title: At what phase in rendering does clipping occur?
body: <p>I've got some OpenGL drawing code that I'm trying to optimize.  It's currently testing all drawing objects for visibility client-side before deciding whether or not to send rendering data to OpenGL. (This is easier than it sounds.  It's drawing a 2D scene so clipping is trivial: just test against the current coordinates of the viewport rectangle.)</p>
  
  <p>It occurs to me that the entire model could be greatly simplified by passing the entire scene to OpenGL and letting the GPU take care of the clipping.  But sometimes the total can be very, very complex, involving up to 100,000 total sprites, most of which never get rendered because they're off-camera, and I'd prefer to not end up killing the framerate in the name of simplicity.</p>
  
  <p>I'm using OpenGL 2.0, and I've got a pretty simple vertex shader and a much more complicated fragment shader.  Is there any guarantee that says that if the vertex shader runs and determines coordinates that are completely off-camera for all vertices of a polygon, that a clipping test will be applied somewhere between there and the fragment shader and prevent the fragment shader from ever running for that polygon?  And if so, is this automatic or is there something I need to do to enable it?  I've looked around online for information on this but I haven't found anything conclusive...</p>