Line-drawing usually focuses on creating back-and-white lines which are able to trace out objects by outlining features or matching tones. However, none of the algorithms proposed before can produce parallel lines that change spacings and thicknesses with neighbors automatically.
We proposed a coordinated particle system which is capable of tracing out features and details with parallel lines changing directions and thicknesses automatically. To match tones and generate parallel lines, we allow new particles to be created in areas that have small spacings and let particles be terminated when collisions occur or when the desired spacings become larger. Natural yet irregular patterns are achieved by adding some randomness to particles' directions.