title: Get data back from OpenGL shader?
body: <p>My computer doesn't support OpenCL on the GPU or OpenGL compute shaders so I was wondering if it would be a straight forward process to get data from a vertex or fragment shader?</p>
  
  <p>My goal is to pass 2 textures to the shader and have the shader computer the locations where one texture exists in the other. Where there is a pixel match. I need to retrieve the locations of possible matches from the shader.</p>
  
  <p>Is this plausible? If so, how would I go about it? I have the basic OpenGL knowledge, I have set up a program that draws polygons with colors. I really just need a way to get position values back from the shader.</p>