Method _computeLabelSizes

src/core/core.scale.js:819–870

* Returns {width, height, offset} objects for the first, last, widest, highest tick * labels where offset indicates the anchor point offset from the top in pixels. * @return {{ first: object, last: object, widest: object, highest: object, widths: Array, heights: array }} * @private

(ticks, length, maxTicksLimit)

	 * @private
	 */
  _computeLabelSizes(ticks, length, maxTicksLimit) {
    const {ctx, _longestTextCache: caches} = this;
    const widths = [];
    const heights = [];
    const increment = Math.floor(length / getTicksLimit(length, maxTicksLimit));
    let widestLabelSize = 0;
    let highestLabelSize = 0;
    let i, j, jlen, label, tickFont, fontString, cache, lineHeight, width, height, nestedLabel;

    for (i = 0; i < length; i += increment) {
      label = ticks[i].label;
      tickFont = this._resolveTickFontOptions(i);
      ctx.font = fontString = tickFont.string;
      cache = caches[fontString] = caches[fontString] || {data: {}, gc: []};
      lineHeight = tickFont.lineHeight;
      width = height = 0;
      // Undefined labels and arrays should not be measured
      if (!isNullOrUndef(label) && !isArray(label)) {
        width = _measureText(ctx, cache.data, cache.gc, width, label);
        height = lineHeight;
      } else if (isArray(label)) {
        // if it is an array let's measure each element
        for (j = 0, jlen = label.length; j < jlen; ++j) {
          nestedLabel = /** @type {string} */ (label[j]);
          // Undefined labels and arrays should not be measured
          if (!isNullOrUndef(nestedLabel) && !isArray(nestedLabel)) {
            width = _measureText(ctx, cache.data, cache.gc, width, nestedLabel);
            height += lineHeight;
          }
        }
      }
      widths.push(width);
      heights.push(height);
      widestLabelSize = Math.max(width, widestLabelSize);
      highestLabelSize = Math.max(height, highestLabelSize);
    }
    garbageCollect(caches, length);

    const widest = widths.indexOf(widestLabelSize);
    const highest = heights.indexOf(highestLabelSize);

    const valueAt = (idx) => ({width: widths[idx] || 0, height: heights[idx] || 0});

    return {
      first: valueAt(0),
      last: valueAt(length - 1),
      widest: valueAt(widest),
      highest: valueAt(highest),
      widths,
      heights,
    };
  }

  /**
	 * Used to get the label to display in the tooltip for the given value