Christiaan P. Gribble

Distributed interactive ray tracing for large volume visualization

We have constructed a distributed parallel ray tracing system that interactively produces isosurface renderings from large data sets on a cluster of commodity PCs. The program was derived from the SCI Institutes interactive ray tracer (*-Ray), which utilizes small to large shared memory platforms, such as the SGI Origin series, to interact with very large-scale data sets. Making this approach work efficiently on a cluster requires attention to numerous system-level issues, especially when rendering data sets larger than the address space of each cluster node. The rendering engine is an image parallel ray tracer with a supervisor/workers organization. Each node in the cluster runs a multithreaded application. A minimal abstraction layer on top of TCP links the nodes, and enables asynchronous message handling. For large volumes, render threads obtain data bricks on demand from an object-based software distributed shared memory. Caching improves performance by reducing the amount of data transfers for a reasonable working set size. For large data sets, the cluster-based interactive ray tracer performs comparably with an SGI Origin system. We examine the parameter space of the renderer and provide experimental results for interactive rendering of large (7.5 GB) data sets.

Coherent ray tracing via stream filtering

We introduce an approach to coherent ray tracing based on a new stream filtering algorithm. This algorithm, which is motivated by breadth-first ray traversal and elimination of inactive ray elements, exploits the coherence exhibited by processing arbitrarily-sized groups of rays in SIMD fashion. These groups are processed by a series of filters that partition rays into active and inactive subsets throughout the various stages of the rendering process. We present results obtained with a detailed cycle-accurate simulation of a hardware architecture that supports wider-than-four SIMD processing and efficient scatter/gather memory and stream partitioning operations. In this context, stream filtering achieves frame rates of 15-25 fps for scenes of high geometric complexity rendered with path tracing and a variety of advanced visual effects.

A Coherent Grid Traversal Approach to Visualizing Particle-Based Simulation Data

We present an approach to visualizing particle-based simulation data using interactive ray tracing and describe an algorithmic enhancement that exploits the properties of these data sets to provide highly interactive performance and reduced storage requirements. This algorithm for fast packet-based ray tracing of multilevel grids enables the interactive visualization of large time-varying data sets with millions of particles and incorporates advanced features like soft shadows. We compare the performance of our approach with two recent particle visualization systems: one based on an optimized single ray grid traversal algorithm and the other on programmable graphics hardware. This comparison demonstrates that the new algorithm offers an attractive alternative for interactive particle visualization.

Memory-savvy distributed interactive ray tracing

Interactive ray tracing in a cluster environment requires paying close attention to the constraints of a loosely coupled distributed system. To render large scenes interactively, memory limits and network latency must be addressed efficiently. In this paper, we improve previous systems by moving to a page-based distributed shared memory layer, resulting in faster and easier access to a shared memory space. The technique is designed to take advantage of the large virtual memory space provided by 64-bit machines. We also examine task reuse through decentralized load balancing and primitive reorganization to complement the shared memory system. These techniques improve memory coherence and are valuable when physical memory is limited.

StreamRay: a stream filtering architecture for coherent ray tracing

The wide availability of commodity graphics processors has made real-time graphics an intrinsic component of the human/computer interface. These graphics cores accelerate the z-buffer algorithm and provide a highly interactive experience at a relatively low cost. However, many applications in entertainment, science, and industry require high quality lighting effects such as accurate shadows, reflection, and refraction. These effects can be difficult to achieve with z-buffer algorithms but are straightforward to implement using ray tracing. Although ray tracing is computationally more complex, the algorithm exhibits excellent scaling and parallelism properties. Nevertheless, ray tracing memory access patterns are difficult to predict and the parallelism speedup promise is therefore hard to achieve. This paper highlights a novel approach to ray tracing based on stream filtering and presents StreamRay, a multicore wide SIMD microarchitecture that delivers interactive frame rates of 15-32 frames/second for scenes of high geometric complexity and exhibits high utilization for SIMD widths ranging from eight to 16 elements. StreamRay consists of two main components: the ray engine, which is responsible for stream assembly and employs address generation units that generate addresses to form large SIMD vectors, and the filter engine, which implements the ray tracing operations with programmable accelerators. Results demonstrate that separating address and data processing reduces data movement and resource contention. Performance improves by 56% while simultaneously providing 11.63% power savings per accelerator core compared to a design which does not use separate resources for address and data computations.

Enhancing interactive particle visualization with advanced shading models

Particle-based simulation methods are used to model a wide range of complex phenomena and to solve time-dependent problems of various scales. Effective visualization of the resulting state should communicate subtle changes in the three-dimensional structure, spatial organization, and qualitative trends within a simulation as it evolves. We take steps toward understanding and using advanced shading models in the context of interactive particle visualization. Specifically, the impact of ambient occlusion and physically based diffuse interreflection is investigated using a formal user study. We find that these shading models provide additional visual cues that enable viewers to better understand subtle features within particle datasets. We also describe a visualization process that enables interactive navigation and exploration of large particle datasets, rendered with illumination effects from advanced shading models. Informal feedback from application scientists indicates that the results of this process enhance the data analysis tasks necessary for understanding complex particle datasets.

Memory sharing for interactive ray tracing on clusters

Abstract We present recent results in the application of distributed shared memory to image parallel ray tracing on clusters. Image parallel rendering is traditionally limited to scenes that are small enough to be replicated in the memory of each node, because any processor may require access to any piece of the scene. We solve this problem by making all of a cluster’s memory available through software distributed shared memory layers. With gigabit ethernet connections, this mechanism is sufficiently fast for interactive rendering of multi-gigabyte datasets. Object- and page-based distributed shared memories are compared, and optimizations for efficient memory use are discussed.

Ray tracing is the future and ever will be...

The primary objective of this course is to present a coherent summary of the state of the art in ray tracing technology. The course covers the most recent developments and practical aspects of the parallel construction of acceleration data structures and traversal of such acceleration data structures using highly parallel processors, including a discussion of divergent code paths and memory accesses as well as occupancy. Ray tracing in real-time games is considered one of the main application opportunities, but an important part of the course focuses on hardware for ray tracing applications in mobile platforms.

A case study: visualizing material point method data

The Material Point Method is used for complex simulation of solid materials represented using many individual particles. Visualizing such data using existing polygonal or volumetric methods does not accurately encapsulate both the particle and macroscopic properties of the data. In this case study we present various methods used to visualize the particle data as spheres and explain and evaluate two methods of augmenting the visualization using silhouette edges and advanced illumination such as ambient occlusion. We also present informal feedback received from the application scientists who use these methods in their workflow.

Ray tracing visualization toolkit

The Ray Tracing Visualization Toolkit (rtVTK) is a collection of programming and visualization tools supporting visual analysis of ray-based rendering algorithms. rtVTK leverages layered visualization within the spatial domain of computation, enabling investigators to explore the computational elements of any ray-based renderer. Renderers utilize a library for recording and processing ray state, and a configurable pipeline of loosely coupled components allows run-time control of the resulting visualization. rtVTK enhances tasks in development, education, and analysis by enabling users to interact with a visual representation of ray tracing computations.