question about drm backend

[zou lan]

Hi pekka

Thank you for your reply. I have other questions about drm backend.
 I find weston 5.0 modify so much about drm backend and the interfaces of
compositor communicate with drm backend.
Is there any documents about the drm backend design?
Why compositor need to add a structure weston_head? Is weston_output not
enough? why not let drm backend to judge whether to do
repaint/repaint_flush/repaint_cancel to keep libweston separate from drm
backend?

Thank you!
Best Regards
Nancy



Pekka Paalanen <ppaalanen at gmail.com> 于2018年11月14日周三 下午11:34写道：

> On Wed, 14 Nov 2018 23:00:21 +0800
> zou lan <nancy.lan.zou at gmail.com> wrote:
>
> > Hi pekka & all
> >
> > I find weston support many xdg shell versions in different weston
> versions,
> > as far as I know,
> > applications only use the genernal xdg shell interfaces to create a
> window,
> > for example, waylandsink. If the weston upgrade, should the applications
> > modify its xdg shell interface or are they  just backward compatible.
> Does
> > weston only support stable/xdg-shell.xml in the future?  How could make
> > weston upgrade not impact applications?
>
> Hi Nancy,
>
> Weston still supports even wl_shell, I don't think there is much
> pressure to drop the deprecated versions. I would imagine Weston will
> carry the support for a good number of years if not indefinitely.
> Weston still doesn't have an implementation for the stable xdg-shell
> though.
>
> Applications are recommended to move on to the stable xdg-shell version.
>
> xdg-shell v5 support was dropped quite some time ago as maintaining it
> with the other revisions became inconvenient. The revisions other than
> v5 should not suffer from similar issues.
>
> A compositor can support several major revisions at the same time, and
> Weston does. Clients can also choose which one they use and they can
> see what the compositor supports.
>
> The stable xdg-shell will be developed in a backwards-compatible way.
> Actually all Wayland extensions are developed that way, both stable and
> unstable ones. The difference is that unstable ones may get a new
> incompatible revision through renaming most of the interfaces, which
> technically allows both compositors and clients to support multiple
> incompatible versions at the same time.
>
> If you are worried about loosing something, you can always follow the
> Weston merge requests in Gitlab and chime in if something you care
> about is about to disappear.
>
> I don't think bringing xdg-shell v5 support back would be impossible if
> someone really wanted to, but I suspect it would be much more work than
> just reverting the removal. xdg-shell v5 is actually multiple
> incompatible versions IIRC, it was using an ad hoc versioning mechanism
> which didn't turn out to be that good in the long run.
>
>
> Thanks,
> pq
>
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