xinput -> core pointer - Transformation?

Peter Hutterer peter.hutterer at
Thu Oct 13 16:01:05 PDT 2011

On Thu, Oct 13, 2011 at 01:51:26PM +0200, Roman Seidl wrote:
> Thnaks for answering my request. Well it does not seem to be a
> Problem with Xournal - it ist the same with the current stable and
> the development version. Furthermore it ist the same problem with
> GIMP when i activate the Xinput.
> So is there any information onf how the pointer gets transformed?

dix/getevents.c:transformAbsolute() in the server. The theory is that for
any coordinate x/y that the driver posts the actual event coordinates given
a matrix M are x(m)/y(m). So you should never see the original coordinates.
Simplest example, a driver with range 0..100 that has a matrix mapping to
the left 50% should only ever have 0..50 in the events.
Provided the server does this correctly, the rest is in the client side.


> best regards
> roman
> Am 2011-09-30 07:20, schrieb Peter Hutterer:
> >On Wed, Sep 28, 2011 at 11:36:41PM +0200, roman wrote:
> >>Hi!
> >>
> >>I have a tablet and i want to use an external monitor that covers
> >>just a part of the screen. This is no problem concering xrandr as i
> >>can set a scale and a position.
> >>
> >>The problem is with the pen. The pen core pointer is automatically
> >>postioned the right way - even in this situation. But no
> >>transformation matrix whatsoever is set in the xinput settings for
> >>the device.
> >>
> >>Sounds nice BUT I want to use direct xinput for using xournal.
> >>
> >>So i would like to modify the Transformation matrix. If i do so the
> >>xinput can be set to be in line with the monitors - but then the
> >>core pointer is wrong.
> >>
> >>How is the xinput transformed into postions on screen for the core pointer?
> >>
> >>Is there any way to get infos on the transformation that takes place?
> >>
> >>Is it possible to modify it?
> >
> >I don't quite understand. Changing the device matrix should also change the
> >XI coordinates and map them into the same range. What isn't working here?
> >Does xournal scale somehow differently again?
> >
> >Cheers,
> >   Peter
> >
> >
> -- 
> mail   roman at
> web
> tel    +43-650-2041643
> jabber rot at

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