title: OpenGL: blur only one part of the texture; can using vertex shader speed up?
body: <p>Let's say there is one texture: 6000x6000</p>
  
  <p>I only need to blur one part, let's say the center rectangle 100x100</p>
  
  <p>If I use vertex shader to put the interested area to this center rectangle, by inputting the coordinates of the 4 points and their corresponding texture coordinates in the big texture, I think the fragment shader only process the pixels in the center rectangle. </p>
  
  <p>In my understanding, a regular GPU cannot really handle 6000x6000 pixels concurrently; it will divide to several segments. 
  Now with 100x100, all pixels can be processed simultaneously, so it would be faster.</p>
  
  <p>Is my understanding correct?</p>