Serious Putty
"Serious Putty" was an interactive, direct-manipulation system for sculpting free-form surfaces in three dimensions. The system offered an exceptionally simple way to construct free-form surfaces from infinitely stretchy curve and surface elements. The user could grab any curve or surface at any point using the mouse, and pin points or curves to fixed locations in space using "thumbtacks" to create a set of interpolation constraints for the surface. Surface sheets could be stitched together into arbitrary topologies.
Under the hood, a finite-element mesh was continually optimized, both for smoothness in three dimensions (shape optimization) and reasonably positioned grid points (mesh optimization). The underlying mesh would refine and un-refine in response to local changes in surface area.
Here's the
SIGGRAPH paper describing this work, the
dissertation behind it, and a thumbnail movie of a surface in motion: