title: What is the relationship between gl_Color and gl_FrontColor in both vertex and fragment shaders
body: <p>I have pass-through vertex and fragment shaders.</p>
  
  <p>vertex shader</p>
  
  <pre><code>void main(void)
  {
      gl_TexCoord[0] = gl_MultiTexCoord0;
      gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
  }
  </code></pre>
  
  <p>fragment shader</p>
  
  <pre><code>void main(void)
  {
      gl_FragColor = gl_Color;
  }
  </code></pre>
  
  <p>Those produce empty rendering (black not background color like glClearBuffer does).</p>
  
  <p>If I modify the vertex shader to set the gl_FrontColor to gl_Color it does render untouched OpenGl buffer ... with is the expected behavior of pass-through shaders.</p>
  
  <pre><code>void main(void)
  {
      gl_FrontColor = gl_Color; //Added line
      gl_TexCoord[0] = gl_MultiTexCoord0;
      gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
  }
  </code></pre>
  
  <p>I am confused, how settings the gl_FrontColor in the vertex shader can change the value of the gl_Color in the fragment one ? What I am missing ?</p>