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

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

On Fri, Jan 28, 2011 at 11:01:39AM -0800, Ping Cheng wrote:
> On Fri, Jan 28, 2011 at 10:46 AM, Dmitry Torokhov
> <dmitry.torokhov@gmail.com> wrote:
> > 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.
> 
> At the time when we worked on that, we did not consider resolution. We
> only scaled the logical values.
> 
> > Devices have only one set of physical axes (MT or not)
> 
> You are right if the device only supports one type of tools. Yes, ST
> or pen can go with ABS_X/Y. MT goes with MT. However, we are dealing
> with a dual tool case: pen and touch on the same port. Using only one
> set of axes would not be able to cover both tool events and pass the
> resolution to the userland.
> 
> > 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.
> 
> max/min is different from resolution. We can scale max/min since they
> are logical data. But we can not change the device's physical size.
> That's the root cause of the "stubborn" nature of resolution.

This is the same device so it should have the same physical dimensions,
right?

-- 
Dmitry
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