vue 使用openlayers导出渲染的地图

下载地图官方示例： 

http://openlayers.org/en/latest/examples/export-map.html 

http://openlayers.org/en/latest/examples/export-pdf.html

我这儿使用到了  file-saver （下载图片、附件）

npm install file-saver --save

import { saveAs } from 'file-saver'; 

// 执行下载
    download() {
      this.chartMap.once("rendercomplete", () => {
        const mapCanvas = document.createElement("canvas");
        const size = this.chartMap.getSize();
        console.log(size);
        mapCanvas.width = size[0];
        mapCanvas.height = size[1];
        const mapContext = mapCanvas.getContext("2d");
        Array.prototype.forEach.call(
          this.chartMap
            .getViewport()
            .querySelectorAll(".ol-layer canvas, canvas.ol-layer"),
          function (canvas) {
            if (canvas.width > 0) {
              const opacity =
                canvas.parentNode.style.opacity || canvas.style.opacity;
              mapContext.globalAlpha = opacity === "" ? 1 : Number(opacity);
              let matrix;
              const transform = canvas.style.transform;
              if (transform) {
                matrix = transform
                  .match(/^matrix\(([^\(]*)\)$/)[1]
                  .split(",")
                  .map(Number);
              } else {
                matrix = [
                  parseFloat(canvas.style.width) / canvas.width,
                  0,
                  0,
                  parseFloat(canvas.style.height) / canvas.height,
                  0,
                  0,
                ];
              }
              CanvasRenderingContext2D.prototype.setTransform.apply(
                mapContext,
                matrix
              );
              const backgroundColor = "#192A3D";
              if (backgroundColor) {
                mapContext.fillStyle = backgroundColor;
                mapContext.fillRect(0, 0, canvas.width, canvas.height);
              }
              mapContext.drawImage(canvas, 0, 0);
            }
          }
        );
        mapContext.globalAlpha = 1;
        mapContext.setTransform(1, 0, 0, 1, 0, 0);
        let href = mapCanvas.toDataURL();
        saveAs(href, "万家寨水轮机.png");
      });
      this.chartMap.renderSync();
    },