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

[Po Lu <luangruo@yahoo.com>]

Brian Cully <bjc@spork.org> writes:

> 	I may have missed this earlier in the thread, but where would
> these mappings of device identifier (name, USB VID:PID, whatever) to
> device classes come from? How would that work for devices that can be
> made to look like a *lot* of different input types?

We look at the device name provided by the X input extension.  It is not
calculated based on any USB identifiers.

> 	I’ve got a Steam Controller I can set up as a joystick, keyboard
> (HID report and boot protocols), relative and absolute mouse, all at the
> same time, and I can swap its functions on the fly. I’ve got a mouse
> that can send both “pixel” scroll events as well as normal line-based
> ones depending on how it’s configured. I have a programmable keyboard
> that I can make look like any USB device I want.

That can be identified by the kind of event it is currently sending.
When it sends "smooth" scroll events, Emacs gets a wheel event with the
right valuators.  When it sends line-based scroll events, Emacs gets one
without.  If it's configured as a relative mouse, Emacs will get mouse
movement events; as an absolute mouse, touch events (I think).

>      Is Emacs going to be responsible for mapping thousands of device
> identifiers to device classes (which may change at runtime?) I just
> don’t understand what this looks like from a user’s perspective.

The input driver is responsible to name the devices and to set the
appropriate properties.  Otherwise the devices will not work correctly
with any other program either.