title: how can get 3D obj file from canvas in webgl?
body: <p>Some question asked about how can use <code>obj</code> in <code>webgl</code>. 
  But my question is how can get/save/export <code>obj</code> or <code>ply</code> file from content of canvas in <code>webgl</code>?! 
  For example how can I get two objects in <code>obj</code> format in following link?
  <a href="http://learningwebgl.com/lessons/lesson04/index.html" rel="noreferrer">http://learningwebgl.com/lessons/lesson04/index.html</a></p>
  
  <p>Of course all of my <code>webgl</code> target not is simple such as upper link, and and converting <code>gl</code> code from <code>webgl</code> to <code>opengl</code> is so hard and time consuming.</p>
  
  <p>Then I have to get result object from <code>webgl</code>; but how?</p>