[Piglit] [PATCH 1/1] Add a test for viewport clipping

[Stuart Abercrombie]

I'll update all.tests, add some comments and alter the name to be a
little clearer.

The context is this Chrome OS bug:
http://code.google.com/p/chromium-os/issues/detail?id=33526.

I don't actually know what is happening on earlier hardware.  For the
driver we run, rendering stays in the viewport, but I haven't checked
whether that is down to 3D clipping or 2D scissoring.

My understanding is that it would be wrong to do scissoring, for the
reason you mention -- other primitives that should in some cases
render outside the viewport.  The spec. seems to imply that guard-band
clipping needs to be turned off in the case where the viewport doesn't
extend to the buffer bounds.

A test for whether we don't clip/scissor when we shouldn't does seem
like a good idea.

Stuart