[PATCH xserver] present: Only send PresentCompleteNotify events to the presenting client

[Michel Dänzer]

On 20/10/17 11:45 PM, Keith Packard wrote:
> "Keith Packard" <keithp at keithp.com> writes:
> 
>> I'm *not* saying this isn't a good patch in practice, I just want to
>> understand whether the system was designed wrong, or if we've
>> implemented it wrong.
> 
> I spent some time this afternoon on IRC chatting with Pierre-Loup. Valve
> has an application (vrcompositor in 'extended' mode) which is using
> multiple display connections and selecting for Present events on all of
> them. I thought for a while that this was doing precisely what we didn't
> think reasonable -- expecting PresentCompleteNotify events generated
> from a PresentPixmap request sent by client 'A' to be delivered via an
> event selection by client 'B'. Nope, they're using the Vulkan
> presentation API (which eventually sends PresentPixmap) on connection
> 'A', and PresentNotifyMSC on connection 'B'. The only events connection
> 'B' is interested in are those generated by the PresentNotifyMSC, not
> those generated by the PresentPixmap sent on connection 'A'.
> 
> Thinking about this some more, I believe we can look at CopyArea and
> GraphicsExposure events as a good analog -- in that case, the
> GraphicsExposure events are *only* delivered to the client who sent the
> CopyArea request. I think the Present extension is badly designed in
> this area; it shouldn't have bothered to place event selection on the
> window, and should have instead made it part of the generating request,
> just like CopyArea does (well, it's part of the GC state, which is
> effectively part of the request, not part of the drawable state).

Note that this patch only changes the behaviour for
PresentCompleteKindNotifyMsc events specifically. In contrast to those,
with PresentCompleteKindPixmap I can at least imagine a use for seeing
events from other clients, e.g. so multiple clients can consistently
count the number of presentations performed to a window.


-- 
Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer

-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 224 bytes
Desc: OpenPGP digital signature
URL: <https://lists.x.org/archives/xorg-devel/attachments/20171023/d0b77dd1/attachment.sig>