The Iray Light Transport Simulation and Rendering System

While ray tracing has become increasingly common and path tracing is well understood by now, a major challenge lies in crafting an easy-to-use and efficient system implementing these technologies. Following a purely physically-based paradigm while still allowing for artistic workflows, the Iray light transport simulation and rendering system allows for rendering complex scenes by the push of a button and thus makes accurate light transport simulation widely available. In this document we discuss the challenges and implementation choices that follow from our primary design decisions, demonstrating that such a rendering system can be made a practical, scalable, and efficient real-world application that has been adopted by various companies across many fields and is in use by many industry professionals today

Efficient From-Point Visibility for Global Illumination in Virtual Scenes with Participating Media

Sichtbarkeitsbestimmung ist einer der fundamentalen Bausteine fotorealistischer Bildsynthese. Da die Berechnung der Sichtbarkeit allerdings äußerst kostspielig zu berechnen ist, wird nahezu die gesamte Berechnungszeit darauf verwendet. In dieser Arbeit stellen wir neue Methoden zur Speicherung, Berechnung und Approximation von Sichtbarkeit in Szenen mit streuenden Medien vor, die die Berechnung erheblich beschleunigen, dabei trotzdem qualitativ hochwertige und artefaktfreie Ergebnisse liefern

Photon Splatting Using a View-Sample Cluster Hierarchy

Splatting photons onto primary view samples, rather than gathering from a photon acceleration structure, can be a more efficient approach to evaluating the photon-density estimate in interactive applications, where the number of photons is often low compared to the number of view samples. Most photon splatting approaches struggle with large photon radii or high resolutions due to overdraw and insufficient culling. In this paper, we show how dynamic real-time diffuse interreflection can be achieved by using a full 3D acceleration structure built over the view samples and then splatting photons onto the view samples by traversing this data structure. Full dynamic lighting and scenes are possible by tracing and splatting photons, and rebuilding the acceleration structure every frame. We show that the number of view-sample/photon tests can be significantly reduced and suggest further culling techniques based on the normal cone of each node in the hierarchy. Finally, we present an approximate variant of our algorithm where photon traversal is stopped at a fixed level of our hierarchy, and the incoming radiance is accumulated per node and direction, rather than per view sample. This improves performance significantly with little visible degradation of quality

Efficient Many-Light Rendering of Scenes with Participating Media

We present several approaches based on virtual lights that aim at capturing the light transport without compromising quality, and while preserving the elegance and efficiency of many-light rendering. By reformulating the integration scheme, we obtain two numerically efficient techniques; one tailored specifically for interactive, high-quality lighting on surfaces, and one for handling scenes with participating media

Towards Fully Dynamic Surface Illumination in Real-Time Rendering using Acceleration Data Structures

The improvements in GPU hardware, including hardware-accelerated ray tracing, and the push for fully dynamic realistic-looking video games, has been driving more research in the use of ray tracing in real-time applications. The work described in this thesis covers multiple aspects such as optimisations, adapting existing offline methods to real-time constraints, and adding effects which were hard to simulate without the new hardware, all working towards a fully dynamic surface illumination rendering in real-time.Our first main area of research concerns photon-based techniques, commonly used to render caustics. As many photons can be required for a good coverage of the scene, an efficient approach for detecting which ones contribute to a pixel is essential. We improve that process by adapting and extending an existing acceleration data structure; if performance is paramount, we present an approximation which trades off some quality for a 2–3× improvement in rendering time. The tracing of all the photons, and especially when long paths are needed, had become the highest cost. As most paths do not change from frame to frame, we introduce a validation procedure allowing the reuse of as many as possible, even in the presence of dynamic lights and objects. Previous algorithms for associating pixels and photons do not robustly handle specular materials, so we designed an approach leveraging ray tracing hardware to allow for caustics to be visible in mirrors or behind transparent objects.Our second research focus switches from a light-based perspective to a camera-based one, to improve the picking of light sources when shading: photon-based techniques are wonderful for caustics, but not as efficient for direct lighting estimations. When a scene has thousands of lights, only a handful can be evaluated at any given pixel due to time constraints. Current selection methods in video games are fast but at the cost of introducing bias. By adapting an acceleration data structure from offline rendering that stochastically chooses a light source based on its importance, we provide unbiased direct lighting evaluation at about 30 fps. To support dynamic scenes, we organise it in a two-level system making it possible to only update the parts containing moving lights, and in a more efficient way.We worked on top of the new ray tracing hardware to handle lighting situations that previously proved too challenging, and presented optimisations relevant for future algorithms in that space. These contributions will help in reducing some artistic constraints while designing new virtual scenes for real-time applications

Real-time rendering of cities at night

En synthèse d’images, déterminer la couleur d’une surface au pixel d’une image doit considérer toutes les sources de lumière de la scène pour évaluer leur contribution lumineuse sur la surface en question. Cette évaluation de la visibilité et en l’occurrence de la radiance incidente des sources de lumière est très coûteuse. Elle n’est généralement pas traitée pour chaque source de lumière en rendu temps-réel. Une ville en pleine nuit est un exemple de telle scène comportant une grande quantité de sources de lumière pour lesquelles les rendus temps-réel modernes ne peuvent pas évaluer la visibilité de toutes les sources de lumière individuelles. Nous présentons une technique exploitant la cohérence spatiale des villes et la co-hérence temporelle des rendus temps-réel pour accélérer le calcul de la visibilité des sources de lumière. Notre technique de visibilité profite des bloqueurs naturels et pré-dominants de la ville pour rapidement réduire la liste de sources de lumière à évaluer etainsi, accélérer le calcul de la visibilité en assumant des bloqueurs sous forme de boîtes alignées majoritairement selon certains axes dominants. Pour garantir la propagation des occultations, nous fusionnons les bloqueurs adjacents dans un seul et même bloqueur conservateur en termes d’occultations. Notre technique relie la visibilité de la caméra avec la visibilité des surfaces pour réduire le nombre d’évaluations à effectuer à chaque rendu, et ne calcule la visibilité que pour les surfaces visibles du point de vue de la caméra. Finalement, nous intégrons la technique de visibilité avec une technique de rendu réaliste, Lightcuts, qui a été mise à jour sur GPU dans un scénario de rendu temps-réel. Même si notre technique ne permettra pas d’atteindre le temps-réel en général dans une scène complexe, elle réduit suffisamment les contraintes pour espérer y arriver un jour.In image synthesis, to determine the final color of a surface at a specific image pixel,we must consider all potential light sources and evaluate if they contribute to the illumination. Since such evaluation is slow, real-time renderers traditionally do not evaluate each light source, and instead preemptively choose locally important light sources for which to evaluate visibility. A city at night is such a scene containing many light sources for which modern real-time renderers cannot allow themselves to evaluate every light source at every frame.We present a technique exploiting spatial coherency in cities and temporal coherency of real-time walkthroughs to reduce visibility evaluations in such scenes. Our technique uses the natural and predominant occluders of a city to efficiently reduce the number of light sources to evaluate. To further accelerate the evaluation we project the bounding boxes of buildings instead of their detailed model (these boxes should be oriented mostly along a few directions), and fuse adjacent occluders on an occlusion plane to form larger conservative occluders. Our technique also integrates results from camera visibility to further reduce the number of visibility evaluations executed per frame, and evaluates visible light sources for facades visible from the point of view of the camera. Finally, we integrate an offline rendering technique, Lightcuts, by adapting it to real-time GPU rendering to further save on rendering time.Even though our technique does not achieve real-time frame rates in a complex scene,it reduces the complexity of the problem enough so that we can hope to achieve such frame rates one day

Real-Time Ray Traced Global Illumination using Fast Sphere Intersection Approximation for Dynamic Objects

Realistic lighting models are an important component of modern computer generated, interactive 3D applications. One of the more difficult to emulate aspects of real-world lighting is the concept of indirect lighting, often referred to as global illumination in computer graphics. Balancing speed and accuracy requires carefully considered trade-offs to achieve plausible results and acceptable framerates. We present a novel technique of supporting global illumination within the constraints of the new DirectX Raytracing (DXR) API used with DirectX 12. By pre-computing spherical textures to approximate the diffuse color of dynamic objects, we build a smaller set of approximate geometry used for second bounce lighting calculations for diffuse light rays. This speeds up both the necessary intersection tests and the amount of geometry that needs to be updated within the GPU\u27s acceleration structure. Our results show that our approach for diffuse bounced light is faster than using the conservative mesh for triangle-ray intersection in some cases. Since we are using this technique for diffuse bounced light the lower resolution of the spheres is close to the quality of traditional raytracing techniques for most materials