Browsing by Author "Santos, Luís Paulo"

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    GPU Ray Casting
    (The Eurographics Association, 2021) Marques, Ricardo; Leškovský, Peter; Santos, Luís Paulo; Paloc, Céline; Coelho, António and Cláudio, Ana Paula
    For many applications, such as walk-throughs or terrain visualization, drawing geometric primitives is the most efficient and effective way to represent the data. In contmst, other applications require the visualiza-tion of data that is inherently volumetric. For example, in biomedical imaging, it might be necessary to visualize 3D datasets obtained from GT or J\1RI scanners as a meaningful 2D image, in a process called volume rendering. As a result of the popularity and usefulness of volume data, a broad class of volume rendering techniques has emerged. Ray casting is one of these techniques. It allows for high quality volume rendering, but is a computationally expensive technique which, with current technology, lacks interactivity when visualizing large datasets, if processed on the CPU. The advent of efficient GPUs, available on almost every modern workstations, combined with their high deg ree of programmability opens up a wide field of new applications for the graphics cards. Ray casting is among these applications, exhibiting an intrinsic parallelism, in the form of completely independent light rays, which allows to take advantage of the massively parallel architecture of the GPU. This paper describes the implementation and analysis of a set of shaders which allow interactive volume rendering on the GPU by resorting to my casting techniques.
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    Proceedings Info
    (Eurographics Association, 2021-11-03) Santos, Luís Paulo; Fonseca, Manuel João; Dias, Miguel; Jorge, Joaquim A.; Santos, Vítor
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    Visualização em Tempo Real de um Modelo Esparso de Mistura Paramétrica para Síntese da BTF
    (The Eurographics Association, 2021) Silva, Nuno; Santos, Luís Paulo; Branco, Pedro and Rodrigues, Rui
    As funções de textura bidirecionais (Bidirectional Texture Functions - BTF) permitem visualizações de alta qualidade de materiais reais, que exibem detalhes complexos na sua aparência, e que não podem ser fielmente representados por funções paramétricas mais simples. Representações fiéis deste tipo de materiais requerem grandes quantidades de dados, dificultando a sua visualização em tempo real. A compressão de BTFs constitui um compromisso entre qualidade visual e tempo de síntese. Este artigo apresenta um visualizador a correr integralmente no GPU, usando um motor de ray tracing, de uma representação recente para BTFs, o Modelo Esparso de Mistura Paramétrica (Sparse Parametric Mixture Model - SPMM). A escalabilidade com o número de BTFs e o número de luzes é também estudado.
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    Workload Distribution for Ray Tracing in Multi-Core Systems
    (The Eurographics Association, 2021) Nunes, Miguel; Santos, Luís Paulo; Coelho, António and Cláudio, Ana Paula
    One of the features that made interactive ray tracing possible over the last Jew years was the careful exploitation of the computational power and parallelism available on modern multicore processors. Multithreaded interactive ray tracing engines have to share the workload (rays to be processed) among rendering threads. This may be achieved by storing tasks on a shared FIFO-queue, accessed by all threads. Accessing this shared data structure requires a data access control mechanism, which ensures that the data structure is not corrupted. This access mechanism must incur minimal overheads such that pe,formance is not penalized. This paper proposes a lock-free data access control mechanism to such queue, which avoids all locks by carefully reordering instructions. This technique is compared with a classical lock-based approach and with a conservative local technique, where each thread maintains its local queue of tasks and shares nothing with other threads. Although the local approach outperforms the other two due to very good load balancing conditions, we demonstrate that the lock-free approach outperforms the lock-based one for large processor counts. Efficient and reliable sharing of data structures within a shared memory system is becoming a very relevant problem with the advent of many core processors. Lock free approaches are a promising manner of achieving such goal.