title: GLSL, literal constant Input Layout Qualifiers
body: <p>I wonder if I may have something like this:</p>
  
  <pre><code>layout (location = attr.POSITION) in vec3 position;
  </code></pre>
  
  <p>Where for example <code>Attr</code> is a constant structure</p>
  
  <pre><code>const struct Attr
  {
      int POSITION;
  } attr = Attr(0);
  </code></pre>
  
  <p>I already tried, but it complains </p>
  
  <blockquote>
    <p>Shader status invalid: 0(34) : error C0000: syntax error, unexpected
    integer constant, expecting identifier or template identifier or type
    identifier at token ""</p>
  </blockquote>
  
  <p>Or if there is no way with structs, may I use something else to declare a literal input qualifier such as <code>attr.POSITION</code>?</p>