title: How do I modify a GPUImageGaussianSelectiveBlurFilter to operate over a rectangle instead of a circle?
body: <p>I have used the GPUImage framework for a blur effect similar to that of the Instagram application, where I have made a view for getting a picture from the photo library and then I put an effect on it. </p>
  
  <p>One of the effects is a selective blur effect in which only a small part of the image is clear the rest is blurred. The GPUImageGaussianSelectiveBlurFilter chooses the circular part of the image to not be blurred. </p>
  
  <p>How can I alter this to make the sharp region be rectangular in shape instead?</p>