title: What is the range of gl_FragCoord
body: <p>What is the range of <code>gl_FragCoord.xy</code> ? I know <code>gl_FragCoord</code>s are screen coordinates but what is the actual range? <code>( 0, width - 1 )</code> or <code>( 1, width )</code>? And what kind of error (if any) would glsl compiler generate say I did something like <code>gl_FragCoord.x - 5</code> when i do some fragcoord based calculation?</p>
  
  <p>ps: I don't need normalization.</p>