JavaScript HTML5 QR

/* Lizenz
//---------------------------------------------------------------------
// JavaScript-HTML5 QRCode Generator
//
// Copyright (c) 2011 Amanuel Tewolde
//
// Licensed under the MIT license:
// http://www.opensource.org/licenses/mit-license.php
//
//---------------------------------------------------------------------
*/

/* Kurzbeschreibung
// Generates a QRCode of text provided.
// First QRCode is rendered to a canvas.
// The canvas is then turned to an image PNG
// before being returned as an <img> tag.
*/

function showQRCode(text) {

  var dotsize = 3; // size of box drawn on canvas
  var padding = 10; // (white area around your QRCode)
  var black = "rgb(0, 0,0)";
  var white = "rgb(255,255,255)";
  var QRCodeVersion = 4;
  // 1-40 Es gibt verschiedene Versionen an QR-Codes die unterschiedlich viel an Daten aufnehmen können;
  // eine Übersicht ist hier zu sehen: http://goo.gl/S6RHA

  /* Begründung Version 4
  // das Level 4 ist mindestends notwendig um folgendes darzustellen:
  // pcn: P07062
  // inv: 200700610
  // snr: 648061
  // mac:
  */

    var canvas=document.createElement('canvas');

    var qrCanvasContext = canvas.getContext('2d');
  try {
    /* Errorlevel-Beschreibung
    // QR Code Error Correction Capability
    // Higher levels improves error correction capability while decreasing the amount of data QR Code size.
    // QRErrorCorrectLevel.L (5%) QRErrorCorrectLevel.M (15%) QRErrorCorrectLevel.Q (25%) QRErrorCorrectLevel.H (30%)
    // eg. L can survive approx 5% damage...etc.
    */
    var qr = new QRCode(QRCodeVersion, QRErrorCorrectLevel.M);
    qr.addData(text);
    qr.make();
   }

  // Errors abfangen
  catch(err) {
  var errorChild = document.createElement("p");
  var errorMSG = document.createTextNode("Erstellung fehlgeschlagen. " + err);
    errorChild.appendChild(errorMSG);
    return errorChild;
  }

  var qrsize = qr.getModuleCount();
  canvas.setAttribute('height',(qrsize * dotsize) + padding);
  canvas.setAttribute('width',(qrsize * dotsize) + padding);
  var shiftForPadding = padding / 2;
  if (canvas.getContext){
    for (var r = 0; r < qrsize; r++) {
      for (var c = 0; c < qrsize; c++) {
      if (qr.isDark(r, c))
      qrCanvasContext.fillStyle = black;
      else
      qrCanvasContext.fillStyle = white;
      qrCanvasContext.fillRect ((c*dotsize) + shiftForPadding, (r*dotsize) + shiftForPadding, dotsize, dotsize); // x, y, w, h
      }
    }
  }

  var imgElement = document.createElement("img");
  imgElement.src = canvas.toDataURL("image/png");

  return imgElement;
}