[PATCH wayland-protcols v2] unstable: add xdg-toplevel-decoration protocol

Quentin Glidic sardemff7+wayland at sardemff7.net
Sun Mar 11 21:17:52 UTC 2018

On 3/11/18 9:49 PM, Simon Ser wrote:
> [snip]
>>> +
>>> +  <interface name="zxdg_toplevel_decoration_manager_v1" version="1">
>>> +    <description summary="window decoration manager">
>>> +      This interface permits choosing between client-side and server-side
>>> +      window decorations for a toplevel surface.
>>> +
>>> +      A window decoration is a user interface component used to move, resize and
>>> +      change a window's state. It can be managed either by the client (part of
>>> +      the surface) or by the server.
>> You mention decorations only, but this (or some other text below maybe)
>> should mention shadows as well. You may consider them as part of the
>> decoration, but xdg_surface.set_window_geometry() is designed to include
>> decoration and exclude shadows. Yet, e.g. GTK+ allows to resize using
>> shadows IIRC.
>> Nit: I think GTK+ allows to move from any dead zone in the surface too. :-)
> xdg-shell's wording includes drop-shadows as part of decorations:
>> Client-side decorations often have invisible portions like drop-shadows which
>> should be ignored for the purposes of aligning, placing and constraining
>> windows.
> So "decorations" here stand for both visible parts such as the titlebar and
> invisible parts such as drop-shadows. Do you think the protocol needs to
> disambiguate these concepts?

You’re right, though I would rather be too precise (while not 
exhaustive) that not enough, just in case. But others may have a 
different opinion so let’s wait for more reviews here.

> [snip]
>>> +
>>> +    <request name="set_mode">
>>> +      <description summary="set the decoration mode">
>>> +        Set the toplevel surface decoration mode.
>>> +
>>> +        After requesting a decoration mode, the compositor will respond by
>>> +        emitting a xdg_surface.configure event. The client should then update
>>> +        its content, drawing it with or without decorations depending on the
>>> +        received mode. The client must also acknowledge the configure when
>>> +        committing the new content (see xdg_surface.ack_configure).
>>> +
>>> +        The compositor can ignore this request.
>>> +      </description>
>>> +      <arg name="mode" type="uint" enum="mode" summary="the decoration mode"/>
>>> +    </request>
>> This request I’m still not sure about it.
>> Why would an SSD-capable client would want to switch from CSD
>> back-and-forth? What is the use case here? (Preferably a user use case.)
> One reason is consistency with xdg-shell.

Not all states can be client-initiated though.

> But there are also real use-cases:
> - A compositor might prefer SSDs or CSDs depending of the window container. For
>    instance, a tiled compositor might prefer SSDs for tiled windows and CSDs for
>    floating windows. Windows can be moved between a tiling and a floating
>    container at run-time.

That I’m 100% ok with, your point is clear and makes a lot of sense. I 
would even object if someone wanted to remove that. :-)

> - Clients might expose a user setting that allows toggling SSDs. For instance,
>    Chrome/Chromium already has such a feature. Requiring the user to restart the
>    app or to quickly close and reopen the main window offers poor UX.

I’m not convinced a client should have such a setting. For consistency 
and UX, I would rather have a central point of setting (the compositor). 
If we make it harder (though possible) to switch, then we can hopefully 
limit the number of clients wanting to support such a setting.
Since we must have the destructor support anyway, on both sides, I think 
it is enough for this feature.

> [snip]
>> Last but not least: it should be much much clearer that the compositor
>> is in charge here. This is not about magic SSD, clients must support CSD
>> in all cases and should not error out if this global is not here. And
>> even then, it may want CSD in some cases.
> I've added this in the protocol description:
>> Note that even if the server supports server-side window decorations, clients
>> must still support client-side decorations.

I think people already got that part, though it does no harm to say it 
again, but I was speaking about the configure event. It may happen *at 
any time* and the client must be prepared (e.g for the cases you mentioned).



Quentin “Sardem FF7” Glidic

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