2009-10-25

How to enable autologin in Ubuntu Jaunty with GDM

To enable automatic login in Ubuntu Jaunty running GDM (default) without clicking, add something like this to the [daemon] section of /etc/gdm/gdm.conf-custom:
TimedLoginEnable=true
TimedLoginDelay=10
TimedLogin=myusername
Once done, restart gdm (this will force an immediate logout):
$ sudo /etc/init.d/gdm restart

2009-10-23

Using the Hama MCE remote on Linux with MPlayer

This blog post describes how to control your MPlayer media playback using the Hama MCE remote control on Linux. The instructions and software were tested on Ubuntu Jaunty, but they should work on any Linux 2.6 system which has sysfs mounted and which has USB HID support compiled to the kernel (can be checked with ls -l /sys/bus/usb/drivers/usbhid).

The instructions are for the model Hama MCE Remote 52451, also known as VRC-1100, but similar instructions might work with other remotes as well.

If you want to use the Hama MCE with XBMC, see these instructions.

The Hama MCE dongle, when connected to the USB port of a Linux machine, registers itself as two USB HID devices: a keyboard and a mouse. Most of its buttons generate regular keyboard events, for example, the numeric keys correspond to numpad keys, and its Enter key corresponds to the Enter key. You can use its mouse controls to move the mouse or click (the left and right buttons). On Ubuntu Jaunty, even the volume buttons work (they adjust the master volume).

However, if you don't want to use your Hama MCE remote as a regular keyboard or mouse, but you'd like to control MPlayer (and possibly some few other applications you specify) with it, then you need special software. LIRC, the de facto standard remote control driver and server does support USB HID devices in general, but the Hama MCE sends some quite unusual events which LIRC seems to be impossible to make recognize. (For example, the hashmark button sends Shift, 3 and 5, and some other buttons send Shift or Control too, and LIRC doesn't seem to be able to track the Shift and Control state, which would be needed to distinguish some buttons from each other.)

So I've implemented my own lircd, hama_mce_lircd.py, which can read button presses and other events from the Hama MCE remote, and it can broadcast them to applications via the socket /dev/lircd, using the traditional lircd protocol. The link above contains installation, usage and configuration instructions for controlling MPlayer with Hama MCE, using hama_mce_lircd.py.

Each button works and can be bound to any MPlayer input.conf command, with the following limitations (of the dongle hardware):

  • the ok and enter buttons are the same;
  • the play and pause buttons are the same;
  • the right click and the info buttons are the same;
  • most buttons don't repeat when held down for a long time.

An alternative and more generic Python Linux event reading and mangling library with Hama MCE support is available at http://github.com/rmt/pyinputevent/.

Here is how to use hama_mce_lircd.py with MPlayer:

$ wget -O /tmp/lircrc.hama \
  http://pts-mini-gpl.googlecode.com/svn/trunk/hama-mce-linux/lircrc
$ wget -O /tmp/hama_mce_lircd.py \
  http://pts-mini-gpl.googlecode.com/svn/trunk/hama-mce-linux/hama_mce_lircd.py
$ sudo killall lircd
$ sudo mkdir -p /var/run/lirc
$ sudo python /tmp/hama_mce_lircd.py /var/run/lirc/lircd
(connect the USB dongle, wait 3 seconds, and watch the script detect it)
(keep it running, open another terminal window)
$ mplayer -lircconf /tmp/lircrc.hama ${VIDEO_FILENAME}

The most important Hama MCE remote keys supported by lircrc.hama: Pause, Stop, Volume Up, Volume Down, Channel Plus (to speed up playback), Channel Minus (to slow down playback), Info (for showing/hiding OSD with the time indicator) the big round button (for seeking), the up and down arrows (for adjusting the subtitle delay).

2009-10-22

Design and print your own geek clock with LaTeX and TikZ



Would you like to have your custom clock for geeks (geek clock, math clock)? You can
design and print the front plate of your own analog geek clock using LaTeX and TikZ. Here is how I did it (download):
% geek_clock.tex
% by pts@fazekas.hu at Thu Oct 22 14:24:35 CEST 2009
\documentclass[a4paper]{article}
\usepackage{tikz}
\usepackage[latin2]{inputenc}
\usepackage{t1enc}
\usepackage{lmodern}

\pdfpagewidth=\paperwidth
\pdfpageheight=\paperheight

\newenvironment{fullpage}{%
\shipout\vbox\bgroup\kern-1in\moveleft1in\vbox to\paperheight\bgroup
\parindent0pt\hsize\paperwidth
}{%
\vfil\egroup\egroup
}

\begin{document}

% Define a few constants for easy configuration
\def\framehalf{9.2cm}
\def\radius{8.8cm}
\def\onedegrad{8.6cm}
\def\fivedegrad{8.5cm}
\def\tendegrad{8.2cm}
\def\labelrad{8.3cm}

\begin{fullpage}
\vfil\noindent\hfil
\begin{tikzpicture}[scale=1]
\draw (-\framehalf,-\framehalf) --
(\framehalf,-\framehalf) --
(\framehalf,\framehalf) --
(-\framehalf,\framehalf) -- cycle;
\draw (0,0) circle (\framehalf);
\draw (0,0) circle (\radius);
\draw[fill=black] (0,0) circle (2.5mm);
\node[draw, circle, inner sep=.2mm] (a) at (0,0) {};
% main lines
\foreach \x in {0, 6,...,360}
\draw[line width=1.5pt] (\x:\onedegrad) -- (\x:\radius);
% labels and longer lines at every 6 degrees
\foreach \x in {30, 60, ..., 360} {
\draw[line width=4pt] (\x:\tendegrad) -- (\x:\radius);
}
\node[scale=3,anchor=north east] at (450-1*30:\labelrad)
{$B'_L$\kern-1ex};
\node[scale=2.5,anchor=east] at (450-2*30:\labelrad)
{\lower8ex\hbox{$\displaystyle \sum_{i=0}^{\infty}1/2^i$\kern-2ex}};
\node[scale=3,anchor=east] at (450-3*30:\labelrad)
{$7\odot-5$};
\node[scale=3,anchor=south east] at (450-4*30:\labelrad)
{$\lceil\pi\rceil$};
\node[scale=3,anchor=south east] at (450-5*30:\labelrad)
{$(2\varphi-1)^2$\kern-4ex};
\node[scale=3,anchor=south] at (450-6*30:\labelrad)
{$3!$};
\node[scale=3,anchor=south west] at (450-7*30:\labelrad)
{$\!6.\overline{9}$};
\node[scale=4,anchor=west] at (450-8*30:\labelrad)
{\raise1ex\hbox{${\bullet}{\circ}{\circ}{\circ}$}};
\node[scale=2.5,anchor=west] at (450-9*30:\labelrad)
{$\lfloor(7\cdot.1\!-\!.7)^{\textrm{-6e-2}}\rfloor$};
\node[scale=2.5,anchor=west] at (450-10*30:\labelrad)
{\lower6ex\hbox{$\displaystyle{5\choose2}$}};
\node[scale=2.5,anchor=north west] at (450-11*30:\labelrad)
{\lower3ex\hbox{\kern-3ex$7^5\mathop{\mathrm{mod}} 13$}};
\node[scale=3,anchor=north] at (450-12*30:\labelrad)
{$\sqrt[3]{1728}$};
\end{tikzpicture}
\end{fullpage}

\end{document}
I used pdflatex and TikZ in TeX Live 2008 to compile the file above to a PDF file, which I printed, cut and glued to a stock clock.

References:

2009-10-21

Screen blanking, DPMS, screen saver control and timeout settings on X11

This blog post explains how to blank and unblank the screen manually, how to activate and deactivate display power saving (DPMS), and how to specify inactivity timeouts for screen blanking on X11. The examples were tried with Ubuntu Jaunty, X.Org 7.4 and icewm. This blog post doesn't explain how to make your changes permanent after logout, or how to change your GNOME settings.

The results below may be distorted if gnome-screensaver is running. To get rid of it, do this:
$ gconftool-2 --type boolean -s /apps/gnome_settings_daemon/screensaver/start_screensaver false
$ killall gnome-screensaver
Without setting start_screensaver to false above, gnome-settings-daemon would restart gnome-screensaver whenever a GNOME application gets started. (Firefox a GNOME Terminal is GNOME applications in Ubuntu Jaunty, but icewm and xterm aren't.)

X11 supports two distinct features for power saving when the user is away from the computer: screen blanking and power saving. Confusingly enough, the man page for xset uses the term screen saver instead of screen blanking. In our terminology, screen blanking is a feature to display a blank (solid black) screen after long enough user inactivity. However, screen saver is a program which gets started upon long enough user inactivity, which draws some simple animation on the screen, and asks the user's password before letting him back to his screen and applications. Power saving (DPMS turns the display off or puts it to some power-saving mode after long enough user inactivity. In power saving mode the display doesn't show anything, but it consumes much less power, see the DPMS link above for typical watt values for the power-saving modes standby, suspend and off (and also in the mode on, when power saving is inactive). User inactivity means that the user doesn't use the keyboard or the mouse for a configurable number of seconds. The typical default inactivity timeouts are around 2 minutes. By default, the X server disables screen blanking and power saving as soon as the user presses a key or moves the mouse. From now on we assume that there is no screen saver running, or its timeout is set to be high enough so it won't ever trigger. Screen blanking and power saving are independent features, they have to be configured independently.

How to set up the timeouts

  • To disable screen blanking, run xset s off
  • To make the screen blank after 600 seconds of user inactivity, run xset s 600
  • To put the display to standby after 100 seconds, to suspend after 200 seconds, and turn it off after 300 seconds, run xset dpms 100 200 300
  • To disable power saving, run xset dpms 0 0 0
  • To make the screen blanking display thee X11 logo on a blue background instead of displaying a solid black screen, run xset s noblank
  • To make the screen blanking display a solid black screen (default), run xset s blank

How to change the screen state immediately

  • To blank the screen, run xset s activate
  • To unblank the screen, run xset s reset
  • To turn the screen off, run xset dmps force off
  • To activate the suspend power-saving mode (good savings, good resume time), run xset dpms force suspend
  • To activate the standby power-saving mode (minimal savings, very quick resume time), run xset dpms force standby
  • To turn the display on, run xset dpms force on; xset s reset (the latter is necessary because the screen was blanked automatically when power saving was activated).

How to prevent screen blanking and power saving in MPlayer

Most media player applications disable blanking and power saving while they are playing a video. To enable this functionality in MPlayer, start it with mplayer -stop-xscreensaver or add the line stop-xscreensaver=1 to your ~/.mplayer/config . By doing so, MPlayer will simulate user activity (just as if the user has moved the mouse) upon startup and then each 30 seconds. So this will prevent the screen from blanking or going to power saving mode if all your timeouts are larger than 30 seconds. Please note that the name of the flag is confusing, because its effect isn't related to screen savers, it just simulates user activity. If a screen saver is running, it may or may not pick up the simulated activity generated by MPlayer. To prevent screen saver activation in this case, you may have to run mplayer -heartbeat-cmd "xscreensaver-command -deactivate" or mplayer -heartbeat-cmd "gnome-screensaver-command -p" .

2009-10-04

JavaScript and ActionScript performance for big integer multiplication

This blog post documents the speed measurement of various JavaScript and ActionScript (and other) implementations multiplying 2048-bit big integers. I needed big integer multiplication for the Diffie-Hellman key exchange in one of my projects.

Since neither JavaScript nor ActionScript has big integer support built in, I had to implement it. I represent a big integer as a JavaScript array of digits in base 32768, in the base To multiply two 2048-bit integers use Karatsuba multiplication, which does 3 multiplications with 1024-bit operand size. To multiply two 1024-bit integers, I use Karatsuba multiplication (again), which does 3 multiplications with 512-bit operand size. To multiply two 512-bit integers, I use traditional O(n^2) ``schoolbook'' multiplication. (The Karatsuba multiplication would have been slower for this size.) All JavaScript and ActionScript code is heavily optimized, constants are inlined, and functions are instantiated for different operand sizes.

I did at least 500 multiplications of 2048-bit operand size. Here is the average number of milliseconds needed for 1 multiplication in the various implementations on an Intel Core 2 Duo 1.5 GHz machine running 32-bit Unbuntu Hardy:
  • 00.0156 ms: Python (C) 2.4 gmpy (mpz of libgmp)
  • 00.0396 ms: Java 1.6.0_16 BigInteger
  • 00.0516 ms: Ruby (C) 1.9.1 Bignum
  • 00.0650 ms: Python (C) 2.4 long
  • 01.3030 ms: JavaScript Google Chrome V8 1.1.1.4
  • 02.1750 ms: ActionScript 3 for Flash Player 10
  • 02.7120 ms: JavaScript Google Chrome V8 1.1.1.4 using BigInt.js' mult()
  • 04.5150 ms: JavaScript Firefox 3.5 TraceMonkey from Mercurial on 2009-10-04
  • 05.0400 ms: JavaScript Firefox 3.5.2 TraceMonkey
  • 05.2860 ms: JavaScript Firefox 3.0.14 TraceMonkey (?) JavaScript
  • 06.9050 ms: ActionScript 3 for Flash Player 9 on Flash Player 9
  • 08.5320 ms: ActionScript 3 for Flash Player 9 on Flash Player 10
  • 10.2900 ms: JavaScript SpiderMonkey command-line interpreter 1.7.0 2007-10-03
The speed tests were run on multiple 32 and 64-bit Debian and Ubuntu installations, and the ratios came out almost the same as above.

The JavaScript and ActionScript (and some other) sources are avaialble at http://code.google.com/p/pts-mini-gpl/source/browse/#svn/trunk/javascript-multiplication.

Conclusion: If you need big integer arithmetic in the browser, detect Java and use its BigInteger from JavaScript. Otherwise, if the browser is Google Chrome, then do it in JavaScript. Otherwise, if there is Flash Player 10, do it in ActionScript 3. Otherwise, use JavaScript (and suggest installation of Java or Flash to the user).

How to create an ActionScript 3 (AS3) flash movie (SWF) without a GUI

This blog post explains how to create a Flash movie completely automatically, without using a GUI, just by writing a program in the language ActionScript 3 (AS3). The post gives instructions for Linux, but they should work with minor modifications on other operating systems as well since the compilers to be used are either written in Java or they are available for multiple systems.

ActionScript is a language similar to JavaScript, with some differences and incompatibilities. The most important difference is that you can declare types of variables (strongly recommended in ActionScript 3), and it has class-based inheritance, so classes are declared and use differently from JavaScript, more similarly to Java. To get a quick introduction to ActionScript, read http://en.wikipedia.org/wiki/ActionScript. The reference manual is hosted by Adobe, at http://livedocs.adobe.com/flash/9.0/ActionScriptLangRefV3/. The filename extension is .as.

ActionScript has two major versions in used today: ActionScript 2 (AS2) is supported by Flash Player 7, 8, 9 and 10. ActionScript 3 (AS3) is supported by Flash Player 9 and 10. ActionScript 2 is about 3.5 times (or even more) slower than the JavaScript interpreter in Firefox 3.0 (SpiderMonkey). ActionScript 3, as implemented in Flash Player 9, has just about the same speed as Firefox 3.0 JavaScript. ActionScript 3, as implemented in Flash Player 10, can be up to 4 times faster than FireFox 3.0 JavaScript if int is used instead of Number for integer computations, and Vector.<int> is used instead of Vector. Both Flash Players 9 and 10 have a JIT engine that compiles ActionScript to native code, but this doesn't seem to become faster than Firefox 3.0 JavaScript in some number-crunching applications.

It is possible to call a JavaScript function from ActionScript and vice versa, using the ExternalInterface ActionScript class (flash.external.ExternalInterface). Please note that ExternalInterface doesn't work for the file:/// protocol due to security reasons (as documented by Adobe here) – you have to upload both your .swf and .html files to the same web server to make use of ExternalInterface.

To compile ActionScript 2 to an SWF file, the free MTASC compiler is recommended, which is very fast, works at the command line, and is said to be safer than the compilers written by Adobe. An example ActionScript2 script:
// Tuto2.as, an example ActionScript 2 script
import flash.external.ExternalInterface;
class Tuto2 {
static var app : Tuto2;
function Tuto2() {
_root.createTextField("tf",0,0,0,800,200);
_root.tf.mutliline = true;
_root.tf.text = "first";
var myformat = new TextFormat();
myformat.color = 0x00000;
myformat.underline = true;
myformat.size = 30;
// Set this, because the default font, "Times New Roman" may not be available on Linux.
myformat.font = "serif";
_root.tf.setTextFormat(myformat);
_root.tf.text = ExternalInterface.call + "\nHello";
// Call this again after changing the text, otherwise the formatting is lost.
_root.tf.setTextFormat(myformat);
}
static function main(mc) { // Entry point.
app = new Tuto2();
}
}
To compile it, download MTASM first:
$ wget http://www.mtasc.org/zip/mtasc-1.12-linux.tgz
$ mkdir mtasc
$ cd mtasc
$ tar xzvf ../mtasc-1.12-linux.tgz
$ cp .../Tuto2.as .
Then compile with:
$ ./mtasc -version 8 -swf tuto2.swf -main -header 800:200:20 Tuto2.as
The corresponding HTML would look like this for Firefox:
<embed src="tuto2.swf"
quality="high" bgcolor="#eeeeee" fgcolor="#000000" width="800" height="2
name="tuto" id="tuto" align="middle" allowScriptAccess="always"
allowFullScreen="true" type="application/x-shockwave-flash"
pluginspage="http://www.macromedia.com/go/getflashplayer" />
To make it cross-browser, use SWFObject to embed it. Once created, load the HTML in your browser to view the Flash animation you've just created.

From now on we focus on ActionScript 3 and Flash Player 10. Adobe provides the Flex SDK, which contains a compiler (called mxmlc, or mxmlc.exe on Windows) which can compie ActionScript 3 .as source files to .swf. The Flex SDK is free to use and is partially open source, and it is implemented in Java. Download version 3.4 (which is the most recent stable version at the time of writing this blog post, and is about 120 MB compressed) from http://opensource.adobe.com/wiki/display/flexsdk/Downloads. Also make sure you have Java (at least a JRE) installed. Here are the corresponding download command-lines:
$ wget http://fpdownload.adobe.com/pub/flex/sdk/builds/flex3/flex_sdk_3.4.0.9271.zip
$ mkdir flex
$ cd flex
$ unzip ../flex_sdk_3.4.0.9271.zip
$ bin/mxmlc -help
Here is a sample ActionScript 3 program:
// Tuto3.as, a sample ActionScript3 program
package {
import flash.display.Sprite;
import flash.events.Event;
import flash.text.TextField;
import flash.text.TextFormat;
import flash.utils.getTimer;
import flash.external.ExternalInterface;
public class Tuto3 extends Sprite {
function Tuto3() : void {
var circle : Sprite = new Sprite();
circle.graphics.beginFill(0xFF7744);
circle.graphics.drawCircle(0, 0, 30);
circle.graphics.endFill();
addChild(circle);
//myInit();
//addEventListener(Event.ADDED_TO_STAGE, myInit);
ExternalInterface.addCallback("myFunction", myInit);
}
public function myInit(e : Event = null) : String {
var startTime : Number = getTimer();
var tField : TextField = new TextField();
var tFormat : TextFormat = new TextFormat();
tFormat.size = 20;
// Set this, because the default font, "Times New Roman" may not be available on Linux.
tFormat.font = "serif";
tField.autoSize = "left";
tField.background = true;
tField.border = true;
tField.multiline = true;
tField.x = 20;
tField.y = 40;
tField.text = "hello1";
tField.setTextFormat(tFormat);
var endTime : Number = getTimer();
trace('hello2 ' + startTime + ' ' + (endTime - startTime));
tField.text = 'ms=' + (endTime - startTime);
// Call this again after changing the text, otherwise the formatting is lost.
tField.setTextFormat(tFormat);
addChild(tField);
}
}
}
Here is how to compile it (creates Tuto3.swf):
$ ./bin/mxmlc -target-player 10 -default-size 800 200 -optimize Tuto3.as
Here is the corresponding HTML:
<html><head><script type="text/javascript">
function myonload() {
// document.tuto for Firefox, window.tuto for Internet Explorer
var tuto = document.tuto || window.tuto || document.getElementById("tuto");
if (tuto && tuto.myFunction)
document.getElementById("result").innerHTML = tuto.myFunction();
}
</script></head><body onload="myonload()">
<embed src="Tuto3.swf"
quality="high" bgcolor="#eeeeee" fgcolor="#000000" width="800" height="200"
name="tuto" id="tuto" align="middle" allowScriptAccess="always"
allowFullScreen="true" type="application/x-shockwave-flash"
pluginspage="http://www.macromedia.com/go/getflashplayer" />
<div id="result">no result yet</div>
</body></html>
The HTML above also demonstrates calling an ActionScript method form JavaScript. To call a JavaScript function from ActionScript, do
ExternalInterface.call("JavaScriptFunctionName", arg1, ...)
Don't forget to copy the .html and the .swf to a http:// location, otherwise ExternalInterface won't work because the security limitations imposed by the Flash Player.

Please note that according to Adobe, AVM2, the virtual machine in Flash Player 9 and 10 for ActionScript 3 execution does a JIT for all functions and methods except for constructors. So don't put performance-critical code to the constructor. I couldn't measure any speed difference in the constructor and other methods. The last statement that the constructor is not JITted I could find is from 2007 (http://blog.pixelbreaker.com/flash/as30-jit-vs-interpreted/).

2009-10-03

How to compile TraceMonkey for the Linux command-line

This blog posts describes how to compile TraceMonkey, Firefox's 3.5 fast JavaScript interpreter at the i386 32-bit Linux command-line. The created executable, js will not work in a browser, but it can be used for benchmarking JavaScript code (without HTML or DOM). The instructions below have been tested on an Ubuntu Hardy system.

The corresponding old, slow JavaScript interpreter (shipping Firefox 3.0 and older) is SpiderMonkey. The command-line version can be installed with
$ apt-get install spidermonkey-bin
After that, the command smjs file.js is available. In the executed JavaScript, the function print(expr) can be used to print a line to the terminal window, and load(filename) can be used to load another .js file.

To get the same functionality with TraceMonkey, you have to compile TraceMonkey for yourself. Here is how to do it:
$ sudo apt-get install gcc g++ make autoconf2.13 mercurial
$ hg clone http://hg.mozilla.org/tracemonkey/
$ cd tracemonkey/js/src
$ CC='gcc -m32' CXX='g++ -m32' AR=ar \
./configure --disable-debug --enable-optimize --target=i686-pc-linux-gnu
$ make
$ ls -l shell/js
This creates the shell/js executable, which can be used just like smjs.

To get a statically linked version of the TraceMonkey command-line interpreter, run this after the regular compilation with make:
$ bash -c '
cd shell || exit 1; rm -f js
function c++() { command c++ -static "$@"; }
function g++() { command g++ -static "$@"; }
eval "`make js`"; cd ..; ls -l shell/js'
More information about compiling and benchmarking TraceMonkey can be found on http://blog.mozilla.com/nnethercote/2009/07/27/how-i-work-on-tracemonkey/.