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

[Brian Cully]

Po Lu <luangruo@yahoo.com> writes:

> 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 did not mean to imply it was, just that there was some way of
obtaining a unique name for a device.

>>      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.

        But my input driver is, for instance, a USB HID driver, and only
cares about the usage tables my device is using. I can plug whatever
device I want in, regardless of any kind of unique or stable identifier,
by virtue of it responding correctly to probes from the USB layer
describing its capabilities. Everything built on top of this stack Just
Works, no matter how I name the device.

        I see very much the value in being able to differentiate similar
or identical events based on their source, but my worry has been about
having Emacs somehow decide for me that because my device is named “X”
it has capabilities w, y, and z.

        In a previous email, it seems as though your thoughts are around
having the user specify capabilities or event mappings themselves based
on the device name. I don’t know nearly enough about the specifics to
comment on any particular approach, but I am reasonably sure I don’t
want Emacs making those decisions for me.

-bjc