emit "smooth scrolling/pixel perfect" events

[Antoine Martin]

On 05/01/15 06:52, Peter Hutterer wrote:
> On Mon, Dec 29, 2014 at 08:07:31PM +0100, dustin wrote:
>> Hi,
>>
>> i recently started to play around with the input facilitys of X. My goal is
>> to develop a remote control for my PC and for that purpose i want to control
>> the mouse with an android tablet. (Maybe other embeded devices)
>>
>> I found a few ways to do this namely xtest and uinput/evdev (and untested
>> xlib/xcb). Both working out of the box but i think i'll stick with
>> uinput/evdev cuz i think this approach should work with libinput(wayland) as
>> well? One problem arises that i can't circumvent and this is the scrolling.
>> my first implementation works by simply emitting button 4/5 events like what
>> ordinary mouse wheels do (looking at xev xinput tools) but what i am rally
>> looking for is emitting "smooth scroll events"/"pixel perfect scrolling"
>> (whatever this means). I came across some articles from Peter Hutterer
>> talking about this and that Gnome implemented this. One can see this in live
>> action via touchpad and the epiphany webbrowser. What i discovered was, that
>> a client program has to catch XI2 events (XIDeviceEvent)and watch for
>> XI_Motion and its valuators. But i really don't know how to emit these? with
>> uinput/evdev even if i am emiting EV_REL, REL_WHEEL events and not button
>> 4/5 events i got ordinary scrolling. what is the "right way" to emit these
>> XIDeviceEvent/XI_Motion events (if these are really the ones i am looking
>> for)
>>
>> what i was seeing from xinput --test-xi2 for ordinary mouse wheels was
>>
>> EVENT type 17 (RawMotion)
>>    device: 2 (10)
>>    detail: 0
>>    valuators:
>>    flags:
>>          2: -1.00 (-1.00)
>>
>> EVENT type 15 (RawButtonPress)
>>    device: 2 (10)
>>    detail: 5
>>    valuators:
>>    flags: emulated
>>
>> EVENT type 16 (RawButtonRelease)
>>    device: 2 (10)
>>    detail: 5
>>    valuators:
>>    flags: emulated
>>
>> As i understand this right the first XI_RawMotion is the "now" the regular
>> new event and the button presses are for compatibility and can be ignored
>> cuz of the "emulated" flag
>>
>> the valuator 2 means
>>
>> Class originated from: 10. Type: XIValuatorClass
>>    Detail for Valuator 2:
>> 	Label: Rel Vert Wheel
>> 	Range: -1.000000 - -1.000000
>> 	Resolution: 1 units/m
>> 	Mode: relative
>>
>> if i scroll with my touchpad i get
>>
>> EVENT type 17 (RawMotion)
>>    device: 2 (13)
>>    detail: 0
>>    valuators:
>>    flags:
>>          3: 4.00 (4.00)
>>
>> there i have a valuator 3 which i guess means Rel Vert Scroll regarding to
>> this
>>
>> Class originated from: 13. Type: XIValuatorClass
>>    Detail for Valuator 3:
>> 	Label: Rel Vert Scroll
>> 	Range: 0.000000 - -1.000000
>> 	Resolution: 0 units/m
>> 	Mode: relative
>>
>> So the difference must somehow be with the different valuators. If so i just
>> don't know how i can influence this with uinput/evdev. Maybe its only doable
>> with xlib/xcb/xtest etc. i don't know.
>>
>> all i want is to simulate the "pixel perfect smooth scrolling" i get from
>> regular laptop touchpads so that apps who respond to this will do from my
>> application.
> 
> the output of xinput should also include a XIScrollClass. That contains
> information whether it's vertical/horizontal and refers to the valuator
> number. If such a class is present, the valuator listed is a scrolling
> valuator and should be interpreted as such.
> 
> You don't have to do anything special in uinput, just send REL_WHEEL and the
> rest of the xorg stack will do the right thing. Though since REL_WHEEL is
> discreet, you won't get as much use out of smooth scrolling as you would
> from a touchpad.
When I send REL_WHEEL via uinput, applications that normally do smooth
scrolling (ie: a browser) will scroll a few lines of text at a time, as
if I had used the wheel using my mouse. That's expected.

What I would like to be able to do is emulate the behaviour I get from
my trackpad with two-finger scrolling.

I was hoping that simply setting uinput's absmax would have an effect on
the valuator that gets assigned but this makes no difference.
I assume that I need to get uinput to emulate a more "complete" device,
but all my attempts have failed so far.
Any ideas?

Thanks
Antoine


> 
> Cheers,
>    Peter
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