title: opengl and mtl parameters
body: <p>I am trying to parse line items from "mtl" file and use the values as parameters to opengl functions.</p>
  
  <p>I could use values of ambience (Ka), specular(Ks) and diffuse(Kd) using glMaterialfv. But I don't know the use for Ni (optical density), d (dissolve), illum (illumination) values given in the mtl file.</p>
  
  <p>Which opengl function should be used with these values?</p>
  
  <p>Any help with these line items?</p>
  
  <pre><code>....
  Ni 1.000000
  d 1.000000
  illum 2
  ...
  </code></pre>