hdr auto-toggle script for Sway

hdr_toggle.sh

#!/usr/bin/env bash

# hdr-toggle — enable HDR on a sway output for the duration of a command
#
# Turns HDR on for an HDR-capable output, runs the wrapped command, then
# restores the output's previous HDR state

set -euo pipefail

usage() {
	cat <<'EOF'
Usage: hdr-toggle [--] <command> [args...]

Enable HDR on a sway output, run <command>, then restore the prior HDR state
once it exits.

Output selection (in order of precedence):
  1. HDR_OUTPUT                 — output name; must be HDR-capable.
  2. WAYLANDDRV_PRIMARY_MONITOR — Wine's primary monitor; used if HDR-capable,
                                  otherwise ignored with a warning.
  3. The first HDR-capable output.

      HDR_OUTPUT=DP-2 hdr-toggle <command> [args...]

  List output names with:  swaymsg -t get_outputs -r | jq -r '.[].name'

Environment:
  HDR_OUTPUT    Force the target output by name (overrides everything below).
  HDR_DELAY     Seconds to wait after enabling HDR before running the command,
                for monitors slow to switch (e.g. HDR_DELAY=2). Accepts decimals.

Options:
  -h, --help    Show this help and exit.

Examples:
  hdr-toggle gamescope -- mygame
  HDR_OUTPUT=DP-1 hdr-toggle steam -applaunch 123456
  HDR_DELAY=2 hdr-toggle mygame
EOF
}

case "${1-}" in
	-h | --help)
		usage
		exit 0
		;;
	"")
		usage >&2
		exit 1
		;;
	--)
		shift
		;;
esac

if [[ $# -eq 0 ]]; then
	echo "hdr-toggle: no command given" >&2
	usage >&2
	exit 1
fi

command -v swaymsg >/dev/null 2>&1 || {
	echo "hdr-toggle: swaymsg not found (is sway installed?)" >&2
	exit 1
}
command -v jq >/dev/null 2>&1 || {
	echo "hdr-toggle: jq not found" >&2
	exit 1
}

if [[ -n "${HDR_DELAY-}" ]] && ! [[ "$HDR_DELAY" =~ ^[0-9]+(\.[0-9]+)?$ ]]; then
	echo "hdr-toggle: HDR_DELAY must be a non-negative number of seconds" >&2
	exit 1
fi

outputs=$(swaymsg -t get_outputs -r 2>/dev/null) || {
	echo "hdr-toggle: cannot reach sway IPC (is sway running? is SWAYSOCK set?)" >&2
	exit 1
}

# Returns an output's .features.hdr value ("true"/"false"), or "" if not found.
output_hdr_cap() {
	jq -r --arg o "$1" '.[] | select(.name==$o) | .features.hdr' <<<"$outputs"
}

# Select the target output by precedence:
#   1. HDR_OUTPUT                 — explicit; hard error if missing/not capable.
#   2. WAYLANDDRV_PRIMARY_MONITOR — hint; warn and fall back if missing/not capable.
#   3. first HDR-capable output.
OUTPUT=""
if [[ -n "${HDR_OUTPUT-}" ]]; then
	cap=$(output_hdr_cap "$HDR_OUTPUT")
	if [[ -z "$cap" ]]; then
		echo "hdr-toggle: output '$HDR_OUTPUT' not found" >&2
		exit 1
	fi
	if [[ "$cap" != "true" ]]; then
		echo "hdr-toggle: output '$HDR_OUTPUT' is not HDR-capable" >&2
		exit 1
	fi
	OUTPUT="$HDR_OUTPUT"
elif [[ -n "${WAYLANDDRV_PRIMARY_MONITOR-}" ]]; then
	cap=$(output_hdr_cap "$WAYLANDDRV_PRIMARY_MONITOR")
	if [[ "$cap" == "true" ]]; then
		OUTPUT="$WAYLANDDRV_PRIMARY_MONITOR"
	elif [[ -z "$cap" ]]; then
		echo "hdr-toggle: WAYLANDDRV_PRIMARY_MONITOR='$WAYLANDDRV_PRIMARY_MONITOR' not found; using first HDR-capable output" >&2
	else
		echo "hdr-toggle: WAYLANDDRV_PRIMARY_MONITOR='$WAYLANDDRV_PRIMARY_MONITOR' is not HDR-capable; using first HDR-capable output" >&2
	fi
fi

if [[ -z "$OUTPUT" ]]; then
	OUTPUT=$(jq -r '[.[] | select(.features.hdr==true)][0].name // empty' <<<"$outputs")
	if [[ -z "$OUTPUT" ]]; then
		echo "hdr-toggle: no HDR-capable output found" >&2
		exit 1
	fi
fi

PRIOR=$(jq -r --arg o "$OUTPUT" '.[] | select(.name==$o) | .hdr' <<<"$outputs")

restored=0
# shellcheck disable=SC2329  # invoked indirectly via trap
restore_hdr() {
	[[ $restored -eq 1 ]] && return
	restored=1
	if [[ "$PRIOR" == "true" ]]; then
		swaymsg output "$OUTPUT" hdr on >/dev/null
	else
		swaymsg output "$OUTPUT" hdr off >/dev/null
	fi
}
trap restore_hdr EXIT INT TERM

# Enable HDR (no-op if it was already on).
if [[ "$PRIOR" != "true" ]]; then
	swaymsg output "$OUTPUT" hdr on >/dev/null
	# Give a slow monitor time to switch modes before launching the command.
	[[ -n "${HDR_DELAY-}" ]] && sleep "$HDR_DELAY"
fi

# Run the wrapped command, preserving its exit code. The trap restores HDR.
set +e
"$@"
rc=$?
set -e
exit "$rc"