title: Fragment shaders: output variables
body: <p>Reading the GLSL 1.40 specification:</p>
  
  <blockquote>
    <p>Fragment outputs can only be float,
    floating-point vectors, signed or
    unsigned integers or integer vectors,
    or arrays of any these. Matrices and
    structures cannot be output. Fragment
    outputs are declared as in the
    following examples:</p>
    
    <p>out vec4 FragmentColor;
    out uint Luminosity;</p>
  </blockquote>
  
  <p>The fragment color is defined writing gl_FragColor... is it right? Somebody could clear my ideas about these outputs? May I write only 'FragmentColor' of the example to determine fragment color? May I read back them ('Luminosity' for example)?</p>