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Real Time Ray Tracing of Analytic and Implicit Surfaces
Abstract
Real-time ray-tracing debuted to consumer GPU hardware in 2018. Primary examples however, have been of hybrid raster and ray-tracing methods that are restricted to triangle mesh geometry. Our research looks at the viability of procedural methods in the real-time setting. We give implementations of analytical and implicit geometry in the domain of the global illumination algorithms bi-directional path-tracing, and GPU Photon-Mapping-both of which we have adapted to the new ray-tracing shader stages, as shown in Figure 1. Despite procedural intersections being more expensive than triangle intersections in Nvidia's RTX hardware, our results show that these descriptions still run at interactive rates within computationally expensive multi-pass ray-traced global illumination and demonstrate the practical benefits of the geometry.
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Most of the research on the global illumination problem in computer graphics has been concentrated on finite-element (radiosity) techniques. Monte Carlo methods are an intriguing alternative which are attractive for their ability to handle very general scene descriptions without the need for meshing. In this paper we study techniques for reducing the sampling noise inherent in pure Monte Carlo approaches to global illumination. Every light energy transport path from a light source to the eye can be generated in a number of different ways, according to how we partition the path into an initial portion traced from a light source, and a final portion traced from the eye. Each partitioning gives us a different unbiased estimator, but some partitionings give estimators with much lower variance than others. We give examples of this phenomenon and describe its significance. We also present work in progress on the problem of combining these multiple estimators to achieve near-optimal variance, with the goal of producing images with less noise for a given number of samples.
We describe an extension to photon mapping that recasts the most expensive steps of the algorithm -- the initial and final photon bounces -- as image-space operations amenable to GPU acceleration. This enables global illumination for real-time applications as well as accelerating it for offline rendering. Image Space Photon Mapping (ISPM) rasterizes a light-space bounce map of emitted photons surviving initial-bounce Russian roulette sampling on a GPU. It then traces photons conventionally on the CPU. Traditional photon mapping estimates final radiance by gathering photons from a k-d tree. ISPM instead scatters indirect illumination by rasterizing an array of photon volumes. Each volume bounds a filter kernel based on the a priori probability density of each photon path. These two steps exploit the fact that initial path segments from point lights and final ones into a pinhole camera each have a common center of projection. An optional step uses joint bilateral upsampling of irradiance to reduce the fill requirements of rasterizing photon volumes. ISPM preserves the accurate and physically-based nature of photon mapping, supports arbitrary BSDFs, and captures both high- and low-frequency illumination effects such as caustics and diffuse color interreflection. An implementation on a consumer GPU and 8-core CPU renders highquality global illumination at up to 26 Hz at HD (1920x1080) resolution, for complex scenes containing moving objects and lights.
Sphere tracing is a new technique for rendering implicit surfaces using geometric distance. Distance-based models are common in computer-aided geometric design and in the modeling of articulated figures. Given a function returning the distance to an object, sphere tracing marches along the ray toward its first intersection in steps guaranteed not to penetrate the implicit surface. Sphere tracing is particularly adept at rendering pathological surfaces. Creased and rough implicit surfaces are defined by functions with discontinuous or undefined derivatives. Current root finding techniques such as L-G surfaces and interval analysis require periodic evaluation of the derivative, and their behavior is dependent on the behavior of the derivative. Sphere tracing requires only a bound on the magnitude of the derivative, robustly avoiding problems Manuscript, July 1994. Recommended for publication: The Visual Computer. 5-70 where the derivative jumps or vanishes. This robustness and scope ...
Indirect lighting, also known as global illumination, is a crucial effect in photorealistic images. While there are a number of effective global illumination techniques based on precomputation that work well with static scenes, including global illumination for scenes with dynamic lighting and dynamic geometry remains a challenging problem. In this chapter, we describe a real-time global illumination algorithm based on photon mapping that evaluates several bounces of indirect lighting without any precomputed data in scenes with both dynamic lighting and fully dynamic geometry. We explain both the pre- and post-processing steps required to achieve dynamic high-quality illumination within the limits of a realtime frame budget.
Photon mapping is a global illumination technique for rendering caustics and indirect lighting by simulating the transportation of photons emitted from the light. This chapter introduces a technique to render caustics with photon mapping in screen space with hardware ray tracing and a screen-space denoiser in real time.
Quadric surfaces are common modeling primitives for a variety of computer graphics and computer-aided-design applications. Ray tracing or ray firing is also a popular method used for realistic renderings of quadric surfaces. This chapter presents an algorithm for locating the intersection points between a ray and general quadratic surfaces, including ellipsoids, cones, cylinders, paraboloids, and hyperboloids. The chapter describes a means for determining the surface normal at the point of intersection. The normal is required in lighting model computations. For a variety of common quadric surfaces in standard position, that is, positioned at the origin with the y-axis being the axis of symmetry, the coefficient matrices can be quickly constructed. The position and orientation of a quadric can be conveniently defined using any two of the three unit vectors describing the local coordinate system of that quadric. The intersection of a ray with a quadric surface can be found by substituting the vector expression of the parametric ray equations into the matrix form of the general quadric surface. A quick and efficient bounding test for eliminating unnecessary ray-quadric surface intersections involves bounding the quadric with an infinite cylinder.
We describe the design space for real-time photon density estimation, the key step of rendering global illumination (GI) via photon mapping. We then detail and analyze efficient GPU implementations of four best-of-breed algorithms. All produce reasonable results on NVIDIA GeForce 670 at 1920 × 1080 for complex scenes with multiple-bounce diffuse effects, caustics, and glossy reflection in real-time. Across the designs we conclude that tiled, deferred photon gathering in a compute shader gives the best combination of performance and quality.
The creation of photorealistic images of three-dimensional models is central to computer graphics. Photon mapping, an extension of ray tracing, makes it possible to efficiently simulate global illumination in complex scenes. Photon mapping can simulate caustics (focused light, like shimmering waves at the bottom of a swimming pool), diffuse inter-reflections (e.g., the bleeding of colored light from a red wall onto a white floor, giving the floor a reddish tint), and participating media (such as clouds or smoke). This book is a practical guide to photon mapping; it provides both the theory and the practical insight necessary to implement photon mapping and simulate all types of direct and indirect illumination efficiently.
The creation of photorealistic images of three-dimensional models is central to computer graphics. Photon mapping, an extension of ray tracing, makes it possible to efficiently simulate global illumination in complex scenes. Photon mapping can simulate caustics (focused light, like shimmering waves at the bottom of a swimming pool), diffuse inter-reflections (e.g., the bleeding of colored light from a red wall onto a white floor, giving the floor a reddish tint), and participating media (such as clouds or smoke). This book is a practical guide to photon mapping; it provides both the theory and the practical insight necessary to implement photon mapping and simulate all types of direct and indirect illumination efficiently.
Lambert's model for body reflection is widely used in computer graphics. It is used extensively by rendering techniques such as radiosity and ray tracing. For several realworld objects, however, Lambert's model can prove to be a very inaccurate approximation to the body reflectance. While the brightness of a Lambertian surface is independent of viewing direction, that of a rough surface increases as the viewing direction approaches the light source direction. In this paper, a comprehensive model is developed that predicts body reflectance from rough surfaces. The surface is modeled as a collection of Lambertian facets. It is shown that such a surface is inherently non-Lambertian due to the foreshortening of the surface facets. Further, the model accounts for complex geometric and radiometric phenomena such as masking, shadowing, and interreflections between facets. Several experiments have been conducted on samples of rough diffuse surfaces, such as, plaster, sand, clay, and cloth. All...
DirectX ray-tracing functional spec
- Microsoft
Microsoft,
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ray-tracing
functional
spec,"
2018,
https://microsoft.github.io/DirectX-Specs/d3d/Raytracing.html.
Nvidia optix TM ray tracing engine
- Nvidia
Nvidia,
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optix TM
ray
tracing
engine,"
2018,
https://developer.nvidia.com/optix.
Gpu-optimized bidirectional path tracing
- D Bogolepov
- D Ulyanov
- D Sopin
- V Turlapov
D. Bogolepov, D. Ulyanov, D. Sopin, and V. Turlapov, "Gpu-optimized bidirectional path tracing," 2013.