title: Android WebView HTML5 canvas error
body: <p>I have an Android application which uses WebView to load the GUI using HTML. There is a &lt;canvas&gt; element into which i draw charts using Chart.js Javascript library for plotting charts. 
  It was tested on 3 devices. On two of them it works fine (Android 2.2 and 2.6), but on a later vesion of android (4.1.2) the canvas makes it double: all the charts are visible twice in the canvas, one of them is shifted a bit up and to the left.</p>
  
  <p><img src="https://i.stack.imgur.com/2VJu4.png" alt="canvas with double chart"></p>
  
  <p>What is the problem with the canvas? Why does it double the things rendered? How can i made it render only once?</p>
  
  <p>Here's the code:</p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;canvas id="graph_canvas"&gt;&lt;/canvas&gt;
  </code></pre>
  
  <p>JavaScript:</p>
  
  <pre><code>var canvas=document.getElementById("graph_canvas");
  canvas.height=200;
  canvas.width=200;
  var graphSelection=document.getElementById("graphSelection");
  var ctx = canvas.getContext("2d");
  var data_=JSON.parse(JI.getGraphData(graphSelection.value));    
  var myNewChart = new Chart(ctx).Line(data_);
  </code></pre>
  
  <p>Where graphSelection is a &lt;select&gt; element with which we select the chart,
  JI.getGraphData returns JSON data for Chart.js.</p>