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Shadows are essential to realistic and visually appealing images, but they are di cult to compute in most display environments. This survey will characterize the various types of shadows, describe most existing shadow algorithms, and for each one discuss their complexities, their advantages and their shortcomings. The types of shadows examined are hard shadows, soft shadows, shadows of transparent objects, and shadows for complex modeling primitives. For each t ype, we examine shadow algorithms within various rendering techniques. The goal of the survey is to provide readers with enough background and insight on the various methods to allow t h e m t o c hoose the algorithm best suited to their needs. It is also hoped that our analysis will help identify the areas that need more research, and point to possible solutions.

Figure 1: A high-quality animated production model (Ptex T-rex model c Walt Disney Animation Studios.) rendered in real time under directional and environment lighting using LEADR mapping on an NVidia GTX 480 GPU. The surface appearance is preserved at all scales, using a single shading sample per pixel. Combined with adaptive GPU tessellation, our method provides the fastest, seamless, and antialiased progressive representation for displaced surfaces. AbstractWe present Linear Efficient Antialiased Displacement and Reflectance (LEADR) mapping, a reflectance filtering technique for displacement mapped surfaces. Similarly to LEAN mapping, it employs two mipmapped texture maps, which store the first two moments of the displacement gradients. During rendering, the projection of this data over a pixel is used to compute a noncentered anisotropic Beckmann distribution using only simple, linear filtering operations. The distribution is then injected in a new, physically based, rough surface microfacet BRDF model, that includes masking and shadowing effects for both diffuse and specular reflection under directional, point, and environment lighting. Furthermore, our method is compatible with animation and deformation, making it extremely general and flexible. Combined with an adaptive meshing scheme, LEADR mapping provides the very first seamless and hardware-accelerated multi-resolution representation for surfaces. In order to demonstrate its effectiveness, we render highly detailed production models in real time on a commodity GPU, with quality matching supersampled ground-truth images.

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A re ection and refraction model for anisotropic surfaces is introduced. The anisotropy is simulated by small cylinders added or subtracted distributed on the anisotropic surface. Di erent levels of anisotropy are achieved by varying the distance between each cylinder and or rising the cylinders more or less from the surface. Multidirectional anisotropy is modelled by orienting groups of cylinders in di erent direction. The intensity of the re ected light is computed by determining the visible and illuminated portion of the cylinders, taking self-blocking into account. We present t wo techniques to compute this in practice. In one the intensity is computed by sampling the surface of the cylinders. The other is an analytic solution. In the case of the di use component, the solution is exact. In the case of the specular component, an approximation is developed using a Chebyshev polynomial approximation of the specular term, and integrating the polynomial.This model can be implemented easily within most rendering system, given a suitable mechanism to de ne and alter surface tangents. The e ectiveness of the model and the visual importance of anisotropy are illustrated with some pictures.

This paper presents a method for animating long hair while modelling both interactions between the hair and the character's body and between different hair wisps. Our method relies on a layered model paradigm. Hair is structured into a number of volumetric wisps whose motion and deformation are computed using a layered model: A first layer, the skeleton curve, computes the large scale motion of a wisp. This skeleton is coated by a second layer, the deformable wisp envelope, linked to the skeleton through highly viscous springs. A third layer is used for rendering the individual hair strands within each wisp. During motion, anisotropic interactions are computed between hair wisps, in addition to interactions with character body: two quasi-parallel wisps are allowed to interpenetrate while a viscous collision is computed between colliding wisps of different orientation. This results in a visually-realistic animation, that captures both continuities and discontinuities that can be observed in thick, long hair.

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