[PATCH evdev] man: add a warning that wheel emu inertia must be set and it isn't inertia

Peter Hutterer peter.hutterer at who-t.net
Wed Jan 13 17:39:18 PST 2016

First, it's not actually inertia, it's simply the scroll distance, yay for the

And it needs to be set for any device that is more fine-grained than a
mouse, especially absolute devices. For example the VirtualBox device has an
abs max of 32767, so a simple motion may have a delta of to 2000 units and
that results in 200 scroll events. That's a bit excessive.

Related to: https://bugs.freedesktop.org/show_bug.cgi?id=93617

Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
 man/evdev.man | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/man/evdev.man b/man/evdev.man
index e70ae1f..8d84364 100644
--- a/man/evdev.man
+++ b/man/evdev.man
@@ -125,6 +125,19 @@ Property: "Evdev Wheel Emulation Button".
 Specifies how far (in pixels) the pointer must move to generate button
 press/release events in wheel emulation mode.  Default: 10. Property: "Evdev
 Wheel Emulation Inertia".
+This value must be set for any device does not resemble a standard mouse.
+Specifically, on absolute devices such as tablets the value should be set to
+a reasonable fraction of the expected movement to avoid excess scroll events.
+the name \*qinertia\*q is a misnomer. This option defines the distance
+required to generate one scroll event similar to the
+.B VertScrollDelta
+.B HorizScrollDelta
+options. It does not enable inertia in the
+physical sense, scrolling stops immediately once the movement has stopped.
 .TP 7
 .BI "Option \*qEmulateWheelTimeout\*q \*q" integer \*q
 Specifies the time in milliseconds the

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