canvas转成base64 后生成的图片问题 会有叠影重叠的现象。

SVG格式的图片：
base64放入img src中：
代码：

export

$(".exportImageButton").on("click", function() {
var svg = document.querySelector("svg");
var rect = document.querySelector("rect")
rect.setAttribute("fill", "green")
var svgData = new XMLSerializer().serializeToString(svg);
var canvas = document.createElement("canvas");
var svgSize = svg.getBoundingClientRect();
canvas.width = svgSize.width * 3;
canvas.height = svgSize.height * 3;
canvas.style.width = svgSize.width;
canvas.style.height = svgSize.height;
var ctx = canvas.getContext("2d");
ctx.scale(3, 3);
var img = document.createElement("img");
img.setAttribute("src", "data:image/svg+xml;base64," + btoa(unescape(encodeURIComponent(svgData))));
rect.setAttribute("fill", "red")
img.onload = function() {
ctx.drawImage(img, 0, 0);
var canvasdata = canvas.toDataURL("image/png", 1);

var pngimg = '<img src="' + canvasdata + '">';
d3.select("#pngdataurl").html(pngimg);

var a = document.createElement("a");
a.download = "download_img" + ".png";
a.href = canvasdata;
document.body.appendChild(a);
a.click();

};
})

转图片。

var Svg = chart.getSVG();是highchart获取svg的方法。

Canvas在每次重新绘制前要先进行清除。