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This is an archived copy of my old (academic) homepage formerly hosted at Chalmers. It is no longer being updated.

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For other papers by the Graphics Group at Chalmers, look here.

Efficient Virtual Shadow Maps for Many Lights

Abstract: Recently, several algorithms have been introduced that enable real-time performance for many lights in applications such as games. In this paper, we explore the use of hardware-supported virtual cube-map shadows to efficiently implement high-quality shadows from hundreds of light sources in real time and within a bounded memory footprint. In addition, we explore the utility of ray tracing for shadows from many lights and present a hybrid algorithm combining ray tracing with cube maps to exploit their respective strengths. Our solution supports real-time performance with hundreds of lights in fully dynamic high-detail scenes.

Authors: Ola Olsson, Erik Sintorn, Viktor Kämpe, Markus Billeter and Ulf Assarsson.

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Tiled Forward Shading

In this article we explore the tiled forward shading algorithm. Tiled forward shading is an extension/modification of tiled deferred shading, which improves upon traditional deferred shading methods.

Tiled forward shading attempts to combine some of the advantages normally associated with deferred shading with the advantages of forward shading, namely the capability to use alpha blending for transparency and various hardware-assisted multi-sampling schemes.

Authors: Ola Olsson, Markus Billeter & Ulf Assarsson.

[GPU Pro 4]

Tiled and Clustered Forward Shading

Abstract: Tiled and Clustered Forward Shading are new techniques that enable support for thousands of lights, while eliminating many of the drawbacks of deferred techniques. Ths talk shows how these techniques can be used and extended to support transparency with high efficiency.

Authors: Ola Olsson, Markus Billeter & Ulf Assarsson.


Clustered Shading

Abstract: This paper presents and investigates Clustered Shading for deferred and forward rendering. In Clustered Shading, view samples with similar properties (e.g. 3D-position and/or normal) are grouped into clusters. This is comparable to tiled shading, where view samples are grouped into tiles based on 2D-position only. We show that Clustered Shading creates a better mapping of light sources to view samples than tiled shading, resulting in a significant reduction of lighting computations during shading. Additionally, Clustered Shading enables using normal information to perform per-cluster back-face culling of lights, again reducing the number of lighting computations. We also show that Clustered Shading not only outperforms tiled shading in many scenes, but also exhibits better worst case behaviour under tricky conditions (e.g. when looking at high-frequency geometry with large discontinuities in depth). Additionally, Clustered Shading enables real-time scenes with two to three orders of magnitudes more lights than previously feasible (up to around one million light sources)

Full title is "Clustered Deferred and Forward Shading". Authors: Ola Olsson, Markus Billeter & Ulf Assarsson. Presented at HPG 2012.

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Multiple Scattering with Light Propagation Volumes

Abstract: This paper introduces a new GPU-based, real-time method for rendering volumetric lighting effects produced by scattering in a participating medium. The method includes support for indirect illumination by scattered light, high-quality single-scattered volumetric shadows, and approximate multiple scattered volumetric lighting effects in isotropic and homogeneous media. The method builds upon an improved propagation scheme for light propagation volumes. This scheme models scattering according to the radiative light transfer equation during propagation. The initial state of the light propagation volumes is based on single-scattered light identified with shadow maps; this allows generation of a high quality initial distribution of radiance. After propagation, the resulting distribution is used as a source of diffuse light during rendering and is also ray marched for volumetric effects from multiple scattering. Volumetric shadows from single-scattered light are rendered separately. We compare the new method to single-scattered volumetric shadows produced by contemporary techniques, plain light propagation volumes (which this new method extends), and a simple composition thereof.

Full title is "Real-Time Multiple Scattering using Light Propagation Volumes". Authors: Markus Billeter, Erik Sintorn & Ulf Assarsson. Presented at I3D 2012.

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Two-level Grids for Ray Tracing on GPUs


Abstract: We investigate the use of two-level nested grids as acceleration structure for ray tracing of dynamic scenes. We propose a massively parallel, sort-based construction algorithm and show that the two-level grid is one of the structures that is fastest to construct on modern graphics processors. The structure handles non-uniform primitive distributions more robustly than the uniform grid and its traversal performance is comparable to those of other high quality acceleration structures used for dynamic scenes. We propose a cost model to determine the grid resolution and improve SIMD utilization during ray-triangle intersection by employing a hybrid packetization strategy. The build times and ray traversal acceleration provide overall rendering performance superior to previous approaches for real time rendering of animated scenes on GPUs.

Full title: "Two-level Grids for Ray Tracing on GPUs". Authors: Javor Kalojanov, Markus Billeter & Philipp Slusallek. Presented at Eurographics 2011 by Javor.

Volumetric Shadows using Polygonal Light Volumes

Abstract: This paper presents a more efficient way of computing single scattering effects in homogeneous participating media for real-time purposes than the currently popular ray-marching based algorithms. These effects include halos around light sources, volumetric shadows and crepuscular rays. By displacing the vertices of a base mesh with the depths from a standard shadow map, we construct a polygonal mesh that encloses the volume of space that is directly illuminated by a light source. Using this volume we can calculate the airlight contribution for each pixel by considering only points along the eye-ray where shadow-transitions occur. Unlike previous ray-marching methods, our method calculates the exact airlight contribution, with respect to the shadow map resolution, at real time frame rates.

Full title is "Real Time Volumetric Shadows using Polygonal Light Volumes". Authors: Markus Billeter, Erik Sintorn & Ulf Assarsson. Presented at High Performance Graphics 2010.

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Efficient Stream Compaction

Abstract: Stream compaction is a common parallel primitive used to remove unwanted elements in sparse data. This allows highly parallel algorithms to maintain performance over several processing steps and reduces overall memory usage.

For wide SIMD many-core architectures, we present a novel stream compaction algorithm and explore several variations thereof. Our algorithm is designed to maximize concurrent execution, with min- imal use of synchronization. Bandwidth and auxiliary storage requirements are reduced significantly, which allows for substantially better performance.

We have tested our algorithms using CUDA on a PC with an NVIDIA GeForce GTX280 GPU. On this hardware, our reference implementation provides a 3× speedup over previous published algorithms.

Full title is "Efficient Stream Compaction on Wide-SIMD Many-Core Architectures". Authors: Markus Billeter, Ola Olsson & Ulf Assarsson. Presented at High Performance Graphics 2009.

[Software] [Paper] [Presentation]