Fluids real-time rendering

In this thesis the existing methods for realistic visualization of uids in real-time are reviewed. The correct handling of the interaction of light with a uid surface can highly increase the realism of the rendering, therefore method for physically accurate rendering of re ections and refractions will be used. The light- uid interaction does not stop at the surface, but continues inside the uid volume, causing caustics and beams of light. The simulation of uids require extremely time-consuming processes to achieve physical accuracy and will not be explored, although the main concepts will be given. Therefore, the main goals of this work are: Study and review the existing methods for rendering uids in realtime. Find a simpli ed physical model of light interaction, because a complete physically correct model would not achieve real-time. Develop an application that uses the found methods and the light interaction model

Extending backward polygon beam tracing of glossy scattering surfaces

Backward polygon beam tracing methods, that is beam tracing from the light source (L), are well suited to gather path coherency from specular (S) scattering surfaces. These methods are useful for modelling and efficiently simulating caustics on diffuse (D) surfaces; an effect due to LS+D transport paths. This paper generalizes backward polygon beam tracing to include a glossy (G) scattering surface. To this end the details of a beam tracing lumped model and implementation of L (S\G) D transport paths are presented. Although we limit the discussion to short transport paths, we show that backward beam tracing is faster than photon mapping by an order of magnitude for rendering caustics from glossy and specular surfaces.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1467-8659

Fluids real-time rendering

In this thesis the existing methods for realistic visualization of uids in real-time are reviewed. The correct handling of the interaction of light with a uid surface can highly increase the realism of the rendering, therefore method for physically accurate rendering of re ections and refractions will be used. The light- uid interaction does not stop at the surface, but continues inside the uid volume, causing caustics and beams of light. The simulation of uids require extremely time-consuming processes to achieve physical accuracy and will not be explored, although the main concepts will be given. Therefore, the main goals of this work are: Study and review the existing methods for rendering uids in realtime. Find a simpli ed physical model of light interaction, because a complete physically correct model would not achieve real-time. Develop an application that uses the found methods and the light interaction model

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 algorithms for the realistic simulation of fluids

Nowadays there is great demand for realistic simulations in the computer graphics field. Physically-based animations are commonly used, and one of the more complex problems in this field is fluid simulation, more so if real-time applications are the goal. Videogames, in particular, resort to different techniques that, in order to represent fluids, just simulate the consequence and not the cause, using procedural or parametric methods and often discriminating the physical solution. This need motivates the present thesis, the interactive simulation of free-surface flows, usually liquids, which are the feature of interest in most common applications. Due to the complexity of fluid simulation, in order to achieve real-time framerates, we have resorted to use the high parallelism provided by actual consumer-level GPUs. The simulation algorithm, the Lattice Boltzmann Method, has been chosen accordingly due to its efficiency and the direct mapping to the hardware architecture because of its local operations. We have created two free-surface simulations in the GPU: one fully in 3D and another restricted only to the upper surface of a big bulk of fluid, limiting the simulation domain to 2D. We have extended the latter to track dry regions and is also coupled with obstacles in a geometry-independent fashion. As it is restricted to 2D, the simulation loses some features due to the impossibility of simulating vertical separation of the fluid. To account for this we have coupled the surface simulation to a generic particle system with breaking wave conditions; the simulations are totally independent and only the coupling binds the LBM with the chosen particle system. Furthermore, the visualization of both systems is also done in a realistic way within the interactive framerates; raycasting techniques are used to provide the expected light-related effects as refractions, reflections and caustics. Other techniques that improve the overall detail are also applied as low-level detail ripples and surface foam

Interactive global illumination on the CPU

Computing realistic physically-based global illumination in real-time remains one of the major goals in the fields of rendering and visualisation; one that has not yet been achieved due to its inherent computational complexity. This thesis focuses on CPU-based interactive global illumination approaches with an aim to develop generalisable hardware-agnostic algorithms. Interactive ray tracing is reliant on spatial and cache coherency to achieve interactive rates which conflicts with needs of global illumination solutions which require a large number of incoherent secondary rays to be computed. Methods that reduce the total number of rays that need to be processed, such as Selective rendering, were investigated to determine how best they can be utilised. The impact that selective rendering has on interactive ray tracing was analysed and quantified and two novel global illumination algorithms were developed, with the structured methodology used presented as a framework. Adaptive Inter- leaved Sampling, is a generalisable approach that combines interleaved sampling with an adaptive approach, which uses efficient component-specific adaptive guidance methods to drive the computation. Results of up to 11 frames per second were demonstrated for multiple components including participating media. Temporal Instant Caching, is a caching scheme for accelerating the computation of diffuse interreflections to interactive rates. This approach achieved frame rates exceeding 9 frames per second for the majority of scenes. Validation of the results for both approaches showed little perceptual difference when comparing against a gold-standard path-traced image. Further research into caching led to the development of a new wait-free data access control mechanism for sharing the irradiance cache among multiple rendering threads on a shared memory parallel system. By not serialising accesses to the shared data structure the irradiance values were shared among all the threads without any overhead or contention, when reading and writing simultaneously. This new approach achieved efficiencies between 77% and 92% for 8 threads when calculating static images and animations. This work demonstrates that, due to the flexibility of the CPU, CPU-based algorithms remain a valid and competitive choice for achieving global illumination interactively, and an alternative to the generally brute-force GPU-centric algorithms

Visually pleasing real-time global illumination rendering for fully-dynamic scenes

Global illumination (GI) rendering plays a crucial role in the photo-realistic rendering of virtual scenes. With the rapid development of graphics hardware, GI has become increasingly attractive even for real-time applications nowadays. However, the computation of physically-correct global illumination is time-consuming and cannot achieve real-time, or even interactive performance. Although the realtime GI is possible using a solution based on precomputation, such a solution cannot deal with fully-dynamic scenes. This dissertation focuses on solving these problems by introducing visually pleasing real-time global illumination rendering for fully-dynamic scenes. To this end, we develop a set of novel algorithms and techniques for rendering global illumination effects using the graphics hardware. All these algorithms not only result in real-time or interactive performance, but also generate comparable quality to the previous works in off-line rendering. First, we present a novel implicit visibility technique to circumvent expensive visibility queries in hierarchical radiosity by evaluating the visibility implicitly. Thereafter, we focus on rendering visually plausible soft shadows, which is the most important GI effect caused by the visibility determination. Based on the pre-filtering shadowmapping theory, wesuccessively propose two real-time soft shadow mapping methods: "convolution soft shadow mapping" (CSSM) and "variance soft shadow mapping" (VSSM). Furthermore, we successfully apply our CSSM method in computing the shadow effects for indirect lighting. Finally, to explore the GI rendering in participating media, we investigate a novel technique to interactively render volume caustics in the single-scattering participating media.Das Rendern globaler Beleuchtung ist für die fotorealistische Darstellung virtueller Szenen von entscheidender Bedeutung. Dank der rapiden Entwicklung der Grafik-Hardware wird die globale Beleuchtung heutzutage sogar für Echtzeitanwendungen immer attraktiver. Trotz allem ist die Berechnung physikalisch korrekter globaler Beleuchtung zeitintensiv und interaktive Laufzeiten können mit "standard Hardware" noch nicht erzielt werden. Obwohl das Rendering auf der Grundlage von Vorberechnungen in Echtzeit möglich ist, kann ein solcher Ansatz nicht auf voll-dynamische Szenen angewendet werden. Diese Dissertation zielt darauf ab, das Problem der globalen Beleuchtungsberechnung durch Einführung von neuen Techniken für voll-dynamische Szenen in Echtzeit zu lösen. Dazu stellen wir eine Reihe neuer Algorithmen vor, die die Effekte der globaler Beleuchtung auf der Grafik-Hardware berechnen. All diese Algorithmen erzielen nicht nur Echtzeit bzw. interaktive Laufzeiten sondern liefern auch eine Qualität, die mit bisherigen offline Methoden vergleichbar ist. Zunächst präsentieren wir eine neue Technik zur Berechnung impliziter Sichtbarkeit, die aufwändige Sichbarkeitstests in hierarchischen Radiosity-Datenstrukturen vermeidet. Anschliessend stellen wir eine Methode vor, die weiche Schatten, ein wichtiger Effekt für die globale Beleuchtung, in Echtzeit berechnet. Auf der Grundlage der Theorie über vorgefilterten Schattenwurf, zeigen wir nacheinander zwei Echtzeitmethoden zur Berechnung weicher Schattenwürfe: "Convolution Soft Shadow Mapping" (CSSM) und "Variance Soft Shadow Mapping" (VSSM). Darüber hinaus wenden wir unsere CSSM-Methode auch erfolgreich auf den Schatteneffekt in der indirekten Beleuchtung an. Abschliessend präsentieren wir eine neue Methode zum interaktiven Rendern von Volumen-Kaustiken in einfach streuenden, halbtransparenten Medien

Perceptually-motivated, interactive rendering and editing of global illumination

This thesis proposes several new perceptually-motivated techniques to synthesize, edit and enhance depiction of three-dimensional virtual scenes. Finding algorithms that fit the perceptually economic middle ground between artistic depiction and full physical simulation is the challenge taken in this work. First, we will present three interactive global illumination rendering approaches that are inspired by perception to efficiently depict important light transport. Those methods have in common to compute global illumination in large and fully dynamic scenes allowing for light, geometry, and material changes at interactive or real-time rates. Further, this thesis proposes a tool to edit reflections, that allows to bend physical laws to match artistic goals by exploiting perception. Finally, this work contributes a post-processing operator that depicts high contrast scenes in the same way as artists do, by simulating it "seen'; through a dynamic virtual human eye in real-time.Diese Arbeit stellt eine Anzahl von Algorithmen zur Synthese, Bearbeitung und verbesserten Darstellung von virtuellen drei-dimensionalen Szenen vor. Die Herausforderung liegt dabei in der Suche nach Ausgewogenheit zwischen korrekter physikalischer Berechnung und der künstlerischen, durch die Gesetze der menschlichen Wahrnehmung motivierten Praxis. Zunächst werden drei Verfahren zur Bild-Synthese mit globaler Beleuchtung vorgestellt, deren Gemeinsamkeit in der effizienten Handhabung großer und dynamischer virtueller Szenen liegt, in denen sich Geometrie, Materialen und Licht frei verändern lassen. Darauffolgend wird ein Werkzeug zum Editieren von Reflektionen in virtuellen Szenen das die menschliche Wahrnehmung ausnutzt um künstlerische Vorgaben umzusetzen, vorgestellt. Die Arbeit schließt mit einem Filter am Ende der Verarbeitungskette, der den wahrgenommen Kontrast in einem Bild erhöht, indem er die Entstehung von Glanzeffekten im menschlichen Auge nachbildet