EGPGV16: Eurographics Symposium on Parallel Graphics and Visualization

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https://diglib.eg.org/handle/10.2312/15271

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High-Performance Mesh Partitioning and Ghost Cell Generation for Visualization Software
(The Eurographics Association, 2016) Biddiscombe, John; Enrico Gobbetti and Wes Bethel
Post-processing large datasets efficiently in parallel requires good load balancing of geometry supplied to the visualization pipeline. When datasets are not pre-partitioned or cannot be read back from simulation output in well controlled pieces, it is necessary to perform a partitioning step before certain algorithms may be applied. Spatially sensitive operations such as resampling, smoothing or certain field advection/stencil algorithms require datasets/meshes to be contiguous and provide ghost cells so that artefacts do not occur at process boundaries where discontinuities occur. This paper presents an integration of the mesh partitioning library Zoltan, into the Visualization Toolkit framework, VTK and the parallel visualization tool ParaView. The implementation allows seamless generation of well partitioned datasets using a user provided weighting and a selection of ghost cell generation options. The algorithms, and results obtained with the partitioning classes are presented with representative use cases that show an order of magnitude increase in performance compared to the off-the-shelf partitioning available previously, improving performance and reducing memory consumption/duplication.
Parallel Spatial Splits in Bounding Volume Hierarchies
(The Eurographics Association, 2016) Fuetterling, Valentin; Lojewski, Carsten; Pfreundt, Franz-Josef; Ebert, Achim; Enrico Gobbetti and Wes Bethel
Bounding volume hierarchies (BVH) are essential for efficient ray tracing. In time-constrained situations such as real-time or large model visualization, fast construction of BVHs usually compromises hierarchy quality, resulting in reduced rendering speed. We propose a parallel framework for the state-of-the-art BVH construction algorithm with spatial splits (SBVH) that provides highest quality hierarchies within a time frame competitive with lowquality builders optimized for construction speed. We leverage both data and task parallelism to employ threading and single instruction, multiple data (SIMD) capabilities of modern CPUs. Our key contribution is a lightweight memory management and load balancing scheme that maximizes parallel efficiency.
EGPGV 2016: Frontmatter
(Eurographics Association, 2016) Enrico Gobbetti; Wes Bethel;
Interacting with Large Distributed Datasets Using Sketch
(The Eurographics Association, 2016) Budiu, Mihai; Isaacs, Rebecca; Murray, Derek; Plotkin, Gordon; Barham, Paul; Al-Kiswany, Samer; Boshmaf, Yazan; Luo, Qingzhou; Andoni, Alexandr; Enrico Gobbetti and Wes Bethel
We present Sketch, a library and a distributed runtime for building interactive tools for exploring large datasets, distributed across multiple machines. We have built several applications using Sketch; here we describe a billionrow spreadsheet, and a distributed-systems performance analyzer. Sketch applications allow interactive and responsive exploration of complex distributed datasets, scaling effectively to use large computational resources.
A Scalable Streamline Generation Algorithm Via Flux-Based Isocontour Extraction
(The Eurographics Association, 2016) Biswas, Ayan; Strelitz, Richard; Woodring, Jonathan; Chen, Chun-Ming; Shen, Han-Wei; Enrico Gobbetti and Wes Bethel
Streamlines are commonly used for visualizing flow fields, but particle-tracing based streamline computation usually does not scale well as the data size and complexity increase. Large flow simulations like global ocean or climate models can obtain near perfect load balancing and the resulting data sets are generally analyzed in two dimensional slices. To match the computational properties of these simulations, we propose the use of flux- based stream functions for generating streamlines in parallel. In our method, local stream functions are efficiently generated per block based on flux conservation property, followed by low-cost communication of flux offsets among neighboring blocks. A scalar field is thus generated where streamlines can be extracted through parallel iso- contouring. Experimental results show that our system offers higher streamline computation performance with higher scalability than traditional particle-tracing based method.
Adaptive Collision Culling for Large-Scale Simulations by a Parallel Sweep and Prune Algorithm
(The Eurographics Association, 2016) Capannini, Gabriele; Larsson, Thomas; Enrico Gobbetti and Wes Bethel
We propose a parallel Sweep and Prune algorithm that solves the dynamic box intersection problem in three dimensions. It scales up to very large datasets, which makes it suitable for broad phase collision detection in complex moving body simulations. Our algorithm gracefully handles high-density scenarios, including challenging clustering behavior, by using a dual-axis sweeping approach and a cache-friendly succinct data structure. The algorithm is realized by three parallel stages for sorting, candidate generation, and object pairing. By the use of temporal coherence, our sorting stage runs with close to optimal load balancing. Furthermore, our approach is characterized by a work-division strategy that relies on adaptive partitioning, which leads to almost ideal scalability. Experimental results show high performance for up to millions of objects on modern multi-core CPUs.
Web-enabled Server-based and Distributed Real-time Ray-Tracing
(The Eurographics Association, 2016) Tamm, Georg; Slusallek, Philipp; Enrico Gobbetti and Wes Bethel
As browsers expand their functionality, they continuously act as a platform for portable application development within a web page. To bring interactive 3D graphics closer to the web developer, frameworks allowing a declarative scene description in line with the HTML markup exist. However, these approaches utilize client-side rendering and are thus limited in the scene complexity and rendering algorithms they can provide on a given device. We present the extension of the declarative 3D framework XML3D to support server-based rendering. The server back-end enables distributed rendering with an arbitrary hierarchy of cluster nodes. In the back-end, we deploy a custom real-time ray-tracer. To distribute the ray-tracer, we present a load balancing method which exploits frame-to-frame coherence in a real-time context. The load balancer achieves strong scalability without inducing communication overhead during rendering to coordinate the workers.
Dynamic Work Packages in Parallel Rendering
(The Eurographics Association, 2016) Steiner, David; Paredes, Enrique G.; Eilemann, Stefan; Pajarola, Renato; Enrico Gobbetti and Wes Bethel
Interactive visualizations of large-scale datasets can greatly benefit from parallel rendering on a cluster with hardware accelerated graphics by assigning all rendering client nodes a fair amount of work each. However, interactivity regularly causes unpredictable distribution of workload, especially on large tiled displays. This requires a dynamic approach to adapt scheduling of rendering tasks to clients, while also considering data locality to avoid expensive I/O operations. This article discusses a dynamic parallel rendering load balancing method based on work packages which define rendering tasks. In the presented system, the nodes pull work packages from a centralized queue that employs a locality-aware dynamic affinity model for work package assignment. Our method allows for fully adaptive implicit workload distribution for both sort-first and sort-last parallel rendering.
External Facelist Calculation with Data-Parallel Primitives
(The Eurographics Association, 2016) Lessley, Brenton; Binyahib, Roba; Maynard, Robert; Childs, Hank; Enrico Gobbetti and Wes Bethel
External facelist calculation on three-dimensional unstructured meshes is used in scientific visualization libraries to efficiently render the results of operations such as clipping, interval volumes, and material boundaries. With this study, we consider the external facelist algorithm on many-core architectures. We design and introduce two novel approaches, one based on sorting and one based on hashing. Both of these algorithms consist entirely of data-parallel primitive operations, in an effort to achieve portable performance across different architectures. We study the performance of the algorithms via experiments varying over data set, hardware, and other factors. Overall, we observe that the hashing-based implementation achieves better runtime performance for the majority of configurations, while also achieving the most-stable performance on highly unstructured data sets.
Dynamically Scheduled Region-Based Image Compositing
(The Eurographics Association, 2016) Grosset, A. V. Pascal; Knoll, Aaron; Hansen, Charles; Enrico Gobbetti and Wes Bethel
Algorithms for sort-last parallel volume rendering on large distributed memory machines usually divide a dataset equally across all nodes for rendering. Depending on the features that a user wants to see in a dataset, all the nodes will rarely finish rendering at the same time. Existing compositing algorithms do not often take this into consideration, which can lead to significant delays when nodes that are compositing wait for other nodes that are still rendering. In this paper, we present an image compositing algorithm that uses spatial and temporal awareness to dynamically schedule the exchange of regions in an image and progressively composite images as they become available. Running on the Edison supercomputer at NERSC, we show that a scheduler-based algorithm with awareness of the spatial contribution from each rendering node can outperform traditional image compositing algorithms.
Data Mining Tornadogenesis Precursors
(The Eurographics Association, 2016) Foss, Greg; McGovern, Amy; Potvin, Corey; Abram, Greg; Bowen, Anne; Hulkoti, Neena; Kaul, Arnav; Enrico Gobbetti and Wes Bethel
We investigate the value of 3-D visualization to data mining techniques for identifying tornadogenesis precursors in supercell thunderstorm simulations. We've found results will assist defining storm objects extracted and input to the data mining. The video shows samples of updrafts, downdrafts, cold pools, and regions of strong vorticity.

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