[Piglit] New test for partial blits after a buffer swap

[Federico Mena Quintero]

On Tue, 2013-10-29 at 13:52 -0700, Eric Anholt wrote:

Awesome, thanks for the quick reply :)

> Ouch.  Doing anything to GL_FRONT is really punitive to performance in
> DRI2.  Any chance we could convince clutter to use
> GLX_MESA_copy_sub_buffer/EGL_NV_post_sub_buffer instead?  Then you
> wouldn't get that fullscreen copy.

Clutter/cogl will already use copy_sub_buffer if it is available, but
it's not with drisw.

> Of course, the thing clutter really needs is buffer_age.  We need to
> write tests so we can actually merge some code for it.

How would this work?  I've seen a couple of comments in clutter/cogl
about buffer_age, but I can't really visualize it.

> Sounds like we have a problem here of not updating our frake front with
> the current real front contents.  I forget what the state of things was,
> but at one point I recall issues with vsynced swaps versus copies from
> front to fake front.

Hmmmm, where should this copy be done (from the fake front to the real
front)?  I think the real front gets created just as a result of
validate_state() (or however it is called), but I'm not sure if that's
the right place to do it.

  Federico