animating_bezier_curve_helpers.dart

//get the position of the latest coordinate on the curve at any point in animation based on animation position(t)
class BezierTween extends Tween<Offset> {
  BezierTween({required this.begin, required this.end, required this.control})
      : super(begin: begin, end: end);
  @override
  final Offset begin;
  @override
  final Offset end;
  final Offset control;

  @override
  Offset lerp(double t) {
    final double t1 = 1 - t;
    return begin * t1 * t1 + control * 2 * t1 * t + end * t * t;
  }
}

// Implementation of De Casteljau's algorithm in dart
// ref -  https://pomax.github.io/bezierinfo/#splitting, https://en.wikipedia.org/wiki/De_Casteljau%27s_algorithm,

List<List<math.Point<num>>> drawCurvePoint(List<math.Point> points, double t) {
  final List<math.Point<num>> left = <math.Point>[];
  final List<math.Point<num>> right = <math.Point>[];
  if (points.length == 1) {
    left.add(points[0]);
    right.add(points[0]);

    return [left, right];
  } else {
    final List<math.Point<num>> newpoints =
        List<math.Point>.filled(points.length - 1, const math.Point(0, 0));
    for (int i = 0; i < newpoints.length; i++) {
      if (i == 0) {
        left.add(points[i]);
      }
      if (i == newpoints.length - 1) {
        right.add(points[i + 1]);
      }
      newpoints[i] = math.Point(points[i].x, points[i].y) * (1 - t) +
          math.Point(points[i + 1].x, points[i + 1].y) * t;
    }

    final List<List<math.Point<num>>> newPoints = drawCurvePoint(newpoints, t);

    left.addAll(newPoints[0]);
    right.addAll(newPoints[1]);

    return [left, right];
  }
}


// example usage

// get the current coordinate on the curve
final Offset currentPosition = BezierTween(
      begin: startingPoint,
      end: destination,
      control: controlPoint,
    ).evaluate(animationController);

    endingPoint = currentPosition;

// get the first half and second half of the arcs based on animation position(t)
final List<List<math.Point<num>>> segments = drawCurvePoint(
      [
        math.Point(startingPoint.dx, startingPoint.dy),
        math.Point(controlPoint.dx, controlPoint.dy),
        math.Point(destination.dx, destination.dy),
      ],
      animationController.value,
    );

// segment[0] is list points forming the first half of the curve, read more abt how splitting is done here->https://pomax.github.io/bezierinfo/#splitting


    startingPoint = Offset(
      segments[0][0].x.toDouble(),
      segments[0][0].y.toDouble(),
    );
    controlPoint = Offset(
      segments[0][1].x.toDouble(),
      segments[0][1].y.toDouble(),
    );
    endingPoint = Offset(
      segments[0][2].x.toDouble(),
      segments[0][2].y.toDouble(),
    );