Interactive white boards and Fedora Xorg setup

Rodd Clarkson rodd at
Wed Jul 7 05:29:24 UTC 2010

On Wed, 2010-07-07 at 11:01 +1000, Peter Hutterer wrote:
> [faked-up reply, I'm not on the list, ajax pointed it out to me on the
> archives. please make sure you CC me for any replies]

Thanks for the reply, and it's nice to know that ajax noticed this (as
it appears ajax has much to do with Xorg on fedora (and I'm guessing

> > Unlike a mouse, these pointer devices move the mouse pointer to where
> > you touch the screen.  For example, if the IWB is to the right of my
> > laptop screen and I touch the right edge of the screen then the mouse
> > pointer appears on the right side of my laptop screen, and not where
> > I've touched the screen.
> > 
> > The pointer device included with the IWB needs to be able to be
> > configured to do two things:
> > 1.  Only work as a device for the IWB screen.  The mouse shouldn't be
> > able to be moved off the screen, only around it.
> > 2.  Calibrate the pointer so that you can declare the
> > top/bottom/left/right of the screen (as where the image falls on the
> > pointer device isn't usually at the extremes of the device.)
> >
> > Is this possible?
> The 1.9 X server that's already in rawhide has an coordinate transformation
> matrix to restrict absolute devices to essentially any rectangle on the
> screen. The matrix is a property on each device and can be modified with the
> xinput commandline tool (no GUI tools yet).
> For example, I've got a 1440x900 and a 1920x1200 display. To restrict my
> tablet to the right (larger) screen:
> $> xinput --set-prop "Wacom Intuos4 6x9" "Coordinate Transformation Matrix"
> 0.58 0 0.42 0 1 0 0 0 1  
> The matrix thus looks like this:
> | 0.58 0 0.42 |
> | 0    1 0    |
> | 0    0 1    |
> giving us a scale into 58% of the screen range with an offset of 42%. Your
> numbers will likely vary but that should fix the issue for you.

This looks like a great start, but I'm guessing it only works in 1.9 at
this stage. Will this also work in 1.8?

Obviously a nice GUI tool for this where you can specify the pointer and
the region visually would be the finishing touches (as this will vary
for me from IWB to IWB and I'm a Relief Teacher that sees a lot of
different IWBs.)   Presumably this would be easy enough to implement in
the Monitor Preferences (System > Preferences > Monitor) by including
options to limit pointer devices to a particular display.

The other bit of the problem is defining the mouse region for the
pointer device.  Unlike your wacom device (and similar devices) where
the top left point of the device is quite easier to assume as the top
left corner of the display, IWBs aren't so simple.

IWBs have the image projected onto the screen which is also the pointer
device, but it's very unlikely that the top left corner of the projected
image is also at the same place as the top left corner of the screen.
Since the mouse pointer moves to where you place you finger on the
screen, it's important that this maps precisely so you can click buttons
and drag items without a level of hit and miss (and incorrectly buttons
pressed).  I've even seen IWBs where the image isn't even square on the
IWB, and I guess this needs to be addressed too.

Any suggestions for this?


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