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

Petr Cvek
2017-02-20T22:26:22Z

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@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.

cheers,
Petr