Heiko Friedrich

Ray Tracing on the Cell Processor

Over the last three decades, higher CPU performance has been achieved almost exclusively by raising the CPUs clock rate. Today, the resulting power consumption and heat dissipation threaten to end this trend, and CPU designers are looking for alternative ways of providing more compute power. In particular, they are looking towards three concepts: a streaming compute model, vector-like SIMD units, and multi-core architectures. One particular example of such an architecture is the cell broadband engine architecture (CBEA), a multi-core processor that offers a raw compute power of up to 200 GFlops per 3.2 GHz chip. The cell bears a huge potential for compute-intensive applications like ray tracing, but also requires addressing the challenges caused by this processors unconventional architecture. In this paper, we describe an implementation of realtime ray tracing on a cell. Using a combination of low-level optimized kernel routines, a streaming software architecture, explicit caching, and a virtual software-hyperthreading approach to hide DMA latencies, we achieve for a single cell a pure ray tracing performance of nearly one order of magnitude over that achieved by a commodity CPU

Faster isosurface ray tracing using implicit KD-trees

The visualization of high-quality isosurfaces at interactive rates is an important tool in many simulation and visualization applications. Today, isosurfaces are most often visualized by extracting a polygonal approximation that is then rendered via graphics hardware or by using a special variant of preintegrated volume rendering. However, these approaches have a number of limitations in terms of the quality of the isosurface, lack of performance for complex data sets, or supported shading models. An alternative isosurface rendering method that does not suffer from these limitations is to directly ray trace the isosurface. However, this approach has been much too slow for interactive applications unless massively parallel shared-memory supercomputers have been used. In this paper, we implement interactive isosurface ray tracing on commodity desktop PCs by building on recent advances in real-time ray tracing of polygonal scenes and using those to improve isosurface ray tracing performance as well. The high performance and scalability of our approach will be demonstrated with several practical examples, including the visualization of highly complex isosurface data sets, the interactive rendering of hybrid polygonal/isosurface scenes, including high-quality ray traced shading effects, and even interactive global illumination on isosurfaces.

Ray Tracing Animated Scenes using Motion Decomposition

Though ray tracing has recently become interactive, its high precomputation time for building spatial indices usually limits its applications to walkthroughs of static scenes. This is a major limitation, as most applications demand support for dynamically animated models. In this paper, we present a new approach to ray trace a special but important class of dynamic scenes, namely models whose connectivity does not change over time and for which all possible poses are known in advance.

Exploring the use of ray tracing for future games

Rasterization hardware and computer games have always been tightly connected: The hardware implementation of rasterization has made complex interactive 3D games possible while requirements for future games drive the development of increasingly parallel GPUs and CPUs. Interestingly, this development - together with important algorithmic improvements - also enabled ray tracing to achieve realtime performance recently.In this paper we explore the opportunities offered by ray tracing based game technology in the context of current and expected future performance levels. In particular, we are interested in simulation-based graphics that avoids pre-computations and thus enables the interactive production of advanced visual effects and increased realism necessary for future games. In this context we analyze the advantages of ray tracing and demonstrate first results from several ray tracing based game projects. We also discuss ray tracing API issues and present recent developments that support interactions and dynamic scene content. We end with an outlook on the different options for hardware acceleration of ray tracing.

Interactive Isosurface Ray Tracing of Time-Varying Tetrahedral Volumes

We describe a system for interactively rendering isosurfaces of tetrahedral finite-element scalar fields using coherent ray tracing techniques on the CPU. By employing state-of-the art methods in polygonal ray tracing, namely aggressive packet/frustum traversal of a bounding volume hierarchy, we can accommodate large and time-varying unstructured data. In conjunction with this efficiency structure, we introduce a novel technique for intersecting ray packets with tetrahedral primitives. Ray tracing is flexible, allowing for dynamic changes in isovalue and time step, visualization of multiple isosurfaces, shadows, and depth-peeling transparency effects. The resulting system offers the intuitive simplicity of isosurfacing, guaranteed-correct visual results, and ultimately a scalable, dynamic and consistently interactive solution for visualizing unstructured volumes.

Interactive Volume Rendering with Ray Tracing

Recent research on high-performance ray tracing has achieved rea l-time performance even for highly complex surface models already on a single PC. In this report we provide an over view of techniques for extending real-time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. T he physically-based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume, and other primitives in a scene, while fully accounting for all of their optical interactions. We presen t optimized implementations and discuss the use of upcoming high-performance processors for volume ray tracing.

Interactive iso-surface ray tracing of massive volumetric data sets

The visualization of iso-surfaces from gridded volume data is an important tool in many scientific applications. Today, it is possible to ray trace high-quality iso-surfaces at interactive frame rates even on commodity PCs. However, current algorithms fail if the data set exceeds a certain size either because they are not designed for outof- core data sets or the loading times are too high because there is too much overhead involved in the out-of-core (OOC) techniques. We propose a kD-tree based OOC data structure that allows to ray trace iso-surfaces of large volumetric data sets of many giga bytes at interactive frame rates on a single PC. A LOD technique is used to bridge loading times of data that is fetched asynchronously in the background. Using this framework we are able to ray trace iso-surfaces between 2 and 4 fps on a single dual-core Opteron PC at 640×480 resolution and an in-core memory footprint that is only a fraction of the entire data size.

Efficient CPU-based Volume Ray Tracing Techniques

Recent research on high‐performance ray tracing has achieved real‐time performance even for highly complex surface models already on a single PC. In this report, we provide an overview of techniques for extending real‐time ray tracing also to interactive volume rendering. We review fast rendering techniques for different volume representations and rendering modes in a variety of computing environments. The physically‐based rendering approach of ray tracing enables high image quality and allows for easily mixing surface, volume and other primitives in a scene, while fully accounting for all of their optical interactions. We present optimized implementations and discuss the use of upcoming high‐performance processors for volume ray tracing.