title: How does gl_PointSize work
body: <p>Coming from a DX background, I am trying to comprehend exactly what/how gl_PointSize and gl_PointCoord work. I've searched online and the man pages, but haven't had a really good explanation on them. Say I have a 300x300 output buffer, and I defined a vertex shader with 90,000 points, corresponding to every location in the 300x300 buffer (with increments of 1 in each dimension). Now in the vertex shader if I define a gl_PointSize of 2, does it invoke the fragment shader 90,000 times or 360,000 times?? If it's 360,000 times, I can understand what gl_PointCoord represents. But if it's only 90,000 times, does that mean each fragment output then represents 4 pixels? And in this case, what does gl_PointCoord represent? Wouldn't it always be 0.5,0.5 and not really useful??</p>
  
  <p>Thanks</p>