Rappid - PNG with Background Image

joint.ui.Raster plugin: PNG export with background image.

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/backbone.js/1.3.3/backbone-min.js"></script>
<script src="http://taxflowcharts.com/rappid/build/rappid.min.js"></script>
<link rel="stylesheet" href="http://taxflowcharts.com/rappid/build/rappid.min.css">
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.3/jquery.min.js"></script>
<!-- Rappid Fiddle -->
<button id="print">print</button>
<div id="paper"></div>

CSS

#paper {
  display: inline-block;
  border: 1px solid gray;
}

JavaScript

// getTransformToElement pollyfill for older version of rappid.
SVGElement.prototype.getTransformToElement = (function() {
  var polyfill = function(toElement) {
    return toElement.getScreenCTM().inverse().multiply(this.getScreenCTM());
  };
  if (typeof SVGGraphicsElement !== 'undefined') {
    return SVGGraphicsElement.prototype.getTransformToElement || SVGElement.prototype.getTransformToElement || polyfill;
  } else {
    return SVGElement.prototype.getTransformToElement || polyfill;
  }
}());

// background image
var bgDataUri =...