Cloth animation

Cloth animation
One of the biggest challenges in computer animation has been to simulate how clothing bunches up and then relaxes again, as when a character's elbow bends or arm moves across the front of the body. The problem with conventional cloth simulation techniques is that during such motions, fabric becomes sandwiched in areas where it intersects with the body and itself and it gets pulled stretched and tangled. As a result, it can flutter, wiggle and appear jagged. And then, when the body parts separate, it can remain pinched and tangled instead of falling loosely and naturally back to its original shape.

To avoid these problems, David Baraff, Andrew witkin and michael kass of Pixar (owned by Disney), have devised two cloth simulation and collision algorithms described in Siggraph in a paper called "Untangling cloth". The first is called collision flypapering, which eliminates nearly all visible artifacts in regions of body intersection by carefully controlling the motion of any trapped or pinched cloth points. The accompanying figure shows how the fly-papering algorithm produces realistic cloth simulations when clothing would otherwise get pinched from typical body motions of a CG charater.

The researches also have developed a cloth-to-cloth collision algorithm that peforms a global intersection analysis of the intersecting cloth meshes. It instantaneously charaterizes the current intersection state of the fabric in order to guide the cloth back to an untangled state where the intersections occur.