A Bidirectional Deposition Model of Wax Crayons
Author(s): Dave Rudolf, David Mould, Eric Neufeld.
Article: Computer Graphics Forum, Vol. 24, No. 1, pp. 27--39, March,
2005.
[BibTeX] 
Abstract:
We present a physically inspired model of wax crayons, which synthesizes drawings from collections of user-specified strokes. Paper is represented by a height-field texture, and a crayon is modeled with a 2D mask that evolves as it interacts with the paper. The amount of wax deposition is computed based on the crayon contact profile, contact force and friction. Previously deposited wax is smeared by crayon action, based on wax softness and contact information. Deposited wax can also be carved from the paper by the crayon and redeposited at another location. The distributed wax is rendered using a simplified Kubelka-Monk model, which approximates light transmission and scattering effects.