Made available in DSpace on 2015-03-05T13:53:45Z (GMT). No. of bitstreams: 0 Previous issue date: 25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Esse trabalho tem por objetivo apresentar um modelo para geração e animação de céus em tempo-real, onde as nuvens possuem uma representação volumétrica e sua visualização é feita através de billboards. A iluminação das nuvens utiliza vertex-shaders e uma técnica de absorção de luz similar a ray-casting. A principal aplicação deste modelo é em jogos e entretenimento interativo, onde grandes áreas de natureza são exibidas e portanto faz-se necessário uma representação realista do céu. As principais contribuições deste trabalho são: a geração semi-automática de modelos tridimensionais de nuvens, iluminação das nuvens levando-se em conta a perda de energia da luz no interior da nuvem e o conceito de variação climática. / The objective of this work is to present a model for generation and animation of skies, in real-time, where clouds have a volumetric representation implemented using billboards. Clouds illumination performed using vertex-shader and a technique of light absorption similar to ray-casting algorithms. The main application of the model is for games and interactive entertainment, where large areas of nature must be visualized in a realistic representation. The main contributions of this work are: semi-automatic generation of three-dimensional clouds models, cloud illumination using a technique of light absorption to simulate dark areas of the cloud and the concept of climatic variation.

Volumetric clouds are often used in video games in order to improve the realism or graphical quality of the game. However, in order to achieve real-time rendered clouds, optimizations have to be implemented as part of the rendering algorithm. These kinds of optimizations improve the performance, but can also have a negative impact on the visual quality of the clouds. This thesis investigates the use of bilinear interpolation for the purpose of improving the performance of a volumetric cloud renderer, while trying to avoid any substantial reduction in visual quality. This is extended by looking at the effect of adaptively sampling the pixel colors. The renderer itself is created in Unity3D using a ray marching algorithm. As part of the literature study, this research also explores different ways of measuring visual quality within real-time rendering. As a result of this, the thesis uses the Structural Similarity Index Measure to measure the visual quality. The research found that utilizing bilinear interpolation to ray march every eighth pixel results in a performance gain of 45%. However, it also reduces the visual quality of the volumetric clouds. This is counteracted by using adaptive sampling to interpolate only where the standard deviation of pixel colors is below a threshold. We cannot, however, determine the optimal value of this parameter, since it depends on the requirements of the renderer. Instead, it has to be determined on a case-by-case basis. / Volymetriska moln används i spel för att uppnå realism och förbättra den grafiska kvaliteten. Men för att uppnå realtidsrendering så måste optimeringar göras. Dessa typer av optimeringar förbättrar prestandan av programmet, men kan också försämra den visuella kvalteten. Den här studien undersöker hur en optimering baserad på bilinjär interpolering kan användas för att förbättra prestandan av volymetriska moln, utan att försämra den visuella kvaliteten i någon större utsträckning. Studien tittar även på hur adaptiv sampling av pixlarna påverkar optimeringen. För att utföra detta renderas molnen i Unity3D med hjälp av en ray marching-algoritm. Som del av litteraturstudien utforskas även olika sätt att evaluera visuell kvalitet inom realtidsrendering. Utifrån denna använder studien måttet Structural Similarity Index Measure för att mäta visuell kvalitet. Studien fann att den bilinjära interpoleringen resulterade i att prestandan ökade med 45% när endast var åttonde pixel är beräknad med ray marching, och resten interpoleras. Dock reduceras även den visuella kvaliteten av molnen. Detta kan motverkas med hjälp av adaptiv sampling. Då interpoleras endast pixlar där standardavvikelsen av de kringliggande pixlarna är under ett fördefinierat värde. Vi kan däremot inte definiera ett universiellt optimalt värde på detta värde. Det beror på att det optimala värdet beror på kraven vi har på programmet. Dessa kan variera från program till program. Därför måste detta bestämmas individuellt för varje program.

The paper describes a theoretical base and realization of realistic volumetric clouds visualization in an environment of real-time simulator. The first part is concerned with a meteorological background of this problem. I show international classification of ten basic cloud types including a short description and cases of occurence. The following part is concerned with an interaction between cloudiness and simulation core, which is based on the fact, that each cloud acts as a mechanical or an electromagnetic obstacle. This should be considered on some way in simulation. The next part describes technologies and practical implementations of visualization and evaluates their characteristics. Finally, the last chapter describes my implementation and tries to outline project advancement.