title: GLSL time for function in shader
body: <p>I would like to know if there is a way to calculate the time (or number of operations) that a function take in glsl program?<br>
  Being quite new to glsl and the way GPU works, it's hard and take me time to optimize a glsl shader; and my multipass rendering is very laggy.
  So my goal would be to focus more on slower function.
  Does a thing could help me?</p>
  
  <p>I'm working on VS2015, and sadly, my GPU doesn't allow NSight to works.</p>