Capturing all events from a presentation remote while allowing all other events to be sent normally

[Peter Hutterer]

On Tue, Apr 30, 2019 at 08:07:18AM -0400, Eric Sokolowsky wrote:
> Yes, I checked the status of the XIGrabDevice call. It was 0. I followed
> your suggestion on using the device's id, and it does appear to work
> better, at least well enough for my purposes. The only confusing thing now
> is that I am getting event 35 (GenericEvent) back to my application when
> the buttons on the remote are pressed. Do you have any pointers to
> documentation on how I might get the key events from these?  Thanks for
> your help.

all XI2 events are generic events and you need to handle those accordingly.
google for "XI2 recipes", I think that set of blog post has the
explanations and should get you started. Otherwise, the xinput source code
(for 'test-xi2') will be helpful too as it's sort-of the minimal client for
XI2 event handling.

Cheers,
   Peter

> On Mon, Apr 29, 2019 at 9:27 PM Peter Hutterer <peter.hutterer at who-t.net>
> wrote:
> 
> > On Mon, Apr 29, 2019 at 05:42:46PM -0400, Eric Sokolowsky wrote:
> > > I have an application that is used as a control system for a
> > presentation,
> > > under Linux and using X11. I have a USB presentation remote that acts as
> > a
> > > very miniature keyboard (four buttons: Page Up, Page Down, and two
> > others)
> > > which can be used to advance and go back in the presentation. I would
> > like
> > > to have my presentation application to receive all of the events from
> > this
> > > remote regardless of where the mouse focus is. But I would also like to
> > be
> > > able to receive the normal mouse and keyboard events if the current
> > window
> > > focus is on the presentation application. Using XIGrabDevice() I was able
> > > to receive all events from the remote in the presentation application
> > > regardless of the current focus but I was not able to receive any events
> > > from the mouse or other keyboard while the grab was active. Is what I'm
> > > trying to do possible?
> > >
> > > Here's the code I'm using:
> > >
> > > XIEventMask masks[1];
> > > unsigned char mask[(XI_LASTEVENT+7)/8];
> > > memset(mask, 0, sizeof(mask));
> > > XISetMask(mask, XI_KeyPress);
> > > masks[0].deviceid = XIAllMasterDevices;
> >
> > replace this with the device ID of the remote.
> >
> > > masks[0].mask_len = sizeof(mask);
> > > masks[0].mask = mask;
> > > Status result = XIGrabDevice(dpy, deviceid, win, CurrentTime, None,
> > > XIGrabModeAsync, XIGrabModeAsync, True, masks);
> > >
> > > Any help would be appreciated. Thank you.
> >
> > did you check the status? XIGrabDevice with XIAllMasterDevices should fail
> > because it doesn't resolve into any device (this is one of the requests
> > where you can't use that fake device ID). Not sure why this worked at all.
> > Either way, using the remote's ID should work.
> >
> > Cheers,
> >    Peter
> >

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