Twisting, Tearing and Flicking Effects in String Animations

Witawat Rungjiratananon¹ Yoshihiro Kanamori² Napaporn Metaaphanon³ Yosuke Bando⁴ Bing-Yu Chen⁵ Tomoyuki Nishita¹
¹The University of Tokyo ²University of Tsukuba ³Square Enix ⁴TOSHIBA Corporation ⁵National Taiwan University

String-like objects in our daily lives including shoelaces, threads and rubber cords exhibit interesting behaviors such as twisting, tearing and bouncing back when pulled and released. In this paper, we present a method that enables these behaviors in traditional string simulation methods that explicitly represent a string by particles and segments. We offer the following three contributions. First, we introduce a method for handling twisting effects with both uniform and non-uniform torsional rigidities. Second, we propose a method for estimating the tension acting in inextensible objects in order to reproduce tearing and flicking (bouncing back); whereas the tension for an extensible object can be easily computed via its stretched length, the length of an inextensible object is maintained constant in general, and thus we need a novel approach. Third, we introduce an optimized grid-based collision detection for an efficient computation of collisions. We demonstrate that our method allows visually plausible animations of string-like objects made of various materials and is a fast framework for interactive applications such as games.

Conference paper (3.3MB, PDF) and Video (16MB, MOV):
Proceedings of Motion in Games 2011, pp.192-203, 2011.
Journal version (1.5MB, PDF):
"Animating Strings with Twisting, Tearing and Flicking Effects," Computer Animation and Virtual Worlds, Vol. 23, No. 2, pp.113-124, 2012.

Various twisted strings (left) and torn ropes of a suspension bridge (right).
- Traditional inextensible (strain limited) string directly falls down when tension is suddenly released (left).
- With the proposed model, a string bounces back (center).
- Even more complex flicking behaviors can be seen if a string is twisted beforehand (right).
Supplementary Video 1 (69MB, MOV) and Video 2 (6MB, MOV):
Video game examples using the string model that twists, tears, and flicks.

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Various twisted strings (left) and torn ropes of a suspension bridge (right).