[PATCH weston v3 3/3] Introduce wl_relative_pointer interface

[Jonas Ådahl]

On Thu, Oct 29, 2015 at 02:58:33PM +1000, Peter Hutterer wrote:
> On Thu, Oct 15, 2015 at 09:45:56AM +0100, Daniel Stone wrote:
> > Hi,
> > 
> > On 15 October 2015 at 09:32, Jonas Ådahl <jadahl at gmail.com> wrote:
> > > On Thu, Oct 15, 2015 at 09:16:14AM +0100, Daniel Stone wrote:
> > >> On 15 October 2015 at 04:56, Jonas Ådahl <jadahl at gmail.com> wrote:
> > >> > On Thu, Oct 08, 2015 at 12:15:10PM -0500, Derek Foreman wrote:
> > >> >> Perhaps I should read what's in phabricator before I continue to
> > >> >> comment, though.
> > >> >
> > >> > Hmm. I can't find it any more. It was in the fdo phabricator task
> > >> > <https://phabricator.freedesktop.org/T1> but all those comments are no
> > >> > longer there. I have no idea why.
> > >>
> > >> Hmm, is it in the individual commits for review?
> > >>
> > >> e.g. https://phabricator.freedesktop.org/D13
> > >
> > > "You Shall Not Pass: Restricted Differential Revision"
> > 
> > Oops. Given that was the first revision (D1!) ever in there, it was
> > against an old repository import that I later junked. Phabricator got
> > confused since it partly inherits the permission from the repository -
> > fixed now. As you can probably guess from all the spam in your inbox
> > ...
> > 
> > >> > I wonder if we should put "wl_double_fixed" in wayland/ and declare that
> > >> > an "official mutli part type" thing so we don't have to reimplement the
> > >> > awkward from/to functions all over the place. Maybe even
> > >> > a wl_double_fixed_t type as was suggested at an earlier point?
> > >>
> > >> I'm still a bit uneasy on the actual need for this: wl_fixed_t gives
> > >> us 1/256th-pixel precision. Is that not enough? Surely changes less
> > >> than that cannot affect the viewport, so why would we spam clients
> > >> with them rather than accumulating internally and sending when it
> > >> passes the threshold? Is it just about implementing acceleration on
> > >> the client side?
> > >
> > > For absolute motions I agree. For relative, I don't know. I'm no high
> > > end gaming device expert (or where high precision might be relevant)
> > > There were discussions about this before that resulted in changing
> > > from ms to us timestamps and from 32 bit to 64 bit fixed for deltas,
> > > because we didn't want to pretend to be sure that the precision we had
> > > was definitely enough for all relative pointer use cases.
> > 
> > Ack, fair enough. Anyone?
> 
> mostly thinking aloud here:
> The precision that humans can consciously control a mouse with is very high.
> Whether 24.8 is insufficient for *us*, I'm not sure.
> Maybe leave it at wl_fixed_t for now and figure out a transition plan for
> making this a latched event in the style of the wl_pointer.axis_discrete
> proposal, if we ever need it? 
> 
> i'd stick with the 64-bit timestamps though, we know we have devices out
> there that exceed the current granularity.

Except that if we use 64 bit timestamps with 32 bit wl_fixed_t, the
timestamps would not represent actual movement anyway since it doesn't
fit in a wl_fixed_t[0]. That was the point of the 64 bit fixed point deltas
from the beginning wasn't it?


Jonas

[0] https://bugs.freedesktop.org/show_bug.cgi?id=85715

> 
> Cheers,
>    Peter