76 lines
2.2 KiB
Dart
76 lines
2.2 KiB
Dart
import 'dart:ui' as ui;
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import 'package:collection/collection.dart';
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import 'package:flutter/material.dart';
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import 'package:flutter/rendering.dart';
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// as of Flutter v3.3.7, text style background does not have consistent height
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// when rendering multi-script text, so we paint the background behind via a stack instead
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class TextBackgroundPainter extends StatelessWidget {
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final List<TextSpan> spans;
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final TextStyle style;
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final TextAlign textAlign;
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final Widget child;
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const TextBackgroundPainter({
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super.key,
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required this.spans,
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required this.style,
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required this.textAlign,
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required this.child,
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});
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@override
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Widget build(BuildContext context) {
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final backgroundColor = style.backgroundColor;
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if (backgroundColor == null || backgroundColor.alpha == 0) {
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return child;
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}
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return LayoutBuilder(
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builder: (context, constraints) {
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final paragraph = RenderParagraph(
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TextSpan(
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children: spans,
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style: style,
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),
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textAlign: textAlign,
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textDirection: Directionality.of(context),
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textScaleFactor: MediaQuery.textScaleFactorOf(context),
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)..layout(constraints, parentUsesSize: true);
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final textLength = spans.map((v) => v.text?.length ?? 0).sum;
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final allBoxes = paragraph.getBoxesForSelection(
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TextSelection(baseOffset: 0, extentOffset: textLength),
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boxHeightStyle: ui.BoxHeightStyle.max,
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);
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// merge boxes to avoid artifacts at box edges, from anti-aliasing and rounding hacks
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final lineRects = groupBy<TextBox, double>(allBoxes, (v) => v.top).entries.map((kv) {
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final top = kv.key;
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final lineBoxes = kv.value;
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return Rect.fromLTRB(
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lineBoxes.map((v) => v.left).min,
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top,
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lineBoxes.map((v) => v.right).max,
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lineBoxes.first.bottom,
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);
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});
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return Stack(
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children: [
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...lineRects.map((rect) {
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return Positioned.fromRect(
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rect: rect,
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child: ColoredBox(
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color: backgroundColor,
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),
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);
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}),
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child,
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],
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);
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},
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);
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}
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}
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