[xkbcommon] How to distinguish left-shift and right-shift

Ran Benita ran234 at gmail.com
Wed Sep 25 11:26:33 PDT 2013

On Tue, Sep 24, 2013 at 08:02:30PM -0300, Wander Lairson Costa wrote:
> Hi,


> I am working for some time porting Blender to wayland [1] and I am now
> adding keyboard handing support. For that, I am following weston
> clients code as reference and using libxkbcommon.
> To make a long history short, I need to differentiate left-shift and
> right-shift modifiers, but I didn't figure out how to do that with
> libxkbcommon. I printed all modifiers names and there is just one
> "Shift" modifier, there aren't "LShift" and "RShift" like there are
> for control and alt key modifiers.

I'm afraid we have no way to do that. We currently only expose the 8 old
X11 modifiers, which only have Shift. There are also what's called
virtual modifiers, which I have some pending work to expose, but these
*too* don't have separate RShift and LShift modifiers (as opposed to
e.g. LControl and RControl) - that's in current xkeyboard-config, which
is the project where all the keyboard data is maintained. And there was
some sensible resistence to addings these, for example here:

Of course, X11/XKB is in exactly the same boat here, so I from a quick
look I found that what the blender X11 backend does (as far as I can
see), is that it gets the key state with the XQueryKeymap(3) request,
and then sees if the left/right *keys* are down. That's not entirely
correct purely speaking, but I guess it works in 99.9999% percent of the
cases. So I can only suggest you do the same for now for Wayland.

But... xkbcommon doesn't (and prefereably won't) expose an equivalent of
XQueryKeymap itself, and the Wayland protocol only provides it on the
wl_keyboard enter event (with the 'keys' field). So unfortunatly what
you have do is get/reset this array on wl_keyboard enter event, and
keep it updated manually on the client side on key events. That should
work... Unless someone has a better idea!


> [1] https://github.com/walac/blender-wayland
> -- 
> Best Regards,
> Wander Lairson Costa
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