Snow is a challenging natural phenomenon to visually simulate. While the graphics community has previously considered accumulation and rendering of snow, animation of snow dynamics has not been fully addressed. Additionally, existing techniques for solids and fluids have difficulty producing convincing snow results. Specifically, wet or dense snow that has both solid- and fluid-like properties is difficult to handle. Consequently, this paper presents a novel snow simulation method utilizing a usercontrollable elasto-plastic constitutive model integrated with a hybrid Eulerian/Lagrangian Material Point Method. The method is continuum based and its hybrid nature allows us to use a regular Cartesian grid to automate treatment of self-collision and fracture. It also naturally allows us to derive a grid-based semi-implicit integration scheme that has conditioning independent of the number of Lagrangian particles. We demonstrate the power of our method with a variety of snow phenomena including complex character interactions.
Ray-traced global illumination is becoming widespread. However, incoherent ray traversal and shading has traditionally limited ray tracing to scenes that fit in memory. To combat these issues, we introduce a sorting strategy for large, potentially out-of-core ray batches, and we sort and defer shading of ray hits. As a result, we achieve perfectly coherent shading and texture access, removing the need for a shading cache.
We present a simple generalized impact model motivated by both the successes and pitfalls of two popular approaches: pair-wise propagation and linear complementarity models. Our algorithm is the first to satisfy all identified desiderata, including simultaneously guaranteeing symmetry preservation, kinetic energy conservation, and allowing break-away.
Vectorization provides a link between raster scans of pencil-and-paper drawings and modern digital processing algorithms that require accurate vector representations. We propose a vectorization algorithm specialized for clean line drawings that analyzes the drawing's topology in order to overcome junction ambiguities.
The principled, faithful simulation of complex collisions for deformable objects, such as cloth and other flexible materials, remains an open, challenging, and important problem. We propose to place safety and correctness on an equal footing with progress. To overcome the fundamental opposition between these requirements, we turn to asynchronous integration, which integrates each geometric element of a discrete shape (e.g., the stretching resistance of cloth defined across a triangle) at its own pace, not in lockstep with the entire object.
We present a new algorithm for near-interactive simulation of skeleton driven, high resolution elasticity models. Our methodology is used for soft tissue deformation in character animation. The algorithm targets performance through parallelism using a fully vectorized and branch-free SVD algorithm as well as a stable one-point quadrature scheme on a hexahedral grid.
Ball-morphs use the automatic ball-map correspondence, proposed by Chazal et al., from which we derive different vertex trajectories (linear, circular, and parabolic). All three morphs are symmetric, meeting both curves with the same angle, which is a right angle for the circular and parabolic. We provide simple constructions for these ball-morphs and compare them to each other and other simple morphs.
We present a method for generating art-directable volumetric effects, ranging from physically-accurate to non-physical results. Our system mimics the way experienced artists think about volumetric effects by using an intuitive lighting primitive, and decoupling the modeling and shading of this primitive. We integrate our approach into a real-world production pipeline and couple our volumetric effects to surface shading.
This paper addresses the problem of unintended light contributions due to physical properties of display systems. We propose an automatic, perceptually-based computational compensation framework, which formulates pollution elimination as a minimization problem. Our method aims to distribute the error introduced by the pollution in a perceptually optimal manner.
A novel parallel algorithm to animate the deformation of a soft body in response to collision. The algorithm incorporates elements of physically-based methods, and at the same time, it allows artistic control of general deformation behavior. The proposed solver has important benefits for practical use, such as evaluation of animation frames in an arbitrary order and effective approximation of volume preservation.
This paper introduces a novel approach for creating an art-directable hair shading model from existing physically based models. Through an informal user study we show that this system is easier to use compared to existing systems. In practice, the new approach has been integrated into our production pipeline and is being used in the production of the upcoming feature film Tangled.
We present a novel algorithm for deforming a locally smooth polygonal mesh by sliding its vertices over the surface. This sliding deformation creates the visual appearance of texture animation without requiring an explicit global surface parameterization or the overhead of storing texture coordinates.
While designing the stereoscopic conversion process for Beauty and the Beast 3D, the engineering team at Walt Disney Animation Studios quickly recognized the benefit of desk-side 3D viewing for 2D to 3D conversion artists. This paper outlines the technical and creative requirements of the project that supported that opinion along with the criteria established to analyze available solutions. The evolution of internal prototypes as well as 3rd party devices are then explored along with a description of the final choices made and wish-lists for future development.
We build upon work from classical fluid mechanics to design an algorithm that allows us to accurately precompute the turbulence being generated around an object immersed in a flow. This is made possible by modeling turbulence formation based on an averaged flow field, and relying on universal laws describing the flow near a wall.
This paper presents a hybrid Eulerian/Lagrangian approach to handling both self and body collisions with hair efﬁciently while still maintaining detail.
The production pipeline for Bolt was designed with the goal of delivering the full artistic vision of the directors for the 2D film that the majority of filmgoers would see, yet deliver an uncompromising immersive experience to 3D audiences.
We develop a method for reliable simulation of elastica in complex contact scenarios. Our focus is on firmly establishing three parameter-independent guarantees: that simulations of well-posed problems (a) have no interpenetrations, (b) obey causality, momentum and energy conservation laws, and (c) complete in finite time.
This paper presents a novel mesh fairing method to remove unwanted geometric artifacts such as dents. The key element of the proposed method is our unique algorithm for the assignment of weights in the discrete Laplacian.
We present an algorithm for robust and efficient contact handling of deformable objects. By being aware of the internal dynamics of the colliding objects, our algorithm provides smooth rolling and sliding, stable stacking, robust impact handling, and seamless coupling of heterogeneous objects, all in a unified manner.
Robust treatment of complex collisions is a challenging problem in cloth simulation. We present a fail-safe that cancels impact but not sliding motion. This reduces artificial dissipation considerably. We equip the proposed fail-safe with an approximation of Coulomb friction, allowing finer control of sliding dissipation.
Old cinema dead, Digital cinema now, hybrid theatre future.
We prefilter occlusion of aggregate geometry, e.g., foliage or hair, storing local occlusion as a directional opacity in each node of a bounding volume hierarchy (BVH). During intersection, we terminate rays early at BVH nodes based on ray differential, and composite the stored opacities.
We study approximate topological matching of quadrilateral meshes; that is, the problem of ﬁnding as large a set as possible of matching portions of two quadrilateral meshes.
We describe algorithms for canonically partitioning semi-regular quadrilateral meshes into structured submeshes, using an adaptation of the geometric motorcycle graph of Eppstein and Erickson to quad meshes.
We propose a new texture mapping method for Catmull-Clark subdivision surfaces that requires no explicit parameterization. Our method, Ptex, stores a separate texture per quad face of the subdivision control mesh, along with a novel per-face adjacency map, in a single texture file per surface.
We present a new approach to accelerate collision detection for deformable models. Our formulation applies to all triangulated models and significantly reduces the number of elementary tests between features of the mesh, i.e., vertices, edges and faces. We introduce the notion of Representative-Triangles, and use this representation to achieve better collision query performance.
We extend the eigenbasis method of Jos Stam to evaluate Catmull-Clark subdivision surfaces near extraordinary vertices on B-spline boundaries.
We present a novel algorithm for accurately detecting all contacts, including self-collisions, between deformable models. We precompute a chromatic decomposition of a mesh into non-adjacent primitives using graph coloring algorithms. This enables us to check for collisions between non-adjacent primitives using a linear-time culling algorithm.
We present a method for applying complex textures to hand-drawn characters in cel animation. The method correlates features in a simple, textured, 3-D model with features on a hand-drawn figure, and then distorts the model to conform to the hand-drawn artwork.
The approach is motivated by a traditional technique used in 2D cel animation, in which a single background image, which we call a multiperspective panorama, is used to incorporate multiple views of a 3D environment as seen from along a given camera path. In this paper, we explore how such backdrops can be created from 3D models and camera paths.
We present a technique for rendering animations in a painterly style. The difﬁculty in using existing still frame methods for animation is getting the paint to “stick” to surfaces rather than randomly change with each frame, while still retaining a hand-crafted look.
We present dRig, Disney Animation's novel approach to rigging that allows for efficient reuse and extension of assets, fast authoring of per-element variations, and accessibility of rig code through a proprietary language and user interface.
In these course notes we describe the development of a new BRDF model used on Wreck-It Ralph and subsequent productions at Walt Disney Animation Studios. We begin with observations from studying measured materials along with insights we've gleaned about which models fit the measured data and where they fall short. We then present our new model, describe our experience of adopting this new model in production, and discuss how we were able to add the right level of artistic control while preserving simplicity and robustness.
Much like the character animation in Tangled, the goal of the dam break sequence was to bring classic Disney 2D sensibilities to CG effects. Hand-drawn effects animation in films such as Pinocchio and Fantasia served as inspiration. The water shapes drawn in these films were very stylized yet conveyed recognizable forms of nature. The concept was to emulate these shapes and then enhance them with the modern benefits of CG rendering such as ray traced reflections and ambient occlusion.
We describe a hybrid approach leveraging the power of custom hair dynamics with the artistic control of key-framed animation that was key to the success of directing hair motion on Tangled.
We implemented the recent Photon Beams algorithm in Photorealistic RenderMan to efficiently render artistically-directed volumetric lighting effects for the feature-length animated movie Tangled. With the knowledge that most fall-off functions defined by our artists would be polynomial-smooth, we use Gaussian Quadrature to accurately and efficiently estimate the lighting contribution of these camera-containing beams.
This paper presents an automated means to select targets for DrivenShape. These targets enable DrivenShape to produce the lowest error in common contexts.
This paper presents a hybrid approach to facial rigging that uses Pose Space Deformation (PSD) to seamlessly combine both geometric deformations and blendshapes.
A point based representation was extensively used on "Tangled" to generate occlusion and indirect illumination involving the characters' hair.
For the creation of brilliant light displays, flickering control tower buttons and vibrant computer monitors, the Effects Department goal was to build a motion graphics pipeline capable of running nearly unattended - all while maintaining the flexibility of downstream artist input, should problems arise.
We designed a system of authoring trees based around a language of hierarchical curves. Our system lets artists interactively sketch out a base skeleton representation of a tree and grow procedural twigs and leaves out to a canopy shell by tweaking a limited number of parameters.
We present several key techniques used for simulating Rapunzel's 70 feet of hair for the animated feature “Tangled”; these techniques range from methods to improve the run-time efficiency of the simulations to achieving the desired art direction of the hair.
Look development on Walt Disney's Tangled called for artists to paint hundreds of organic elements with high resolution textures on a tight schedule. We found that example-based texture synthesis, where an artist paints a small exemplar texture, indicating the desired pattern that the system synthesizes over arbitrary surfaces, would alleviate some of the burden. In this talk we describe how we adapted existing synthesis methods to our Ptex-based workflow, scaled them to production sized methods and expose it to artists using a one click interface.
Prep and Landing had multiple snow variants in a large number of shots - ranging from gentle falling snow outside windows, to near blizzard-like conditions. Snowfall was necessary to help the world the characters inhabited feel believable. Managing the workflow and complexity involved in creating snow variety was the challenge.
We suggest a method for artists to better understand RBF behavior through visualization and to evaluate RBF functions according to the requirements of a production environment.
Pose Space Deformation (PSD) [Lewis2000] is a shape interpolation technique for animation. This paper presents some practical experience with PSD acquired while creating the film "BOLT."
We designed a system to facilitate the modeling of cracked and shattered objects, enabling the automatic generation of a large number of fragments while retaining the ﬂexibility to artistically control the density and complexity of the crack formation.
To perform the stereoscopic conversion of Disney’s Beauty and the Beast, we developed novel extensions to standard medial axis techniques.
We focused on fundamental ideas such as massing, a term in painting which refers to the process of editing detail into bigger shapes, and also edge quality, the use of the painter's brush to vary edges of shapes which can bring emphasis to the image and/or direct the eye. This led to the development of new algorithms and tools for the film "Bolt".
In Disney’s Bolt, the character of Rhino poses many technical challenges. He spends a majority of the movie inside a plastic ball, frequently contacts the ground surface, and presents a complicated skinning problem. Innovative tools and technology were developed to solve these issues for the production.
Using an anatomically motivated approach, our method to produce realistic convincing deformations of the skin and flesh surrounding the eye is unique, not only due to the novel approaches employed, but also because our method is entirely procedural.
iBind smoothly deforms vertices using a control cage by uniquely leveraging heat diffusion on closed, thin layers across a structured set of mean value coordinates. Dynamic rebinding is still useful, so iBind implements it, but for most cases of character articulation, a static binding option is used.
Rendering hair and simulating refraction, when performed separately, are both time and memory intensive. To overcome these problems, a process was developed for "Bolt" which involved exporting 3D data from the render stage so that the calculation of the refraction could be delayed until the composite stage.