#!/bin/bash

# gammatrip.sh by B. Watson, licensed under the WTFPL.
# Randomly change gamma in X, crude simulation of an acid trip.
# It's also similar to the Atari 400/800/XL/XE "Atrract Mode"

#### user-tweakable knobs:

# seconds to sleep between gamma changes
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}

#### end of user-tweakable knobs.

init() {
	trap cleanup SIGINT SIGABRT SIGHUP SIGTERM
	OUTPUT="${OUTPUT:-$( xrandr | grep ' connected' | cut -d' ' -f1 )}"
	echo "Using output '$OUTPUT'"
}

cleanup() {
	echo "Restoring default gamma"
	xrandr --output "$OUTPUT" --gamma "1.0:1.0:1.0"
	exit 0
}

getrand() {
	range=$(( MAX - MIN ))
	echo $(( ( RANDOM % range ) + MIN ))
}

cycle() {
	r=0; g=0; b=0
	r="$( getrand )"
	g="$( getrand )"
	b="$( getrand )"
	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 $cmd | sed 's,:$,,' )"

	echo $cmd
	$cmd
}

init
while true; do
	cycle
	sleep "$DELAY"
done