Am 17.06.24 um 19:18 schrieb Pierre Ossman:
On 17/06/2024 18:09, Michel Dänzer wrote:
Can I know whether it is needed or not? Or should I be cautious and
always do it?
Assuming GBM in the X server uses the GPU HW driver, I'd say it
shouldn't be needed.
It does not (except the driver libgbm loads). We're trying to use this
in Xvnc, so it's all CPU. We're just trying to make sure the
applications can use the full power of the GPU to render their stuff
before handing it over to the X server. :)
That whole approach won't work.
When you don't have a HW driver loaded or at least tell the client that
it should render into a linear buffer somehow then the data in the
buffer will be tilled in a hw specific format.
As far as I know you can't read that vendor agnostic with the CPU, you
need the hw driver for that.
Regards,
Christian.
A recording of the issue is available here, in case the behaviour
rings a bell for anyone:
http://www.cendio.com/~ossman/dri3/Screencast%20from%202024-06-17%2017-06-50.webm
Interesting. Looks like the surroundings (drop shadow region?) of the
window move along with it first, then the surroundings get fixed up
in the next frame.
As far as I know, mutter doesn't move window contents like that on
the client side; it always redraws the damaged output region from
scratch. So I wonder if the initial move together with surroundings
is actually a blit on the X server side (possibly triggered by mutter
moving the X window in its function as window manager). And then the
surroundings fixing themselves up is the correct output from mutter
via DRI3/Present.
If so, the issue isn't synchronization, it's that the first blit
happens at all.
Hmm... The source of the blit is CopyWindow being called as a result
of the window moving. But I would have expected that to be inhibited
by the fact that a compositor is active. It's also surprising that
this only happens if DRI3 is involved.
I would also have expected something similar with software rendering.
Albeit with a PutImage instead of PresentPixmap for the correct data.
But everything works there.
I will need to dig further.
Regards,
