[RFC] xserver: Masked valuators, DIDs, and ABS_MT_SLOT

[Henrik Rydberg]

Hi Chase,
[...]
>> The rangeToMask allocates memory in the inner event loop...
>>
>> The whole mapping construction seems a bit backwards. If unused valuators are
>> never referenced, there is no need to do all those extra copies. As a side effect,
>>
>> *EventsM(events, pDev, type, key_code, mask, num_valuators, all_valuators);
>>
>> could be implemented like
>>
>> *EventsM(events, pDev, type, key_code, mask, num_valuators + first_valuator,
>> valuators - first_valuator);
> 
> My thought was to keep the API simple and in line with previous
> functions. Thus, the bitmask and the valuators arrays start at the 0th
> valuator index of the device.
> 
> To get around doing any copying when *Events functions are called, we
> could either duplicate the code so that we don't send *Events calls
> through *EventsM, or we could change the *EventsM valuators argument
> meaning: instead of being an array starting at the 0th valuator, it
> would start at the first valid valuator in the bitmask.
> 
> Though not as simple in theory, it's not that complicated, so I'll just
> change the meaning of the valuators argument and get rid of the copying.

But it does complicate things a bit, doesn't it? Peter, how much is that
first_valuator actually used, i.e., different from zero? Perhaps one could
simply change the api higher up as well, and get rid of the problem altogether.
Maybe this was implicit in Peter's response?

> 
>> The bit mask is memory efficient, why not allocate in on the stack? It would
>> certainly be a lot faster.
> 
> Yeah, that makes more sense. I'll update the code.

Good good. All in all, this is great work, and we are much farther down a useful
route now than a couple of weeks ago.

Cheers,
Henrik