Jean-Eudes Marvie

GPU Shape Grammars

GPU Shape Grammars provide a solution for interactive procedural generation, tuning and visualization of massive environment elements for both video games and production rendering. Our technique generates detailed models without explicit geometry storage. To this end we reformulate the grammar expansion for generation of detailed models at the tesselation control and geometry shader stages. Using the geometry generation capabilities of modern graphics hardware, our technique generated massive, highly detailed models. GPU Shape Grammars integrate within a scalable framework by introducing automatic generation of levels of detail at reduced cost. We apply our solution for interactive generation and rendering of scenes containing thousands of buildings and trees.

Sub-pixel shadow mapping

The limited resolution of shadow maps may result in erroneous shadowing, yielding artificially jagged edges (Figure 1) and temporally crawling shadows even using perspective optimization techniques. Dai et al. [2008] propose an explicit storage of geometry within shadow map texels to avoid aliasing. Each texel stores the coordinates of the closest triangle only, potentially leading to false negatives in the intersection computation while incurring large memory consumption. These artifacts are reduced by intersecting the triangles stored in numerous neighboring texels, resulting in significant performance hit while still missing some intersections.n We introduce Sub-Pixel Shadow Maps (SPSM) for real-time shadow mapping with sub-pixel precision. Our technique is based on the storage of a fixed-size partial representation of the scene geometry using conservative rasterization, combined with an original reconstruction of shadow edges.

Transmittance function mapping

The interaction between light and participating media involves complex physical phenomena including light absorption and scattering. Media such as fog, clouds or smoke feature complex lighting interactions that are intrinsically related to the properties of their constitutive particles. As a result, the radiance transmitted by the medium depends on the varying properties on the entire light paths, which generate soft light shafts and opacity variations.n Simulating light scattering in these media usually requires complex offline estimations. Real-time applications are either based on heavy precomputations, limited to homogeneous media or relying on simplistic rendering techniques such as billboards. We propose a generic method for fast estimation of single scattering within participating media. Introducing the concept of Transmittance Function Maps and Uniform Projective Space Sampling, our method leverages graphics hardware for interactive support of dynamic light sources, viewpoints and participating media. Our method also accounts for the shadows cast from solid objects, providing a full-featured solution for fast rendering of participating media which potentially embrace the entire scene.

Accurate analytic approximations for real-time specular area lighting

Accurate real-time rendering of specular surfaces is a challenging task when considering area light source illumination. The difficulty resides in the evaluation of a surface integral for which no practical solution exists except using expensive Monte Carlo methods. Recent techniques like the most representative point approach [Drobot 2014] alleviate this problem but make some accuracy trade-off to achieve real-time performance. We introduce analytic approximations for accurate real-time rendering of specular surfaces illuminated by polygonal light sources. Our solution is based on a reformulation of the contour integral [Arvo 1995] we approximate analytically with simple peak functions. In addition, using simple geometric operations, we extend the solution to handle more physically plausible BRDFs. Our solution works without any assumption on light source shape nor surface roughness, bringing real-time performances with a quality close to the ground truth.

Streaming and synchronization of multi-user worlds through HTTP/1.1

As the trend of online multi-user worlds gets more and more momentum, such worlds usually require heavy infrastructures both in terms of hardware and software: servers often manage the entire world simulation, and hence limit the number of simultaneous connections. The data exchanges are performed using proprietary protocols, requiring specific server applications and the use of dedicated ports which leads to potentially complex proxy issues for connection. Also, online virtual worlds usually target specific platforms (e.g. PC for Second Life, or game stations for Playstation Home), and even reduce the use of the world to a subset of available platforms due to bandwidth or hardware requirements.

Many-core event evaluation

We present a Many-Core Event Evaluation framework for real-time execution of many complex animation schemes applicable to a wide range of domains such as gaming and interactive pre-visualization in studio production. Our technique takes advantages of task parallelism on many-core CPU architecture using a two-level scheduling approach. Our generic approach can deal with tens of thousands event-processing nodes, event loops, non-deterministic and interaction-driven animation modifications at runtime. Versatility is further enforced through a native support of hierarchical animation graphs using prototypes and inline files. Our implementation based on the X3D event-based animation model exhibits performances approaching the theoretical upper bounds of parallelization.

Boundary-Aware Extinction Mapping

We introduce Boundary-Aware Extinction Maps for interactive rendering of massive heterogeneous volumetric datasets. Our approach is based on the projection of the extinction along light rays into a boundary-aware function space, focusing on the most relevant sections of the light paths. This technique also provides an alternative representation of the set of participating media, allowing scattering simulation methods to be applied on arbitrary volume representations. Combined with a simple out-of-core rendering framework, Boundary-Aware Extinction Maps are valuable tools for interactive applications as well as production previsualization and rendering.

Poisson disk ray-marched ambient occlusion

Ambient occlusion (AO) [Pharr and Green 2004] provides an approximation to global illumination. It can be computed in real-time if restricted to screen-space [Mittring 2007; Loos and Sloan 2010], at the cost of an approximation of solutions computed in geometric space, thus introducing a loss of quality.

Analytic Approximations for Real-Time Area Light Shading

We introduce analytic approximations for accurate real-time rendering of surfaces lit by non-occluded area light sources. Our solution leverages the Irradiance Tensors developed by Arvo for the shading of Phong surfaces lit by a polygonal light source. Using a reformulation of the 1D boundary edge integral, we develop a general framework for approximating and evaluating the integral in constant time using simple peak shape functions. To overcome the Phong restriction, we propose a low cost edge splitting strategy that accounts for the spherical warp introduced by the half vector parametrization. Thanks to this novel extension, we accurately approximate common microfacet BRDFs, providing a practical method producing specular stretches that closely match the ground truth in real-time. Finally, using the same approximation framework, we introduce support for spherical and disc area light sources, based on an original polygon spinning method supporting non-uniform scaling operations and horizon clipping. Implemented on a GPU, our method achieves real-time performances without any assumption on area light shape nor surface roughness.

Volume-aware extinction mapping

The simulation of the lighting effects produced by the interaction of participating media with the light contributes to the production of visually compelling effects such as translucence and volumetric shadowing. However, the complex inner structure of participating media requires vast amounts of memory for storage and costly computations for rendering.