Stefan Brabec

Interactive global illumination using selective photon tracing

We present a method for interactive global illumination computation which is embedded in the framework of Quasi-Monte Carlo photon tracing and density estimation techniques. The method exploits temporal coherence of illumination by tracing photons selectively to the scene regions that require illumination update. Such regions are identified with a high probability by a small number of the pilot photons. Based on the pilot photons which require updating, the remaining photons with similar paths in the scene can be found immediately. This becomes possible due to the periodicity property inherent to the multi-dimensional Halton sequence, which is used to generate photons. If invalid photons cannot all be updated during a single frame, frames are progressively refined in subsequent cycles. The order in which the photons are updated is decided by inexpensive energy- and perception-based criteria whose goal is to minimize the perceivability of outdated illumination. The method buckets all photons on-the-fly in mesh elements and does not require any data structures in the temporal domain, which makes it suitable for interactive rendering of complex scenes. Since mesh-based reconstruction of lighting patterns with high spatial frequencies is inefficient, we use a hybrid approach in which direct illumination and resulting shadows are rendered using graphics hardware.

Shadow Volumes on Programmable Graphics Hardware

One of the best choices for fast, high quality shadows is the shadow volume algorithm. However, for real timeapplications the extraction of silhouette edges can significantly burden the CPU, especially with highly tessellatedinput geometry or when complex geometry shaders are applied.

Shadow Mapping for Hemispherical and Omnidirectional Light Sources

In this paper we present a shadow mapping technique for hemispherical and omnidirectional light sources using dual-paraboloid mapping. In contrast to the traditional perspective projection this parameterization has the benefit that only a minimal number of rendering passes is needed during generation of the shadow maps, making the method suitable for dynamic environments and real time applications. By utilizing programmable features available on state-of-the-art graphics cards we show how the algorithm can be efficiently mapped to hardware.

Soft Shadow Maps for Linear Lights

Soft shadows and penumbra regions generated by extended light sources such as linear and area lights are visual effects that significantly contribute to the realism of a scene. In interactive applications, shadow computations are mostly performed by either the shadow volume or the shadow map algorithm. Variants of these methods for soft shadows exist, but they require a significant number of samples on the light source, thereby dramatically increasing rendering times.

Practical shadow mapping

Abstract In this paper, we present several methods that can greatly improve image quality when using the shadow mapping algorithm. Shadow artifacts introduced by shadow mapping are mainly due to low resolution shadow maps and/or the limited numerical precision used when performing the shadow test. These problems especially arise when the light sources viewing frustum, from which the shadow map is generated, is not adjusted to the actual camera view. We show how a tight-fitting frustum can be computed such that the shadow mapping algorithm concent rates on the visible parts of the scene and takes advantage of nearly the full available precision. Furthermore, we recommend uniformly spaced depth values in contrast to perspectively spaced depths in order to equally sample the scene seen from the light source.

Hardware-accelerated rendering of antialiased shadows with shadow maps

We present a hardware-accelerated method for rendering high quality, antialiased shadows using the shadow map approach. Instead of relying on dedicated hardware support for shadow map filtering, we propose a general rendering algorithm that can be used on most graphics workstations. The filtering method softens shadow boundaries by using a technique called percentage closer filtering which is commonly used in software renderers, e.g. ray tracing. We describe how the software algorithm can be efficiently mapped to hardware. In order to achieve real-time or at least interactive frame rates we also propose a slightly modified shadow filtering method that saves valuable hardware resources while still achieving good image quality.

Shadow Techniques for Interactive and Real-Time Applications

Shadows provide important visual cues for the relative position of objects in threedimensional space. For interactive and real-time applications, e.g. in virtual reality systems or games, the shadow computation needs to be extremely fast, usually synchronized with the display’s refresh rate. Using dynamic scenes with many, movable light sources, shadow computation is therefore often the main bottleneck in a rendering system. In this thesis we will discuss this problem in detail: Originating from Williams’ shadow maps and Crow’s shadow volumes, we will present hardware-accelerated shadow techniques that are able to generate shadows of high-quality while still being fast enough to be used in real-time or interactive applications. We will show algorithms for the computation of hard shadows as well as for the more complex problem of approximating soft shadows caused by area light sources.