doc: add example calibration-helper script

This is not to be installed, except maybe as a doc. It is just an
example of what one might do.  It also has not been tested, it's just
for giving an idea of what it should do.

It also contains untested speculation.

v2:
- use syspath instead of devpath
- add license blurb

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>

Makefile.am

@@ -1605,6 +1605,7 @@ SUFFIXES = .1 .5 .7 .man
 	$(AM_V_GEN)$(SED) $(MAN_SUBSTS) < $< > $@
 
 EXTRA_DIST +=					\
+	doc/calibration-helper.bash		\
 	man/weston.man				\
 	man/weston-drm.man			\
 	man/weston-rdp.man			\

doc/calibration-helper.bash

@@ -0,0 +1,66 @@
+#!/bin/bash
+
+# Copyright 2018 Collabora, Ltd.
+# Copyright 2018 General Electric Company
+#
+# Permission is hereby granted, free of charge, to any person obtaining
+# a copy of this software and associated documentation files (the
+# "Software"), to deal in the Software without restriction, including
+# without limitation the rights to use, copy, modify, merge, publish,
+# distribute, sublicense, and/or sell copies of the Software, and to
+# permit persons to whom the Software is furnished to do so, subject to
+# the following conditions:
+#
+# The above copyright notice and this permission notice (including the
+# next paragraph) shall be included in all copies or substantial
+# portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+# This is an example script working as Weston's calibration helper.
+# Its purpose is to permanently store the calibration matrix for the given
+# touchscreen input device into a udev property. Since this script naturally
+# runs as the user that runs Weston, it presumably cannot write directly into
+# /etc. It is left for the administrator to set up appropriate files and
+# permissions.
+
+# To use this script, one needs to edit weston.ini, in section [libinput], add:
+#   calibration_helper=/path/to/bin/calibration-helper.bash
+
+# exit immediately if any command fails
+set -e
+
+# The arguments Weston gives us:
+SYSPATH="$1"
+MATRIX="$2 $3 $4 $5 $6 $7"
+
+# Pick something to recognize the right touch device with.
+# Usually one would use something like a serial.
+SERIAL=$(udevadm info "$SYSPATH" --query=property | \
+	awk -- 'BEGIN { FS="=" } { if ($1 == "ID_SERIAL") { print $2; exit } }')
+
+# If cannot find a serial, tell the server to not use the new calibration.
+[ -z "$SERIAL" ] && exit 1
+
+# You'd have this write a file instead.
+echo "ACTION==\"add|change\",SUBSYSTEM==\"input\",ENV{ID_SERIAL}==\"$SERIAL\",ENV{LIBINPUT_CALIBRATION_MATRIX}=\"$MATRIX\""
+
+# Then you'd tell udev to reload the rules:
+#udevadm control --reload
+# This lets Weston get the new calibration if you unplug and replug the input
+# device. Instead of writing a udev rule directly, you could have a udev rule
+# with IMPORT{file}="/path/to/calibration", write
+# "LIBINPUT_CALIBRATION_MATRIX=\"$MATRIX\"" into /path/to/calibration instead,
+# and skip this reload step.
+
+# Make udev process the new rule by triggering a "change" event:
+#udevadm trigger "$SYSPATH"
+# If you were to restart Weston without rebooting, this lets it pick up the new
+# calibration.