Rendu de scènes 3D imitant le style «dessin animé»

Projet SYNTIMNous décrivons un algorithme de rendu qui génère des images imitant le style «dessin animé» traditionnel (ou «bande dessinée») à partir de la description tridimens- ionnelle d'une scène fixe ou animée. Pour ce faire, l'algorithme fait appel à des techniques qui permettent: - de détourer les objets (profils et arêtes sont dessinés en traits noirs), - de colorer uniformément les surfaces intérieures à ces contours, - de faire apparaître sur les objets les ombres propres et les ombres portées dues aux sources de lumière éclairant la scène

Fast Hydraulic Erosion Simulation and Visualization on GPU

International audienceNatural mountains and valleys are gradually eroded by rainfall and river flows. Physically-based modeling of this complex phenomenon is a major concern in producing realistic synthesized terrains. However, despite some recent improvements, existing algorithms are still computationally expensive, leading to a time-consuming process fairly impractical for terrain designers and 3D artists. In this paper, we present a new method to model the hydraulic erosion phenomenon which runs at interactive rates on today's computers. The method is based on the velocity field of the running water, which is created with an efficient shallow-water fluid model. The velocity field is used to calculate the erosion and deposition process, and the sediment transportation process. The method has been carefully designed to be implemented totally on GPU, and thus takes full advantage of the parallelism of current graphics hardware. Results from experiments demonstrate that our method is effective and efficient. It can create realistic erosion effects by rainfall and river flows, and produce fast simulation results for terrains with large sizes

Real-Time Marker Level Set on GPU

International audienceLevel set methods have been extensively used to track the dynamical interfaces between different materials for physically based simulation, geometry modeling, oceanic modeling and other scientific and engineering applications. Due to the inherent Eulerian characteristics, interface evolution based on level set usually suffers from numerical diffusion, sharp feature missing and mass loss. Although some effective methods such as Particle Level Set (PLS) and Marker Level Set (MLS) have been proposed to tackle these difficulties, the complicated correction process and the high computational cost pose severe limitations for real-time applications. In this paper we provide an efficient parallel implementation of the Marker Level Set method on latest graphics hardware. Each step of the MLS method is fully mapped on GPU with an innovative combination of different computation techniques. Relying on GPU's parallelism and flexible programmability, the method provides real-time performance for large size 2D examples and moderate 3D examples, which is significantly faster than previous CPU based methods

Rendering Forest Scenes in Real-Time

International audienceForests are crucial for scene realism in applications such as flight simulators. This paper proposes a new representation allowing for the real-time rendering of realistic forests covering an arbitrary terrain. It lets us produce dense forests corresponding to continuous non-repetitive fields made of thousands of trees with full parallax. Our representation draws on volumetric textures and aperiodic tiling: the forest consists of a set of edge-compatible prisms containing forest samples which are aperiodically mapped onto the ground. The representation allows for quality rendering, thanks to appropriate 3D non-linear filtering. It relies on LODs and on a GPU-friendly structure to achieve real-time performance. Dynamic lighting and shadowing are beyond the scope of this paper. On the other hand, we require no advanced graphics feature except 3D textures and decent fill and vertex transform rates. However we can take advantage of vertex shaders so that the slicing of the volumetric texture is entirely done on the GPU

Tests of achromatic phase shifters performed on the SYNAPSE test bench: a progress report

The achromatic phase shifter (APS) is a component of the Bracewell nulling interferometer studied in preparation for future space missions (viz. Darwin/TPF-I) focusing on spectroscopic study of Earth-like exo-planets. Several possible designs of such an optical subsystem exist. Four approaches were selected for further study. Thales Alenia Space developed a dielectric prism APS. A focus crossing APS prototype was developed by the OCA, Nice, France. A field reversal APS prototype was prepared by the MPIA in Heidelberg, Germany. Centre Spatial de Li\`ege develops a concept based on Fresnel's rhombs. This paper presents a progress report on the current work aiming at evaluating these prototypes on the SYNAPSE test bench at the Institut d'Astrophysique Spatiale in Orsay, France

Virtual Garments: A Fully Geometric Approach for Clothing Design

International audienceModeling dressed characters is known as a very tedious process. It usually requires specifying 2D fabric patterns, positioning and assembling them in 3D, and then performing a physically-based simulation. The latter accounts for gravity and collisions to compute the rest shape of the garment, with the adequate folds and wrinkles. This paper presents a more intuitive way to design virtual clothing. We start with a 2D sketching system in which the user draws the contours and seam-lines of the garment directly on a virtual mannequin. Our system then converts the sketch into an initial 3D surface using an existing method based on a precomputed distance field around the mannequin. The system then splits the created surface into different panels delimited by the seam-lines. The generated panels are typically not developable. However, the panels of a realistic garment must be developable, since each panel must unfold into a 2D sewing pattern. Therefore our system automatically approximates each panel with a developable surface, while keeping them assembled along the seams. This process allows us to output the corresponding sewing patterns. The last step of our method computes a natural rest shape for the 3D garment, including the folds due to the collisions with the body and gravity. The folds are generated using procedural modeling of the buckling phenomena observed in real fabric. The result of our algorithm consists of a realistic looking 3D mannequin dressed in the designed garment and the 2D patterns which can be used for distortion free texture mapping. The patterns we create also allow us to sew real replicas of the virtual garments

Geometric Deformation by Merging a 3D-Object with a Simple Shape

Deformation techniques are often used to model the shape of geometric objects. This paper presents a new geometric deformation technique allowing local deformation of the shape of an object by merging the object with a simple 3D-shape (sphere, ellipsoid,...). Two kinds of effects can be obtained: the simple shape is used to produce either a bump or a dent on the object. The object is deformed so that it includes or it embeds the simple shape. In order to deform the object, the 3D-space where it lies is continuously deformed so that the object is bumped and the shape of the bump corresponds to the simple 3D-shape. If the surfaces of both the original object and the simple shape are smooth (continuously differentiable), the surface of the deformed object is also smooth. Moreover, topological properties of the object are unchanged, and the volume variation of the deformed object is controlled by the volume delimited by the simple shape. An interactive deformation tool based on this technique is presented. It comprises a convex 3D-shape and a center (a 3D point included in the shape). The user can interactively control the deformation by changing the parameters of the tool shape and the position of the tool center. Control of the parameters is particularly intuitive

Packing Square Tiles into One Texture

This paper deals with the packing of square tiles of the same size into one texture. Texture size is constrained by the graphics hardware. In particular, width and height resolutions must be powers of two. To cover the whole texture and avoid space loss, common schemes pack a number of tiles that is a power of two. We show that numbers of tiles like 5, 13, 17, 25, 34 and others can also be reached without wasting memory. To achieve this, our scheme takes advantage of texture rotation and the wrapping capability of texture-addressing, which gives a torus topology to the texture space

Rendering Forest Scenes in Real-Time

International audienceForests are crucial for scene realism in applications such as flight simulators. This paper proposes a new representation allowing for the real-time rendering of realistic forests covering an arbitrary terrain. It lets us produce dense forests corresponding to continuous non-repetitive fields made of thousands of trees with full parallax. Our representation draws on volumetric textures and aperiodic tiling: the forest consists of a set of edge-compatible prisms containing forest samples which are aperiodically mapped onto the ground. The representation allows for quality rendering, thanks to appropriate 3D non-linear filtering. It relies on LODs and on a GPU-friendly structure to achieve real-time performance. Dynamic lighting and shadowing are beyond the scope of this paper. On the other hand, we require no advanced graphics feature except 3D textures and decent fill and vertex transform rates. However we can take advantage of vertex shaders so that the slicing of the volumetric texture is entirely done on the GPU