DAIM a well known graffiti artist has developed a way of shooting or smearing a virtual spray of fluorescent light.
Equipped with the appropriate technology, DAIM sprays graffiti into empty space. In a large hall, three cameras using Motion Capturing record DAIM's position and the movements he executes with a virtual spray can. The assimilated data is shown to him in real time in a pair of video glasses - as free-floating 3D graffiti in space. In this way he can decide how and where to apply his strokes, and via a Bluetooth controller can also determine the colours, strength of brushstrokes and textures of his work.
The software used is the ARToolKit (or Augmented Reality Toolkit), which is an open source project.
Source