[Wayland-bugs] [Bug 85715] wl_fixed is not precise enough for high dpi mice

[bugzilla-daemon at freedesktop.org]

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

--- Comment #9 from Peter Hutterer <peter.hutterer at who-t.net> ---
(In reply to x414e54 from comment #8)
> I am not even sure the raw events should be normalized. As far as I know
> they are not on other platforms (but worth checking). 
> 
> Gamers expect that a higher dpi setting will move the mouse faster, and use
> the mouse dpi switch for sensitivity as Sniper mode or run mode etc. 
> 
> You do not want it that your 400 <-> 8200 dpi setting or Sniper mode button
> works in one way on Windows but then is slower/faster on Linux in the same
> game with the same settings.

fwiw, we only normalize the "default" setting, whatever that is. since we can't
detect when the HW changes resolution, doubling the resolution through a switch
on the mouse will provide deltas twice as high.

> > Some of these gamer mice also have ludicrous poll rates (1kHz is common, I'm
> > not making this up.  Please future reader don't feel the need to explain
> > screen refresh rates to me - I did not design these mice.) is it worthwhile
> > to try to keep the size of these events smaller than a double?
> 
> I think 1000hz plus would also begin to cause a problem because the extra
> calculations libinput is doing are essentially delaying the event delivery
> and causing extra cpu usage. You may have so much data buffered that the
> next time the client requests the raw events the compositor has not finished
> processing them.

I wonder if that's a real issue at this point. The calculations for normal mice
are fairly limited (acceleration only) so before we start optimising here I'd
like to see some real-world issues.
fwiw, one of the things the X server used to do for exactly this problem was to
squash motion events together. easy since everything was already in absolute
coords by then but some smarter squashing could probably be done by the
compositor.

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