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#!/bin/bash
# gammatrip.sh by B. Watson <urchlay@slackware.uk>.
# Licensed under the WTFPL. See http://www.wtfpl.net/txt/copying/ for details.
# Developed on Slackware 14.2, should work on most modern Linux distros.
# Randomly change gamma in X, crude simulation of an acid trip.
# It's also similar to the Atari 400/800/XL/XE "Attract Mode".
# Runs until killed via ^C or closing its terminal window, at which time
# it restores the original gamma setting, then exits.
#### User-tweakable knobs. If you don't feel like editing the script,
# just put them on the command line, in front of the command:
# $ DELAY=0.5 MAX=150 MIN=0 gammatrip.sh
# XRandR output to use. Leaving this blank means to use the
# first output listed by the xrandr command. Usual values are
# e.g. VGA-1 or DVI-1.
OUTPUT=
# Seconds to sleep between gamma changes. Decimal point allowed, so
# long as your system's sleep command allows it.
DELAY=${DELAY:-3}
# Max gamma for each individual color. Lower number here means darker
# colors on average. Units are 1/100ths of xrandr's --gamma floats,
# MAX=100 means 1.0. Maximum value for MAX is 999.
MAX=${MAX:-100}
# Minimum gamma for each color. Don't set higher than MAX!
# Same units as MAX.
MIN=${MIN:-30}
# VERBOSE=y to see the commands as they're executed, anything else
# means don't display them.
VERBOSE=y
#### End of user-tweakable knobs.
printmsg() {
[ "$VERBOSE" = "y" ] && echo "$@"
}
errmsg() {
echo "$SELF:" "$@" 1>&2
}
# Check knobs for sane(ish) settings, set up signal handlers,
# guess the active XRandR output if not provided. Get original
# gamma setting, so we can restore it later.
init() {
SELF="$( basename $0 )"
err=0
if [ "$MAX" -ge 1000 ]; then
errmsg "You can't set MAX >= 1000"
err=1
fi
if [ "$MIN" -ge "$MAX" ]; then
errmsg "You can't set MIN >= MAX"
err=1
fi
if [ "$#" != "0" ]; then
errmsg "No arguments accepted."
errmsg "Edit script or set MIN/MAX/OUTPUT/DELAY/VERBOSE in environment."
err=1
fi
if [ -z "$DISPLAY" ]; then
errmsg "DISPLAY not set (are you running X?)"
err=1
fi
[ "$err" -gt 0 ] && exit "$err"
# SIGINT is ^C, SIGHUP is what we get when our xterm is closed.
# SIGABRT is ^\, I hardly ever remember it exists. Trapping it here
# doesn't work: ^\ sends the abort signal to the active child
# process (usually sleep). Oh well. The other signals are 'just in case'.
trap cleanup SIGINT SIGABRT SIGHUP SIGTERM SIGHUP
OUTPUT="${OUTPUT:-$( xrandr | grep ' connected' | cut -d' ' -f1 )}"
if [ -z "$OUTPUT" ]; then
errmsg "Invalid OUTPUT in environment, or XRandR not supported."
exit 1
fi
# Try to save the old gamma, for cleanup() to restore. Not thoroughly
# tested (works on my system).
OLDGAMMA="$( xrandr --verbose | sed -n '/^'$OUTPUT' /,/^[A-Z]/s/.*Gamma: *//p' )"
# If the above command fails:
OLDGAMMA="${OLDGAMMA:-1.0:1.0:1.0}"
printmsg "Using output '$OUTPUT', old gamma '$OLDGAMMA'. Have a nice trip!"
}
# Called when we get a signal we trapped in init().
cleanup() {
echo
printmsg "Restoring old gamma"
xrandr --output "$OUTPUT" --gamma "$OLDGAMMA"
exit 0
}
# Takes 2 agruments: min and max. Returns a random number between
# min and max (actually >= min and < max).
getrand() {
min="$1"
max="$2"
range=$(( max - min ))
echo $(( ( RANDOM % range ) + min ))
}
# Pick random RBG values between MIN and MAX, use them to set the gamma.
cycle() {
r="$( getrand $MIN $MAX )"
g="$( getrand $MIN $MAX )"
b="$( getrand $MIN $MAX )"
cmd="xrandr --output $OUTPUT --gamma "
for i in $r $g $b; do
cmd="$cmd$( printf "%03d" $i | sed 's,^.,&.,' ):"
done
# Remove trailing colon. Actually, xrandr doesn't care about it,
# but someday it might.
cmd="$( echo $cmd | sed 's,:$,,' )"
printmsg $cmd
$cmd
}
### main()
init "$@"
while true; do
cycle
sleep "$DELAY"
done
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