paint_arrow.dart

void _paintArrow(
  Canvas canvas, {
  required Color color,
  required Offset offset,
  required double angle,
  double length = 12.0,
}) {
  final height = length * (sqrt(3) / 2);
  final top = Offset(0, -height / 2);
  final left = Offset(-length / 2, height / 2);
  final right = Offset(length / 2, height / 2);
  final leftFace = Offset.lerp(top, left, 0.5)!;
  final rightFace = Offset.lerp(top, right, 0.5)!;
  final bottomFace = Offset.lerp(left, right, 0.5)!;
  final path = Path()
    ..moveTo(leftFace.dx, leftFace.dy)
    ..cubicTo(top.dx, top.dy, top.dx, top.dy, rightFace.dx, rightFace.dy)
    ..cubicTo(
        right.dx, right.dy, right.dx, right.dy, bottomFace.dx, bottomFace.dy)
    ..cubicTo(left.dx, left.dy, left.dx, left.dy, leftFace.dx, leftFace.dy)
    ..close();
  canvas.save();
  canvas.translate(offset.dx, offset.dy);
  canvas.rotate(angle + pi);
  canvas.drawPath(
    path,
    Paint()
      ..color = color
      ..strokeJoin = StrokeJoin.round,
  );
  canvas.restore();
}