title: GLSL and glVertexAttribPointer
body: <p>Is it possible to know from inside a shader script if an attribute has been
  enabled with <code>glVertexAttribPointer</code> and <code>glEnableVertexAttribArray</code>?</p>
  
  <p>When I try to read the attribute without using the <code>glVertexAttribPointer</code> the program 
  at least doesn't crash and the value seems to be 0.0. Is it valid to try to read
  an attribute that isn't defined?</p>
  
  <p>The problem I'm trying to solve is that I have two objects, one with attributes and one without and I would like to know if i can/should use the same shader program for both objects (assuming the value of the attributes is 0 for the object without them).</p>