Implementing smooth scrolling in an X client

[Paul Vojta]

Folks:

I've started working on implementing smooth scrolling in xdvi, and I have a
question about it.

When I do

	xinput --test 9

(where 9 is the deviceid of my Synaptics touchpad) and stroke my finger
down the right-hand side of the touchpad, I get an increasing sequence of
numbers:

motion a[3]=1935 
motion a[3]=1950 
motion a[3]=1964 
motion a[3]=1979 
motion a[3]=2007 
motion a[3]=2017 
motion a[3]=2034 
motion a[3]=2062 
motion a[3]=2088 
motion a[3]=2124 
motion a[3]=2154 
motion a[3]=2185 
motion a[3]=2210 

etc.  So far I've modified xdvi so that I can get a similar printout from
xdvi.

I guess that what I'm supposed to do with these numbers is keep track of
the most recently reported number, and scroll based on the differences
between the numbers.

But now if I move my mouse to some other window (e.g., xterm), scroll in
that window for a while, and then move back, the numbers reported to
xdvi would reflect the scrolling activity done in the other window.

So I would need to keep track of EnterNotify events for each window for
which I'm doing smooth scrolling, and set a flag each time such an event
is received.

A problem with this (other than the extra programming effort required)
is that on four-button Synaptics touchpads, the first button press of
the third or fourth button after returning to the xdvi window would
(I think) have no effect anymore.  (More generally, the first scrolling
distance would be ignored for every return to the window, but would not
be noticeable unless it was produced by a button press or simulated button
press.)

Is this correct?

And, more to the point, is there some way by which I could just receive the
deltas of the scrolling valuators for when the pointer is in the designated
window?

I am using Debian on x86_64, with the following package versions:

	xserver-xorg-core  2:1.12.1.902-1
	xserver-xorg-input-synaptics  1.6.1-1
	xinput  1.6.0-1

Sincerely,


Paul Vojta