HI Pavel, > Am 20.02.2017 um 20:29 schrieb Pavel Machek <pavel@xxxxxx>: > > Hi! > >> 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? > > If I draw a line in gimp, I don't expect it to have steps because of > "barely noticeable" errors. You can't draw a line with exactly 1 pixel distance on such a touch screen. > >> 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). > > Resistive touch is used for drawing, too. Yes, for taking handwritten notes but not for high-precision graphics design. For that you take a bigger screen and zoom the relevant areas. > >> So the discussion boils down to "what gives the better usability?": >> a) getting rid of the nasty user-space calibration step (and plethora of different tools) >> b) getting highest theoretical precision which has a low practical relevance >> >> I am in favor of a). Like most users we ask. A minority is in favor of b). >> Since we don't exclude b) users from reconfiguring their system to get it done >> as they like. I think this is the best we can achieve. > > Do you even read what I wrote? > > Because I presented way to have both a) _and_ b). I am not aware that you did this. You made a proposal for the X system but not for others, e.g. Replicant. > >>>>> No. You have to design interface such that they _can_ be improved, and >>>>> what you propose does not work that way. >>>> >>>> It works. Please do real world tests... >>> >>> You do a real world test on N900, and propose upgrade path. >> >> I have no N900 running. But since it uses a tsc2004/5 controller which seems >> to be quite similar, you can likely copy&paste some code or add the algorithm: >> >> ABS_X = (touchscreen-size-x * (adc_x - adc_min_x)) / (adc_max_x - adc_min_x) >> >> Thats it. >> >> If you set touchscreen-size-x = (adc_max_x - adc_min_x) you get maximum precision >> you can achieve with integer arithmetic. And if you set adc_min_x = 0 your >> user-space gets what it would have got before adding such a formula and then you >> can and must do calibration there. >> >> Taking this as the defaults if none of the new properties is specified, makes >> the scaling feature completely disappear. And I don't care about 2 additional >> subtractions, one multiplication and one division per axis. >> >> So the upgrade path is: >> 1. introduce new optional properties, parse and store them in the struct >> 2. set defaults for the optional properties as described above >> 3. add the formula to the code (1 line for each axis) >> 4. deploy - nobody will notice > > Good so far. Ok! > >> 5. update the DT and remove user-space calibration - people will be happy >> that they do not have to calibrate first any more > > You can't do this. And this is fatal problem with your proposal. > > If I update the DT in the kernel, my users will be very unhappy, > because their screens will now be miscalibrated. If you tell them that they should recalibrate once, after they upgrade to Linux 4.12 because they no longer need it I doubt they will not be very unhappy. And as said I do not expect or force you to take step 5 for the N900 touch screen. Not even step 1. I would take this more sensitive if you would use the same chip. > New kernel must not > force users to update their userland at the same time. Yes, it shouldn't. But to be honest, this is not my experience. I have to tweak userland a little almost every time a new kernel merge window is done. Admittedly not in the input system. And I may be using the wrong distribution. But if you ever want to deploy better features it is really difficult to avoid. Nevertheless, what problem do you have to implement steps 1-4 in kernel and step 5 outside? BR and thanks, Nikolaus
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