[Letux-kernel] [PATCH v9 1/8] drivers:input:tsc2007: add new common binding names, pre-calibration, flipping and rotation

H. Nikolaus Schaller hns at goldelico.com
Tue Feb 21 09:29:53 CET 2017


Hi Petr and all,

> Am 20.02.2017 um 23:26 schrieb Petr Cvek <petr.cvek at tul.cz>:
> 
> Hi
> 
> Dne 20.2.2017 v 17:50 H. Nikolaus Schaller napsal(a):
>> Hi Pavel,
>> 
>>> Am 19.02.2017 um 23:19 schrieb Pavel Machek <pavel at ucw.cz>:
>>> 
>>> hi!
>>> 
>>>>>> But as said I don't think we need float or fixed point for practical systems
>>>>>> at all.
>>>>> 
>>>>> So you are going to loose precision. And if userspace decides to
>>>>> calibrate it slightly differently from kernel, lost precision will
>>>>> matter.
>>>> 
>>>> Really?
>>> 
>>> Really.
>>> 
>>>> Example:
>>>> 
>>>> ADC values go 100 .. 3995 (i.e. touch margin is 100 steps in pre-calibration)
>>>> 
>>>> This is scaled to let's say 0..640.
>>> 
>>> Ok. Now userspace realizes that kernel alignemnt is off, and it would
>>> want to scale it to 1..642.
>> 
>> Screen coordinates are still 0..639.
>> 
>>> That will mean that single pixel will be
>>> inaccessible, right?
>> 
>> Yes, that can happen if the additional user-space scale is > 1.0.
>> 
>> As long as it is small (I expect <1.01 = 1% error in scale) it is
>> barely noticeable.
>> 
>> Therefore, I asked before: how big in pixels is your finger or stylus?
>> Does this effect matter?
>> 
>> A resistive touch is a man-machine-interface where people press buttons of at
>> least 12x12 pixels size (or they are no longer visually recognizable).
> 
> Smallest kernel font is 4x6 (i think) and I'm regularly using 8x8. I would like
> to be able to select a single letter in the console.

So you probably have exceptionally good eyes and reading a terminal on a touch
screen is not a typical use case (except for us hard-core programmers).

Anyways, if there is only a single pixel is not accessible due do rescaling and integer
truncation effects (which is what Pavel complained) you can still select single letters
in a 4x6 font.

---

So, let's close commenting this patch here since in my opinion everything is said
and the maintainers have decided not to accept it.

I hope that I have not forgotten anyone to answer.

Thank you very much to all participants for this discussion, because it was
really enlightening to me and contains a lot of new perspectives.

BR and thanks,
Nikolaus


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