Util for smoothing of line joins, with quadratic beziers.

quadratic_bezier.dart

import 'dart:ui';

class QuadraticBezier {
  final Offset p0;
  final Offset p1;
  final Offset p2;

  /// Returns a list of [QuadraticBezier]s which represent smooth line joins between knots.
  ///
  /// To reduce the smoothing at the joins reduce [maxJoinSegmentLength].
  static List<QuadraticBezier> lineJoins({
    List<Offset> line,
    maxJoinSegmentLength = 10.0,
  }) {
    assert(line != null);
    assert(maxJoinSegmentLength != null);

    if (line.length < 3) return [];

    final joins = List<QuadraticBezier>();

    Offset joinSegment(Offset from, Offset to) {
      // Divide by half to ensure lhs and rhs segments do not overlap.
      var segment = (to - from) / 2;
      var segmentLength = segment.distance;
      if (segmentLength > maxJoinSegmentLength) {
        segment /= (segmentLength / maxJoinSegmentLength);
      }

      return segment;
    }

    for (var i = 1; i < line.length - 1; i++) {
      final prev = line[i - 1];
      final cur = line[i];
      final next = line[i + 1];

      var lhsSegment = joinSegment(prev, cur);
      var rhsSegment = joinSegment(cur, next);

      final p0 = cur - lhsSegment;
      final p1 = cur;
      final p2 = cur + rhsSegment;

      joins.add(QuadraticBezier(p0: p0, p1: p1, p2: p2));
    }

    return joins;
  }

  QuadraticBezier({
    this.p0,
    this.p1,
    this.p2,
  })  : assert(p0 != null),
        assert(p1 != null),
        assert(p2 != null);
}