Re: [PATCH] input : wacom - report resolution for ABS_MT events

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Fri, Jan 28, 2011 at 10:23:59AM -0800, Ping Cheng wrote:
> On Fri, Jan 28, 2011 at 9:30 AM, Henrik Rydberg <rydberg@euromail.se> wrote:
> > Hi Ping,
> >
> >> This is mainly required by the serial pen and touch devices since
> >> both pen and touch are on the same port. Updated the USB ones to
> >> keep MT event definition consistent among serial and USB devices.
> >
> > Why is this change performed? What does the patch do? Please elaborate
> > a little bit.
> 
> Let's see if I can explain it clearer or not.
> 
> We need to report resolution to userland for wacom_w8001.c. Since pen
> and touch data are reported through the same logical port for serial
> devices, using input_abs_set_res  for ABS_X/Y,  we can only pass the
> resolution for pen or touch. So, I let ABS_X/Y report pen resolution
> since most legacy ST clients process pen data over touch. However, for
> multi-touch clients, especially for those that support gestures, touch
> resolution is needed to calculate the physical distance between two
> touch points. Using  ABS_MT_POSITION_X/Y does not cause confusion and
> it is quite intuitive.

We just went through the round of why we should scale events from
different tools when they use the same event devices and I do not see
why MT data is any different.

Devices have only one set of physical axes (MT or not) so I believe
min, max and resultion should be reported on ABS_X, Y, X, etc, or, if
you want to have this data in ABS_MT_POSITION, it should be trhe same.

ABS_MT_POSITION is just a vehicle of delivering multipe contacts, not a
new device axis.

Thanks.

-- 
Dmitry