title: Enabling OpenGL extensions
body: <p>I'm trying to perform some integer operations (division and modulo) in my GLSL shader, but they don't seem to work and I read that I need to enable <code>EXT_GPU_shader4</code> in order to get integer operations.  What I can't find, however, is how to do that.  Is the line:</p>
  
  <pre><code>#version 330 core
  #extension GL_EXT_GPU_SHADER4 : require
  </code></pre>
  
  <p>enough?  Or do I need to enable it using the C API somehow too?  Currently I get an error during compilation that the extension is not supported.  I'm on a GeForce 670; a pretty recent card.</p>