title: Draw only shadows on html5-canvas
body: <p>I'm trying to figure out how I can draw something on canvas and show only it's shadow, for example:</p>
  
  <pre><code>var c=document.getElementById("myCanvas");
  var ctx=c.getContext("2d");
  ctx.shadowBlur=100;
  ctx.shadowOffsetX = 150;
  ctx.shadowColor="red";
  ctx.fillStyle="rgba(0,0,0,0.7)";
  ctx.fillRect(20,20,100,80);
  </code></pre>
  
  <p>Here I draw a black rectangle and add a red shadow with an offset, I'd like to see only the shadow without the rectangle.</p>
  
  <p>As you can see on the example, I tried using rgba color but when I set opacity it affects the shadow as well.</p>
  
  <p>here is a fiddle for this code: <a href="http://jsfiddle.net/YYvFw/">http://jsfiddle.net/YYvFw/</a></p>