[Mesa-dev] [PATCH] mesa: add GL_UNSIGNED_INT_24_8 to _mesa_pack_depth_span

Kenneth Graunke kenneth at whitecape.org
Fri Oct 2 21:06:01 PDT 2015

On Friday, October 02, 2015 05:04:21 PM Ilia Mirkin wrote:
> On Fri, Oct 2, 2015 at 4:47 PM, Ian Romanick <idr at freedesktop.org> wrote:
> > On 10/01/2015 12:15 PM, Ilia Mirkin wrote:
> >> On Thu, Oct 1, 2015 at 3:12 PM, Ian Romanick <idr at freedesktop.org> wrote:
> >>> I'm just
> >>> wondering because Mesa doesn't support that extension.  How is this even
> >>> being hit?
> >>
> >> See 81d2fd91a90 (mesa: add NV_read_{depth,stencil,depth_stencil} extensions)
> >
> > Okay, that's weird.  I must have had some old branch checked out at the
> > time.  I did 'grep -r NV_read_depth src/', and it came back empty.  Now
> > I just get to be irritated that we enabled THREE extensions for which we
> > have ZERO tests... and least one is clearly completely broken. :(
> >
> > I guess now I at least have something concrete to point to then next
> > time I object to enabling an ES extension that "just" allows some
> > desktop functionality. ;)
> I believe Rob tested at least some of it with qapitrace[1], as
> otherwise there was no way to get access to the data in a
> renderbuffer, which can be quite useful for debugging. Not all of us
> have your level of familiarity with how GL works, but how will we
> learn without making some mistakes? :)
> No matter how many tests we might have, they'll always leave
> *something* out. The fact that there are no tests at all for this ext
> isn't great, of course. But there are also no functional tests for
> {ARB,AMD}_conservative_depth and probably a number of others.
>   -ilia

I think we can all agree that enabling a feature with 0 tests is bad
practice.  Just because people have done it before doesn't make it wise.
Or in a positive spin: our commitment to Piglit is one of the reasons
we have such high quality drivers.  It's worth it, even if it can be a
bunch of unglamorous and annoying work.

I'm OK with not adding comprehensive tests for ES extensions that port
over GL functionality, but at least touch testing the feature is

Also...GL_ARB_conservative_depth is a bit different.  It provides a hint
which the driver can use to speed up some operations - but there's no
new feature, or observable behavior.  Drivers can completely ignore it
and still have a valid, correct implementation of the extension.  So
it's a bit tricky to test (but we could at least look for breakage...)

In contrast, GL_NV_read_depth_stencil turns a GL call that used to be an
error into a functioning read of depth data, which seems straightforward
to test.

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