メタボール
Blinn, James F. "A Generalization of Algebraic Surface Drawing." ACM Transactions on Graphics 1(3), July 1982, pp. 235–256.
T. Nishita, E. Nakamae, "A Method for Displaying Metaballs by using Bezier Clipping," Computer Graphics Forum, Vol.13, No.3, 1994, pp.271-280.