protocol questions

[Jason Ekstrand]

On Sat, Mar 30, 2013 at 8:44 PM, Daniel Stone <daniel at fooishbar.org> wrote:
> Hi,
>
> On 30 March 2013 16:55, Thiago Macieira <thiago.macieira at intel.com> wrote:
>>
>> On sábado, 30 de março de 2013 09.34.24, Matthias Clasen wrote:
>> > > Monotonic (ideally) time in an undefined domain, i.e. they're only
>> > > meaningful on relation to each other.
>> >
>> > What can you do with them ? For the use case that Giulio mentioned
>> > (double-click detection), I'd need to know at least if the difference
>> > between two times is seconds or milliseconds or microseconds...
>>
>> The protocol needs to specify the unit. It can't be dependent on the
>> device
>> driver, that makes no sense. If it's in milliseconds, it will overflow
>> every
>> 49.7 days. If it's microseconds, it will overflow every 71.6 minutes.
>
>
> Yes, they are in milliseconds, I just explained it poorly.
>
>>
>> It also needs to specify which timestamps are in the same time domain. Can
>> two
>> timestamps be compared to each other only if:
>>
>>  - they are in the same input device (same mouse, same keyboard), but not
>> across devices
>>  - they are in the same seat, but not across seats
>>  - they are in input event messages, but not other types of messages that
>> carry timestamps
>>  - no restriction
>
>
> Personally, I think either #1 or #2.  Definitely not #3 or #4.  We want to
> be able to use the evdev timestamps rather than gettimeofday() when we
> receive it, so we can ensure that if someone clicks twice slowly, and the
> compositor takes a while to process the same event, it's not interpreted as
> a double-click.
>
>>
>> For example, imagine the case of trying to ensure that a Ctrl key was
>> pressed
>> before a mouse click happened, after the events were plucked out of the
>> event
>> stream.
>>
>> Or is there another, recommended way of doing that, such as by using the
>> serials?
>
>
> Hmmm.  I was going to say using the event order, but it all depends on which
> order the devices were read in.  So I guess for this case we'd need to go
> with #2.

As a side note, #2 also makes more sense for the wl_pointer which is
an agrigate from more than one source.
--Jason Ekstrand

>
> Cheers,
> Daniel
>
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