[Bug 90836] Ksnapshot (KDE) broken when using xf86-video-intel-2.99.916 + DRI3

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90836

--- Comment #11 from Loïc Yhuel <loic.yhuel at gmail.com> ---
(In reply to Chris Wilson from comment #9)
Great, I can confirm the issue is fixed :)

(In reply to Chris Wilson from comment #8)
> (In reply to Loïc Yhuel from comment #5)
> > (In reply to Chris Wilson from comment #4)
> > > Let's narrow down the reproduction steps then. How do you have kwin
> > > configured?
> > Compositing type : OpenGL 2.0
> > Tearing Prevention : Full scene repaints
> > IIRC with this config and DRI3, kwin uses the GLX_EXT_buffer_age extension
> > (this is why I enable DRI3, else I have to choose between tear-free and
> > performance when I use two screens).
> 
> Note that there a few caveats here. GLX_EXT_buffer_age in the client without
> support in mesa means that damage is not propagated back to the display
> server so that if you are using vnc, or udl, or something else like that it
> only sees full screen repaints and is so much slower than expected.
With Wayland, there would be EGL_EXT_swap_buffers_with_damage, I guess
something like this could be useful on GLX.

> The other caveat is that DRI3 does not support single CRTC flipping like
> DRI2. That is you cannot have a single fullscreen application on one CRTC
> updating independently with the second screen (e.g. having a game/video on
> the primary monitor whilst reading email on the second). In this case DRI3
> forces both screens to flip (and the compositor to repaint as required to
> correct damage), whereas ideally we would only update the single active CRTC
> and not touch the idle CRTC/buffer at all.
I don't think kwin supports flipping a single CRTC, else I wouldn't see any
performance difference in animations on the primary monitor when I plug the
second one.

Anyway, I need to set kwin to "full scene repaints" to avoid tearing, with DRI3
it does in fact partial repaints using GLX_EXT_buffer_age, which is faster than
real full screen repaints with DRI2.

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