Real-time Shadows for Gigapixel Displacement Maps

Shadows portray helpful information in scenes. From a scientific visualization standpoint, they help to add data without unnecessary clutter. In video games they add realism and depth. In common graphics pipelines, due to the independent and parallel rendering of geometric primitives, shadows are difficult to achieve. Objects require knowledge of each other and therefore multiple renders are needed to collect the necessary data. The collection of this data comes with its own set of trade offs. Our research involves adding shadows into a lunar rendering framework developed by Dr. Robert Kooima. The NASA-collected data contains a multi-gigapixel displacement map describing the lunar topology. This map does not fit entirely into main memory and therefore out-of-core paging is utilized to achieve real-time speeds. Current shadow techniques do not attempt to generate occluder data on such a scale, and therefore we have developed a novel approach to fit this situation. By using a chain of pre-processing steps, we analyze the structure of the displacement map and calculate horizon lines at each vertex. This information is saved into several images and used to generate shadows in a single pass, maintaining real-time speeds. The algorithm is even capable of generating soft shadows without extra information or loss of speed. We compare our algorithm with common approaches in the field as well as two forms of ground truth; one from ray tracing and the other from the gigapixel lunar texture data, showing real shadows at the time it was collected

Large-Scale Rendering Using Shadowmaps

Shadow mapovanie je najpoužívanejšia metóda ktorá sa využíva v real-time 3D grafike na tvorbu tieňov v lokálnych osvetlovacích modeloch. Táto práca krok-za-krokom vysvetľuje proces vytvárania shadow máp. Porovnané su metódy výpočtu hĺbkovej odchylky ako aj filtrovacie metódy, a zároveň je odvodený výpočet normálovej odchýlky pre filtrovacie kernely s premennou veľkosťou. Taktiež popíšeme proces ako efektívne obaliť frustum kamery kaskádovým frustumom. Popri tom vysvetlíme ako využiť moderné OpenGL API na zníženie výkonnostných nedostatkov.Shadow mapping is the most widely used method in real-time 3D graphics for producing shadows in local light models. This thesis step-by-step explains the process of creating shadow maps. Depth biasing as well as filtering methods are analysed, then the calculation of normal offset bias for variable sized kernels is derived. We describe the process of efficiently fitting stable cascade frustums to view frustum. Also shown is how to use modern OpenGL to reduce performance overhead.

Robust object-based algorithms for direct shadow simulation

En informatique graphique, les algorithmes de générations d'ombres évaluent la quantité de lumière directement perçue par une environnement virtuel. Calculer précisément des ombres est cependant coûteux en temps de calcul. Dans cette dissertation, nous présentons un nouveau système basé objet robuste, qui permet de calculer des ombres réalistes sur des scènes dynamiques et ce en temps interactif. Nos contributions incluent notamment le développement de nouveaux algorithmes de génération d'ombres douces ainsi que leur mise en oeuvre efficace sur processeur graphique. Nous commençons par formaliser la problématique du calcul d'ombres directes. Tout d'abord, nous définissons ce que sont les ombres directes dans le contexte général du transport de la lumière. Nous étudions ensuite les techniques interactives qui génèrent des ombres directes. Suite à cette étude nous montrons que mêmes les algorithmes dit physiquement réalistes se reposent sur des approximations. Nous mettons également en avant, que malgré leur contraintes géométriques, les algorithmes d'ombres basées objet sont un bon point de départ pour résoudre notre problématique de génération efficace et robuste d'ombres directes. Basé sur cette observation, nous étudions alors le système basé objet existant et mettons en avant ses problèmes de robustesse. Nous proposons une nouvelle technique qui améliore la qualité des ombres générées par ce système en lui ajoutant une étape de mélange de pénombres. Malgré des propriétés et des résultats convaincants, les limitations théoriques et de mise en oeuvre limite la qualité générale et les performances de cet algorithme. Nous présentons ensuite un nouvel algorithme d'ombres basées objet. Cet algorithme combine l'efficacité de l'approche basée objet temps réel avec la précision de sa généralisation au rendu hors ligne. Notre algorithme repose sur l'évaluation locale du nombre d'objets entre deux points : la complexité de profondeur. Nous décrivons comment nous utilisons cet algorithme pour échantillonner la complexité de profondeur entre les surfaces visibles d'une scène et une source lumineuse. Nous générons ensuite des ombres à partir de cette information soit en modulant l'éclairage direct soit en intégrant numériquement l'équation d'illumination directe. Nous proposons ensuite une extension de notre algorithme afin qu'il puisse prendre en compte les ombres projetées par des objets semi-opaque. Finalement, nous présentons une mise en oeuvre efficace de notre système qui démontre que des ombres basées objet peuvent être générées de façon efficace et ce même sur une scène dynamique. En rendu temps réel, il est commun de représenter des objets très détaillés encombinant peu de triangles avec des textures qui représentent l'opacité binaire de l'objet. Les techniques de génération d'ombres basées objet ne traitent pas de tels triangles dit "perforés". De par leur nature, elles manipulent uniquement les géométries explicitement représentées par des primitives géométriques. Nous présentons une nouvel algorithme basé objet qui lève cette limitation. Nous soulignons que notre méthode peut être efficacement combinée avec les systèmes existants afin de proposer un système unifié basé objet qui génère des ombres à la fois pour des maillages classiques et des géométries perforées. La mise en oeuvre proposée montre finalement qu'une telle combinaison fournit une solution élégante, efficace et robuste à la problématique générale de l'éclairage direct et ce aussi bien pour des applications temps réel que des applications sensibles à la la précision du résultat.Direct shadow algorithms generate shadows by simulating the direct lighting interaction in a virtual environment. The main challenge with the accurate direct shadow problematic is its computational cost. In this dissertation, we develop a new robust object-based shadow framework that provides realistic shadows at interactive frame rate on dynamic scenes. Our contributions include new robust object-based soft shadow algorithms and efficient interactive implementations. We start, by formalizing the direct shadow problematic. Following the light transport problematic, we first formalize what are robust direct shadows. We then study existing interactive direct shadow techniques and outline that the real time direct shadow simulation remains an open problem. We show that even the so called physically plausible soft shadow algorithms still rely on approximations. Nevertheless we exhibit that, despite their geometric constraints, object-based approaches seems well suited when targeting accurate solutions. Starting from the previous analyze, we investigate the existing object-based shadow framework and discuss about its robustness issues. We propose a new technique that drastically improve the resulting shadow quality by improving this framework with a penumbra blending stage. We present a practical implementation of this approach. From the obtained results, we outline that, despite desirable properties, the inherent theoretical and implementation limitations reduce the overall quality and performances of the proposed algorithm. We then present a new object-based soft shadow algorithm. It merges the efficiency of the real time object-based shadows with the accuracy of its offline generalization. The proposed algorithm lies onto a new local evaluation of the number of occluders between $two$ points (\ie{} the depth complexity). We describe how we use this algorithm to sample the depth complexity between any visible receiver and the light source. From this information, we compute shadows by either modulate the direct lighting or numerically solve the direct illumination with an accuracy depending on the light sampling strategy. We then propose an extension of our algorithm in order to handle shadows cast by semi opaque occluders. We finally present an efficient implementation of this framework that demonstrates that object-based shadows can be efficiently used on complex dynamic environments. In real time rendering, it is common to represent highly detailed objects with few triangles and transmittance textures that encode their binary opacity. Object-based techniques do not handle such perforated triangles. Due to their nature, they can only evaluate the shadows cast by models whose their shape is explicitly defined by geometric primitives. We describe a new robust object-based algorithm that addresses this main limitation. We outline that this method can be efficiently combine with object-based frameworks in order to evaluate approximative shadows or simulate the direct illumination for both common meshes and perforated triangles. The proposed implementation shows that such combination provides a very strong and efficient direct lighting framework, well suited to many domains ranging from quality sensitive to performance critical applications

Soft bilateral filtering shadows using multiple image-based algorithms

This study introduces Soft Bilateral Filtering Shadows method of dynamic scenes, which uses multi-matrices of the light sample points due to lack realism in soft shadows generation in real time. While geometry-based shadow algorithm requires one pass per polygon for rendering shadow that requires time-consuming, the adopted shadow map algorithm needs a single rendering pass for each sample point of the light source to generate shadow at low cost. This method renders a complex scenes and accurately eliminating the inherent deficiencies in shadow maps. In order to compute shadow maps, view matrices were used for each sample point of the extended light source. Then penumbra region was used for interpolation based on bilateral filtering to create the soft shadows. They depend on multiple shadow maps which provide antialiasing shadow maps. The method uses fragment shader for rendering multiple shadow maps with penumbra and umbra regions. The main contribution of this article is introducing interpolation bilaterally of image-based shadows. This method makes the most effect of the computation significantly appear at the edges of the penumbra region. Furthermore, the filtering allows to obtain on the soft shadow marvelously at the lowest number possible of the light sample points. The generated soft shadows have good performance and high quality therefore, they are suitable for interactive applications. © 2016 Springer Science+Business Media New Yor

Analytical motion blurred shadows

A rendering framework supporting analytical visibility is extended with shadow mapping. Shadow maps containing analytical visibility data are used, leading to cases where both the projections to the shadow map and the depth tests can be time-dependent. For receivers that are static with respect to the camera, the depth tests are solved analytically over time. For dynamic receivers, point sampling is used. Problems arising from time-dependence, limited precision and necessary simplifications are investigated, and potential solutions are discussed.En rastrerare med stöd för analytisk rörelseoskärpa integreras med shadow mapping. Shadow maps med analytisk synlighetsinformation används för detta, vilket leder till situationer där både projiceringarna till shadow map:en och djupjämförelserna kan vara tidsberoende. Djupjämförelserna utförs analytiskt över tiden för mottagare som är statiska i förhållande till kameran. För dynamiska mottagare används point sampling istället. Problem som uppstår på grund av tidsberoende, begränsad precision och nödvändiga förenklingar undersöks, och potentiella lösningar diskuteras

Ambient occlusion and shadows for molecular graphics

Computer based visualisations of molecules have been produced as early as the 1950s to aid researchers in their understanding of biomolecular structures. An important consideration for Molecular Graphics software is the ability to visualise the 3D structure of the molecule in a clear manner. Recent advancements in computer graphics have led to improved rendering capabilities of the visualisation tools. The capabilities of current shading languages allow the inclusion of advanced graphic effects such as ambient occlusion and shadows that greatly improve the comprehension of the 3D shapes of the molecules. This thesis focuses on finding improved solutions to the real time rendering of Molecular Graphics on modern day computers. The methods of calculating ambient occlusion and both hard and soft shadows are examined and implemented to give the user a more complete experience when navigating large molecular structures