In XI2.1, XISlaveSwitch events don't give accurate values for the vertical scroll valuator (and probably others). To duplicate: Have two pointing devices attached to the system. At least one of them (call it Mouse A) should use the evdev device. Start up an application that supports smooth scrolling. In the application window, with Mouse A, scroll the wheel to make its valuator nonzero. Start using the other pointing device, then resume using Mouse A. When you first click the scroll wheel, it'll show a large scroll event. This is because the XISlaveSwitch notification says that the valuator has value 0, but its value is whatever it was before starting to use the other mouse.
http://patchwork.freedesktop.org/patch/13387/
commit 23d1bc69f305edd5a6e2cfec3dfc84befda0881c Author: Peter Hutterer <peter.hutterer@who-t.net> Date: Thu Mar 14 11:07:57 2013 +1000 dix: send the current axis value in DeviceChangedEvents (#62321)
I find that the bug is not yet fixed (as of xorg-server-1.14.2). I now get nonzero values in XISlaveSwitch events, and they correspond to previous values of the valuator, but they don't reflect the situation in those cases in which the valuator is cleared. I attach some debugging output (with explanation), and a proposed patch (which should be self-exlanatory).
Created attachment 82526 [details] Debugging output that exhibits the bug (as it exists currently)
Created attachment 82527 [details] [review] Suggested patch
I've found that the problem also occurs with the values returned by XIQueryDevice. To reproduce (again, with a synaptics touchpad (synaptics driver) and a standard mouse (evdev driver)): 1. Before starting the application, scroll the synaptics driver up to get a large negative valuator value. 2. Switch to the standard mouse, and then back to the touchpad. 3. Start up the application. 4. Scroll using the touchpad, and note that the window scrolls to the bottom at first. Here is some debugging output (explanations same as before, but 8 is standard mouse, 10 is synaptics: IV 8 0 IV 10 -6610 dv 10 -6610 -> -4 dv 10 -5 -> -12 dv 10 -11.25 -> -14 dv 10 -13.75 -> -19 dv 10 -18.75 -> -21
Created attachment 82855 [details] [review] Sample patch (apply on top of previous patch)
This is a mass change of bugs. Bugs assigned to me that haven't been updated in the last 3 years are closed as WONTFIX, because, well, let's at least be honest about it. Please do not re-open unless you have a really good reason to do so (e.g. you're fixing it yourself). If it hasn't been fixed in the last 3 years, it probably won't be fixed anytime soon either. Sorry.
Use of freedesktop.org services, including Bugzilla, is subject to our Code of Conduct. How we collect and use information is described in our Privacy Policy.