Function _getStartAndCountOfVisiblePoints

src/helpers/helpers.extras.ts:88–136

(meta: ChartMeta<'line' | 'scatter'>, points: PointElement[], animationsDisabled: boolean)

 * @private
 */
export function _getStartAndCountOfVisiblePoints(meta: ChartMeta<'line' | 'scatter'>, points: PointElement[], animationsDisabled: boolean) {
  const pointCount = points.length;

  let start = 0;
  let count = pointCount;

  if (meta._sorted) {
    const {iScale, vScale, _parsed} = meta;
    const spanGaps = meta.dataset ? meta.dataset.options ? meta.dataset.options.spanGaps : null : null;
    const axis = iScale.axis;
    const {min, max, minDefined, maxDefined} = iScale.getUserBounds();

    if (minDefined) {
      start = Math.min(
        // @ts-expect-error Need to type _parsed
        _lookupByKey(_parsed, axis, min).lo,
        // @ts-expect-error Need to fix types on _lookupByKey
        animationsDisabled ? pointCount : _lookupByKey(points, axis, iScale.getPixelForValue(min)).lo);
      if (spanGaps) {
        const distanceToDefinedLo = (_parsed
          .slice(0, start + 1)
          .reverse()
          .findIndex(
            point => !isNullOrUndef(point[vScale.axis])));
        start -= Math.max(0, distanceToDefinedLo);
      }
      start = _limitValue(start, 0, pointCount - 1);
    }
    if (maxDefined) {
      let end = Math.max(
        // @ts-expect-error Need to type _parsed
        _lookupByKey(_parsed, iScale.axis, max, true).hi + 1,
        // @ts-expect-error Need to fix types on _lookupByKey
        animationsDisabled ? 0 : _lookupByKey(points, axis, iScale.getPixelForValue(max), true).hi + 1);
      if (spanGaps) {
        const distanceToDefinedHi = (_parsed
          .slice(end - 1)
          .findIndex(
            point => !isNullOrUndef(point[vScale.axis])));
        end += Math.max(0, distanceToDefinedHi);
      }
      count = _limitValue(end, start, pointCount) - start;
    } else {
      count = pointCount - start;
    }
  }

  return {start, count};
}

/**
 * Checks if the scale ranges have changed.