Articles

This is my little collection of papers I found about the topics I am interested in.

Real-time and Interactive Global Illumination

The State of the Art in Interactive Global Illumination

Tobias Ritschel, Carsten Dachsbacher, Thorsten Grosch, Jan Kautz

Abstract

The interaction of light and matter in the world surrounding us is of striking complexity and beauty. Since the very beginning of computer graphics, adequate modeling of these processes and efficient computation is an intensively studied research topic and still not a solved problem. The inherent complexity stems from the underlying physical processes as well as the global nature of the interactions that let light travel within a scene. This article reviews the state of the art in interactive global illumination computation, that is, methods that generate an image of a virtual scene in less than one second with an as exact as possible, or plausible, solution to the light transport. Additionally, the theoretical background and attempts to classify the broad field of methods are described. The strengths and weaknesses of different approaches, when applied to the different visual phenomena, arising from light interaction are compared and discussed. Finally, the article concludes by highlighting design patterns for interactive global illumination and a list of open problems.

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Real-Time Global Illumination using Precomputed Light Field Probes

Morgan McGuire, Mike Mara, Derek Nowrouzezahrai, David Luebke

Abstract

We introduce a new data structure and algorithms that employ it to compute real-time global illumination from static environments. Light field probes encode a scene’s full light field and internal visibility. They extend current radiance and irradiance probe structures with per-texel visibility information similar to a G-buffer and variance shadow map. We apply ideas from screen-space and voxel cone tracing techniques to this data structure to efficiently sample radiance on world space rays, with correct visibility information, directly within pixel and compute shaders. From these primitives, we then design two GPU algorithms to efficiently gather real-time, viewer-dependent global illumination onto both static and dynamic objects. These algorithms make different tradeoffs between performance and accuracy. Supplemental GLSL source code is included.

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Interactive Indirect Illumination Using Voxel Cone Tracing

Cyril Crassin, Fabrice Neyret, Miguel Sainz, Simon Green, Elmar Eisemann

Abstract

Indirect illumination is an important element for realistic image synthesis, but its computation is expensive and highly dependent on the complexity of the scene and of the BRDF of the involved surfaces. While off-line computation and pre-baking can be acceptable for some cases, many applications (games, simulators, etc.) require real-time or interactive approaches to evaluate indirect illumination. We present a novel algorithm to compute indirect lighting in real-time that avoids costly precomputation steps and is not restricted to low-frequency illumination. It is based on a hierarchical voxel octree representation generated and updated on the fly from a regular scene mesh coupled with an approximate voxel cone tracing that allows for a fast estimation of the visibility and incoming energy. Our approach can manage two light bounces for both Lambertian and glossy materials at interactive framerates (25-70FPS). It exhibits an almost scene-independent performance and can handle complex scenes with dynamic content thanks to an interactive octree-voxelization scheme. In addition, we demonstrate that our voxel cone tracing can be used to efficiently estimate Ambient Occlusion.

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 Cascaded Light Propagation Volumes for Real-Time Indirect Illumination

Anton Kaplanyan, Carsten Dachsbacher

Abstract

This paper introduces a new scalable technique for approximating indirect illumination in fully dynamic scenes for real-time applications, such as video games. We use lattices and spherical harmonics to represent the spatial and angular distribution of light in the scene. Our technique does not require any precomputation and handles large scenes with nested lattices. It is primarily targeted at rendering single-bounce indirect illumination with occlusion, but can be extended to handle multiple bounces and participating media. We demonstrate that our method produces plausible results even when running on current game console hardware with a budget of only a few milliseconds for performing all computation steps for indirect lighting. We evaluate our technique and show it in combination with a variety of popular real-time rendering techniques.

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Approximating Dynamic Global Illumination in Image Space

Tobias Ritschel, Thorsten Grosch, Hans-Peter Seidel

Abstract

Physically plausible illumination at real-time framerates is often achieved using approximations. One popular example is ambient occlusion (AO), for which very simple and efficient implementations are used extensively in production. Recent methods approximate AO between nearby geometry in screen space (SSAO). The key observation described in this paper is, that screen-space occlusion methods can be used to compute many more types of effects than just occlusion, such as directional shadows and indirect color bleeding. The proposed generalization has only a small overhead compared to classic SSAO, approximates direct and one-bounce light transport in screen space, can be combined with other methods that simulate transport for macro structures and is visually equivalent to SSAO in the worst case without introducing new artifacts. Since our method works in screen space, it does not depend on the geometric complexity. Plausible directional occlusion and indirect lighting effects can be displayed for large and fully dynamic scenes at real-time frame rates.

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Imperfect Shadow Maps for Efficient Computation of Indirect Illumination

T. Ritschel, T. Grosch, M. H. Kim, H.-P. Seidel, C. Dachsbacher, J. Kautz

Abstract

We present a method for interactive computation of indirect illumination in large and fully dynamic scenes based on approximate visibility queries. While the high-frequency nature of direct lighting requires accurate visibility, indirect illumination mostly consists of smooth gradations, which tend to mask errors due to incorrect visibility. We exploit this by approximating visibility for indirect illumination with imperfect shadow maps—low-resolution shadow maps rendered from a crude point-based representation of the scene. These are used in conjunction with a global illumination algorithm based on virtual point lights enabling indirect illumination of dynamic scenes at real-time frame rates. We demonstrate that imperfect shadow maps are a valid approximation to visibility, which makes the simulation of global illumination an order of magnitude faster than using accurate visibility.

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Reflective Shadow Maps

Carsten Dachsbacher, Marc Stamminger

Abstract

In this paper we present ”reflective shadow maps”, an algorithm for interactive rendering of plausible indirect illumination. A reflective shadow map is an extension to a standard shadow map, where every pixel is considered as an indirect light source. The illumination due to these indirect lights is evaluated on-the-fly using adaptive sampling in a fragment shader. By using screen-space interpolation of the indirect lighting, we achieve interactive rates, even for complex scenes. Since we mainly work in screen space, the additional effort is largely independent of scene complexity. The resulting indirect light is approximate, but leads to plausible results and is suited for dynamic scenes. We describe an implementation on current graphics hardware and show results achieved with our approach.

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A Rapid Hierarchical Radiosity Algorithm

Pat Hanrahan, David Salzman, Larry Aupperle

Abstract

This paper presents a rapid hierarchical radiosity algorithm for illuminating scenes containing large polygonal patches. The algorithm constructs a hierarchic“J representation of the form factor matrix by adaptively subdividing patches into subpatches according to a user-supplied error bound. The algorithm guarantees that all form factors are calculated to the same precision, removing many common image artifacts due to inaccurate form factors. More importantly, the algorithm decomposes the form factor matrix into at most O n) blocks (where n is the number of elements). Previous radiosity algorithms represented the element-to-element transport interactions with n2 form factors. Visibility algorithms are given that work well with this approach. Standard techniques for shooting and gathering can be used with the hierarchical representation to solve for equilibrium radiosities, but we also discuss using a brightness-weighted error criteria, in conjunction with multigridding, to even more rapidly progressively refine the image.

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