修改svg后，使用javascript将svg转换为png

Question

我有一个SVG，我正在使用下面的JavaScript代码转换为PNG

$(".exportImageButton").on("click",function(){
  var svg = document.querySelector( "svg" );
  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))) );

  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();
  };

但是我想在将svg元素转换为png之前对其进行更改。另外，我也不想在屏幕上向用户显示变化。

我只想向x轴标签添加不透明度1并转换为png，并让屏幕上的svg保持不变，而x轴标签的不透明度为0。

我怎样才能做到这一点 。任何帮助表示赞赏。

Answer 1

正如罗伯特建议的那样，就做吧...

$(".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();
  };
})

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<button class="exportImageButton">export</button>
<svg>
  <rect width="200" height="200" fill="red" />
</svg>
<canvas width="200px" height="200px" />