title: how to make a fog effect or blur effect in canvas with js?
body: <p>I'm using javascript and <code>THREE.js</code> 3d engine,</p>
  
  <p>and I want to do a fog effect,</p>
  
  <p>here's an example <a href="http://mrdoob.github.com/three.js/examples/webgl_geometry_terrain_fog.html" rel="nofollow">http://mrdoob.github.com/three.js/examples/webgl_geometry_terrain_fog.html</a></p>
  
  <p>but it only support <code>WebGL</code>,</p>
  
  <p>so is there any way to simulate <code>fog effect</code>, or a <code>blur effect</code> with javascript and canvas?</p>
  
  <p>thanks alot.</p>