Direct Delta Mush (DDM) is a high-quality, direct skinning method with a low setup cost. However, its storage and run-time computing cost are relatively high for two reasons: its skinning weights are 4 X 4 matrices instead of scalars like other direct skinning methods, and its computation requires one 3 X 3 Singular Value Decomposition per vertex. In this paper, we introduce a compression method that takes a DDM model and splits it into two layers: the first layer is a smaller DDM model that computes a set of virtual bone transformations and the second layer is a Linear Blend Skinning model that computes per-vertex transformations from the output of the first layer. The two-layer model can approximate the deformation of the original DDM model with significantly lower costs. Our main contribution is a novel problem formulation for the DDM compression based on a continuous example-based technique, in which we minimize the compression error on an uncountable set of example poses. This formulation provides an elegant metric for the compression error and simplifies the problem to the common linear matrix factorization. Our formulation also takes into account the skeleton hierarchy of the model, the bind pose, and the range of motions. In addition, we propose a new update rule to optimize DDM weights of the first layer and a modification to resolve the floating-point cancellation issue of DDM.

The widely used ambient occlusion (AO) technique provides an approximation of some global illumination effects and is efficient enough for use in real-time applications. Because it relies on computing the visibility from each point on a surface, AO computation is expensive for dynamically deforming objects, such as characters in particular. In this paper, we describe an algorithm for producing high-quality dynamically changing AO for characters. Our fundamental idea is to factorize the AO computation into a coarse-scale component in which visibility is determined by approximating spheres, and a fine-scale component that leverages a skinning-like algorithm for efficiency, with both components trained in a regression against ground-truth AO values. The resulting algorithm accommodates interactions with external objects and generalizes without requiring carefully constructed training data. Extensive comparisons illustrate the capabilities and advantages of our algorithm.

No abstract available.

An explicit spline representation of smooth free-form surfaces is combined with a hierarchy of meshes to form the basis of an interactive sculpting environment.The environment offers localii hierarchical modeling at different levels of detail, direct surface manipulation, change of connectivity for extrusion and to form holes and bridges, and built-in tangent continuity across th& surface where wanted.The free-form surface is represented and can be exported either in NURBS form or as cubic triangular BCzier patches.Key characteristics of the approach are: (1) mesh pieces and surface pieces are related by strictly local averaging rules; (2) refinement rules depend only on direct, coarser-level ancestors and not on adjacent submeshes or patches; (3) submeshes at different levels look alike.The underlying data structure is a single winged-edge structure with additional pointem to support the hierarchy.Multiply refined regions may be directly adjacent to umefined regions, and mesh fragments at different levels of refinement can be connected.CR Categories: 1.

Combining a polynomial free-form surface representation with Gauss' divergence theorem allows efficient and exact calculation of the moments of the enclosed objects. For example, for an cubic representation, volume, center of mass, and the inertia tensor can be computed in seconds even for complex objects with serval thousand patches while change due to local modification of the surface geometry can be computed in real-time as feedback for animation or design. Speed and simplicity of the approach allow solving the inverse problem of modeling to match prescribed moments.