For almost two decades researchers have argued that ray tracing will eventually become faster than the rasterization technique that completely dominates todays graphics hardware. However, this has not happened yet. Ray tracing is still exclusively being used for off-line rendering of photorealistic images and it is commonly believed that ray tracing is simply too costly to ever challenge rasterization-based algorithms for interactive use. However, there is hardly any scientific analysis that supports either point of view. In particular there is no evidence of where the crossover point might be, at which ray tracing would eventually become faster, or if such a point does exist at all.

Visibility algorithms for walkthrough and related applications have grown into a significant area, spurred by the growth in the complexity of models and the need for highly interactive ways of navigating them. In this survey, we review the fundamental issues in visibility and conduct an overview of the visibility culling techniques developed in the last decade. The taxonomy we use distinguishes between point-based and from-region methods. Point-based methods are further subdivided into object and image-precision techniques, while from-region approaches can take advantage of the cell-and-portal structure of architectural environments or handle generic scenes.

In this paper, we present a system for interactive computation of global illumination in dynamic scenes. Our system uses a novel scheme for caching the results of a high quality pixel-based renderer such as a bidirectional path tracer. The Shading Cache is an objectspace hierarchical subdivision mesh with lazily computed shading values at its vertices. A high frame rate display is generated from the Shading Cache using hardware-based interpolation and texture mapping. An image space sampling scheme refines the Shading Cache in regions that have the most interpolation error or those that are most likely to be affected by object or camera motion. Our system handles dynamic scenes and moving light sources efficiently, providing useful feedback within a few seconds and high quality images within a few tens of seconds, without the need for any pre-computation. Our approach allows us to significantly outperform other interactive systems based on caching ray-tracing samples, especially in dynamic scenes. Based on our results, we believe that the Shading Cache will be an invaluable tool in lighting design and modelling while rendering.

This paper presents a new interactive rendering and display technique for complex scenes with expensive shading, such as global illumination. Our approach combines sparsely sampled shading (points) and analytically computed discontinuities (edges) to interactively generate high-quality images. The edge-and-point image is a new compact representation that combines edges and points such that fast, table-driven interpolation of pixel shading from nearby point samples is possible, while respecting discontinuities. The edge-and-point renderer is extensible, permitting the use of arbitrary shaders to collect shading samples. Shading discontinuities, such as silhouettes and shadow edges, are found at interactive rates. Our software implementation supports interactive navigation and object manipulation in scenes that include expensive lighting effects (such as global illumination) and geometrically complex objects. For interactive rendering we show that high-quality images of these scenes can be rendered at 8–14 frames per second on a desktop PC: a speedup of 20–60 over a ray tracer computing a single sample per pixel.

Analytic visibility algorithms, for example methods which compute a subdivided mesh to represent shadows, are notoriously unrobust and hard to use in practice. We present a new method based on a generalized definition of extremal stabbing lines, which are the extremities of shadow boundaries. We treat scenes containing multiple edges or vertices in degenerate configurations, (e.g., collinear or coplanar). We introduce a robust ɛ method to determine whether each generalized extremal stabbing line is blocked, or is touched by these scene elements, and thus added to the line's generators. We develop robust blocker predicates for polygons which are smaller than ɛ. For larger ɛ values, small shadow features merge and eventually disappear. We can thus robustly connect generalized extremal stabbing lines in degenerate scenes to form shadow boundaries. We show that our approach is consistent, and that shadow boundary connectivity is preserved when features merge. We have implemented our algorithm, and show that we can robustly compute analytic shadow boundaries to the precision of our chosen ɛ threshold for non-trivial models, containing numerous degeneracies.

The addition of global illumination can dramatically increase the realism achievable when rendering virtual environments.

We propose an adaptive form of frameless rendering with the potential to dramatically increase rendering speed over conventional interactive rendering approaches. Without the rigid sampling patterns of framed renderers, sampling and reconstruction can adapt with very fine granularity to spatio-temporal color change. A sampler uses closed-loop feedback to guide sampling toward edges or motion in the image. Temporally deep buffers store all the samples created over a short time interval for use in reconstruction and as sampler feedback. GPU-based reconstruction responds both to sampling density and space-time color gradients. Where the displayed scene is static, spatial color change dominates and older samples are given significant weight in reconstruction, resulting in sharper and eventually antialiased images. Where the scene is dynamic, more recent samples are emphasized, resulting in less sharp but more up-to-date images. We also use sample reprojection to improve reconstruction and guide sampling toward occlusion edges, undersampled regions, and specular highlights. In simulation our frameless renderer requires an order of magnitude fewer samples than traditional rendering of similar visual quality (as measured by RMS error), while introducing overhead amounting to 15 % of computation time.

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.

Bright patterns of light focused via reflective or refractive objects onto matte surfaces are called “caustics”. We present a method for rendering dynamic scenes with moving caustics at interactive rates. This technique requires some simplifying assumptions about caustic behavior allowing us to consider it a local spatial property which we sample in a pre-processing stage. Storing the caustic locally limits caustic rendering to a simple lookup. We examine a number of ways to represent this data, allowing us to trade between accuracy, storage, run time, and precomputation time. 1.