[Wayland-bugs] [Bug 99961] Wacom tablet produces wiggly bent lines when using libinput driver.

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=99961

--- Comment #9 from s at ecloud.org <s at ecloud.org> ---
I finally got around to testing Qt with xf86-input-libinput and various
tablets, and I see this too.

Sometimes when "jittery lines" have happened in the past, people have said that
we're doing the coordinate conversion wrong here:

http://code.qt.io/cgit/qt/qtbase.git/tree/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp#n1171

given a xXIDeviceEvent, we convert event_x and event_y from fixed 16.16 format
to floating-point by simply dividing by 65536.0.  The alternate way might be to
use axis valuators.  But it seems to me that using either xf86-input-wacom or
xf86-input-evdev, I don't normally see jittery lines using this approach.  (But
maybe sometimes one driver or the other has been buggy... not sure.  Krita
users and developers complain about it from time to time, and usually I can't
reproduce it the same way that they're complaining about.)  With
xf86-input-libinput I definitely do see the jitters though, so it's good that
you can too.  Good luck with the fix.

Do you think using event_x and event_y is the right way to do it?  Or should we
rather do it like this:
https://codereview.qt-project.org/#/c/110334/2/src/plugins/platforms/xcb/qxcbconnection_xi2.cpp
 Which way is do you think is more portable between all 3 drivers, and the
least likely to ever see these jitters again?

I have an Intuos 3 with all the styli, Intuos Pro, Bamboo CTH-470, a couple of
Genius and a Trust tablet for testing.  FWIW, those knockoffs don't work with
xf86-input-libinput at all right now (it says it doesn't recognize them as
tablets), whereas xf86-input-evdev works fine.  But that's a different bug.

-- 
You are receiving this mail because:
You are the assignee for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/wayland-bugs/attachments/20170303/b0076de2/attachment.html>