Saturday, March 20, 2010

A harmonograph in JavaScript

What's a harmonograph, you ask? Well, it's something like a Spirograph for grown-ups. A harmonograph uses a construction with pendulums to draw pretty patterns.

One particular incarnation uses two pendulums of nearly equal length, each about two metres. To the right pendulum, a slowly revolving disk is attached, which is driven by a small electrical motor. The drawing paper is taped onto the disk. To the left pendulum, an arm is attached with the pen at the end. When the pressure and thus the friction of the pen is sufficiently low, the pendulums can keep swinging for tens of minutes.

For learning and fun, I replicated this harmonograph in JavaScript with the HTML5 canvas element. The pendulum motion is approximated by a sine function, and friction by an exponential, but apart from that it should be pretty physically accurate.

Without further ado, I present to you: Harmonograph in JavaScript. Usage should be self-evident. Although some input validation is done, you will be able to break it with strange values.

With the link at the top, you can save and bookmark your creations or send them to your friends. Enjoy!

Update, 2017-01-22: Hosting is now done here on GitHub Pages. The old location redirects you. I also published the source code (“View Source” still works just fine, but it's now officially MIT licensed as well).

Sunday, March 14, 2010

Capitalizing MP3s from the command line

For my own future reference and your enjoyment, here's a neat little oneliner to transform 01 - some song.mp3 into 01 - Some Song.mp3:

rename "s/([^._'])\b(\w)(\w*)/\$1\U\$2\L\$3/g" *.mp3

It needs the prename utility from Perl, which on Ubuntu is available by default under the name rename.