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Handling Tablet Buttons in GTK+ on Wayland




Hello,
As some of you may be aware, I've been working with Carlos Garnacho in
order to implement support in GTK+ for the current draft protocol for
using tablets on Wayland. You can find the latest preview branch of
weston, modified to work with this protocol, here:

	https://github.com/Lyude/weston

And you can find the WIP branch for GTK+ support here:

	https://github.com/Lyude/gtk-

So, right now we've run into something that we believe needs some more
discussion in terms of how it will be implemented: handling tablet
buttons in GTK+ with the Wayland backend. Right now, the tablet-support
branch of libinput only supports the buttons on the actual styluses for
the tablet, not the buttons on the tablet pad, so we only need to worry
about those for the time being.

The problem is right now with the X11 backend is that these buttons
aren't exactly handled in an ideal manner. On the average GNOME setup,
gnome-settings-daemon tells xf86-input-wacom which mouse buttons each
button on the tablet tool should be mapped to (for example: button #1 on
the stylus may be mapped to a right click, and button #2 may be mapped
to a left click), and X forwards them to the clients as such. This means
that GDK only knows which emulated mouse buttons are being pressed as
opposed to the actual tablet tool buttons, and only forwards what it
gets from the xf86-input-wacom. So, there isn't even actually any
infrastructure in GDK right now to handle actual tablet tool button
presses, just mouse button presses. This leaves us with an issue, since
the libinput API for tablets doesn't do any such emulation, and there's
no emulation for this in the Wayland protocol (and I think it would be a
good idea not to add any, IMO any emulation of this manner should be
handled by the clients, not the compositor). Since there's quite a few
ways to go about it, me and Carlos thought it would be appropriate to
bring this up on the mailing list.

Let me know what your ideas are.

Cheers,
	Lyude
	AKA Stephen Chandler Paul

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