This paper presents a divide-and-conquer ray-traced volume rendering algorithm and a parallel image compositing method, along with their implementation and performance on the Connection Machine CM-5, and networked workstations. This algorithm distributes both the data and the computations to individual processing units to achieve fast, high-quality rendering of high-resolution data. The volume data, once distributed, is left in place, regardless of viewing position. The processing nodes perform local raytracing of their subvolume concurrently. No communication between processing units is needed during this local ray-tracing process. A subimage is generated by each processing unit and the final image is obtained by compositing subimages in the proper order, which can be determined a priori. Composition is done in parallel via a new algorithm we call BinarySwap compositing. Test results on both the CM-5 and a group of networked workstations demonstrate the practicality of our rendering ...

In computer graphics, rendering is the process by which an abstract description of a scene is converted to an image. When the scene is complex, or when high-quality images or high frame rates are required, the rendering process becomes computationally demanding. To provide the necessary levels of performance, parallel computing techniques must be brought to bear. Although parallelism has been exploited in computer graphics since the early days of the field, its initial use was primarily in specialized applications. The VLSI revolution of the late 1970Õs and the advent of scalable parallel computers during the late 1980Õs changed this situation. Today, parallel hardware is routinely used in graphics workstations, and numerous software-based rendering systems have been developed for general-purpose parallel architectures. This article provides a broad introduction to the subject of parallel rendering, encompassing both hardware and software systems. The focus is on the underlying concepts and the issues which arise in the design of parallel rendering algorithms and systems. We examine the different types of parallelism and how they can be applied in rendering applications. Concepts from parallel computing, such as data decomposition, task granularity, scalability, and load balancing, are considered in relation to the rendering

We describeatechnique for achieving fast volume ray casting on parallel machines, using a load balancing scheme and an e#cient pipelined approach to compositing. We propose a new model for measuring the amount of work one needs to perform in order to render a given volume, and use this model to obtain a better load balancing scheme for distributed memory machines. We also discuss in detail the design tradeo #s of our technique. In order to validate our model we have implemented it on the Intel iPSC#860 and the Intel Paragon, and conducted a detailedperformance analysis. 1 Introduction As researchers and engineers use volume rendering to study complex physical and abstract structures they need a coherent, powerful, easy to use visualization tool, that lets them interactively change all the necessary parameters. Unfortunately,even with the latest volume rendering acceleration techniques running on top-of-the-line workstations, it still takes a few seconds to a few minutes to volume ren...

. The distributed shared volume buffer (DSVB) is a software package we developed to facilitate general, parallel volume ray-tracing on networked workstations. It is internally implemented with messagepassing and adopts the cache-coherent shared memory model. Thus the cache efficiency of volume data access is of utter importance to the performance of a DSVB-based ray-tracer. For a given data set, the data access behavior of a volume ray-tracer depends mostly on the way in which pixels of the image are traversed. This paper addresses the cache coherence problem and compares three kinds of pixel traversal order: one-way, two-way and along a space filling curve. Experiments show that traversing pixels along a space filling curve (e.g. a Hilbert curve) greatly enhances cache efficiency especially when size of the cache is small compared to that of the volume data, and in the meantime greatly simplifies task distribution and management. Keywords: Pixel Traversal, Parallel Volume Ray-tracing...

The development of e#ective parallel rendering algorithms for unstructured volume data is challenging due to the irregular and adaptive nature of the corresponding meshes. Most of the algorithms developed previously have been mainly for shared-memory architectures. Only a distributed approach can better meet the computational and memory requirements of the rendering calculations. This paper presents a volume rendering algorithm that distributes both the data and the rendering process among the processors. At each processor, ray-casting of local data is performed independent of the other processors. The global image compositing processes, which require inter-processor communication, are overlapped with the local ray-casting processes to achieve better parallel e#ciency. In theory, this algorithm should attain high parallel e#ciency but its implementation on the Intel Paragon shows otherwise. Besides the added ray-casting overhead, a critical factor is the imbalanced load due to the highly adaptive nature of typical unstructured meshes and the selection of transfer functions. The causes, e#ects and possible cures of the imbalanced load are studied.

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of the Dissertation Parallel Volume Rendering of Irregular Grids by Jos'e Cl'audio Teixeira e Silva Junior Doctor of Philosophy in Computer Science State University of New York at Stony Brook 1996 This dissertation contains our contributions in methods to speed up volume rendering, an important subfield of scientific visualization. We develop a framework composed of a system and a set of algorithms for handling large datasets of various forms (e.g., regular and irregular volumetric grids). A special emphasis of our framework is on the development of practical parallel algorithms for visualization. For the regular grid case, where research of efficient techniques is fairly advanced, we propose a parallelization of a known rendering algorithm. Our major contributions in this case are the introduction of content-based load balancing and the pipelined compositing approach. We present the new algorithms and their implementation. For irregular grids, we propose a fast rendering algorithm...

We describe the PVR (Parallel Volume Rendering) system, which consists of a mix of modular C/Tcl/Tk code. With PVR it is possible to balance rendering efficiency, throughput, and latency over a large number of parallel machines configurations. It supports different rendering schemes and it can be easily augmented with others. PVR has unique capabilities: it can be used to build large and complex distributed visualization environments, and it lets the user control the rendering performance. We also discuss interactivity issues for parallel volume rendering environments. In particular, we give detailed performance numbers we achieved using PVR on an Intel Paragon. 1 Introduction Parallel processing has recently been used for speeding up volume rendering. Several factors seem to have sparked this trend: ffl Volume data sets are usually quite large. High-quality volume rendering normally takes an unacceptably long time when done on uniprocessors. ffl Acceleration techniques, such as te...

In splatting-based volume rendering, there is a well-known problem of attenuation leakage, that occurs due to blending operations on adjacent voxels. Hardware accelerated volume splatting exploits the graphics hardware’s alphablending capability to achieve attenuation from layers of voxels. However, this alpha-blending functionality results in accumulated errors(attenuation leakage), if performed on multiple overlapping alpha-values. In this paper, we introduce the concept of FreeVoxels which are self-sufficient structures in which the data required for operations on voxels are pre-computed and stored. These data are used to render each voxel independently in any order and also to eliminate the attenuation leakage. The drawback of the FreeVoxel data structure, that this paper does not address, is that it requires a significant amount of extra storage. Despite that, the advantages of a FreeVoxel data structure warrant extensive investigations in this direction. Specifically, FreeVoxel can be used, other than in solving the attenuation leakage problem, to achieve order-independent rendering; in parallel volume rendering, use of FreeVoxels allows arbitrary static data distribution with no data migration; it also enables synchronization-free rendering without compromising load-balancing. A similar data structure with comparable memory requirements has also been used for opacity based occlusion culling in volume rendering by [10]. In this paper, we also describe a hierarchical extension of FreeVoxels that lends itself to multi-resolution rendering.

Seismological applications use a 3D grid to represent the subsea rock structure. Many computations, such as detecting layers of rock in the seismic, can be done using the 3D grid exclusively. However, some algorithms for detecting vertical dislocations in the seismic require computations over a discretized polygon surface imposed over the 3D grid to assist geophysicists in interpreting the seismic data. When using seismological applications on clusters, the 3D grid data is distributed between several cluster nodes. This thesis considers how algorithms involving discretized polygon surfaces can efficiently utilize the parallelism provided by clusters, and provides a general framework such algorithms can utilize. The framework consists of three main parts: 1) efficient caching and transfer of voxels between cluster nodes, 2) efficient discretization or voxelization of polygon surfaces, and 3) efficient load-balancing. First, three algorithms for caching and transferring voxels between nodes are introduced. The strategy which only transfers necessary polygon voxels is shown to be superior in most cases for our workloads, obtaining a speedup of 24.28 over a strategy which caches the