JoeWreschnig: HDAPS-based screen rotation for the X61

2009-04-12T08:57:55Z

HDAPS-based screen rotation for the X61

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In the middle of fighting to get the X61's screen rotate button to talk to xrandr, I realized that the laptop already has an accelerometer in it and given that, the screen rotate button was a crappy UI anyway.

So, here's a way to make the laptop automatically rotate the screen, based on the accelerometer, when in tablet mode. It was written on a system running Ubuntu 8.10, but any system with ACPI and HDAPS configured should work.

First, we need two files to tell acpid to stick a flag in the filesystem when switching between tablet and laptop modes.

*/etc/acpi/lenovo-rotate
<pre>
event=ibm/hotkey HKEY 00000080 00005009
action=/usr/bin/touch /var/lib/acpi-support/tablet
</pre>

*/etc/acpi/lenovo-rotate-back
<pre>
event=ibm/hotkey HKEY 00000080 0000500a
action=/bin/rm -f /var/lib/acpi-support/tablet
</pre>

Second, we need something to rotate the screen when the HDAPS device passes a certain movement threshold.

* autorotate.py
<pre>
#!/usr/bin/env python

import glob
import select
import struct
import sys
import os
from fcntl import ioctl

JS_EVENT_FMT = "IhBB"
JS_EVENT_SIZE = struct.calcsize(JS_EVENT_FMT)

# Event types --
JS_EVENT_BUTTON = 0x01 # button pressed/released
JS_EVENT_AXIS = 0x02 # joystick moved
JS_EVENT_INIT = 0x80 # "virtual" event flag

# ioctl magic codes for device info --
JSIOCGAXES = 0x80016a11 # axis count
JSIOCGBUTTONS = 0x80016a12 # button count
JSIOCGNAME = 0x81006a13 # device name

# ~0.56 is straight vertical
TILT_THRESHOLD = 0.38

# Names of xinput devices to rotate with the screen
TOUCH_DEVICES = "stylus eraser pad touch".split()

def find_hdaps():
for filename in glob.glob("/dev/input/js*") + glob.glob("/dev/js*"):
try: dev = open(filename, "rb")
except (IOError, OSError): continue
else:
axes = struct.unpack(
"b", ioctl(dev, JSIOCGAXES, " "))[0]
buttons = struct.unpack(
"b", ioctl(dev, JSIOCGBUTTONS, " "))[0]
name = struct.unpack(
"1024s", ioctl(dev, JSIOCGNAME, " " * 1024))[0]
name = name.rstrip().strip("\x00")
if name == "hdaps":
return dev
else:
dev.close()

def set_state(state):
os.system("xrandr -o %s" % state)
pen_rot = ["normal", "right", "left", "inverted"].index(state)
for dev in TOUCH_DEVICES:
os.system("xsetwacom set %s rotate %d" % (dev, pen_rot))

def main(argv):
state = "normal"

dev = find_hdaps()
if not dev:
raise SystemExit("Unable to find HDAPS joystick device.")
while select.select([dev], [], []):
# Unpack the event and send it!
evt = dev.read(JS_EVENT_SIZE)
time, value, etype, number = struct.unpack(JS_EVENT_FMT, evt)
if etype & JS_EVENT_AXIS:
value = value / 32768.0
if number == 0 and value > TILT_THRESHOLD:
new_state = "normal"
elif number == 0 and value < -TILT_THRESHOLD:
new_state = "inverted"
elif number == 1 and value < -TILT_THRESHOLD:
new_state = "left"
elif number == 1 and value > TILT_THRESHOLD:
new_state = "right"
else:
new_state = state
if state != new_state:
if (new_state != "normal"
and not os.path.exists("/var/lib/acpi-support/tablet")):
new_state = "normal"
if new_state != state:
state = new_state
set_state(state)

if __name__ == "__main__":
main(sys.argv[1:])
</pre>

Then, <code>/etc/init.d/acpid reload</code>, and run <code>autorotate.py</code>. Switch your laptop to tablet mode, and spin it around. The screen should rotate appropriately. If you find it rotates too easily or not easily enough, tweak the TILT_THRESHOLD variable. If you named your XInput devices for the touchscreen differently, change the TOUCH_DEVICES string.

[[Category:X61]]

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JoeWreschnig: HDAPS-based screen rotation for the X61