPainter class should not aggressively invalidate the layout as long
// as `markNeedsLayout` is not called (i.e., the layout cache is still valid).
// See: https://github.com/flutter/flutter/issues/85108
ui.Paragraph? _paragraph;
// Whether _paragraph contains outdated paint information and needs to be
// rebuilt before painting.
bool _rebuildParagraphForPaint = true;
bool get _debugNeedsLayout => _paragraph == null;
/// Marks this text painter's layout information as dirty and removes cached
/// information.
///
/// Uses this method to notify text painter to relayout in the case of
/// layout changes in engine. In most cases, updating text painter properties
/// in framework will automatically invoke this method.
void markNeedsLayout() {
_paragraph = null;
_lineMetricsCache = null;
_previousCaretPosition = null;
_previousCaretPrototype = null;
}
/// The (potentially styled) text to paint.
///
/// After this is set, you must call [layout] before the next call to [paint].
/// 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.
InlineSpan? get text => _text;
InlineSpan? _text;
set text(InlineSpan? value) {
assert(value == null || value.debugAssertIsValid());
if (_text == value)
return;
if (_text?.style != value?.style)
_layoutTemplate = null;
final RenderComparison comparison = value == null
? RenderComparison.layout
: _text?.compareTo(value) ?? RenderComparison.layout;
_text = value;
if (comparison.index >= RenderComparison.layout.index) {
markNeedsLayout();
} else if (comparison.index >= RenderComparison.paint.index) {
// Don't clear the _paragraph instance variable just yet. It still
// contains valid layout information.
_rebuildParagraphForPaint = true;
}
// Neither relayout or repaint is needed.
}
/// How the text should be aligned horizontally.
///
/// After this is set, you must call [layout] before the next call to [paint].
///
/// The [textAlign] property must not be null. It defaults to [TextAlign.start].
TextAlign get textAlign => _textAlign;
TextAlign _textAlign;
set textAlign(TextAlign value) {
assert(value != null);
if (_textAlign == value)
return;
_textAlign = value;
markNeedsLayout();
}
/// The default directionality of the text.
///
/// This controls how the [TextAlign.start], [TextAlign.end], and
/// [TextAlign.justify] values of [textAlign] are resolved.
///
/// This is also used to disambiguate how to render bidirectional text. For
/// example, if the [text] is an English phrase followed by a Hebrew phrase,
/// in a [TextDirection.ltr] context the English phrase will be on the left
/// and the Hebrew phrase to its right, while in a [TextDirection.rtl]
/// context, the English phrase will be on the right and the Hebrew phrase on
/// its left.
///
/// After this is set, you must call [layout] before the next call to [paint].
///
/// This and [text] must be non-null before you call [layout].
TextDirection? get textDirection => _textDirection;
TextDirection? _textDirection;
set textDirection(TextDirection? value) {
if (_textDirection == value)
return;
_textDirection = value;
markNeedsLayout();
_layoutTemplate = null; // Shouldn't really matter, but for strict correctness...
}
/// The number of font pixels for each logical pixel.
///
/// For example, if the text scale factor is 1.5, text will be 50% larger than
/// the specified font size.
///
/// After this is set, you must call [layout] before the next call to [paint].
double get textScaleFactor => _textScaleFactor;
double _textScaleFactor;
set textScaleFactor(double value) {
assert(value != null);
if (_textScaleFactor == value)
return;
_textScaleFactor = value;
markNeedsLayout();
_layoutTemplate = null;
}
/// The string used to ellipsize overflowing text. Setting this to a non-empty
/// string will cause this string to be substituted for the remaining text
/// if the text can not fit within the specified maximum width.
///
/// Specifically, the ellipsis is applied to the last line before the line
/// truncated by [maxLines], if [maxLines] is non-null and that line overflows
/// the width constraint, or to the first line that is wider than the width
/// constraint, if [maxLines] is null. The width constraint is the `maxWidth`
/// passed to [layout].
///
/// After this is set, you must call [layout] before the next call to [paint].
///
/// The higher layers of the system, such as the [Text] widget, represent
/// overflow effects using the [TextOverflow] enum. The
/// [TextOverflow.ellipsis] value corresponds to setting this property to
/// U+2026 HORIZONTAL ELLIPSIS (…).
String? get ellipsis => _ellipsis;
String? _ellipsis;
set ellipsis(String? value) {
assert(value == null || value.isNotEmpty);
if (_ellipsis == value)
return;
_ellipsis = value;
markNeedsLayout();
}
/// The locale used to select region-specific glyphs.
Locale? get locale => _locale;
Locale? _locale;
set locale(Locale? value) {
if (_locale == value)
return;
_locale = value;
markNeedsLayout();
}
/// An optional maximum number of lines for the text to span, wrapping if
/// necessary.
///
/// If the text exceeds the given number of lines, it is truncated such that
/// subsequent lines are dropped.
///
/// After this is set, you must call [layout] before the next call to [paint].
int? get maxLines => _maxLines;
int? _maxLines;
/// The value may be null. If it is not null, then it must be greater than zero.
set maxLines(int? value) {
assert(value == null || value > 0);
if (_maxLines == value)
return;
_maxLines = value;
markNeedsLayout();
}
/// {@template flutter.painting.textPainter.strutStyle}
/// The strut style to use. Strut style defines the strut, which sets minimum
/// vertical layout metrics.
///
/// Omitting or providing null will disable strut.
///
/// Omitting or providing null for any properties of [StrutStyle] will result in
/// default values being used. It is highly recommended to at least specify a
/// [StrutStyle.fontSize].
///
/// See [StrutStyle] for details.
/// {@endtemplate}
StrutStyle? get strutStyle => _strutStyle;
StrutStyle? _strutStyle;
set strutStyle(StrutStyle? value) {
if (_strutStyle == value)
return;
_strutStyle = value;
markNeedsLayout();
}
/// {@template flutter.painting.textPainter.textWidthBasis}
/// Defines how to measure the width of the rendered text.
/// {@endtemplate}
TextWidthBasis get textWidthBasis => _textWidthBasis;
TextWidthBasis _textWidthBasis;
set textWidthBasis(TextWidthBasis value) {
assert(value != null);
if (_textWidthBasis == value)
return;
_textWidthBasis = value;
markNeedsLayout();
}
/// {@macro dart.ui.textHeightBehavior}
ui.TextHeightBehavior? get textHeightBehavior => _textHeightBehavior;
ui.TextHeightBehavior? _textHeightBehavior;
set textHeightBehavior(ui.TextHeightBehavior? value) {
if (_textHeightBehavior == value)
return;
_textHeightBehavior = value;
markNeedsLayout();
}
/// An ordered list of [TextBox]es that bound the positions of the placeholders
/// in the paragraph.
///
/// Each box corresponds to a [PlaceholderSpan] in the order they were defined
/// in the [InlineSpan] tree.
List<TextBox>? get inlinePlaceholderBoxes => _inlinePlaceholderBoxes;
List<TextBox>? _inlinePlaceholderBoxes;
/// An ordered list of scales for each placeholder in the paragraph.
///
/// The scale is used as a multiplier on the height, width and baselineOffset of
/// the placeholder. Scale is primarily used to handle accessibility scaling.
///
/// Each scale corresponds to a [PlaceholderSpan] in the order they were defined
/// in the [InlineSpan] tree.
List<double>? get inlinePlaceholderScales => _inlinePlaceholderScales;
List<double>? _inlinePlaceholderScales;
/// Sets the dimensions of each placeholder in [text].
///
/// The number of [PlaceholderDimensions] provided should be the same as the
/// number of [PlaceholderSpan]s in text. Passing in an empty or null `value`
/// will do nothing.
///
/// If [layout] is attempted without setting the placeholder dimensions, the
/// placeholders will be ignored in the text layout and no valid
/// [inlinePlaceholderBoxes] will be returned.
void setPlaceholderDimensions(List<PlaceholderDimensions>? value) {
if (value == null || value.isEmpty || listEquals(value, _placeholderDimensions)) {
return;
}
assert(() {
int placeholderCount = 0;
text!.visitChildren((InlineSpan span) {
if (span is PlaceholderSpan) {
placeholderCount += 1;
}
return true;
});
return placeholderCount;
}() == value.length);
_placeholderDimensions = value;
markNeedsLayout();
}
List<PlaceholderDimensions>? _placeholderDimensions;
ui.ParagraphStyle _createParagraphStyle([ TextDirection? defaultTextDirection ]) {
// The defaultTextDirection argument is used for preferredLineHeight in case
// textDirection hasn't yet been set.
assert(textAlign != null);
assert(textDirection != null || defaultTextDirection != null, 'TextPainter.textDirection must be set to a non-null value before using the TextPainter.');
return _text!.style?.getParagraphStyle(
textAlign: textAlign,
textDirection: textDirection ?? defaultTextDirection,
textScaleFactor: textScaleFactor,
maxLines: _maxLines,
textHeightBehavior: _textHeightBehavior,
ellipsis: _ellipsis,
locale: _locale,
strutStyle: _strutStyle,
) ?? ui.ParagraphStyle(
textAlign: textAlign,
textDirection: textDirection ?? defaultTextDirection,
// Use the default font size to multiply by as RichText does not
// perform inheriting [TextStyle]s and would otherwise
// fail to apply textScaleFactor.
fontSize: _kDefaultFontSize * textScaleFactor,
maxLines: maxLines,
textHeightBehavior: _textHeightBehavior,
ellipsis: ellipsis,
locale: locale,
);
}
ui.Paragraph? _layoutTemplate;
ui.Paragraph _createLayoutTemplate() {
final ui.ParagraphBuilder builder = ui.ParagraphBuilder(
_createParagraphStyle(TextDirection.rtl),
); // direction doesn't matter, text is just a space
final ui.TextStyle? textStyle = text?.style?.getTextStyle(textScaleFactor: textScaleFactor);
if (textStyle != null)
builder.pushStyle(textStyle);
builder.addText(' ');
return builder.build()
..layout(const ui.ParagraphConstraints(width: double.infinity));
}
/// The height of a space in [text] in logical pixels.
///
/// Not every line of text in [text] will have this height, but this height
/// is "typical" for text in [text] and useful for sizing other objects
/// relative a typical line of text.
///
/// Obtaining this value does not require calling [layout].
///
/// The style of the [text] property is used to determine the font settings
/// that contribute to the [preferredLineHeight]. If [text] is null or if it
/// specifies no styles, the default [TextStyle] values are used (a 10 pixel
/// sans-serif font).
double get preferredLineHeight => (_layoutTemplate ??= _createLayoutTemplate()).height;
// Unfortunately, using full precision floating point here causes bad layouts
// because floating point math isn't associative. If we add and subtract
// padding, for example, we'll get different values when we estimate sizes and
// when we actually compute layout because the operations will end up associated
// differently. To work around this problem for now, we round fractional pixel
// values up to the nearest whole pixel value. The right long-term fix is to do
// layout using fixed precision arithmetic.
double _applyFloatingPointHack(double layoutValue) {
return layoutValue.ceilToDouble();
}
/// The width at which decreasing the width of the text would prevent it from
/// painting itself completely within its bounds.
///
/// Valid only after [layout] has been called.
double get minIntrinsicWidth {
assert(!_debugNeedsLayout);
return _applyFloatingPointHack(_paragraph!.minIntrinsicWidth);
}
/// The width at which increasing the width of the text no longer decreases the height.
///
/// Valid only after [layout] has been called.
double get maxIntrinsicWidth {
assert(!_debugNeedsLayout);
return _applyFloatingPointHack(_paragraph!.maxIntrinsicWidth);
}
/// The horizontal space required to paint this text.
///
/// Valid only after [layout] has been called.
double get width {
assert(!_debugNeedsLayout);
return _applyFloatingPointHack(
textWidthBasis == TextWidthBasis.longestLine ? _paragraph!.longestLine : _paragraph!.width,
);
}
/// The vertical space required to paint this text.
///
/// Valid only after [layout] has been called.
double get height {
assert(!_debugNeedsLayout);
return _applyFloatingPointHack(_paragraph!.height);
}
/// The amount of space required to paint this text.
///
/// Valid only after [layout] has been called.
Size get size {
assert(!_debugNeedsLayout);
return Size(width, height);
}
/// Returns the distance from the top of the text to the first baseline of the
/// given type.
///
/// Valid only after [layout] has been called.
double computeDistanceToActualBaseline(TextBaseline baseline) {
assert(!_debugNeedsLayout);
assert(baseline != null);
switch (baseline) {
case TextBaseline.alphabetic:
return _paragraph!.alphabeticBaseline;
case TextBaseline.ideographic:
return _paragraph!.ideographicBaseline;
}
}
/// Whether any text was truncated or ellipsized.
///
/// If [maxLines] is not null, this is true if there were more lines to be
/// drawn than the given [maxLines], and thus at least one line was omitted in
/// the output; otherwise it is false.
///
/// If [maxLines] is null, this is true if [ellipsis] is not the empty string
/// and there was a line that overflowed the `maxWidth` argument passed to
/// [layout]; otherwise it is false.
///
/// Valid only after [layout] has been called.
bool get didExceedMaxLines {
assert(!_debugNeedsLayout);
return _paragraph!.didExceedMaxLines;
}
double? _lastMinWidth;
double? _lastMaxWidth;
// Creates a ui.Paragraph using the current configurations in this class and
// assign it to _paragraph.
void _createParagraph() {
assert(_paragraph == null || _rebuildParagraphForPaint);
final InlineSpan? text = this.text;
if (text == null) {
throw StateError('TextPainter.text must be set to a non-null value before using the TextPainter.');
}
final ui.ParagraphBuilder builder = ui.ParagraphBuilder(_createParagraphStyle());
text.build(builder, textScaleFactor: textScaleFactor, dimensions: _placeholderDimensions);
_inlinePlaceholderScales = builder.placeholderScales;
_paragraph = builder.build();
_rebuildParagraphForPaint = false;
}
void _layoutParagraph(double minWidth, double maxWidth) {
_paragraph!.layout(ui.ParagraphConstraints(width: maxWidth));
if (minWidth != maxWidth) {
double newWidth;
switch (textWidthBasis) {
case TextWidthBasis.longestLine:
// The parent widget expects the paragraph to be exactly
// `TextPainter.width` wide, if that value satisfies the constraints
// it gave to the TextPainter. So when `textWidthBasis` is longestLine,
// the paragraph's width needs to be as close to the width of its
// longest line as possible.
newWidth = _applyFloatingPointHack(_paragraph!.longestLine);
break;
case TextWidthBasis.parent:
newWidth = maxIntrinsicWidth;
break;
}
newWidth = newWidth.clamp(minWidth, maxWidth);
if (newWidth != _applyFloatingPointHack(_paragraph!.width)) {
_paragraph!.layout(ui.ParagraphConstraints(width: newWidth));
}
}
}
/// Computes the visual position of the glyphs for painting the text.
///
/// The text will layout with a width that's as close to its max intrinsic
/// width as possible while still being greater than or equal to `minWidth` and
/// less than or equal to `maxWidth`.
///
/// The [text] and [textDirection] properties must be non-null before this is
/// called.
void layout({ double minWidth = 0.0, double maxWidth = double.infinity }) {
assert(text != null, 'TextPainter.text must be set to a non-null value before using the TextPainter.');
assert(textDirection != null, 'TextPainter.textDirection must be set to a non-null value before using the TextPainter.');
// Return early if the current layout information is not outdated, even if
// _needsPaint is true (in which case _paragraph will be rebuilt in paint).
if (_paragraph != null && minWidth == _lastMinWidth && maxWidth == _lastMaxWidth)
return;
if (_rebuildParagraphForPaint || _paragraph == null)
_createParagraph();
_lastMinWidth = minWidth;
_lastMaxWidth = maxWidth;
// A change in layout invalidates the cached caret metrics as well.
_previousCaretPosition = null;
_previousCaretPrototype = null;
_layoutParagraph(minWidth, maxWidth);
_inlinePlaceholderBoxes = _paragraph!.getBoxesForPlaceholders();
}
/// Paints the text onto the given canvas at the given offset.
///
/// Valid only after [layout] has been called.
///
/// If you cannot see the text being painted, check that your text color does
/// not conflict with the background on which you are drawing. The default
/// text color is white (to contrast with the default black background color),
/// so if you are writing an application with a white background, the text
/// will not be visible by default.
///
/// To set the text style, specify a [TextStyle] when creating the [TextSpan]
/// that you pass to the [TextPainter] constructor or to the [text] property.
void paint(Canvas canvas, Offset offset) {
final double? minWidth = _lastMinWidth;
final double? maxWidth = _lastMaxWidth;
if (_paragraph == null || minWidth == null || maxWidth == null) {
throw StateError(
'TextPainter.paint called when text geometry was not yet calculated.\n'
'Please call layout() before paint() to position the text before painting it.',
);
}
if (_rebuildParagraphForPaint) {
Size? debugSize;
assert(() {
debugSize = size;
return true;
}());
_createParagraph();
// Unfortunately we have to redo the layout using the same constraints,
// since we've created a new ui.Paragraph. But there's no extra work being
// done: if _needsPaint is true and _paragraph is not null, the previous
// `layout` call didn't invoke _layoutParagraph.
_layoutParagraph(minWidth, maxWidth);
assert(debugSize == size);
}
canvas.drawParagraph(_paragraph!, offset);
}
// Returns true iff the given value is a valid UTF-16 surrogate. The value
// must be a UTF-16 code unit, meaning it must be in the range 0x0000-0xFFFF.
//
// See also:
// * https://en.wikipedia.org/wiki/UTF-16#Code_points_from_U+010000_to_U+10FFFF
static bool _isUtf16Surrogate(int value) {
return value & 0xF800 == 0xD800;
}
// Checks if the glyph is either [Unicode.RLM] or [Unicode.LRM]. These values take
// up zero space and do not have valid bounding boxes around them.
//
// We do not directly use the [Unicode] constants since they are strings.
static bool _isUnicodeDirectionality(int value) {
return value == 0x200F || value == 0x200E;
}
/// Returns the closest offset after `offset` at which the input cursor can be
/// positioned.
int? getOffsetAfter(int offset) {
final int? nextCodeUnit = _text!.codeUnitAt(offset);
if (nextCodeUnit == null)
return null;
// TODO(goderbauer): doesn't handle extended grapheme clusters with more than one Unicode scalar value (https://github.com/flutter/flutter/issues/13404).
return _isUtf16Surrogate(nextCodeUnit) ? offset + 2 : offset + 1;
}
/// Returns the closest offset before `offset` at which the input cursor can
/// be positioned.
int? getOffsetBefore(int offset) {
final int? prevCodeUnit = _text!.codeUnitAt(offset - 1);
if (prevCodeUnit == null)
return null;
// TODO(goderbauer): doesn't handle extended grapheme clusters with more than one Unicode scalar value (https://github.com/flutter/flutter/issues/13404).
return _isUtf16Surrogate(prevCodeUnit) ? offset - 2 : offset - 1;
}
// Unicode value for a zero width joiner character.
static const int _zwjUtf16 = 0x200d;
// 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(includePlaceholders: false);
final int? prevCodeUnit = _text!.codeUnitAt(max(0, offset - 1));
if (prevCodeUnit == null)
return null;
// If the upstream character is a newline, cursor is at start of next line
const int NEWLINE_CODE_UNIT = 10;
// Check for multi-code-unit glyphs such as emojis or zero width joiner.
final bool needsSearch = _isUtf16Surrogate(prevCodeUnit) || _text!.codeUnitAt(offset) == _zwjUtf16 || _isUnicodeDirectionality(prevCodeUnit);
int graphemeClusterLength = needsSearch ? 2 : 1;
List<TextBox> boxes = <TextBox>[];
while (boxes.isEmpty) {
final int prevRuneOffset = offset - graphemeClusterLength;
// Use BoxHeightStyle.strut to ensure that the caret's height fits within
// the line's height and is consistent throughout the line.
boxes = _paragraph!.getBoxesForRange(prevRuneOffset, offset, boxHeightStyle: ui.BoxHeightStyle.strut);
// When the range does not include a full cluster, no boxes will be returned.
if (boxes.isEmpty) {
// When we are at the beginning of the line, a non-surrogate position will
// return empty boxes. We break and try from downstream instead.
if (!needsSearch && prevCodeUnit == NEWLINE_CODE_UNIT) {
break; // Only perform one iteration if no search is required.
}
if (prevRuneOffset < -flattenedText.length) {
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
// faster discovery of very long clusters and reduces the possibility
// of certain large clusters taking much longer than others, which can
// cause jank.
graphemeClusterLength *= 2;
continue;
}
final TextBox box = boxes.first;
if (prevCodeUnit == NEWLINE_CODE_UNIT) {
return Rect.fromLTRB(_emptyOffset.dx, box.bottom, _emptyOffset.dx, box.bottom + box.bottom - box.top);
}
final double caretEnd = box.end;
final double dx = box.direction == TextDirection.rtl ? caretEnd - caretPrototype.width : caretEnd;
return Rect.fromLTRB(dx.clamp(0, _paragraph!.width), box.top, dx.clamp(0, _paragraph!.width), box.bottom);
}
return null;
}
// 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(includePlaceholders: 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)
return null;
// 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;
List<TextBox> boxes = <TextBox>[];
while (boxes.isEmpty) {
final int nextRuneOffset = offset + graphemeClusterLength;
// Use BoxHeightStyle.strut to ensure that the caret's height fits within
// the line's height and is consistent throughout the line.
boxes = _paragraph!.getBoxesForRange(offset, nextRuneOffset, boxHeightStyle: ui.BoxHeightStyle.strut);
// When the range does not include a full cluster, no boxes will be returned.
if (boxes.isEmpty) {
// When we are at the end of the line, a non-surrogate position will
// return empty boxes. We break and try from upstream instead.
if (!needsSearch) {
break; // Only perform one iteration if no search is required.
}
if (nextRuneOffset >= flattenedText.length << 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
// faster discovery of very long clusters and reduces the possibility
// of certain large clusters taking much longer than others, which can
// cause jank.
graphemeClusterLength *= 2;
continue;
}
final TextBox box = boxes.last;
final double caretStart = box.start;
final double dx = box.direction == TextDirection.rtl ? caretStart - caretPrototype.width : caretStart;
return Rect.fromLTRB(dx.clamp(0, _paragraph!.width), box.top, dx.clamp(0, _paragraph!.width), box.bottom);
}
return null;
}
Offset get _emptyOffset {
assert(!_debugNeedsLayout); // implies textDirection is non-null
assert(textAlign != null);
switch (textAlign) {
case TextAlign.left:
return Offset.zero;
case TextAlign.right:
return Offset(width, 0.0);
case TextAlign.center:
return Offset(width / 2.0, 0.0);
case TextAlign.justify:
case TextAlign.start:
assert(textDirection != null);
switch (textDirection!) {
case TextDirection.rtl:
return Offset(width, 0.0);
case TextDirection.ltr:
return Offset.zero;
}
case TextAlign.end:
assert(textDirection != null);
switch (textDirection!) {
case TextDirection.rtl:
return Offset.zero;
case TextDirection.ltr:
return Offset(width, 0.0);
}
}
}
/// Returns the offset at which to paint the caret.
///
/// Valid only after [layout] has been called.
Offset getOffsetForCaret(TextPosition position, Rect caretPrototype) {
_computeCaretMetrics(position, caretPrototype);
return _caretMetrics.offset;
}
/// {@template flutter.painting.textPainter.getFullHeightForCaret}
/// Returns the strut bounded height of the glyph at the given `position`.
/// {@endtemplate}
///
/// Valid only after [layout] has been called.
double? getFullHeightForCaret(TextPosition position, Rect caretPrototype) {
_computeCaretMetrics(position, caretPrototype);
return _caretMetrics.fullHeight;
}
// Cached caret metrics. This allows multiple invokes of [getOffsetForCaret] and
// [getFullHeightForCaret] in a row without performing redundant and expensive
// get rect calls to the paragraph.
late _CaretMetrics _caretMetrics;
// Holds the TextPosition and caretPrototype the last caret metrics were
// computed with. When new values are passed in, we recompute the caret metrics.
// only as necessary.
TextPosition? _previousCaretPosition;
Rect? _previousCaretPrototype;
// Checks if the [position] and [caretPrototype] have changed from the cached
// version and recomputes the metrics required to position the caret.
void _computeCaretMetrics(TextPosition position, Rect caretPrototype) {
assert(!_debugNeedsLayout);
if (position == _previousCaretPosition && caretPrototype == _previousCaretPrototype)
return;
final int offset = position.offset;
assert(position.affinity != null);
Rect? rect;
switch (position.affinity) {
case TextAffinity.upstream: {
rect = _getRectFromUpstream(offset, caretPrototype) ?? _getRectFromDownstream(offset, caretPrototype);
break;
}
case TextAffinity.downstream: {
rect = _getRectFromDownstream(offset, caretPrototype) ?? _getRectFromUpstream(offset, caretPrototype);
break;
}
}
_caretMetrics = _CaretMetrics(
offset: rect != null ? Offset(rect.left, rect.top) : _emptyOffset,
fullHeight: rect != null ? rect.bottom - rect.top : null,
);
// Cache the input parameters to prevent repeat work later.
_previousCaretPosition = position;
_previousCaretPrototype = caretPrototype;
}
/// Returns a list of rects that bound the given selection.
///
/// The [boxHeightStyle] and [boxWidthStyle] arguments may be used to select
/// the shape of the [TextBox]s. These properties default to
/// [ui.BoxHeightStyle.tight] and [ui.BoxWidthStyle.tight] respectively and
/// must not be null.
///
/// A given selection might have more than one rect if this text painter
/// contains bidirectional text because logically contiguous text might not be
/// visually contiguous.
///
/// Leading or trailing newline characters will be represented by zero-width
/// `Textbox`es.
///
/// The method only returns `TextBox`es of glyphs that are entirely enclosed by
/// the given `selection`: a multi-code-unit glyph will be excluded if only
/// part of its code units are in `selection`.
List<TextBox> getBoxesForSelection(
TextSelection selection, {
ui.BoxHeightStyle boxHeightStyle = ui.BoxHeightStyle.tight,
ui.BoxWidthStyle boxWidthStyle = ui.BoxWidthStyle.tight,
}) {
assert(!_debugNeedsLayout);
assert(boxHeightStyle != null);
assert(boxWidthStyle != null);
return _paragraph!.getBoxesForRange(
selection.start,
selection.end,
boxHeightStyle: boxHeightStyle,
boxWidthStyle: boxWidthStyle,
);
}
/// Returns the position within the text for the given pixel offset.
TextPosition getPositionForOffset(Offset offset) {
assert(!_debugNeedsLayout);
return _paragraph!.getPositionForOffset(offset);
}
/// {@template flutter.painting.TextPainter.getWordBoundary}
/// Returns the text range 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 a text range that
/// contains the given text position.
///
/// Word boundaries are defined more precisely in Unicode Standard Annex #29
/// <http://www.unicode.org/reports/tr29/#Word_Boundaries>.
/// {@endtemplate}
TextRange getWordBoundary(TextPosition position) {
assert(!_debugNeedsLayout);
return _paragraph!.getWordBoundary(position);
}
/// Returns the text range of the line at the given offset.
///
/// The newline (if any) is not returned as part of the range.
TextRange getLineBoundary(TextPosition position) {
assert(!_debugNeedsLayout);
return _paragraph!.getLineBoundary(position);
}
List<ui.LineMetrics>? _lineMetricsCache;
/// Returns the full list of [LineMetrics] that describe in detail the various
/// metrics of each laid out line.
///
/// The [LineMetrics] list is presented in the order of the lines they represent.
/// For example, the first line is in the zeroth index.
///
/// [LineMetrics] contains measurements such as ascent, descent, baseline, and
/// width for the line as a whole, and may be useful for aligning additional
/// widgets to a particular line.
///
/// Valid only after [layout] has been called.
List<ui.LineMetrics> computeLineMetrics() {
assert(!_debugNeedsLayout);
return _lineMetricsCache ??= _paragraph!.computeLineMetrics();
}
}