Method getCanvas

src/openlayers/core/StyleUtils.js:741–779

* 获取文字标注对应的canvas * @param style * @returns {{canvas: *, width: number, height: number}}

(style)

   * @returns {{canvas: *, width: number, height: number}}
   */
  static getCanvas(style) {
    let canvas;
    if (style.canvas) {
      if (document.querySelector("#" + style.canvas)) {
        canvas = document.getElemntById(style.canvas);
      } else {
        canvas = this.createCanvas(style);
      }
    } else {
      //不存在canvas，当前feature
      canvas = this.createCanvas(style);
      style.canvas = canvas.id;
    }
    canvas.style.display = "none";
    var ctx = canvas.getContext("2d");
    //行高
    let lineHeight = Number(style.font.replace(/[^0-9]/ig, ""));
    let textArray = style.text.split('\r\n');
    let lenght = textArray.length;
    //在改变canvas大小后再绘制。否则会被清除
    ctx.font = style.font;
    let size = this.drawRect(ctx, style, textArray, lineHeight, canvas);
    this.positionY = padding;
    if (lenght > 1) {
      textArray.forEach(function (text, i) {
        if (i !== 0) {
          this.positionY = this.positionY + lineHeight;
        }
        this.canvasTextAutoLine(text, style, ctx, lineHeight, size.width);
      }, this);
    } else {
      this.canvasTextAutoLine(textArray[0], style, ctx, lineHeight, size.width);
    }
    return {
      canvas: canvas,
      width: size.width,
      height: size.height
    };
  }
  /**
   * 创建当前feature对应的canvas
   * @param {Object} style