William Baxter

William Baxter

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    Dynamic Stylized Shading Primitives
    David Vanderhaeghe
    Romain Vergne
    Pascal Barla
    Proc. Symposium on NonPhotorealistic Animation and Rendering (NPAR 2011), ACM
    Preview abstract Shading appearance in illustrations, comics and graphic novels is designed to convey illumination, material and surface shape characteristics at once. Moreover, shading may vary depending on different configurations of surface distance, lighting, character expressions, timing of the action, to articulate storytelling or draw attention to a part of an object. In this paper, we present a method that imitates such expressive stylized shading techniques in dynamic 3D scenes, and which offers a simple and flexible means for artists to design and tweak the shading appearance and its dynamic behavior. The key contribution of our approach is to seamlessly vary appearance by using a combination of shading primitives that take into account lighting direction, material characteristics and surface features. We demonstrate their flexibility in a number of scenarios: minimal shading, comics or cartoon rendering, glossy and anisotropic material effects; including a variety of dynamic variations based on orientation, timing or depth. Our prototype implementation combines shading primitives with a layered approach and runs in real-time on the GPU View details
    Detail-Preserving Paint Modeling for {3D} Brushes
    Nelson Chu
    Li-Yi Wei
    Naga Govindaraju
    Proc. Symposium on NonPhotorealistic Animation and Rendering (NPAR 2010)
    Preview abstract Recent years have witnessed significant advances in 3D brush modeling and simulation in digital paint tools. Compared with traditional 2D brushes, a 3D brush can be both more intuitive and more expressive by offering an experience closer to wielding a real, physical brush. To support popular media types such as oil and pastel, most previous 3D brush models have implemented paint smearing and mixing. This is generally accomplished by a simple repeated exchange of paint between the 3D brush and 2D canvas, with the paint picked up by the brush typically mapped directly onto the brush surface. In this paper we demonstrate that both repeated exchanges and direct mapping of paint onto brush surfaces are sub-optimal choices, leading to excessive loss of color detail and computational inefficiencies. We present new techniques to solve both problems, first by using a canvas snapshot buffer to prevent repeated paint exchange, and second by mapping brush paint onto a 2D, resolution-matched pickup map that sits underneath the brush, instead of mapping onto the 3D brush itself. Together, these act to minimize resampling artifacts, helping to preserve fine streaks and color details in strokes, while at the same time yielding improved efficiency by never sampling the brush more densely than necessary. We demonstrate the effectiveness of our method in a real-time paint system implemented on the GPU that simulates pastel and oil paint. Our method is simple and effective, and achieves a level of realism for these two media not attained by any previous work. View details
    Simple Data-Driven Modeling of Brushes
    Naga Govindaraju
    Proc. Symposium on Interactive 3D Graphics (I3D 2010)
    Preview abstract We present a new and simple data-driven technique for modeling 3D brushes for use in realistic painting programs. Our technique simplifies and accelerates simulation of the constrained dynamics of brushes by using a small lookup table that efficiently encodes the range of feasible constrained states. The result is a brush model which runs an order of magnitude faster than previous physicsbased methods, while at the same time delivering greater deformation fidelity. View details
    {N}-way Morphing for {2D} Animation
    Pascal Barla
    Ken Anjyo
    Computer Animation and Virtual Worlds (proc. CASA 2009), 20(2009), pp. 79-87
    Preview abstract We present a novel approach to the creation of varied animations from a small set of simple 2D input shapes. Instead of providing a new 2D shape for each keyframe of an animation sequence, we interpolate between a few example shapes in a reduced pose-space. Similar approaches have been presented in the past, but were restricted in the types of input or range of deformations allowed. In order to address these limitations, we reformulate the problem as an N-way morphing process on 2D input bitmap or vector graphics. Our formulation includes an N-way mapping technique, an efficient, rigidity preserving nonlinear blending function, improved extrapolation and a novel scattered data interpolation technique to manage the reduced pose-space. The resulting animations are correlated to paths in the reduced pose-space, allowing users to intuitively and interactively control temporal behaviours with simple gestures.We demonstrate our techniques in several example animations. View details
    Compatible Embedding for {2D} Shape Animation
    Pascal Barla
    Ken Anjyo
    IEEE Transactions Visualization and Computer Graphics, 15(2009), pp. 867-879
    Preview abstract We present new algorithms for the compatible embedding of 2D shapes. Such embeddings offer a convenient way to interpolate shapes having complex, detailed features. Compared to existing techniques, our approach requires less user input, is faster, more robust, and simpler to implement, making it ideal for interactive use in practical applications. Our new approach consists of three parts. First, our boundary matching algorithm locates salient features using the perceptually-motivated principles of scalespace and uses these as automatic correspondences to guide an elastic curve matching algorithm. Second, we simplify boundaries while maintaining their parametric correspondence and the embedding of the original shapes. Finally, we extend the mapping to shapes interiors via a new compatible triangulation algorithm. The combination of our algorithms allows us to demonstrate 2D shape interpolation with instant feedback. The proposed algorithms exhibit a combination of simplicity, speed, and accuracy that has not been achieved in previous work. View details
    Rigid Shape Interpolation Using Normal Equations
    Pascal Barla
    Ken Anjyo
    Proc. Non-Photorealistic Animation and Rendering(2008)
    Preview abstract In this paper we provide a new compact formulation of rigid shape interpolation in terms of normal equations, and propose several enhancements to previous techniques. Specifically, we propose 1) a way to improve mesh independence, making the interpolation result less influenced by variations in tessellation, 2) a faster way to make the interpolation symmetric, and 3) simple modifications to enable controllable interpolation. Finally we also identify 4) a failure mode related to large rotations that is easily triggered in practical use, and we present a solution for this as well. View details
    Locally Controllable Stylized Shading
    Hideki Todo
    Ken-ichi Anjyo
    Takeo Igarashi
    SIGGRAPH 2007(2007)
    Preview abstract Recent progress in non-photorealistic rendering (NPR) has led to many stylized shading techniques that efficiently convey visual information about the objects depicted. Another crucial goal of NPR is to give artists simple and direct ways to express the abstract ideas born of their imaginations. In particular, the ability to add intentional, but often unrealistic, shading effects is indispensable for many applications. We propose a set of simple stylized shading algorithms that allow the user to freely add localized light and shade to a model in a manner that is consistent and seamlessly integrated with conventional lighting techniques. The algorithms provide an intuitive, direct manipulation method based on a paint-brush metaphor, to control and edit the light and shade locally as desired. Our prototype system demonstrates how our method can enhance both the quality and range of applicability of conventional stylized shading for offline animation and interactive applications. View details
    Finite volume flow simulations on arbitrary domains
    Jeremy D. Wendt
    Ipek Oguz
    Ming C. Lin
    Graphical Models, 69(2007), pp. 19-32
    Preview abstract We present a novel method for solving the incompressible Navier-Stokes equations that more accurately handles arbitrary boundary conditions and sharp geometric features in the fluid domain. It uses a space filling tetrahedral mesh, which can be created using many well known methods, to represent the fluid domain. Examples of the method's strengths are illustrated by free surface fluid simulations and smoke simulations of flows around objects with complex geometry. View details
    Tweakable Light and Shade for Cartoon Animation
    Ken-ichi Anjyo
    Shuhei Wemler
    Proc. Symposium on Non-Photorealistic Animation and Rendering (NPAR)(2006), pp. 133-139
    Preview abstract Light and shade in the context of non-photorealistic imaging, such as digital cel animation, are semantic notations, rather than physical phenomena. Therefore stylized light and shade should be intentionally animated instead of simulated. This paper proposes an intuitive, direct manipulation method for animating stylized light and shade in real-time. Our method provides intuitive click-and-drag operations for translating and deforming the shaded areas, including rotation, directional scaling, splitting, and squaring of highlights, all without tedious parameter tuning. Our prototype system demonstrates the algorithms in our method, which are implemented along with a real-time cartoon shader on commodity graphics hardware. This system allows the interactive creation of stylized shading keyframes for animations, illustrating the effectiveness of the proposed techniques. View details
    Latent Doodle Space
    {Ken-ichi} Anjyo
    Computer Graphics Forum (Proc. Eurographics), 25(2006), pp. 477-485
    Preview abstract We propose the concept of a latent doodle space, a low-dimensional space derived from a set of input doodles, or simple line drawings. The latent space provides a foundation for generating new drawings that are similar, but not identical to, the input examples. The two key components of this technique are 1) a heuristic algorithm for finding stroke correspondences between the drawings, and 2) the use of latent variable methods to automatically extract a low-dimensional latent doodle space from the inputs. We present two practical applications that demonstrate the utility of this idea: first, a randomized stamp tool that creates a different image on every usage; and second, "personalized probabilistic fonts," a handwriting synthesis technique that mimics the idiosyncrasies of one's own handwriting. View details
    {IMPaSTo}: A Realistic Model for Paint
    Jeremy Wendt
    Ming C. Lin
    Proc. of Symposium on Non-Photorealistic Animation and Rendering (NPAR)(2004), pp. 45-56
    A Versatile Interactive {3D} Brush Model
    Ming C. Lin
    Proc. of Pacific Graphics 2004(2004), pp. 319-328
    Physically-based Modeling Techniques for Interactive Digital Painting
    Ph.D. Thesis, University of North Carolina, Chapel Hill(2004)
    Haptic Interaction with Fluid Media
    Ming Lin
    The Proceedings of Graphics Interface '04(2004)
    A Viscous Paint Model for Interactive Applications
    Yuanxin Liu
    Ming C. Lin
    Computer Animation and Virtual Worlds (Proc. CASA), 15(2004), pp. 433-442
    Simulation of Cloud Dynamics on Graphics Hardware
    Mark Harris
    Thorsten Scheuermann
    Anselmo Lastra
    Proc. Graphics Hardware(2003)
    {dAb}: Interactive Haptic Painting With {3D} Virtual Brushes
    Vincent Scheib
    Ming C. Lin
    SIGGRAPH 2001, ACM Press / ACM SIGGRAPH, pp. 461-468