question about xdg shell version

[Pekka Paalanen]

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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