Re: ABS_MT_TOUCH_MAJOR metric

[Ferruh Yigit <fery@cypress.com>]

On 05/22/2014 08:23 PM, Dmitry Torokhov wrote:
> Hi Ferruh,
>
> On Thu, May 22, 2014 at 02:03:40PM +0300, Ferruh Yigit wrote:
>> Hi,
>>
>> What is the metric of ABS_MT_TOUCH_MAJOR / ABS_MT_WIDTH_MAJOR events?
>>
>> The Linux documentation
>> <https://www.kernel.org/doc/Documentation/input/multi-touch-protocol.txt> says:
>> "The length of the major axis of the contact. The length should be given
>> in surface units. ..."
>>
>> What does "surface units" means, is it millimeter or pixels?
> It is whatever unit the device reports, similarly to ABS_MT_POSITION_X
> and ABS_MT_POSITION_Y. Userspace can use EVIOCGABS to map device units
> onto common units.
>
> From include/uapi/linux/input.h (struct input_absinfo):
>
>  * Resolution for main axes (ABS_X, ABS_Y, ABS_Z) is reported in
>  * units per millimeter (units/mm), resolution for rotational axes
>  * (ABS_RX, ABS_RY, ABS_RZ) is reported in units per radian.
>
> Hope this helps.
>
Hi Dmitry,

I understand this works for Dmitry ABS_X, ABS_Y,
touchscreen reports between 0..A, screen resolution is 0..B, a mapping
can be done 0..A -> 0..B

But for ABS_MT_TOUCH_MAJOR how this scaling can be done,
touchscreen reports between 0..A, do we know the min/max values for
application side?

-- 

Thanks,
ferruh