Function _updateBezierControlPoints

src/helpers/helpers.curve.ts:186–223

(
  points: SplinePoint[],
  options,
  area: ChartArea,
  loop: boolean,
  indexAxis: 'x' | 'y'
)

 * @private
 */
export function _updateBezierControlPoints(
  points: SplinePoint[],
  options,
  area: ChartArea,
  loop: boolean,
  indexAxis: 'x' | 'y'
) {
  let i: number, ilen: number, point: SplinePoint, controlPoints: ReturnType<typeof splineCurve>;

  // Only consider points that are drawn in case the spanGaps option is used
  if (options.spanGaps) {
    points = points.filter((pt) => !pt.skip);
  }

  if (options.cubicInterpolationMode === 'monotone') {
    splineCurveMonotone(points, indexAxis);
  } else {
    let prev = loop ? points[points.length - 1] : points[0];
    for (i = 0, ilen = points.length; i < ilen; ++i) {
      point = points[i];
      controlPoints = splineCurve(
        prev,
        point,
        points[Math.min(i + 1, ilen - (loop ? 0 : 1)) % ilen],
        options.tension
      );
      point.cp1x = controlPoints.previous.x;
      point.cp1y = controlPoints.previous.y;
      point.cp2x = controlPoints.next.x;
      point.cp2y = controlPoints.next.y;
      prev = point;
    }
  }

  if (options.capBezierPoints) {
    capBezierPoints(points, area);
  }
}