Re: master 3b41141708: Expose the name of an event's input device to Lisp

[Brian Cully <bjc@spork.org>]

Po Lu <luangruo@yahoo.com> writes:

> libinput is libinput.  It is a driver for the X server, but it is
> otherwise completely unrelated to the X input extension, which can only
> operate correctly if each name uniquely identifies a device.

	I think I must be misunderstanding something, because I have
devices that are identically named within X and also operate
correctly. That seems to me to run counter to “can only operate
correctly if each name uniquely identifies a device”.

	I bring up USB because libinput has to get its information from
somewhere, and in the cases of the devices I have that libinput
publishes, that is USB. I could potentially dig out some bluetooth ones,
but that seems uneccesary.

> libinput is the device driver being used, yes.

	I am at a loss, then. I do not know why libinput would choose to
give your devices unique names but not mine. Does the “Device” line of
‘libinput list-devices’ also show unique names?

> Then either the names are different, or the devices behave identically
> in every way, and nobody has yet had a reason to treat the devices
> differently.  If the second "Valve Software Steam Controller" was a foot
> pedal, I'm certain it would not be working correctly in software
> designed for that foot pedal.

	This thread began with a claim that devices were uniquely named,
and thus could be disambiguated within Emacs to provide different
functionality based on their names. If I wanted to treat the pointer on
one Steam Controller as a vertical scroll, and on the other a horizontal
scroll, I do not currently see how I could do that.

> Anyway, that "they work fine in X" proves this is not a problem in
> practice, so we will wait until someone actually complains in real word
> usage.

	What this shows to me is that precious little in the X stack
actually cares about device names. For the most part, they are
irrelevant, as devices are self-describing in terms of capabilities.

	That it is useful for a user to modify the way a device behaves
in the context of Emacs I take at face value, and I also grant that the
name is one possible, though hopefully as is clear by now, not
fool-proof way to do that.

	I do not actually believe this to be a huge problem. Outside of
hardware hackers I don’t think I know anyone who attaches two identical
devices. Maybe musicians? I’m sure they exist, but it’s not a lot of
people. But I also don’t believe this is a problem Emacs can solve using
only the device name, for reasons already stated.

> Did you try asking for the device name using the xinput tool?  What does
> it say?

	I’m not very familiar with that tool, but here is the relevant
output of ‘xinput list’:
---[snip]---
⎡ Virtual core pointer                    	id=2	[master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer              	id=4	[slave  pointer  (2)]
⎜   ↳ Valve Software Steam Controller         	id=9	[slave  pointer  (2)]
⎜   ↳ Valve Software Steam Controller         	id=10	[slave  pointer  (2)]
	⋮
⎣ Virtual core keyboard                   	id=3	[master keyboard (2)]
	⋮
    ↳ Valve Software Steam Controller         	id=24	[slave  keyboard (3)]
    ↳ Valve Software Steam Controller         	id=25	[slave  keyboard (3)]
---[snip]---

> Also, what happens if you run `xinput list-props "Valve Software Steam
> Controller"'?  Can you show the output?

	Gladly (sorry about the length, but I’m not sure what
information you might be looking for):
---[snip]---
$ xinput list-props 'Valve Software Steam Controller'
Warning: There are multiple devices matching 'Valve Software Steam Controller'.
To ensure the correct one is selected, please use the device ID, or prefix the
device name with 'pointer:' or 'keyboard:' as appropriate.

unable to find device Valve Software Steam Controller
$ xinput list-props 24
Device 'Valve Software Steam Controller':
	Device Enabled (154):	1
	Coordinate Transformation Matrix (156):	1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
	libinput Send Events Modes Available (275):	1, 0
	libinput Send Events Mode Enabled (276):	0, 0
	libinput Send Events Mode Enabled Default (277):	0, 0
	Device Node (278):	"/dev/input/event30"
	Device Product ID (279):	10462, 4418
$ xinput list-props 25
Device 'Valve Software Steam Controller':
	Device Enabled (154):	1
	Coordinate Transformation Matrix (156):	1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
	libinput Send Events Modes Available (275):	1, 0
	libinput Send Events Mode Enabled (276):	0, 0
	libinput Send Events Mode Enabled Default (277):	0, 0
	Device Node (278):	"/dev/input/event29"
	Device Product ID (279):	10462, 4418
$ xinput list-props 9
Device 'Valve Software Steam Controller':
	Device Enabled (154):	1
	Coordinate Transformation Matrix (156):	1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
	libinput Natural Scrolling Enabled (290):	0
	libinput Natural Scrolling Enabled Default (291):	0
	libinput Scroll Methods Available (292):	0, 0, 1
	libinput Scroll Method Enabled (293):	0, 0, 0
	libinput Scroll Method Enabled Default (294):	0, 0, 0
	libinput Button Scrolling Button (295):	2
	libinput Button Scrolling Button Default (296):	2
	libinput Button Scrolling Button Lock Enabled (297):	0
	libinput Button Scrolling Button Lock Enabled Default (298):	0
	libinput Middle Emulation Enabled (299):	0
	libinput Middle Emulation Enabled Default (300):	0
	libinput Accel Speed (301):	-0.200000
	libinput Accel Speed Default (302):	0.000000
	libinput Accel Profiles Available (303):	1, 1
	libinput Accel Profile Enabled (304):	0, 1
	libinput Accel Profile Enabled Default (305):	1, 0
	libinput Left Handed Enabled (306):	0
	libinput Left Handed Enabled Default (307):	0
	libinput Send Events Modes Available (275):	1, 0
	libinput Send Events Mode Enabled (276):	0, 0
	libinput Send Events Mode Enabled Default (277):	0, 0
	Device Node (278):	"/dev/input/event30"
	Device Product ID (279):	10462, 4418
	libinput Drag Lock Buttons (308):	<no items>
	libinput Horizontal Scroll Enabled (309):	1
	libinput Scrolling Pixel Distance (310):	15
	libinput Scrolling Pixel Distance Default (311):	15
	libinput High Resolution Wheel Scroll Enabled (312):	1
$ xinput list-props 10
Device 'Valve Software Steam Controller':
	Device Enabled (154):	1
	Coordinate Transformation Matrix (156):	1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
	libinput Natural Scrolling Enabled (290):	0
	libinput Natural Scrolling Enabled Default (291):	0
	libinput Scroll Methods Available (292):	0, 0, 1
	libinput Scroll Method Enabled (293):	0, 0, 0
	libinput Scroll Method Enabled Default (294):	0, 0, 0
	libinput Button Scrolling Button (295):	2
	libinput Button Scrolling Button Default (296):	2
	libinput Button Scrolling Button Lock Enabled (297):	0
	libinput Button Scrolling Button Lock Enabled Default (298):	0
	libinput Middle Emulation Enabled (299):	0
	libinput Middle Emulation Enabled Default (300):	0
	libinput Accel Speed (301):	-0.200000
	libinput Accel Speed Default (302):	0.000000
	libinput Accel Profiles Available (303):	1, 1
	libinput Accel Profile Enabled (304):	0, 1
	libinput Accel Profile Enabled Default (305):	1, 0
	libinput Left Handed Enabled (306):	0
	libinput Left Handed Enabled Default (307):	0
	libinput Send Events Modes Available (275):	1, 0
	libinput Send Events Mode Enabled (276):	0, 0
	libinput Send Events Mode Enabled Default (277):	0, 0
	Device Node (278):	"/dev/input/event29"
	Device Product ID (279):	10462, 4418
	libinput Drag Lock Buttons (308):	<no items>
	libinput Horizontal Scroll Enabled (309):	1
	libinput Scrolling Pixel Distance (310):	15
	libinput Scrolling Pixel Distance Default (311):	15
	libinput High Resolution Wheel Scroll Enabled (312):	1
---[snip]---

-bjc