Chart.js/src/controllers/controller.line.js

import DatasetController from '../core/core.datasetController';
import {isNullOrUndef} from '../helpers';
import {isNumber} from '../helpers/helpers.math';
import {_getStartAndCountOfVisiblePoints, _scaleRangesChanged} from '../helpers/helpers.extras';

export default class LineController extends DatasetController {

  initialize() {
    this.enableOptionSharing = true;
    this.supportsDecimation = true;
    super.initialize();
  }

  update(mode) {
    const meta = this._cachedMeta;
    const {dataset: line, data: points = [], _dataset} = meta;
    // @ts-ignore
    const animationsDisabled = this.chart._animationsDisabled;
    let {start, count} = _getStartAndCountOfVisiblePoints(meta, points, animationsDisabled);

    this._drawStart = start;
    this._drawCount = count;

    if (_scaleRangesChanged(meta)) {
      start = 0;
      count = points.length;
    }

    // Update Line
    line._chart = this.chart;
    line._datasetIndex = this.index;
    line._decimated = !!_dataset._decimated;
    line.points = points;

    const options = this.resolveDatasetElementOptions(mode);
    if (!this.options.showLine) {
      options.borderWidth = 0;
    }
    options.segment = this.options.segment;
    this.updateElement(line, undefined, {
      animated: !animationsDisabled,
      options
    }, mode);

    // Update Points
    this.updateElements(points, start, count, mode);
  }

  updateElements(points, start, count, mode) {
    const reset = mode === 'reset';
    const {iScale, vScale, _stacked, _dataset} = this._cachedMeta;
    const {sharedOptions, includeOptions} = this._getSharedOptions(start, mode);
    const iAxis = iScale.axis;
    const vAxis = vScale.axis;
    const {spanGaps, segment} = this.options;
    const maxGapLength = isNumber(spanGaps) ? spanGaps : Number.POSITIVE_INFINITY;
    const directUpdate = this.chart._animationsDisabled || reset || mode === 'none';
    let prevParsed = start > 0 && this.getParsed(start - 1);

    for (let i = start; i < start + count; ++i) {
      const point = points[i];
      const parsed = this.getParsed(i);
      const properties = directUpdate ? point : {};
      const nullData = isNullOrUndef(parsed[vAxis]);
      const iPixel = properties[iAxis] = iScale.getPixelForValue(parsed[iAxis], i);
      const vPixel = properties[vAxis] = reset || nullData ? vScale.getBasePixel() : vScale.getPixelForValue(_stacked ? this.applyStack(vScale, parsed, _stacked) : parsed[vAxis], i);

      properties.skip = isNaN(iPixel) || isNaN(vPixel) || nullData;
      properties.stop = i > 0 && (Math.abs(parsed[iAxis] - prevParsed[iAxis])) > maxGapLength;
      if (segment) {
        properties.parsed = parsed;
        properties.raw = _dataset.data[i];
      }

      if (includeOptions) {
        properties.options = sharedOptions || this.resolveDataElementOptions(i, point.active ? 'active' : mode);
      }

      if (!directUpdate) {
        this.updateElement(point, i, properties, mode);
      }

      prevParsed = parsed;
    }
  }

  /**
	 * @protected
	 */
  getMaxOverflow() {
    const meta = this._cachedMeta;
    const dataset = meta.dataset;
    const border = dataset.options && dataset.options.borderWidth || 0;
    const data = meta.data || [];
    if (!data.length) {
      return border;
    }
    const firstPoint = data[0].size(this.resolveDataElementOptions(0));
    const lastPoint = data[data.length - 1].size(this.resolveDataElementOptions(data.length - 1));
    return Math.max(border, firstPoint, lastPoint) / 2;
  }

  draw() {
    const meta = this._cachedMeta;
    meta.dataset.updateControlPoints(this.chart.chartArea, meta.iScale.axis);
    super.draw();
  }
}

LineController.id = 'line';

/**
 * @type {any}
 */
LineController.defaults = {
  datasetElementType: 'line',
  dataElementType: 'point',

  showLine: true,
  spanGaps: false,
};

/**
 * @type {any}
 */
LineController.overrides = {
  scales: {
    _index_: {
      type: 'category',
    },
    _value_: {
      type: 'linear',
    },
  }
};