2,907 research outputs found
Flux-Limited Diffusion for Multiple Scattering in Participating Media
For the rendering of multiple scattering effects in participating media,
methods based on the diffusion approximation are an extremely efficient
alternative to Monte Carlo path tracing. However, in sufficiently transparent
regions, classical diffusion approximation suffers from non-physical radiative
fluxes which leads to a poor match to correct light transport. In particular,
this prevents the application of classical diffusion approximation to
heterogeneous media, where opaque material is embedded within transparent
regions. To address this limitation, we introduce flux-limited diffusion, a
technique from the astrophysics domain. This method provides a better
approximation to light transport than classical diffusion approximation,
particularly when applied to heterogeneous media, and hence broadens the
applicability of diffusion-based techniques. We provide an algorithm for
flux-limited diffusion, which is validated using the transport theory for a
point light source in an infinite homogeneous medium. We further demonstrate
that our implementation of flux-limited diffusion produces more accurate
renderings of multiple scattering in various heterogeneous datasets than
classical diffusion approximation, by comparing both methods to ground truth
renderings obtained via volumetric path tracing.Comment: Accepted in Computer Graphics Foru
A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics
This paper presents a survey of ocean simulation and rendering methods in
computer graphics. To model and animate the ocean's surface, these methods
mainly rely on two main approaches: on the one hand, those which approximate
ocean dynamics with parametric, spectral or hybrid models and use empirical
laws from oceanographic research. We will see that this type of methods
essentially allows the simulation of ocean scenes in the deep water domain,
without breaking waves. On the other hand, physically-based methods use
Navier-Stokes Equations (NSE) to represent breaking waves and more generally
ocean surface near the shore. We also describe ocean rendering methods in
computer graphics, with a special interest in the simulation of phenomena such
as foam and spray, and light's interaction with the ocean surface
Tracing Analytic Ray Curves for Light and Sound Propagation in Non-Linear Media
The physical world consists of spatially varying media, such as the atmosphere and the ocean, in which light and sound propagates along non-linear trajectories. This presents a challenge to existing ray-tracing based methods, which are widely adopted to simulate propagation due to their efficiency and flexibility, but assume linear rays. We present a novel algorithm that traces analytic ray curves computed from local media gradients, and utilizes the closed-form solutions of both the intersections of the ray curves with planar surfaces, and the travel distance. By constructing an adaptive unstructured mesh, our algorithm is able to model general media profiles that vary in three dimensions with complex boundaries consisting of terrains and other scene objects such as buildings. Our analytic ray curve tracer with the adaptive mesh improves the efficiency considerably over prior methods. We highlight the algorithm's application on simulation of visual and sound propagation in outdoor scenes
Fast Rendering of Forest Ecosystems with Dynamic Global Illumination
Real-time rendering of large-scale, forest ecosystems remains a challenging problem, in that important global illumination effects, such as leaf transparency and inter-object light scattering, are difficult to capture, given tight timing constraints and scenes that typically contain hundreds of millions of primitives. We propose a new lighting model, adapted from a model previously used to light convective clouds and other participating media, together with GPU ray tracing, in order to achieve these global illumination effects while maintaining near real-time performance. The lighting model is based on a lattice-Boltzmann method in which reflectance, transmittance, and absorption parameters are taken from measurements of real plants. The lighting model is solved as a preprocessing step, requires only seconds on a single GPU, and allows dynamic lighting changes at run-time. The ray tracing engine, which runs on one or multiple GPUs, combines multiple acceleration structures to achieve near real-time performance for large, complex scenes. Both the preprocessing step and the ray tracing engine make extensive use of NVIDIA\u27s Compute Unified Device Architecture (CUDA)
Shallow waters simulation
Dissertação de mestrado integrado em Informatics EngineeringRealistic simulation and rendering of water in real-time is a challenge within the field of computer graphics, as it
is very computationally demanding. A common simulation approach is to reduce the problem from 3D to 2D by
treating the water surface as a 2D heightfield. When simulating 2D fluids, the Shallow Water Equations (SWE)
are often employed, which work under the assumption that the water’s horizontal scale is much greater than it’s
vertical scale.
There are several methods that have been developed or adapted to model the SWE, each with its own advantages
and disadvantages. A common solution is to use grid-based methods where there is the classic approach
of solving the equations in a grid, but also the Lattice-Boltzmann Method (LBM) which originated from the field of
statistical physics. Particle based methods have also been used for modeling the SWE, namely as a variation of
the popular Smoothed-Particle Hydrodynamics (SPH) method.
This thesis presents an implementation for real-time simulation and rendering of a heightfield surface water
volume. The water’s behavior is modeled by a grid-based SWE scheme with an efficient single kernel compute
shader implementation.
When it comes to visualizing the water volume created by the simulation, there are a variety of effects that
can contribute to its realism and provide visual cues for its motion. In particular, When considering shallow water,
there are certain features that can be highlighted, such as the refraction of the ground below and corresponding
light attenuation, and the caustics patterns projected on it.
Using the state produced by the simulation, a water surface mesh is rendered, where set of visual effects are
explored. First, the water’s color is defined as a combination of reflected and transmitted light, while using a Cook-
Torrance Bidirectional Reflectance Distribution Function (BRDF) to describe the Sun’s reflection. These results
are then enhanced by data from a separate pass which provides caustics patterns and improved attenuation
computations. Lastly, small-scale details are added to the surface by applying a normal map generated using
noise.
As part of the work, a thorough evaluation of the developed application is performed, providing a showcase of
the results, insight into some of the parameters and options, and performance benchmarks.Simulação e renderização realista de água em tempo real é um desafio dentro do campo de computação gráfica,
visto que é muito computacionalmente exigente. Uma abordagem comum de simulação é de reduzir o problema
de 3D para 2D ao tratar a superfície da água como um campo de alturas 2D. Ao simular fluidos em 2D, é
frequente usar as equações de águas rasas, que funcionam sobre o pressuposto de que a escala horizontal da
água é muito maior que a sua escala vertical.
Há vários métodos que foram desenvolvidos ou adaptados para modelar as equações de águas rasas, cada
uma com as suas vantagens e desvantagens. Uma solução comum é utilizar métodos baseados em grelhas
onde existe a abordagem clássica de resolver as equações numa grelha, mas também existe o método de Lattice
Boltzmann que originou do campo de física estatística. Métodos baseados em partículas também já foram
usados para modelar as equações de águas rasas, nomeadamente como uma variação do popular método de
SPH.
Esta tese apresenta uma implementação para simulação e renderização em tempo real de um volume de
água com uma superfície de campo de alturas. O comportamento da água é modelado por um esquema de
equações de águas rasas baseado na grelha com uma implementação eficiente de um único kernel de compute
shader.
No que toca a visualizar o volume de água criado pela simulação, existe uma variedade de efeitos que podem
contribuir para o seu realismo e fornecer dicas visuais sobre o seu movimento. Ao considerar águas rasas, existem
certas características que podem ser destacadas, como a refração do terreno por baixo e correspondente
atenuação da luz, e padrões de cáusticas projetados nele.
Usando o estado produzido pela simulação, uma malha da superfície da água é renderizada, onde um conjunto
de efeitos visuais são explorados. Em primeiro lugar, a cor da água é definida como uma combinação de
luz refletida e transmitida, sendo que uma BRDF de Cook-Torrance é usada para descrever a reflexão do Sol.
Estes resultados são depois complementados com dados gerados num passo separado que fornece padrões
de cáusticas e melhora as computações de atenuação. Por fim, detalhes de pequena escala são adicionados à
superfície ao aplicar um mapa de normais gerado com ruído.
Como parte do trabalho desenvolvido, é feita uma avaliação detalhada da aplicação desenvolvida, onde é apresentada
uma demonstração dos resultados, comentários sobre alguns dos parâmetros e opções, e referências
de desempenho
Efficient Methods for Computational Light Transport
En esta tesis presentamos contribuciones sobre distintos retos computacionales relacionados con transporte de luz. Los algoritmos que utilizan información sobre el transporte de luz están presentes en muchas aplicaciones de hoy en día, desde la generación de efectos visuales, a la detección de objetos en tiempo real. La luz es una valiosa fuente de información que nos permite entender y representar nuestro entorno, pero obtener y procesar esta información presenta muchos desafíos debido a la complejidad de las interacciones entre la luz y la materia. Esta tesis aporta contribuciones en este tema desde dos puntos de vista diferentes: algoritmos en estado estacionario, en los que se asume que la velocidad de la luz es infinita; y algoritmos en estado transitorio, que tratan la luz no solo en el dominio espacial, sino también en el temporal. Nuestras contribuciones en algoritmos estacionarios abordan problemas tanto en renderizado offline como en tiempo real. Nos enfocamos en la reducción de varianza para métodos offline,proponiendo un nuevo método para renderizado eficiente de medios participativos. En renderizado en tiempo real, abordamos las limitacionesde consumo de batería en dispositivos móviles proponiendo un sistema de renderizado que incrementa la eficiencia energética en aplicaciones gráficas en tiempo real. En el transporte de luz transitorio, formalizamos la simulación de este tipo transporte en este nuevo dominio, y presentamos nuevos algoritmos y métodos para muestreo eficiente para render transitorio. Finalmente, demostramos la utilidad de generar datos en este dominio, presentando un nuevo método para corregir interferencia multi-caminos en camaras Timeof- Flight, un problema patológico en el procesamiento de imágenes transitorias.n this thesis we present contributions to different challenges of computational light transport. Light transport algorithms are present in many modern applications, from image generation for visual effects to real-time object detection. Light is a rich source of information that allows us to understand and represent our surroundings, but obtaining and processing this information presents many challenges due to its complex interactions with matter. This thesis provides advances in this subject from two different perspectives: steady-state algorithms, where the speed of light is assumed infinite, and transient-state algorithms, which deal with light as it travels not only through space but also time. Our steady-state contributions address problems in both offline and real-time rendering. We target variance reduction in offline rendering by proposing a new efficient method for participating media rendering. In real-time rendering, we target energy constraints of mobile devices by proposing a power-efficient rendering framework for real-time graphics applications. In transient-state we first formalize light transport simulation under this domain, and present new efficient sampling methods and algorithms for transient rendering. We finally demonstrate the potential of simulated data to correct multipath interference in Time-of-Flight cameras, one of the pathological problems in transient imaging.<br /
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