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.

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.

Figure 1: Examples of interactively rendering complex and dynamic scenes with a ray-tracing-based renderer. The scenes show a pre-lighted theatre, robots moving through a city, large numbers of moving trees with sharp shadows, as well as the integration of volumes, lightfields, and procedural shading in an office environment. These examples run interactively at a resolution of 640 × 480 using four to eight dual PCs. Ray-tracing is well-known as a general and flexible rendering algorithm that generates high-quality images. But in the past, raytracing implementations were too slow to be used in an interactive context. Recently, the performance of ray-tracing has been increased by over an order of magnitude, making it interesting as an alternative to rasterization-based rendering. We present a new rendering engine for interactive 3D graphics based on a fast, scalable, and distributed ray-tracer. It offers an extended OpenGL-like API, supports interactive modifications of the scene, handles complex scenes with millions of polygons, and scales efficiently to many client machines. We demonstrate that the new renderer provides more flexibility, more rendering features, and higher performance for complex scenes than current rasterization hardware. Its flexibility enables new types of applications including a system for interactive global illumination.

The term ray tracing is commonly associated with highly realistic images but certainly not with interactive graphics.

Global illumination algorithms have traditionally been very time consuming and were only suitable for off-line computations. Recent research in realtime ray tracing has improved global illumination performance to allow for illumination updates at interactive rates. However, both the traditional off-line and the new interactive systems show significant limitations when dealing with realistically complex scenes containing millions of surfaces, thousands of light sources, and a high degree of occlusion. In this paper,

Recently developed interactive ray tracing systems combine the high-performance of todays CPUs with new algorithms and implementations to achieve a flexible and highperformance rendering system offering high-quality, interactive 3D graphics. However, due to its history in off-line rendering, interactive ray tracing has been limited to static scenes and simple walkthroughs. However, in order to become truly interactive ray tracing must support dynamic scenes efficiently.

Todays rasterization graphics hardware provides impressive speed and features making it the standard tool for interactively visualising virtual prototypes early in the industrial design process. However, due to inherent limitations of the rasterization approach many optical effects can only be approximated. For many products, in particular in the car industry, the resulting visual quality and realism is inadequate as the basis for critical design decisions.

Todays rasterization graphics hardware provides impressive speed and features making it the standard tool for interactively visualising virtual prototypes early in the industrial design process. However, due to inherent limitations of the rasterization approach many optical effects can only be approximated. For many products, in particular in the car industry, the resulting visual quality and realism is inadequate as the basis for critical design decisions. Thus the original goal of using virtual prototyping — significantly reducing the number of costly physical mockups — often cannot be achieved. Interactive ray tracing on a small cluster of PCs is emerging as an alternative visualization technique achieving the required accuracy, quality, and realism. In a case study this paper demonstrates the advantages of using interactive ray tracing for a typical design situation in the car industry: visualizing the prototype of headlights. Due to the highly reflective and refractive nature of headlights, proper quality could only be achieved using a fast interactive ray tracing system. 1.

Research on realtime ray tracing has recently made tremendous advances. Algorithmic improvements together with optimized software implementations already allow for interactive frame rates even on a single desktop PC. Furthermore, recent research has demonstrated several options for realizing realtime ray tracing on different hardware platforms, e.g. via streaming computation on modern graphics processors (GPUs) or via the use of dedicated ray tracing chips. Together, these developments indicate that realtime ray tracing might indeed become a reality and widely available in the near future. As most of todays global illumination algorithms heavily rely on ray tracing, this availability of fast ray tracing technology creates the potential to finally compute even global illumination – the physically correct simulation of light transport – at interactive rates. In this STAR, we will first cover the different research activities for realizing realtime ray tracing on different hardware architectures – ranging from shared memory systems, over PC clusters, programmable GPUs, to custom ray tracing hardware. Based on this overview, we discuss some of the advanced issues, such as support for dynamic scenes and designs for a suitable ray tracing API. The third part of this STAR then builds on top of these techniques by presenting algorithms for interactive global illumination in complex and dynamic scenes that may contain large numbers of light sources. We believe that the improved quality and the increased realism that global illumination adds to interactive environments makes it a potential “killer application” for future 3D graphics.