title: The canvas does not work in mobile
body: <p>I built an app based on <em>Ionic Framework</em>, and I use canvas to do the image crop. It works well in browser:</p>
  
  <p><img src="https://i.stack.imgur.com/pFwb2.png" alt="enter image description here"></p>
  
  <p>But I found it does not work when running in the mobile:</p>
  
  <p><img src="https://i.stack.imgur.com/SjpdY.png" alt="enter image description here"></p>
  
  <p>Anyone knows why?</p>