From the "Smooth Scrolling" section of [XI2Proto.txt][1]:
> One unit of scrolling in either direction is considered to be equivalent to
> one button event, e.g. for a unit size of 1.0, -2.0 on an valuator type
> Vertical sends two button press/release events for button 4. Likewise, a
> button press event for button 7 generates an event on the Horizontal
> valuator with a value of +1.0. The server may accumulate deltas of less than
> one unit of scrolling.
From [What's new in XI 2.1 - smooth scrolling][2]:
> The increment defines what delta the driver considers to be one scroll
> event. For an increment of +5, each delta of 5 should be regarded as one
> scroll unit down. For an increment of -3, each delta of 3 should be regarded
> as one scroll unit up (i.e. inverted).
[1]: http://www.x.org/releases/X11R7.7/doc/inputproto/XI2proto.txt
[2]: http://who-t.blogspot.com/2011/09/whats-new-in-xi-21-smooth-scrolling.html
This fixes scrolling with my Microsoft mouse in X11 on Debian 8.1.
fixes#314 for me.
I've "tested" change by running examples (which prior to change simply
crashed), but since I did not run those examples successfuly ever before,
I don't know whether they worked as intended.
XInput2 has a concept of master and slave devices,
where a slave device is the actual physical device,
attached to a master device representing the cursor or keyboard
focus.
See http://who-t.blogspot.co.uk/2009/05/xi2-recipes-part-1.html
Mouse events were being received from both the master and slave
devices, but we are only interested in events from the master device.
Fixes#533
* Fix an issue where PollEventsIterator::next() would fail to return
keyboard input and mouse events immediately but instead only
return them on the next call to next()
* Inline process_generic_event() and queue_event()
Scroll deltas are calculated in X11 by comparing the current and
previous absolute values for the scroll axis when a scroll motion
event is received. If the user scrolls whilst the cursor is outside
of the window then an incorrect delta is reported when the cursor
re-enters the window.
Fix this by resetting the last-seen axis values whenever the cursor
re-enters the window.
* For the moment we're still using plain core X11 events
for handling keyboard activity, so remove the XInput2 code for that
* Small refactoring of X11 input handling and documentation fixes
Depending on the platform and device, scroll deltas may either
be represented as pixel deltas specifying the amount
in pixels to scroll or they may be expressed in 'lines' or 'chunks'
for low resolution devices (eg. a traditional mouse wheel).
Pixel deltas are currently available on OS X. X11 currently
supports only integer line deltas, though pixel deltas
are available via XInput2. Windows supports fractional
line deltas.
