Pushkar Joshi, Mark Meyer, Tony DeRose, Brian Green, Tom Sanocki
May 2007
In this paper we consider the problem of creating and controlling volume deformations used to articulate characters for use in high-end applications such as computer generated feature films. We introduce a method we call harmonic coordinates that significantly improves upon existing volume deformation techniques. Our deformations are controlled using a topologically flexible structure, called a cage, that consists of a closed three dimensional mesh. The cage can optionally be augmented with additional interior vertices, edges, and faces to more precisely control the interior behavior of the deformation. We show that harmonic coordinates are generalized barycentric coordinates that can be extended to any dimension. Moreover, they are the first system of generalized barycentric coordinates that are non-negative even in strongly concave situations, and their magnitude falls off with distance as measured within the cage.
Additional materials: [HarmonicCoordinates.divx], [SiggraphSlides.pdf]
Available in the proceedings of Siggraph 2007.
Available as Pixar Technical Memo #06-02b
Other versions:
Robert L. Cook, Tony DeRose
August 2005
Noise functions are an essential building block for writing procedural shaders in 3D computer graphics. The original noise function introduced by Ken Perlin is still the most popular because it is simple and fast, and many spectacular images have been made with it. Nevertheless, it is prone to problems with aliasing and detail loss. In this paper we analyze these problems and show that they are particularly severe when 3D noise is used to texture a 2D surface. We use the theory of wavelets to create a new class of simple and fast noise functions that avoid these problems.
Additional materials: [RapLyrics.txt]
Available in the Proceedings of SIGGRAPH 2005
Tony DeRose, Michael Kass, Tien Truong
August 1998
The creation of believable and endearing characters in computer graphics presents a number of technical challenges, including the modeling, animation and rendering of complex shapes such as heads, hands, and clothing. Traditionally, these shapes have been modeled with NURBS surfaces despite the severe topological restrictions that NURBS impose. In order to move beyond these restrictions, we have recently introduced subdivision surfaces into our production environment. Subdivision surfaces are not new, but their use in high-end CG production has been limited.
Here we describe a series of developments that were required in
order for subdivision surfaces to meet the demands of high-end
production. First, we devised a practical technique for
constructing provably smooth variable-radius fillets and blends.
Second, we developed methods for using subdivision surfaces in
clothing simulation including a new algorithm for efficient
collision detection. Third, we developed a method for
constructing smooth scalar fields on subdivision surfaces, thereby
enabling the use of a wider class of programmable shaders. These
developments, which were used extensively in our recently
completed short film Geri's game, have become a highly
valued feature of our production environment.
Available in the Proceedings of SIGGRAPH 1998.