.TH MOUSESCROLLSIZE 3
.SH NAME
mousescrollsize \- compute mouse scroll increment
.SH SYNOPSIS
.B #include <draw.h>
.PP
int	mousescrollsize(int maxlines)
.SH DESCRIPTION
.I Mousescrollsize
computes the number of lines of text that should be scrolled
in response to a mouse scroll wheel click.
.I Maxlines
is the number of lines visible in the text window.
.PP
The default scroll increment is one line.
This default can be overridden by setting the
.B $mousescrollsize
environment variable to an integer, which specifies
a constant number of lines, or to a real number
followed by a percent character, indicating that the
scroll increment should be a percentage of the total
number of lines in the window.
For example, setting 
.B $mousescrollsize
to 
.B 50%
causes a half-window scroll increment.
.PP
.I Mousescrollsize
is used by
.IR 9term (1)
and
.IR acme (1)
to set their scrolling behavior.
.SH SOURCE
.B /usr/local/plan9/src/libdraw/scroll.c
.SH SEE ALSO
.IR 9term (1),
.IR acme (1)
.SH BUGS
.I Libdraw
expects up and down scroll wheel events to be expressed as clicks of mouse buttons 4 and 5,
but the XFree86 default is to ignore the scroll wheel.
To enable the scroll wheel, change your
.B InputDevice
section of
.B XF86Config-4
to look like:
.IP
.EX
Section "InputDevice"
	Identifier	"Mouse0"
	Driver	"mouse"
	Option	"Device" "/dev/psaux"

	# next four lines enable scroll wheel as buttons 4 and 5
	Option	"Buttons" "5"
	Option	"Emulate3Buttons" "off"
	Option	"Protocol" "ImPS/2"
	Option	"ZAxisMapping" "4 5"
EndSection
.EE