title: clear pixels under a shape in HTML canvas
body: <p>I am using an HTML canvas and javascript and I need to clear all of the pixels underneath a shape created by closing a path (for example, I am using <a href="http://code.google.com/p/flot/" rel="nofollow noreferrer">flot</a>, and I want to make rounded corners, and to do this, I first need to remove the square corners by drawing a curve on top of the corner to remove the desired pixels).</p>
  
  <p>Right now, I am doing this by just filling the shape with the same color as the background, which can imitate what I want to do, but, it is not ideal as it makes it impossible to place the chart on top of non-solid backgrounds without seeing the square corners.  I know that there is a clearRect method that would do what I want to do, but with only rectangles, I need to do it with any closed shape.  Is it possible, and if so, how would I do it?</p>