Stretchable, Twistable Bones Skinning project page
Alec Jacobson
September 12, 2011
Olga Sorkine and I have recently received final acceptance for our paper, "Stretchable and Twistable Bones for Skeletal Subspace Deformation", to be presented at SIGGRAPH Asia 2011 and published in the proceedings as a special issue of ACM Transactions on Graphics. I've put a project page on the igl site. There you can find links to the paper, the accompanying video and coming soon more things like prototype code, bonus results, etc.
The abstract:
Skeleton-based linear blend skinning (LBS) remains the most popular method for real-time character deformation and animation. The key to its success is its simple implementation and fast execution. However, in addition to the well-studied elbow-collapse and candy-wrapper artifacts, the space of deformations possible with LBS is inherently limited. In particular, blending with only a scalar weight function per bone prohibits properly handling stretching, where bones change length, and twisting, where the shape rotates along the length of the bone. We present a simple modification of the LBS formulation that enables stretching and twisting without changing the existing skeleton rig or bone weights. Our method needs only an extra scalar weight function per bone, which can be painted manually or computed automatically. The resulting formulation significantly enriches the space of possible deformations while only increasing storage and computation costs by constant factors.