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Item A Rendering Algorithm for Discrete Volume Density Objects(Blackwell Science Ltd and the Eurographics Association, 1993) Blasi, Philippe; Le Saec, Bertrand; Schlick, ChristopheWe present a new algorithm for simulating the effect of light travelling through volume objects. Such objects (haze, fog, clouds.) are usually modelized by voxel grids which define their density distribution in a discrete tridimensional space. The method we propose is a two-pass Monte-Carlo ray-tracing algorithm that does not make any restrictive assumptions neither about the characteristics of the objects (both arbitrary density distributions and phase functions are allowed) nor about the physical phenomena included in the rendering process (multiple scattering is accounted for). The driving idea of the algorithm is to use the phase function for Monte-Carlo sampling, in order to modify the direction of the ray during scattering.Item Rapid Visualization of Large Point-Based Surfaces(The Eurographics Association, 2005) Boubekeur, Tamy; Duguet, Florent; Schlick, Christophe; Mark Mudge and Nick Ryan and Roberto ScopignoPoint-Based Surfaces can be directly generated by 3D scanners and avoid the generation and storage of an explicit topology for a sampled geometry, which saves time and storage space for very dense and large objects, such as scanned statues and other archaeological artefacts [DDGM]. We propose a fast processing pipeline of large point-based surfaces for real-time, appearance preserving, polygonal rendering. Our goal is to reduce the time needed between a point set made of hundred of millions samples and a high resolution visualization taking benefit of modern graphics hardware, tuned for normal mapping of polygons. Our approach starts by an out-of-core generation of a coarse local triangulation of the original model. The resulting coarse mesh is enriched by applying a set of maps which capture the high frequency features of the original data set. We choose as an example the normal component of samples for these maps, since normal maps provide efficiently an accurate local illumination. But our approach is also suitable for other point attributes such as color or position (displacement map). These maps come also from an out-of-core process, using the complete input data in a streaming process. Sampling issues of the maps are addressed using an efficient diffusion algorithm in 2D. Our main contribution is to directly handle such large unorganized point clouds through this two pass algorithm, without the time-consuming meshing or parameterization step, required by current state-of-the-art high resolution visualization methods. One of the main advantages is to express most of the fine features present in the original large point clouds as textures in the huge texture memory usually provided by graphics devices, using only a lazy local parameterization. Our technique comes as a complementary tool to high-quality, but costly, out-of-core visualization systems. Direct applications are: interactive preview at high screen resolution of very detailed scanned objects such as scanned statues, inclusion of large point clouds in usual polygonal 3D engines and 3D databases browsing.Item Sketch and Paint-based Interface for Highlight Modeling(The Eurographics Association, 2008) Pacanowski, Romain; Granier, Xavier; Schlick, Christophe; Poulin, Pierre; Christine Alvarado and Marie-Paule CaniIn computer graphics, highlights capture much of the appearance of light reflection off a surface. They are generally limited to pre-defined models (e.g., Phong, Blinn) or to measured data. In this paper, we introduce new tools and a corresponding highlight model to provide computer graphics artists a more expressive approach to design highlights. For each defined light key-direction, the artist simply sketches and paints the main highlight features (shape, intensity, and color) on a plane oriented perpendicularly to the reflected direction. For other light-and- view configurations, our system smoothly blends the different user-defined highlights. Based on GPU cabilities, our solution allows real-time editing and feedback. We illustrate our approach with a wide range of highlights, with complex shapes and varying colors. This solution also demonstrates the simplicity of introduced tools.Item A Survey of Shading and Reflectance Models(Blackwell Science Ltd and the Eurographics Association, 1994) Schlick, ChristopheSince the beginning of computer graphics, three decades ago, a large number of models intended to describe the behaviour of light on a given point of a surface have been proposed. Almost every author uses his own terminology and/or notation. To understand clearly the similarities and the differences between existing models, reformulating them with a unified notation is essential. This has been done by Hall in 1986. This paper is a new survey of shading and reflectance models, including the most recent models. Moreover, after the lengthy enumeration, some original models are proposed, which attempt to include interesting features of previous disjointed work into new formulations.Item SIMOD: Making Freeform Deformation Size-Insensitive(The Eurographics Association, 2007) Boubekeur, Tamy; Sorkine, Olga; Schlick, Christophe; M. Botsch and R. Pajarola and B. Chen and M. ZwickerFreeform deformation techniques are powerful and flexible tools for interactive 3D shape editing. However, while interactivity is the key constraint for the usability of such tools, it cannot be maintained when the complexity of either the 3D model or the applied deformation exceeds a given workstation-dependent threshold. In this system paper, we solve this scalability problem by introducing a streaming system based on a sampling-reconstruction approach. First an efficient out-of-core adaptive simplification algorithm is performed in a pre-processing step, to quickly generate a simplified version of the model. The resulting model can then be submitted to arbitrary FFD tools, as its reduced size ensures interactive response. Second, a post-processing step performs a featurepreserving reconstruction of the deformation undergone by the simplified version, onto the original model. Both bracketing steps share streaming and point-based basis, making them fully scalable and compatible with pointclouds, non-manifold polygon soups and meshes. Our system also offers a generic out-of-core multi-scale layer to arbitrary FFD tools, since the two bracketing steps remain available for partial upsampling during the interactive session. As a result, arbitrarily large 3D models can be interactively edited with most FFD tools, opening the use and combination of advanced deformation metaphors to models ranging from million to billion samples. Our system also offers to work on models that fit in memory but exceed the capabilities of a given FFD tool. Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Computational Geometry and Object ModelingItem Generic Mesh Refinement on GPU(The Eurographics Association, 2005) Boubekeur, Tamy; Schlick, Christophe; Michael Meissner and Bengt-Olaf SchneiderMany recent publications have shown that a large variety of computation involved in computer graphics can be moved from the CPU to the GPU, by a clever use of vertex or fragment shaders. Nonetheless there is still one kind of algorithms that is hard to translate from CPU to GPU: mesh refinement techniques. The main reason for this, is that vertex shaders available on current graphics hardware do not allow the generation of additional vertices on a mesh stored in graphics hardware. In this paper, we propose a general solution to generate mesh refinement on GPU. The main idea is to define a generic refinement pattern that will be used to virtually create additional inner vertices for a given polygon. These vertices are then translated according to some procedural displacement map defining the underlying geometry (similarly, the normal vectors may be transformed according to some procedural normal map). For illustration purpose, we use a tesselated triangular pattern, but many other refinement patterns may be employed. To show its flexibility, the technique has been applied on a large variety of refinement techniques: procedural displacement mapping, as well as more complex techniques such as curved PN-triangles or ST-meshes.Item Implicit Brushes for Stylized Line-based Rendering(The Eurographics Association and Blackwell Publishing Ltd., 2011) Vergne, Romain; Vanderhaeghe, David; Chen, Jiazhou; Barla, Pascal; Granier, Xavier; Schlick, Christophe; M. Chen and O. DeussenWe introduce a new technique called Implicit Brushes to render animated 3D scenes with stylized lines in realtime with temporal coherence. An Implicit Brush is defined at a given pixel by the convolution of a brush footprint along a feature skeleton; the skeleton itself is obtained by locating surface features in the pixel neighborhood. Features are identified via image-space fitting techniques that not only extract their location, but also their profile, which permits to distinguish between sharp and smooth features. Profile parameters are then mapped to stylistic parameters such as brush orientation, size or opacity to give rise to a wide range of line-based styles.Item Hermitian B-Splines(Blackwell Publishers Ltd and the Eurographics Association, 1999) Grisoni, Laurent; Blanc, Carole; Schlick, ChristopheThis paper proposes to study a spline model, called HB-splines, that is in fact a B-spline representation of Hermite splines, combined with some restriction on the differential values at segment boundaries. Although this model does not appear able to offer something new to the computer graphics community, we think that HB-splines deserve to be considered for themselves because they embed many interesting features. First, they include all the classical properties required in a geometric modeling environment (convex hull, local control, arbitrary orders of parametric or geometric continuity). Second, they have a nice aptitude for direct manipulation (i.e. manipulation without using control points). For this purpose, we propose a new graphic widget, called control sails, that offers the user an intuitive way to specify local properties (position, tangent, curvature) of a curve or a surface. Finally, they provide an elegant formulation of a biorthogonal wavelet family, that permits multiresolution manipulations of the resulting curves or surfaces, in a very efficient way.Item Growing Least Squares for the Analysis of Manifolds in Scale-Space(The Eurographics Association and Blackwell Publishing Ltd., 2012) Mellado, Nicolas; Guennebaud, Gaƫl; Barla, Pascal; Reuter, Patrick; Schlick, Christophe; Eitan Grinspun and Niloy MitraWe present a novel approach to the multi-scale analysis of point-sampled manifolds of co-dimension 1. It is based on a variant of Moving Least Squares, whereby the evolution of a geometric descriptor at increasing scales is used to locate pertinent locations in scale-space, hence the name "Growing Least Squares". Compared to existing scale-space analysis methods, our approach is the first to provide a continuous solution in space and scale dimensions, without requiring any parametrization, connectivity or uniform sampling. An important implication is that we identify multiple pertinent scales for any point on a manifold, a property that had not yet been demonstrated in the literature. In practice, our approach exhibits an improved robustness to change of input, and is easily implemented in a parallel fashion on the GPU. We compare our method to state-of-the-art scale-space analysis techniques and illustrate its practical relevance in a few application scenarios.Item An Inexpensive BRDF Model for Physically-based Rendering(Blackwell Science Ltd and the Eurographics Association, 1994) Schlick, ChristopheA new BRDF model is presented which can be viewed as an kind of intermediary model between empirism and theory. Main results of physics are observed (energy conservation, reciprocity rule, microfacet theory) and numerous phenomena involved in light reflection are accounted for, in a physically plausible way (incoherent and coherent reflection, spectrum modifications, anisotropy, self-shadowing, multiple surface and subsurface reflection, differences between homogeneous and heterogeneous materials). The model has been especially intended for computer graphics applications and therefore includes two main features: simplicity (a small number of intuitively understandable parameters controls the model) and efficiency (the formulation provides adequation to Monte-Carlo rendering techniques and/or hardware implementations).