Two finger scroll gets speedup if another finger is accidentally added

[svenper]

When scrolling with two fingers, and adding a third finger for a split second and then continuing scrolling, the speed is increased what seems to be 10-fold or even 100-fold. After the speedup has occurred, while still scrolling, and tapping with a third finger another time, the speed goes back to normal.

Version 0.5.0 Linux 4.14.19 (musl libc) MacBookPro 12,1

[p2rkw]

Scrolling with third finger on touchpad will be recognized as 3 finger drag. Thus mtrack will send configured button. Actual action taken depend on your setup. On my machine it was toggling fullscreen.

Before I start investigating this, please you have to confirm it's caused by mtrack.

How to check that:

• run xinput --test <dev id>
• reproduce your issue with xinput running
• check in output which button was sent
• send that button with xdotool or something else

If speedup occurs with xdotool, it's not caused with mtrack, otherwise post your configuration (xinput --list-props).

[svenper]

I should clarify that that the added third finger can have two outcomes, depending mostly on how long the tap is and if the third finger also moves, I think.

• With a long deliberate movement I can get the same behaviour you describe, with both events for two finger and three finger scroll (e.g. 4 and 9).
• With a short accidental tap I get the speedup. But most of the time it has no effect at all and continues like a normal scroll.

The xinput prints events 4 and 5 for two finger scroll, and 8 and 9 for deliberate “clean” three finger scroll, but it prints the same button when accidentally tapping a third finger during a current two finger scroll, even when the speed up is apparent. What does happen is that the frequency of button signals increases in relation (and absolutely?) to the motion signals. This would mean that I have nothing worthwhile to send to e.g. xdotool?

Sample xinput output excerpts:

• normal two finger scroll
• after third finger is added and quickly removed

[knedlsepp]

I'm also seeing this behavior.

[p2rkw]

Ok, I need your output of xinput --list-props <dev ID>.

[knedlsepp]

Device 'bcm5974':                                                                                                                                            
        Device Enabled (138):   1                                                                                                                            
        Coordinate Transformation Matrix (140): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000                     
        Device Accel Profile (275):     2                                                                                                                    
        Device Accel Constant Deceleration (276):       2.100000                                                                                             
        Device Accel Adaptive Deceleration (277):       1.000000                                                                                             
        Device Accel Velocity Scaling (278):    1.000000                                                                                                     
        Trackpad Disable Input (279):   0                                                                                                                    
        Trackpad Sensitivity (280):     0.240000                                                                                                             
        Trackpad Touch Pressure (281):  5, 1                                                                                                                 
        Trackpad Button Settings (282): 1, 1                                                                                                                 
        Trackpad Button Emulation Settings (283):       0, 1, 10                                                                                             
        Trackpad Button Emulation Values (284): 1, 3, 2
        Trackpad Tap Settings (285):    50, 150, 400
        Trackpad Tap Button Emulation (286):    1, 3, 2, 0
        Trackpad Thumb Detection (287): 1, 0
        Trackpad Thumb Size (288):      22, 90
        Trackpad Palm Detection (289):  1, 1
        Trackpad Palm Size (290):       40
        Trackpad Gesture Settings (291):        10, 0
        Trackpad Smooth Scroll (292):   1
        Trackpad Scroll Settings (293): 180, 20, 0
        Trackpad Scroll Buttons (294):  4, 5, 6, 7
        Trackpad Swipe Settings (295):  1000, 300, 0
        Trackpad Swipe Buttons (296):   11, 10, 8, 9
        Trackpad Swipe4 Settings (297): 700, 300, 0
        Trackpad Swipe4 Buttons (298):  0, 0, 0, 0
        Trackpad Scroll Coasting (299): 0.050000, 1000.000000
        Trackpad Edge Scroll Settings (300):    105, 20, 0, 0, 0, 0, 0
        Trackpad Edge Sizes (301):      0, 0, 0, 15
        Trackpad Scale Distance (302):  150
        Trackpad Scale Buttons (303):   12, 13
        Trackpad Rotate Distance (304): 150
        Trackpad Rotate Buttons (305):  14, 15
        Trackpad Hold1Move1 Stationary Settings (306):  20, 0
        Trackpad Hold1Move1 Settings (307):     1, 0, 1000
        Trackpad Hold1Move1 Buttons (308):      1, 1, 1, 1
        Trackpad Drag Settings (309):   0, 1, 40, 200, 500
        Trackpad Axis Inversion (310):  0, 0

[svenper]

gist here

Device 'bcm5974':
    Device Enabled (141):   1
    Coordinate Transformation Matrix (143): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    Device Accel Profile (265): 0
    Device Accel Constant Deceleration (266):   1.000000
    Device Accel Adaptive Deceleration (267):   1.000000
    Device Accel Velocity Scaling (268):    10.000000
    Trackpad Disable Input (298):   0
    Trackpad Sensitivity (299): 0.125000
    Trackpad Touch Pressure (300):  5, 5
    Trackpad Button Settings (301): 1, 1
    Trackpad Button Emulation Settings (302):   0, 1, 100
    Trackpad Button Emulation Values (303): 1, 3, 2
    Trackpad Tap Settings (304):    50, 120, 400
    Trackpad Tap Button Emulation (305):    1, 3, 2, 0
    Trackpad Thumb Detection (306): 1, 0
    Trackpad Thumb Size (307):  25, 70
    Trackpad Palm Detection (308):  1, 0
    Trackpad Palm Size (309):   40
    Trackpad Gesture Settings (310):    10, 50
    Trackpad Smooth Scroll (311):   1
    Trackpad Scroll Settings (312): 150, 20, 0
    Trackpad Scroll Buttons (313):  5, 4, 7, 6
    Trackpad Swipe Settings (314):  700, 300, 0
    Trackpad Swipe Buttons (315):   8, 9, 10, 11
    Trackpad Swipe4 Settings (316): 700, 300, 0
    Trackpad Swipe4 Buttons (317):  0, 0, 0, 0
    Trackpad Scroll Coasting (318): 0.100000, 200.000000
    Trackpad Edge Scroll Settings (319):    105, 20, 0, 4, 5, 6, 7
    Trackpad Edge Sizes (320):  0, 10, 0, 0
    Trackpad Scale Distance (321):  150
    Trackpad Scale Buttons (322):   12, 13
    Trackpad Rotate Distance (323): 150
    Trackpad Rotate Buttons (324):  14, 15
    Trackpad Hold1Move1 Stationary Settings (325):  20, 1
    Trackpad Hold1Move1 Settings (326): 1, 0, 1000
    Trackpad Hold1Move1 Buttons (327):  1, 1, 1, 1
    Trackpad Drag Settings (328):   1, 350, 40, 200, 500
    Trackpad Axis Inversion (329):  0, 0

[p2rkw]

Thanks.

I suspect smooth scroll or coasting to have some impact on this. You can try to disable these and see does it change something or not.

[svenper]

I set both ScrollCoastDuration and ScrollCoastEnableSpeed to 0 and cannot reproduce the bug anymore. In a scroll, when tapping or holding the third finger now instead stops both button and motion events. Keeping the single finger pressed (static) and continuing to scroll after this can trigger three-finger scrolls, but very unreliaby.