Temporally coherent sculpture of composite objects

Abstract

We address the problem of virtual sculpting and deformation of shapes composed of small, randomly placed objects. Objects may be tightly packed – such as pebbles, pills, seeds and grains, or be sparsely distributed with an overarching shape – such as flocks of birds or schools of fish. Virtual sculpture has rapidly become a standard in the entertainment industry. Composites, though, are still usually created in a static way by individually placing each object or by sculpting a support surface and procedurally populating the final shape. That raises problems for the generalization to evolving shapes with visual continuity of the components. Large amounts of geometrical data are generated, and must be maintained and processed, both by the CPU and by the GPU. Whenever the shape is deformed, one has to define how these compositing objects should turn, displace or disappear inside the volume, as well as how new instances should become visible to the outside. It is difficult to rely on a physical system to perform that task in real time. The system we suggest can be constructed upon any uniform mesh-based representation that can be deformed and whose connectivity can be updated by operations such as edge splits, collapses, and flips. The mesh remains populated with an aperiodic distribution of composing elements that are automatically updated under deformation. The idea is to sculpt the shape as if it were filled with little objects, without handling the complexity of manipulating volumetric shapes. For this purpose, we suggest exploiting the properties of the uniform sampling of the surface. We show that we are able to properly handle virtual sculpting of composites in real-time and maintaining temporal continuity. This system also uses GPU optimizations to render individual elements efficiently. To our knowledge, no previous sculpting system allows the user to simultaneously see and sculpt agglomerates in such a fast and reliable fashion.