title: WebGL list of shader variables?
body: <p>For example:</p>
  
  <pre><code>var VertexShaderText = [
  
  'attribute vec2 vertPosition;',
  
  'void main()',
  '{',
  '  gl_Position = vec4(vertPosition, 0.0, 1.0);',
  '}'
  ].join('\n');
  </code></pre>
  
  <p>Is there a list online somewhere of all the WebGL shader variables you can code with other than gl_Position?</p>