Abstract
This article presents an evaluation study of point-to-point and collective communication performance on a parallel processing system, a 16 node Parsytec PowerXplorer, using three different communication environments: PARIX, PVM and MPI.

Abstract

Abstract
Physically based global illumination rendering at interactive frame rates would enable users to navigate within complex virtual environments, such as archaeological models. These algorithms, however, are computationally too demanding to allow interactive navigation on current PCs. A technique based on image subsampling and spatiotemporal coherence among successive frames is exploited, while resorting to progressive refinement whenever there is available computing power. A physically based ray tracer (Radiance) is used to compute reflected radiance at the model's triangles vertices. Progressive refinement is achieved increasing the sampling frequency by subdividing certain triangles and requesting shading information for the resulting vertices. This paper proposes and evaluates different criteria for selecting which triangles to subdivide. A random criterium and two criteria based on Normalized Luminance Differences are evaluated: one operating on image space, the other on object space. Results, obtained with a model of an old roman town, show that the object space criterium is able to locate and represent visual discontinuities, such as shadows, and does so requiring less triangle subdivisions than the other two.

Abstract
The computational requirements of full global illumination rendering are such that it is still not possible to achieve high-fidelity graphics of very complex scenes in a reasonable time on a single computer. By identifying which computations are more relevant to the desired quality of the solution, selective rendering can significantly reduce rendering times. In this paper we present a novel component-based selective rendering system in which the quality of every image, and indeed every pixel, can be controlled by means of a component regular expression (crex). The crex provides a flexible mechanism for controlling which components are rendered and in which order. It can be used as a strategy for directing the light transport within a scene and also in a progressive rendering framework. Furthermore, the crex can be combined with visual perception techniques to reduce rendering computation times without compromising the perceived visual quality. By means of a psychophysical experiment we demonstrate how the crex can be successfully used in such a perceptual rendering framework. In addition, we show how the crex's flexibility enables it to be incorporated in a predictive framework for time-constrained rendering. Copyright © 2005 by the Association for Computing Machinery, Inc.

Abstract
The 2006 Eurographics Symposium on Parallel Graphics and Visualization took place at Universidade do Minho, Barga, Portugal. There were a total of 47 registered participants which represents a significant increase in the number of attendees compared to previous editions of the event. The goal was to enable people to attend all events in an attempt to answer a reciprocal interest on research works. It was believed that by organizing related events in the same geographical area it is able to attract more participants for each events. The first keynote was on Rendering on Demand by Alan Chalmers from the University of Bristol. The second keynote was devoted entirely to commodity visualization clusters and many other papers generated results using clusters.

Abstract
Parallelizing rendering algorithms to exploit multiprocessor and multicore machines isn't straightforward. Certain methods require frequent synchronization among threads to obtain benefits similar to the sequential algorithm. One such algorithm is the irradiance cache (IC), an acceleration data structure that caches indirect diffuse irradiance values. In multicore systems, the threads must share the IC to achieve high efficiency. A proposed wait-free mechanism for accessing the shared IC doesn't use the common blocking or busy-waiting methods, thus avoiding most serialization and reducing contention. A comparison with two classic approachesa lock-based mechanism and a local-write techniqueon two systems with up to 24 cores shows that the wait-free approach significantly reduces synchronization overhead, thus improving performance. The Web extra PDF augments the article. The Web extra video is an animation that demonstrates the wait-free IC system running at close to interactive rates on an 8-core machine. © 2006 IEEE.