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Compressed Bounding Volume Hierarchies for Efficient Ray Tracing of Disperse Hair
(The Eurographics Association, 2018) Martinek, Magdalena; Stamminger, Marc; Binder, Nikolaus; Keller, Alexander; Beck, Fabian and Dachsbacher, Carsten and Sadlo, Filip
Ray traced human hair is becoming more and more ubiquitous in photorealistic image synthesis. Despite hierarchical data structures for accelerated ray tracing, performance suffers from the bad separability inherent with ensembles of hair strands. We propose a compressed acceleration data structure that improves separability by adaptively subdividing hair fibers. Compression is achieved by storing quantized as well as oriented bounding boxes and an indexing scheme to specify curve segments instead of storing them. We trade memory for speed, as our approach may use more memory, however, in cases of highly curved hair we can double the number of traversed rays per second over prior work. With equal memory we still achieve a speed-up of up to 30%, with equal performance we can reduce memory by up to 30%.
Topological Triangle Sorting for Predefined Camera Paths
(The Eurographics Association, 2016) Weber, Christoph; Stamminger, Marc; Matthias Hullin and Marc Stamminger and Tino Weinkauf
We present a preprocessing pipeline for triangle meshes that topologically sorts all triangles for a given camera and scene animation in front-to-back or back-to-front order. This allows us to efficiently render a given animation without depth buffer, and to include transparency. We also remove non-contributing triangles, thus improving render time, especially when applying anti-aliasing. To this end we first record the visible triangles of a sequence of frames. For every frame we create a directed graph storing occlusion information. After a topological sort of this graph, all triangles are sorted properly. The contribution of this paper is the reduction of redundancy by merging the graphs of all frames. The result of our pipeline is a single sorted index buffer, over which we slide a window that yields sorted index buffers for each single frame. Circular dependencies are broken by placing duplicates of the affected triangles in the index buffer. Our sliding window then displays only frame specific triangles in their proper order. We conclude by demonstrating the benefits of removing invisible triangles and disabling the hardware visibility test.
On Floating-Point Normal Vectors
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Meyer, Quirin; Suessmuth, Jochen; Sussner, Gerd; Stamminger, Marc; Greiner, Guenther
In this paper we analyze normal vector representations. We derive the error of the most widely used representation, namely 3D floating-point normal vectors. Based on this analysis, we show that, in theory, the discretization error inherent to single precision floating-point normals can be achieved by 250.2 uniformly distributed normals, addressable by 51 bits. We review common sphere parameterizations and show that octahedron normal vectors perform best: they are fast and stable to compute, have a controllable error, and require only 1 bit more than the theoretical optimal discretization with the same error.
Data‐Parallel Decompression of Triangle Mesh Topology
(The Eurographics Association and Blackwell Publishing Ltd., 2012) Meyer, Quirin; Keinert, Benjamin; Sußner, Gerd; Stamminger, Marc; Holly Rushmeier and Oliver Deussen
We propose a lossless, single‐rate triangle mesh topology codec tailored for fast data‐parallel GPU decompression. Our compression scheme coherently orders generalized triangle strips in memory. To unpack generalized triangle strips efficiently, we propose a novel parallel and scalable algorithm. We order vertices coherently to further improve our compression scheme. We use a variable bit‐length code for additional compression benefits, for which we propose a scalable data‐parallel decompression algorithm. For a set of standard benchmark models, we obtain (min: 3.7, med: 4.6, max: 7.6) bits per triangle. Our CUDA decompression requires only about 15% of the time it takes to render the model even with a simple shader.We propose a lossless, single‐rate triangle mesh topology codec tailored for fast data‐parallel GPU decompression. Our compression scheme coherently orders generalized triangle strips in memory. To unpack generalized triangle strips efficiently, we propose a novel parallel and scalable algorithm. We order vertices coherently to further improve our compression scheme. We use a variable bit‐length code for additional compression benefits, for which we propose a scalable data‐parallel decompression algorithm. For a set of standard benchmark models, we obtain (min: 3.7, med: 4.6, max: 7.6) bits per triangle. Our CUDA decompression requires only about 15% of the time it takes to render the model even with a simple shader.
Faster Ray-Traced Shadows for Hybrid Rendering of Fully Dynamic Scenes by Pre-BVH Culling
(The Eurographics Association, 2015) Selgrad, Kai; Müller, Jonas; Stamminger, Marc; Andrea Giachetti and Silvia Biasotti and Marco Tarini
With ever increasing ray traversal and hierarchy construction performance the application of ray tracing to problems often tackled by rasterization-based algorithms is becoming a viable alternative. This is especially desirable as the ground truth for these algorithms is often determined by using ray tracing and thus directly applying it is the simplest way to generate images satisfying the reference. In this paper we propose a very efficient pre-process to speed up the construction and traversal of sub-optimal, but fast-to-build hierarchies used for interactive ray tracing and show how it can be applied to shadow rays in a hybrid environment, where ray tracing is used to sample area lights for scene positions found and shaded via rasterization.
Real-time Local Displacement using Dynamic GPU Memory Management
(ACM, 2013) Schäfer, Henry; Keinert, Benjamin; Stamminger, Marc; Kayvon Fatahalian and Christian Theobalt
We propose a novel method for local displacement events in large scenes, such as scratches, footsteps, or sculpting operations. Deformations are stored as displacements for vertices generated by hardware tessellation. Adaptive mesh refinement, application of the displacement and all involved memory management happen completely on the GPU. We show various extensions to our approach, such as on-the-fly normal computation and multi-resolution editing. In typical game scenes we perform local deformations at arbitrary positions in far less than one millisecond. This makes the method particularly suited for games and interactive sculpting applications.
Level-of-Detail for Production-Scale Path Tracing
(The Eurographics Association, 2015) Prus, Magdalena; Eisenacher, Christian; Stamminger, Marc; David Bommes and Tobias Ritschel and Thomas Schultz
Path-traced global illumination (GI) becomes increasingly important in movie production. With offscreen elements considerably contributing to the path traced image, geometric complexity increases drastically, requiring geometric instancing or a variety of manually created and baked LOD. To reduce artists' work load and bridge the gap between mesh-based LOD (Mip-maps) and voxel-based LOD (brickmaps), we propose to use an SVO with averaged BRDF parameters, e.g. for the Disney-BRDF, and a normal distribution per voxel. During shading we construct a BRDF from the averaged BRDF parameters and evaluate it with a random normal sampled from the distribution. This is simple, memory-efficient, and handles a wide variety of geometry scales and materials seamlessly, with proper filtering. Further it is efficient to construct, which allows quick artist iterations as well as automatic and lazy generation on scene loading.
Proxy Painting
(The Eurographics Association, 2018) Lange, Vanessa; Kurth, Philipp; Keinert, Benjamin; Boss, Martin; Stamminger, Marc; Bauer, Frank; Sablatnig, Robert and Wimmer, Michael
For archaeologists it is often desireable to present statues in their original coloration. With projection mapping real-world surfaces are augmented by digital content to create compelling alterations of the scene's visual appearance without actually altering or even damaging the object. While there are frequent advances in projection quality, content creation is still a chal- lenging and often unintuitive task, especially for non-experts. In our presented system we combine the advantages of digital content creation such as rapid prototyping with the convenience of an analog workflow. Users paint on smaller versions of the projection mapping target, employing real-world brushes and pencils, while the results are presented live on its large counter- part. We further demonstrate the integration of our system into a state-of-art game engine. By leveraging a powerful rendering and material workflow we make creating compelling materials and lighting situations an intuitive experience.
Robust Blending and Occlusion Compensation in Dynamic Multi-Projection Mapping
(The Eurographics Association, 2017) Lange, Vanessa; Siegl, Christian; Colaianni, Matteo; Stamminger, Marc; Bauer, Frank; Adrien Peytavie and Carles Bosch
Using multi-projection systems allows us to immerse users in an altered reality without the need to wear additional head-gear. The immersion of such systems relies on the quality of the calibration which in general will degenerate over time when used outside of a lab environment. This work introduces a novel balance term that allows us to hide high frequency brightness seams caused by self-shadowing of the projected geometry and the borders of the projection frustum. We further use this more robust blending between projectors to compensate for occluding spectators, who enter the projection volume, by filling the resulting shadows with light from other projectors.
Interactive Direct Volume Rendering with Many-light Methods and Transmittance Caching
(The Eurographics Association, 2013) Weber, Christoph; Kaplanyan, Anton S.; Stamminger, Marc; Dachsbacher, Carsten; Michael Bronstein and Jean Favre and Kai Hormann
In this paper we present an interactive global illumination method for Direct Volume Rendering (DVR) based on the many-light approach, a class of global illumination methods which gained much interest recently. We extend these methods to handle transfer function and volume density updates efficiently in order to foster ability of interactive volume exploration. Global illumination techniques accounting for all light transport phenomena are typically computationally too expensive for interactive DVR. Many-light methods represent the light transport in a volume by determining a set of virtual light sources whose direct illumination and single scattering to a view ray approximate full global illumination. Our technique reduces computation caused by transfer function changes by recomputing the contribution of these virtual lights, and rescaling or progressively updating their volumetric shadow maps and locations. We discuss these optimizations in the context of DVR and demonstrate their application to interactive rendering.

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