Ingo Wald

Ray tracing deformable scenes using dynamic bounding volume hierarchies

The most significant deficiency of most of todays interactive ray tracers is that they are restricted to static walkthroughs. This restriction is due to the static nature of the acceleration structures used. While the best reported frame rates for static geometric models have been achieved using carefully constructed kd-trees, this article shows that bounding volume hierarchies (BVHs) can be used to efficiently ray trace large static models.More importantly, the BVH can be used to ray trace deformable models (sets of triangles whose positions change over time) with little loss of performance. A variety of efficiency techniques are used to achieve this performance, but three algorithmic changes to the typical BVH algorithm are mainly responsible. First, the BVH is built using a variant of the surface area heuristic conventionally used to build kd-trees. Second, the topology of the BVH is not changed over time so that only the bounding volumes need to be refit from frame-to-frame. Third, and most importantly, packets of rays are traced together through the BVH using a novel integrated packet-frustum traversal scheme. This traversal scheme elegantly combines the advantages of both packet traversal and frustum traversal and allows for rapid hierarchy descent for packets that hit bounding volumes as well as rapid exits for packets that miss. A BVH-based ray tracing system using these techniques is shown to achieve performance for deformable models comparable to that previously available only for static models.

Realtime ray tracing and interactive global illumination

Interaktive 3D-Computergraphik basiert heutzutage fast ausschliesslich auf dem Rasterisierungsverfahren. Dieses ist heute sehr effizient und gunstig realisierbar, stosst aber zunehmend an seine Grenzen hinsichtlich unterstutzter Szenenkomplexitat und erreichbarer Darstellungsqualitat. Eine Alternative zum Rasterisierungsverfahren ist das Ray Tracing Verfahren, welches zwar allgemein fur bessere Bildqualitat bekannt ist, aber aufgrund hoher Rechenanforderungen bisher als unvereinbar mit interaktiver Performanz galt. In dieser Arbeit geht es um die Entwicklung der Echtzeit Ray Tracing Technologie, mit der das Ray Tracing Verfahren auch fur interaktive Anwendungen ermoglicht wird. Die im Rahmen dieser Dissertation entwickelten Techniken ermoglichen nun erstmalig interaktive Ray Tracing Performanz selbst auf Standard PCs. Die dazu entwickelten Methoden beinhalten unter anderem einen extrem schnellen Ray Tracing Kern, ein effizientes Parallelisierungsframework, die Unterstutzung dynamischer und extrem komplexer Modelle, sowie eine geeignete Programmierschnittstelle. Darauf aufbauend wurden dann weiterhin Verfahren entwickelt, die es erstmalig ermoglichen, auch die globale Lichtausbreitung interaktiv zu simulieren. Die im Rahmen der Dissertation entwickelten Techniken formen ein komplettes Framework fur Echtzeit-Ray Tracing und interaktive Beleuchtungssimulation, welches interaktive Performanz selbst fur massiv komplexe Szenen liefert, sowie erstmalig physikalisch basierte Computergraphik unter Echtzeitbedingungen ermoglicht.

On building fast kd-Trees for Ray Tracing, and on doing that in O(N log N)

Though a large variety of efficiency structures for ray tracing exist, kd-trees today seem to slowly become the method of choice. In particular, kd-trees built with cost estimation functions such as a surface area heuristic (SAH) seem to be important for reaching high performance. Unfortunately, most algorithms for building such trees have a time complexity of O(N log2 N), or even O(N2). In this paper, we analyze the state of the art in building good kd-trees for ray tracing, and eventually propose an algorithm that builds SAH kd-trees in O(N log N), the theoretical lower bound

Ray tracing animated scenes using coherent grid traversal

We present a new approach to interactive ray tracing of moderate-sized animated scenes based on traversing frustum-bounded packets of coherent rays through uniform grids. By incrementally computing the overlap of the frustum with a slice of grid cells, we accelerate grid traversal by more than a factor of 10, and achieve ray tracing performance competitive with the fastest known packet-based kd-tree ray tracers. The ability to efficiently rebuild the grid on every frame enables this performance even for fully dynamic scenes that typically challenge interactive ray tracing systems.

Interactive global illumination using fast ray tracing

Rasterization hardware provides interactive frame rates for rendering dynamic scenes, but lacks the ability of ray tracing required for efficient global illumination simulation. Existing ray tracing based methods yield high quality renderings but are far too slow for interactive use. We present a new parallel global illumination algorithm that perfectly scales, has minimal preprocessing and communication overhead, applies highly efficient sampling techniques based on randomized quasi-Monte Carlo integration, and benefits from a fast parallel ray tracing implementation by shooting coherent groups of rays. Thus a performance is achieved that allows for applying arbitrary changes to the scene, while simulating global illumination including shadows from area light sources, indirect illumination, specular effects, and caustics at interactive frame rates. Ceasing interaction rapidly provides high quality renderings.

On fast Construction of SAH-based Bounding Volume Hierarchies

With ray traversal performance reaching the point where real-time ray tracing becomes practical, ray tracing research is now shifting away from faster traversal, and towards the question what has to be done to use it in truly interactive applications such as games. Such applications are problematic because when geometry changes every frame, the ray tracers internal index data structures are no longer valid. Fully rebuilding all data structures every frame is the most general approach to handling changing geometry, but was long considered impractical except for grid-based grid based ray tracers, trivial scenes, or reduced quality of the index structure. In this paper, we investigate how some of the fast, approximate construction techniques that have recently been proposed for kd-trees can also be applied to bounding volume hierarchies (BVHs). We argue that these work even better for BVHs than they do for kd-trees, and demonstrate that when using those techniques, BVHs can be rebuilt up to 10times faster than competing kd-tree based techniques.

Interactive Distributed Ray Tracing of Highly Complex Models

Many disciplines must handle the creation, visualization, and manipulation of huge and complex 3D environments. Examples include large structural and mechanical engineering projects dealing with entire cars, ships, buildings, and processing plants. The complexity of such models is usually far beyond the interactive rendering capabilities of todays 3D graphics hardware. Previous approaches relied on costly preprocessing for reducing the number of polygons that need to be rendered per frame but suffered from excessive precomputation times —often several days or even weeks. In this paper we show that using a highly optimized software ray tracer we are able to achieve interactive rendering performance for models up to 50 million triangles including reflection and shadow computations. The necessary preprocessing has been greatly simplified and accelerated by more than two orders of magnitude. Interactivity is achieved with a novel approach to distributed rendering based on coherent ray tracing. A single copy of the scene database is used together with caching of BSP voxels in the ray tracing clients.

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

Embree: a kernel framework for efficient CPU ray tracing

We describe Embree, an open source ray tracing framework for x86 CPUs. Embree is explicitly designed to achieve high performance in professional rendering environments in which complex geometry and incoherent ray distributions are common. Embree consists of a set of low-level kernels that maximize utilization of modern CPU architectures, and an API which enables these kernels to be used in existing renderers with minimal programmer effort. In this paper, we describe the design goals and software architecture of Embree, and show that for secondary rays in particular, the performance of Embree is competitive with (and often higher than) existing state-of-the-art methods on CPUs and GPUs.

SaarCOR: a hardware architecture for ray tracing

The ray tracing algorithmis well-known for its ability to generate high-quality images and its flexibility to support advanced rendering and lighting effects. Interactive ray tracing has been shown to work well on clusters of PCs and supercomputers but direct hardware support for ray tracing has been difficult to implement.In this paper, we present a new, scalable, modular, and highly efficient hardware architecture for real-time ray tracing. It achieves high performance with extremely low memory bandwidth requirements by efficiently tracing bundles of rays. The architecture is easily configurable to support a variety of workloads. For OpenGL-like scenes our architecture offers performance comparable to state-of-the-artrasterization chips. In addition, it supports all the usual ray tracing features including exact shadows, reflections, and refraction and is capable of efficiently handling complex scenes with millions of triangles. The architecture and its performance in different configurations is analyzed based on cycle-accurate simulations.