[Wayland-bugs] [Bug 91135] Two-finger scrolling jumpy with Synaptics touchpad

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=91135

--- Comment #21 from Peter Hutterer <peter.hutterer at who-t.net> ---
oh, ffs, I hate these touchpads.

event at 0.968621 has a 6.23mm jump in the x axis
event at 2.340838 has a 8.68mm jump in the x axis

Those two account for the horizontal scroll jump you can see in this recording.

event at 2.487409 has a 8.34mm jump in the y axis

That's the vertical jump close to the end of the recording.

This is in the single-touch emulation, we already disabled true multi-finger
tracking for the semi-mt touchpads because it's unreliable.

it's a bit unclear why this is happening too. The events leading up to this:


 2.292016: ↖↑ 3215/2774 | ↖↑ 3696/1269 | 
 2.316154: ↖↑ 3215/2728 | ↖↑ 3626/1269 | 
 2.340838: ↖↑ 3215/2721 | ↖← 3218/1269 | 
 2.365007: ↖↑ 3215/2715 |              | 
 2.389629: ↖← 3215/2713 |              | 
 2.415441: ↖← 3215/2711 |              | 
 2.464192: ↖← 3215/2709 |              | 
 2.487409: ↖↑ 3215/2678 | ↓↘ 3219/1778 | 
 2.512015: ↑↗ 3216/2658 | ↓↘ 3220/1778 | 
 2.536274: ↑↗ 3220/2658 | ↓↘ 3221/1778 | 

which is a bit confusing because the way I read the kernel's
synaptics_report_semi_mt_data() slot 1 should be the bottom-right touchpoint
but that isn't the case here. but either way, the jump is visible in slot 1

and the single touch emulation tracks slot 1 for coordinates:

 2.292016:  *********** | ↖← 3696/1269 | 
 2.316154:  *********** | ↙← 3626/1270 | 
 2.340838:  *********** | ↙← 3218/1270 | 
 2.365007:  *********** |              | 
 2.389629:  *********** | ↖← 3216/1269 | 
 2.415441:  *********** |              | 
 2.464192:  *********** |              | 
 2.487409:  *********** | ↓↘ 3222/1778 | 
 2.512015:  *********** |              | 
 2.536274:  *********** | →↗ 3224/1777 |


so in short: we don't have a warning about this, it's not caused by a finger
change and all we get is a sudden jump to some other position. which means we
have to find some other heuristics to detect those.

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