void _drawHArrow(Canvas canvas, Size size, Offset from, Offset to, [bool doubleSided = false]) {
    Path path;

    // The arrows usually looks better with rounded caps.
    Paint paint = ... // задается стиль

    var length = sqrt((to.dx - from.dx) * (to.dx - from.dx) +
        (to.dy - from.dy) * (to.dy - from.dy));

    path = Path();
    path.moveTo(from.dx, from.dy);
    path.relativeCubicTo(
        0,
        0,
        -(from.dx + to.dx + length) / (length) - 40,
        -(from.dy + to.dy + length) / (length) - 40,
        to.dx - from.dx,
        to.dy - from.dy);
    path =
        ArrowPath.make(path: path, isDoubleSided: doubleSided, tipLength: 16);
    canvas.drawPath(path, paint);
 }