Pascal Gautron

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.

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.

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.

Triple depth culling

Virtual worlds feature increasing geometric and shading complexities, resulting in a constant need for effective solutions to avoid rendering objects invisible for the viewer. This observation is particularly true in the context of real-time rendering of highly occluded environments such as urban areas, landscapes or indoor scenes. This problem has been intensively researched in the past decades, resulting in numerous optimizations building upon the well-known Z-buffer technique. Among them, extensions of graphics hardware such as early Z-culling [Morein 2000] efficiently avoid shading most of invisible fragments. However, this technique is not applicable when the fragment shader discards fragments or modifies their depth value, or if alpha testing is enabled [nVidia 2008].

Single scattering in heterogenous participating media

The interaction between light and light-transmitting objects, known as participating media, involves complex physical phenomena such as light absorption and scattering. Media such as clouds, smoke and translucent materials often feature heterogeneous scattering properties. Hence the radiance transmitted by the medium potentially depends on such varying properties on the entire light paths, yielding soft light shafts and opacity variations (Figure 1).