Thoughts about decoration information in the xdg_shell

[Alex Elsayed]

Jasper St. Pierre wrote:

> On Fri, Nov 15, 2013 at 6:17 AM, Martin Gräßlin
> <mgraesslin at kde.org> wrote:
> 
<snip, because gmane>
> 
> I think the trap that I personally don't want to run into is the case
> where we have a compositor that doesn't support SSD coupled to a client
> that doesn't support CSD. Nobody can draw the decorations, and at this
> point we've engineered the user into a corner.
>
> For me, the debate about window decorations and Wayland is that we need
> *something* to be mandated to be supported. GNOME wants that to be CSD,
> and KDE wants that to be SSD.

>From Martin's message: "It would require clients to support CSD"

What he's advocating is that, yes, everything must include _support_ for
CSD. But enabling it at _runtime_ should not be mandatory.
 
> From the GNOME side, we're heavily using CSD features in our apps [0]
> (such that we'd probably even ignore the Wayland hint to ignore CSD,
> actually), and SSD code in mutter is a large pile of code I would not like
> to maintain, as it's quite complicated, so it's natural for us to want to
> encourage CSD.

And his proposal explicitly allows that. All it is is a communication
channel; the compositor politely requesting "I'd prefer [not] to draw the
decorations for you" and the application saying "I am [not] drawing my own
decorations."

Without this, the two sides have no clean way to communicate that
information, and to do so requires ad-hoc, hackish attempts to support it at
a layer that support does not belong in. With it, at least the left hand and
right hand can tell what the other is doing.

> I also think that CSD has technical advantages for complex server effects:
> if we simply paint surfaces around the window, if we put the window into
> e.g. Coverflow Alt-Tab, we won't see seams around the window. (And
> personally, I'm of the opinion that any design changes you'd need to make
> to apps to make them usable on a touch device vs. regular device stem far
> beyond the window decorations they use in the end.)

As far as design changes between the devices, those are smaller than you
might think (especially with Qt Quick 2 and the work going on with that; see
[1] and [2])

> I'm fine with a hint telling apps to not draw decorations, but I'd like to
> mandate that CSD is supported by everything.

As I noted, Martin's mail said the same thing.

> [0] http://build.gnome.org/ostree/buildmaster/results/tasks/applicationstest/applicationstest/work-gnome-continuous-x86_64-runtime/screenshot-nautilus.desktop.png
Link is a 404.

[1] http://aseigo.blogspot.com/2012/10/one-code-base-multiple-form-factors.html
[2] http://www.notmart.org/index.php/Software/Components_towards_a_new_plasma