Add module for png generation with librsvg

Thanks to @physikerwelt and @wikimedia!

Author: pkra

lib/mj-librsvg.js

@@ -0,0 +1,26 @@
+var rsvg = require('librsvg').Rsvg;
+var Readable = require('stream').Readable;
+
+exports.svg2png = function(svg, result, scale, width, height, callback, check) {
+  var s = new Readable();
+  var svgRenderer = new rsvg();
+  s._read = function() {
+    s.push(svg);
+    s.push(null);
+  };
+  svgRenderer.on('error', function(err){
+    check(err);
+    return;
+  });
+  svgRenderer.on('finish', function() {
+    // console.log(width, height, scale, svg);
+    var buffer = svgRenderer.render({
+      format: 'png',
+      width: width * scale,
+      height: height * scale
+    }).data;
+    result.png = "data:image/png;base64," + (buffer || "").toString('base64');
+    callback();
+  });
+  s.pipe(svgRenderer);
+};