Environmental Objects for Authoring Procedural Scenes

International audienceWe propose a novel approach for authoring large scenes with automatic enhancement of objects to create geometric decoration details such as snow cover, icicles, fallen leaves, grass tufts or even trash. We introduce environmental objects that extend an input object geometry with a set of procedural effects that defines how the object reacts to the environment, and by a set of scalar fields that defines the influence of the object over of the environment. The user controls the scene by modifying environmental variables, such as temperature or humidity fields. The scene definition is hierarchical: objects can be grouped and their behaviours can be set at each level of the hierarchy. Our per object definition allows us to optimize and accelerate the effects computation, which also enables us to generate large scenes with many geometric details at a very high level of detail. In our implementation, a complex urban scene of 10 000 m², represented with details of less than 1 cm, can be locally modified and entirely regenerated in a few seconds

Interactive Generation of Time-Evolving Snow-Covered Landscaped with Avalanches

We introduce a novel method for interactive generation of visually consistent, snow-covered landscapes and provide control of their dynamic evolution over time. Our main contribution is the real-time phenomenological simulation of avalanches and other user-guided events, such as tracks left by Nordic skiing, which can be applied to interactively sculpt the landscape. The terrain is modeled as a height field with additional layers for stable, compacted, unstable, and powdery snow, which behave in combination as a semi-viscous fluid. We incorporate the impact of several phenomena, including sunlight, temperature, prevailing wind direction, and skiing activities. The snow evolution includes snow-melt and snow-drift, which affect stability of the snow mass and the probability of avalanches. A user can shape landscapes and their evolution either with a variety of interactive brushes, or by prescribing events along a winter season time-line. Our optimized GPU-implementation allows interactive updates of snow type and depth across a large (10×10km) terrain, including real-time avalanches, making this suitable for visual assets in computer games. We evaluate our method through perceptual comparison against exiting methods and real snow-depth data

Simulation du transport de neige

Que ce soit pour des scènes synthétiques de films ou de jeux vidéo, le réalisme des environnements passent par l’ajout d’effets visuels communs à nos expériences. La neige fait partie des phénomènes naturels complexes qui rendent leur simulation physique et visuelle d’autant plus difficile à traiter. En effet, la neige tombe au gré du vent dans les scènes, elle s’entasse et se compacte à des endroits, se brise et retombe, se fait repousser par le vent une fois déposée, se liquéfie ou s’évapore, se glace, accumule des impuretés, etc. Le but de cette maîtrise est de développer un simulateur de transport de neige dans des espaces synthétiques. Ce simulateur se veut à la fois un outil automatique pour enneiger des scènes, mais offrant certains contrôles aux artistes afin de produire des résultats escomptés avec des paramètres simples comme le taux de précipitations de la neige ou la direction du vent. Nous proposons une méthode de simulation du transport de la neige, comportant : 1. Une phase de précalculs afin d’estimer le vent et les précipitations dans la scène. 2. Un modèle physique de transport de la neige permettant même d’observer l’évolution de la neige dans le temps. 3. Une méthode d’implémentation sur processeur graphique. Nos résultats montrent l’intérêt des divers phénomènes sur la simulation réaliste du transport de neige.Whether it is for synthetic scenes in movies or video games, the realism of environments passes by the addition of visual effects common to our experiences. Snow is part of complex natural phenomena that make their physical and visual simulation all the more difficult to treat. In fact, snow falls in scenes under the action of wind. It piles up and is compressed in some areas, breaks and falls, is repelled by wind once deposited, liquefies or evaporates, freezes, accumulates impurities, etc. The goal of this research is to develop a simulator of snow transport in synthetic spaces. This simulator is designed as an automatic tool to integrate snow in scenes by adding its precipitation, transport by wind, simulation of melting and evaporation, but also to offer some control to artists in order to produce the desired results with easy and understandable settings such as the snow precipitation rate or the wind direction and speed in the scene. We propose a method for the simulation of snow transport that consists of : 1. A precomputation phase to estimate wind and precipitations in a scene. 2. A physical model of snow transport to capture its evolution through time. 3. A method of implementation on GPU. Our results demonstrate the need to simulate the various phenomena on the realism of snow distribution