title: GLSL How to retrieve vertex position after a shader process it?
body: <p>I wrote a program that simulates soft bodies using springs. It looks nice but the problem is it consumes a lot of CPU time. So I can not run it on my laptop or any not high end PC.</p>
  
  <p>I thought It would be a good idea to write a vertex shader and move the logic to the GPU. I've read some tutorials and made a toon shader so I thought (wrong) I was ready to go.</p>
  
  <p>The big problem I have is that I need to know the old position of a vertex to calculate the new one. I don't know how could I retrieve a vertex position so I could send it back to the shaders each frame?</p>
  
  <p>I'm not really sure is this even possible to do and maybe I'm trying to do something that shaders are never meant to do. I am still researching but I thought I could ask an see if maybe someone can help.</p>