In bug 976035 we added a pref'able velocity limit to APZC. This took the form of an absolute px/ms value. This works, but is difficult to tune well for devices with different screen sizes and resolutions. The b2g value currently works well for the buri, but is a bit slow for the nexus-4 or nexus-5. We should convert the velocity preference to be expressed in screens/second or some other device neutral fashion. We can then calculate the px/ms from that value. The current limit of 6 px/ms works out to 12.5 screens/second on the buri.

You should be able to multiply APZCTreeManager::GetDPI() to convert to a screen-resolution-dependent unit. See AXIS_BREAKOUT_THRESHOLD and its use site in AsyncPanZoomController.cpp for an example.

I think we should get this into 1.4 since the current velocity cap is tuned for small screens like the buri. The 1.4 production devices like open c have larger screens.

Hamachi has a DPI of 160, so I just divided that out to maintain the same final value on Hamachi, and scale it accordingly on other devices.

Comment on attachment 8391432 [details] [diff] [review] Patch Review of attachment 8391432 [details] [diff] [review]: ----------------------------------------------------------------- I think we want to update the pref name, but otherwise it looks good. I'm not a peer, though, so can I officially review? ::: b2g/app/b2g.js @@ +874,2 @@ > // to avoid checkerboarding. Note, float value must be set as a string. > +pref("apz.max_velocity_pixels_per_ms", "0.0375"); s/pixels/inches/g

Comment on attachment 8391432 [details] [diff] [review] Patch It was explained to me that only one of [reviewer,reviewee] has to be a peer. So r=me with the updated pref name. Thanks!

Good catch, thanks. Updated the pref name and landed: https://hg.mozilla.org/integration/mozilla-inbound/rev/2e54fe94c127

Followup to fix the pref name (doh!): https://hg.mozilla.org/integration/mozilla-inbound/rev/b377204840b9 I also cancelled the build jobs for the previous rev since it's more useful to just get them on this follow-up.

https://hg.mozilla.org/mozilla-central/rev/2e54fe94c127 https://hg.mozilla.org/mozilla-central/rev/b377204840b9