[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 #8 from Chris Wilson <chris at chris-wilson.co.uk> ---
(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.

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.

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