[Bug 74700] Dota2 shimmering artifacts on Mesa 10.0.1 on Iris Pro graphics

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=74700

--- Comment #6 from Jordan Justen <jljusten at gmail.com> ---
(In reply to comment #5)
> (In reply to comment #3)
> > DOTA2 is rendering to a framebuffer bound to an
> > RGB10_A2 texture when the corruption first appears
> > to happen. The undesirable rendering appears on the
> > alpha channel.
> 
> I think dithering is useless on 10-bit colors (because there are enough
> steps in the gradient already), and it's actively harmful on 2-bit
> components (because there aren't enough!).  Let's just always disable
> dithering on RGB10_A2.  There may be a couple other color formats where we
> should also disable it.

Looking in the OpenGL 3.2 Core spec, there is very
little really mentioned about dithering requirements.

The quote I mentioned before does seem to give drivers
plenty of wiggle room for how to implement dithering.
It specifically says that alpha dithering may be
disabled and says that "Dithering algorithms may be
different for different components."

Is fully disabling dithering for this format
acceptable, or do we need to just disable alpha
dithering? I would be all for just blanket disabling
dithering with RGB10_A2 if it is fine spec-wise.

Valve still might want to consider disabling it at
the app level given driver install base issues.
(Assuming that is acceptable for DOTA2 rendering.)

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