Work around SVG drawing issues when capturing screenshot using html2canvas

svg_html2canvas.js

	// Work around an annoying issue in Chrome where SVG images aren't drawn with respect to globalAlpha
	window.CanvasRenderingContext2D.prototype.drawSvgImage = function(image, x, y, w, h) { 
		var canvas = document.createElement('canvas');
		canvas.width = w;
		canvas.height = h;
		var context = canvas.getContext('2d');
		context.drawImage(image, 0, 0, w, h);

		this.drawImage(canvas, x, y, w, h);
	}

	// Returns a screenshot using the awesome html2canvas library. Works around SVG issues.
	function getScreenshot (callback) {
		html2canvas(document.body, {
			onrendered: (function (callbackClosure) {
				return function(renderedCanvas) {
					var renderedCanvasContext = renderedCanvas.getContext('2d');
					renderedCanvasContext.save();
	
					$("object").filter(':visible').each(function(){
						var clientRect = this.getBoundingClientRect();

						var svgSource = $("svg", $(this).documents()[0])[0].outerHTML;
						var svgImage = new Image();
						svgImage.src = "data:image/svg+xml;base64," + window.btoa(svgSource);
	
						renderedCanvasContext.globalAlpha = parseFloat($(this).css("opacity"));
						renderedCanvasContext.drawSvgImage(svgImage, clientRect["left"], clientRect["top"], clientRect["width"], clientRect["height"]);
					});
	
					renderedCanvasContext.restore();
					callbackClosure(renderedCanvas);
				}})(callback)
		});
	}