title: gl_ModelViewProjectionMatrix vs gl_ModelViewMatrix
body: <p>I am beginner at GLSL. I was reading a vertex shader code and I don't understande this part of code:</p>
  
  <pre><code>out vec3 position;
  ...
  gl_Position=gl_ModelViewProjectionMatrix*gl_Vertex; 
  position=vec3(gl_ModelViewMatrix*gl_Vertex); 
  </code></pre>
  
  <p>What are the differences between gl_ModelViewProjectionMatrix and gl_ModelViewMatrix?</p>
  
  <p>What are the differences between gl_Position and position?</p>