ol/webgl/LabelsArray.js

OpenLayers mapping library

/**
 * @module ol/webgl/LabelsArray
 */

const textEncoder = new TextEncoder();

// the underlying typed array will be resized in increments of this amount of bytes
const chunkSize = 100_000;

/**
 * @classdesc
 * This class stores text values using typed arrays internally.
 * Labels are stored as separate UTF-8 characters in a single Uint8Array.
 * The Uint8Array is resized when the capacity exceeds to avoid costly concatenation.
 */
class LabelsArray {
  constructor() {
    /**
     * @private
     */
    this.array_ = new Uint8Array(chunkSize);

    this.actualSize_ = 0;

    /**
     * @type {Map<string, Array<number>>}
     * @private
     */
    this.labelPositionMap_ = new Map();
  }

  /**
   * @param {string} label Label to append to the end of the array
   * @return {Array<number>} An array containing 1/ the position of the label in the typed array and 2/ the size of the label in the array
   */
  push(label) {
    if (label === '') {
      return [0, 0];
    }
    if (this.labelPositionMap_.has(label)) {
      return /** @type {Array<number>} */ (this.labelPositionMap_.get(label));
    }
    const encoded = textEncoder.encode(label);
    if (this.actualSize_ + encoded.length > this.array_.length) {
      const newArray = new Uint8Array(this.array_.length + chunkSize);
      newArray.set(this.array_);
      this.array_ = newArray;
    }
    const position = this.actualSize_;
    this.array_.set(encoded, position);
    this.actualSize_ += encoded.length;
    const result = [position, encoded.length];
    this.labelPositionMap_.set(label, result);
    return result;
  }

  /**
   * @return {Uint8Array} Typed array containing the encoded labels.
   */
  getArray() {
    return this.array_;
  }
}

export default LabelsArray;