Method createCanvas

src/openlayers/core/StyleUtils.js:785–792

* 创建当前feature对应的canvas * @param {Object} style * @returns {HTMLElement}

(style)

   * @returns {HTMLElement}
   */
  static createCanvas(style) {
    let div = document.createElement('div');
    document.body.appendChild(div);
    let canvas = document.createElement('canvas');
    canvas.id = style.canvas ? style.canvas : 'textCanvas' + Util.newGuid(8);
    div.appendChild(canvas);
    return canvas;
  }
  /**
   * 绘制矩形边框背景
   * @param ctx