Hi Chase,
>
> I gave this some more thought, and I was close to accepting it with
> documentation of the above restrictions. Then I thought of how the
> following two devices would be presented to userspace:
>
> 1. A real MT device supporting up to 2 touches (e.g. a bamboo touch)
> - ABS_{X,Y}, BTN_TOUCH, BTN_TOOL_FINGER, and BTN_TOOL_DOUBLETAP for ST
> - ABS_MT_SLOT, ABS_MT_TRACKING_ID, ABS_MT_POSITION_{X,Y}, ABS_MT_TOOL_TYPE
>
> 2. A partial MT device using MT_TOOL_ENVELOPE (e.g. synaptics MT)
> - ABS_{X,Y}, BTN_TOUCH, BTN_TOOL_FINGER, and BTN_TOOL_DOUBLETAP for ST
> - ABS_MT_SLOT, ABS_MT_TRACKING_ID, ABS_MT_POSITION_{X,Y}, ABS_MT_TOOL_TYPE
>
> Note that they are identical! The range of values for each axis would be
> identical too. The only way to tell the two apart would be to watch for
> the ABS_MT_TOOL_TYPE axis.
Ping has touched upon this subject as well, from the pen & touch perspective.
Generally, some ABS axes are actually enumerations, for which we have no direct
abstraction. If we had a way to declare the used values for such enumerations,
it would resolve these and possibly other issues.
Thanks,
Henrik
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