Why multi-touch fail to work for multi-display?

[Peter Hutterer]

On Sat, Oct 19, 2013 at 11:31:08AM +0800, Leslie Zhai wrote:
> Hi Xorg developers,
> 
> I use Projected Capacitive touch screen device
> http://en.wikipedia.org/wiki/Touchscreen#Projected_capacitance
> It can be pasted on the normal monitor, then it is able to touch, the
> cursor
> will move to the position where touched. It experienced like iphone and
> other
> single touch screen device.
> 
> But when I put multiple Projected Capacitive touch screen devices on
> several
> monitors, then touch some of them simultaneously, the cursor of X Window
> was
> only moving in the first monitor, even though it was able to move to other
> monitors` display, it still failed to show the correct position.

default behaviour is to map the device to the set of all monitors together.
if you want to map a device to a specific montior you need to set the input
transformation matrix.

http://sourceforge.net/apps/mediawiki/linuxwacom/index.php?title=Dual_and_Multi-Monitor_Set_Up

because output can change positions, size, orientation, etc. at any time
there is no static (i.e. xorg.conf) option to configure this, it needs to be
set at runtime.

one matrix exists per device, so you can configure multiple touchscreens
easily enough.

Cheers,
   Peter