[PATCH libinput 0/4] some acceleration fixes, mostly for high DPI mice

David Herrmann dh.herrmann at gmail.com
Tue Nov 4 00:41:53 PST 2014


On Tue, Nov 4, 2014 at 4:51 AM, Peter Hutterer <peter.hutterer at who-t.net> wrote:
> On Mon, Nov 03, 2014 at 11:56:59AM +0100, David Herrmann wrote:
>> I haven't spent much time thinking it through, but so far I'd prefer a
>> solid, but basic, heuristic to guess the DPI and then use hwdb for
>> anything that doesn't fit. This allows us to change the heuristic at
>> any time and we don't have to introduce any APIs. We can even ship the
>> hwdb files with libinput.
> tbh, I don't think heuristics will work. there is no reference point and
> when you're looking at relative motion you can't tell if a delta of
> 10 means the pointer has moved a large distance at low-res or a small
> distance at high-res.

I was more talking about the MIN/MAX values reported by the device. I
assumed that high-dpi devices just reported higher precision for the
same interval as low-dpi devices. But as your data shows, this turns
out to be not true... what a bummer!

> Anyway, for some data:
> I recorded my Logitech G500s here with three different dpi settings (400,
> 800, 2000) and a MS Comfort Optical Mouse 3000 (1000 dpi). A couple of
> interesting things: regardless of dpi, virtually all events are within [-3,
> +3] dx/dy and there's nothing over 10. Exception here is the MS mouse which
> goes up to 78 for a delta, for reasons I can't explain yet.

Interesting. This is probably to throttle HID throughput and use
report-on-change, instead of continuous-reporting.

Anyway, if you want, I can come up with a hwdb format to retrieve DPI
settings. Just lemme know what you want to match on for the devices.


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