[Bug 71195] Antialiasing glitches visible under wine (e.g. HD4000)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=71195

--- Comment #9 from Paul Berry <stereotype441 at gmail.com> ---
(In reply to comment #8)
> (In reply to comment #7)
> > This appears to be the same root cause as bug 53077, which was discovered
> > and diagnosed back in 2012 but never fixed.
> > 
> > I've got some experimental code which fixes the problem, but it still needs
> > polishing.  I hope to have a fix out to the mailing list by the end of the
> > day.
> > 
> > *** This bug has been marked as a duplicate of bug 53077 ***
> 
> Wow, I'm impressed by the rapid response. I wonder whether the involvement
> with the framebuffer ties in my finding that, under wine, using the registry
> fix:
> 
>       |  +->OffscreenRenderingMode
>       |  |   [Select the offscreen rendering implementation.
>       |  |        backbuffer - Render offscreen render targets in the
> backbuffer
>       |  |        fbo - Use framebuffer objects for offscreen rendering
> (default)
> 
> to thereby select 'backbuffer', as opposed to framebuffer, resulted in the
> problem going away. Unfortuntately however under Wine this resulted in two
> overlayed images wherein one of the two is rendered upside down(!). This may
> be completely irrelevant. 

I can think of two possible reasons why this might be the case:

(a) It's possible that you don't have a multisampled backbuffer, in which case
the problem is going away because you're not getting multisampling anymore (or,
at least, you're not getting multisampling for the rendering operations that
provoke the bug).

(b) It's possible that by coincidence, the upside down image has far fewer
artifacts than the right-side up image (I recall when I investigated bug 53077
that the bug was highly sensitive to the orientation of the triangles being
drawn). 

In any case, you're right that it's probably irrelevant.  What matters is that
we have an apitrace that reproduces the problem, and a good idea of what's
going wrong under the hood.

> 
> I wonder whether Intel have commented on the matter?

Actually I'm one of the Intel driver developers :).  Back when 53077 was first
discovered, I tried to get in touch with one of the hardware architects to see
if I could get more information about the bug, but I didn't succeed.  I'm going
to talk to some of the other driver devs today, and depending on what we
decide, I may try to ping the hardware architects again.

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