title: How do you mask an arbitrary area of an image to overlay another image?
body: <p>I want to mask an arbitrary convex polygon area of an image and put another image into that area.  I found <a href="https://stackoverflow.com/questions/3632982/mask-image-via-another-image">this posting</a>, but is wasn't clear to me if this applies only to rectangular areas and not arbitrary polygons.</p>
  
  <p>The basic flow I am talking about is to have an (x,y) coordinate on the screen which would serve to be the center of my polygon (center in terms of an arbitrary point which is consistent for me).  I would like to mask this area where the new image (polygonal in nature) would be displayed while leaving the rest of the screen as is.</p>
  
  <p>Can I do this easily and quickly?  </p>