title: Transparency context.fill style in canvas html5
body: <p>I write this javascript code :</p>
  
  <pre><code>context.shadowOffsetX = 5;
  context.shadowOffsetY = 5;
  context.shadowBlur = 4;
  context.shadowColor = 'rgba(255, 0, 0, 0.5)';
  context.fillStyle = '#f00';
  context.fillRect(x, y, w, h);
  </code></pre>
  
  <p>I add this script on a photo , I want see the color of image , but can not add transparency to this script .</p>