Method getPositionX

src/openlayers/core/StyleUtils.js:902–917

* 得到绘制的起点位置，根据align不同，位置也不同 * @param textAlign * @returns {number}

(textAlign, canvasWidth)

   * @returns {number}
   */
  static getPositionX(textAlign, canvasWidth) {
    let x;
    let width = canvasWidth - doublePadding; //减去padding
    switch (textAlign) {
      case 'center':
        x = width / 2;
        break;
      case 'right':
        x = width;
        break;
      default:
        x = 8;
        break;
    }
    return x;
  }

  /**
   * @function StyleUtils.hexToRgb