Hello

I've been playing with xev and I confirmed whet I already suspected : when using button 8 ("back") as a ScrollButton, the choice between "back" and "scroll" is time-based, not events-based.

Explanation :
 1. I press button 8 for ~100ms, then release : "back"
 2. I press button 8 for ~500ms, then release : nothing
 3. I press button 8 for ~100ms, move the pointer, then release : "back"
 4. I press button 8 for ~500ms, move the pointer, then release : scroll

IMHO cases 2 and 3 are wrong : pressing button 8, however long, without any MotionNotify event, then release, should always trigger "back" ; and pressing button 8 however shortly, if I move the pointer, should generate ButtonPress + ButtonRelease for buttons 4 and 5 and not "back"

Correction : case number 3 generates "nothing", not "back" (because ButtonPress/ButtonRelease events for button 8 do not appear)

{{{

Explanation :
 1. I press button 8 for ~100ms, then release : "back"
 2. I press button 8 for ~500ms, then release : nothing
 3. I press button 8 for ~100ms, move the pointer, then release : nothing
 4. I press button 8 for ~500ms, move the pointer, then release : scroll

}}}

good point, that makes sense. that's a fairly trivial fix to make, I recommend having a look at evdev_button_scroll_button() and working your way from there. looks like all we need is an extra boolean that tells us whether we actually sent events so we know whether to filter the button press.

you can test locally with the ./tools/event-debug tool so you don't alway have to restart until it works

https://lists.freedesktop.org/archives/wayland-devel/2017-February/033165.html

commit 6a2870f5ca88d20e9e5a9c668ba95154815e0d49
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Mon Feb 20 13:32:07 2017 +1000

    evdev: add "READY" state to button scrolling

I'm wondering if button scrolling could use the same logic (and code) as two-finger scrolling. The only addition would be to generate button press/release event when scroll button is realeased and scrolling is not in pogress.