How to align text in an arc using Flutter?

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To align text in an arc using Flutter, you can use the CustomPaint widget along with the Canvas and Paint classes. Here are the steps:

1. Create a custom widget ArcText that extends CustomPaint.

2. In the ArcText widget, define a TextSpan object with the text that you want to align in an arc.

3. In the paint() method of the ArcText widget, use the Canvas class to draw an arc and align the text on it.

4. To align the text on the arc, calculate the angle for each character and use it to position the text.

Here is an example code for the ArcText widget:

class ArcText extends CustomPaint {
  final String text;
  final double radius;
  final double startAngle;
  final double endAngle;
  final TextStyle textStyle;

  ArcText({
    required this.text,
    required this.radius,
    required this.startAngle,
    required this.endAngle,
    required this.textStyle,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint()..style = PaintingStyle.stroke;
    paint.color = Colors.black;
    paint.strokeWidth = 1;

    final center = Offset(size.width / 2, size.height / 2);

    final span = TextSpan(text: text, style: textStyle);
    final textPainter = TextPainter(text: span, textAlign: TextAlign.center, textDirection: TextDirection.ltr);
    textPainter.layout();

    final path = Path();
    path.arcToPoint(Offset(0, radius), radius: Radius.circular(radius), clockwise: false);

    final anglePerChar = (endAngle - startAngle) / text.length;

    for (int i = 0; i < text.length; i++) {
      final char = text.substring(i, i + 1);
      final metrics = textPainter.getGlyphMetrics(0);
      final angle = startAngle + anglePerChar * i;
      final x = center.dx + (radius - metrics.width / 2) * cos(angle);
      final y = center.dy + (radius - metrics.width / 2) * sin(angle);

      canvas.save();
      canvas.translate(x, y);
      canvas.rotate(angle + pi / 2);

      textPainter.text = TextSpan(text: char, style: textStyle);
      textPainter.layout();
      textPainter.paint(canvas, Offset(0, 0));

      canvas.restore();
    }

    canvas.drawPath(path, paint);
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => true;
}

To use the ArcText widget, you can call it like this:

ArcText(
  text: 'Hello, world!',
  radius: 150,
  startAngle: pi / 2,
  endAngle: pi * 1.5,
  textStyle: TextStyle(fontSize: 20),
),

This will draw the text "Hello, world!" on an arc with a radius of 150, starting at angle pi/2 and ending at angle pi*1.5 (i.e., a semicircle). The text will be aligned on the arc with a font size of 20.