I rewrote a much played with Processing sketch to openframeworks. This shows a way to do a vertical slit scan (Up/Down, Down/Up) on a live video feed.
This software is only tested on Mac OS X Yosemite and the 0.8.4 release of openframeworks.
Download openframeworks (http://openframeworks.cc). Create a new project via the recommend way (http://openframeworks.cc/tutorials/introduction/001_chapter1.html).
In the new project folder replace the src/ directory with the one given here.