XMotion is a system that enables a performer to design and control in real-time the graphics that are projected onto the background while they are performing.
The system captures the positions of the markers the performer is wearing using a camera sensitive to infrared light (IR). It then extracts the parameters from the video images; position, speed, curvature, etc. of the paths captured for each marker. Then it links a Finite State Machine (FSM) to each marker.
Each state of the FSM is characterized by a graphical behavior that will determine how the drawing parameters are affected for the captured curve parameters. The states transitions (which determines the drawing behaviors) will be projected in accordance with the curve parameters (i.e. for example: Speed x > 0.7 pixels/frame).
The performer can design the FSMs for the markers, as well as control the drawing state while performing.
For more information, check the wiki XMotion.