[Impeller] Nothing drawn for zero length lines. #109077
Description
Zero length lines are supposed to draw their end cap decoration axis aligned at their singular point, but Impeller draws nothing. The following test case will demonstrate the problem if run with --enable-impeller
This issue impacts the implementation of drawPoints as well where the PointMode.points mode draws a zero length line at each point in the array. The current implementation uses a workaround of adding kEhCloseEnough to the second point's X location in order to get the points to render (see flutter/engine#35204)
Test case
import 'package:flutter/material.dart';
void main() {
runApp(const MyApp());
}
class MyApp extends StatelessWidget {
const MyApp({super.key});
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: const MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
const MyHomePage({super.key, required this.title});
final String title;
@override
State<MyHomePage> createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text('butt cap'),
SizedBox(
width: 50,
height: 50,
child: CustomPaint(
painter: ZeroLengthLinePainter(StrokeCap.butt),
),
),
],
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text('square cap'),
SizedBox(
width: 50,
height: 50,
child: CustomPaint(
painter: ZeroLengthLinePainter(StrokeCap.square),
),
),
],
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
const Text('round cap'),
SizedBox(
width: 50,
height: 50,
child: CustomPaint(
painter: ZeroLengthLinePainter(StrokeCap.round),
),
),
],
),
],
),
),
);
}
}
class ZeroLengthLinePainter extends CustomPainter {
ZeroLengthLinePainter(this.cap);
final StrokeCap cap;
@override
void paint(Canvas canvas, Size size) {
Paint paint = Paint()
..strokeWidth = 10
..strokeCap = cap;
canvas.drawLine(size.center(Offset.zero), size.center(Offset.zero), paint);
}
@override
bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}