László Szécsi

Volumetric Ambient Occlusion for Real-Time Rendering and Games

This new algorithm, based on GPUs, can compute ambient occlusion to inexpensively approximate global-illumination effects in real-time systems and games. The first step in deriving this algorithm is to examine how ambient occlusion relates to the physically founded rendering equation. The correspondence stems from a fuzzy membership function that defines what constitutes nearby occlusions. The next step is to develop a method to calculate ambient occlusion in real time without precomputation. The algorithm is based on a novel interpretation of ambient occlusion that measures the relative volume of the visible part of the surfaces tangent sphere. The new formulas integrand has low variation and thus can be estimated accurately with a few samples.

On the efficiency of ray-shooting acceleration schemes

This paper examines the efficiency of different rayshooting acceleration schemes, including the uniform space subdivision, octree and kd-tree. We use simple computational models, which assume that the objects are uniformly distributed in space. The efficiency is characterized by two measures, including the expected number of ray-object intersections needed to identify the firstly intersected object, and the expected number of steps on the space partitioning data structure. We can come to the interesting conclusion that these numbers are constant and are independent of the number of objects in the scene. The number of intersections is determined by how well the cells of the partitioning data structure enclose the objects. Such analysis helps to understand why kd-tree is better than octree and uniform space subdivision and provides hints to improve their implementation.

Combined Correlated and Importance Sampling in Direct Light Source Computation and Environment Mapping

This paper presents a general variance reduction method that is a quasi‐optimal combination of correlated and importance sampling. The weights of the combination are selected automatically in order to keep the merits of both importance and correlated sampling. The proposed sampling method is used for efficient direct light source computation of large area sources and for the calculation of the reflected illumination of environment maps. Importance sampling would be good in these cases if the sources are hidden, while correlated sampling is efficient if the sources are fully visible. The proposed method automatically detects the particular case and provides results that inherit the advantages of both techniques.

Real-time Light Animation

Light source animation is a particularly hard field of real‐time global illumination algorithms since moving light sources result in drastic illumination changes and make coherence techniques less effective. However, the animation of small (point‐like) light sources represents a special but practically very important case, for which the reuse of the results of other frames is possible. This paper presents a fast light source animation algorithm based on the virtual light sources illumination method. The speed up is close to the length of the animation, and is due to reusing paths in all frames and not only in the frame where they were obtained. The possible applications of this algorithm are the lighting design and systems to convey shape and features with relighting.

Hatching for Motion Picture Production

This paper presents a hatching algorithm which – while also allows for an implementation in real‐time – is integrated into the production pipeline of computer generated motion picture. Motion picture production pipelines impose special functional and quality requirements. From the functional point of view, the stages of modeling, 3D rendering, and compositing form a pipeline without feed‐back, and frames are rendered independently, possibly on different computers. Thus, no temporal data can be shared between them while flicker free animation needs to be generated. Quality requirements can be grasped as that of dual consistency: the generated hatching must consistently follow object movement and deformation, and, at the same time, it should have a consistent pattern and density in image‐space to provide the hand‐crafted look. In order to meet both requirements, we apply a particle based method and develop an image‐space density control mechanism using rejection sampling and low‐discrepancy sequences. We also discuss the decomposition of rendering tasks according to the main stages of the production pipeline and demonstrate how the artist can define the illustration style in a convenient way.

Real-Time Metaball Ray Casting with Fragment Lists

In this paper we describe a method for rendering particle-based medium representations. The algorithm builds per-pixel lists of relevant metaballs, then incrementally constructs a piecewise polynomial approximation of summed metaball densities along rays, and finds intersections with the isosurface using those. This new approach scales well for a high number of particles, it can handle local extremities of depth complexity robustly, and it does not suffer from the inaccuracies and limitations of screen-space filtering approximation methods.

Deterministic importance sampling with error diffusion

This paper proposes a deterministic importance sampling algorithm that is based on the recognition that delta‐sigma modulation is equivalent to importance sampling. We propose a generalization for delta‐sigma modulation in arbitrary dimensions, taking care of the curse of dimensionality as well. Unlike previous sampling techniques that transform low‐discrepancy and highly stratified samples in the unit cube to the integration domain, our error diffusion sampler ensures the proper distribution and stratification directly in the integration domain. We also present applications, including environment mapping and global illumination rendering with virtual point sources.

GPU-Based Techniques for Global Illumination Effects

Abstract This book presents techniques to render photo-realistic images by programming the Graphics Processing Unit (GPU). We discuss effects such as mirror reflections, refractions, caustics, diffuse or glossy indirect illumination, radiosity, single or multiple scattering in participating media, tone reproduction, glow, and depth of field. The book targets game developers, graphics programmers, and also students with some basic understanding of computer graphics algorithms, rendering APIs like Direct3D or OpenGL, and shader programming. In order to make the book self-contained, the most important concepts of local illumination and global illumination rendering, graphics hardware, and Direct3D/HLSL programming are reviewed in the first chapters. After these introductory chapters we warm up with simple methods including shadow and environment mapping, then we move on toward advanced concepts aiming at global illumination rendering. Since it would have been impossible to give a rigorous review of all appro...

Specular Effects on the GPU: State of the Art

This survey reviews algorithms that can render specular, i.e. mirror reflections, refractions, and caustics on the GPU. We establish a taxonomy of methods based on the three main different ways of representing the scene and computing ray intersections with the aid of the GPU, including ray tracing in the original geometry, ray tracing in the sampled geometry, and geometry transformation. Having discussed the possibilities of implementing ray tracing, we consider the generation of single reflections/refractions, interobject multiple reflections/refractions, and the general case which also includes self‐reflections or refractions. Moving the focus from the eye to the light sources, caustic effect generation approaches are also examined.

Photon Map Gathering on the GPU

Photon mapping methods obtain the indirect illumination of a point by finding those photon hits that arrived at the neighborhood of the point on the object surface. This paper proposes a method that stores the photon hits in a texture of the graphics hardware and replaces the traditional kd-tree based neighborhood searches by the filtering of this texture. This step finds the irradiance of all points (i.e. all texels) simultaneously in a single step, thus the average irradiance of a point can be obtained by a single texture lookup. Using this approach we can port the final gathering step of photon mapping to the graphics hardware (GPU). The CPU is only responsible for generating new light paths and updating the unfiltered photon map. Thanks to the optimal subdivision of the computation work between the the CPU and the GPU, the proposed algorithm can render globally illuminated scenes interactively.