@inproceedings{SelgradMuellerStamminger, author = {Selgrad, Kai and M{\"u}ller, Jonas and Stamminger, Marc}, title = {Faster Ray-Traced Shadows for Hybrid Rendering of Fully Dynamic Scenes by Pre-BVH Culling}, series = {Smart Tools and Apps for Graphics - Eurographics Italian Chapter Conference}, booktitle = {Smart Tools and Apps for Graphics - Eurographics Italian Chapter Conference}, editor = {Giachetti, Andrea and Biasotti, Silvia and Tarini, Marco}, publisher = {The Eurographics Association}, isbn = {978-3-905674-97-2}, doi = {10.2312/stag.20151295}, abstract = {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.}, language = {en} } @inproceedings{LierSelgradStamminger, author = {Lier, Alexander and Selgrad, Kai and Stamminger, Marc}, title = {DIY Meta Languages with Common Lisp}, series = {Proceedings of the 10th European Lisp Symposium (ELS 2017), Vrije Universiteit Brussel, Brussels, Belgium, April, 3-4 2017}, booktitle = {Proceedings of the 10th European Lisp Symposium (ELS 2017), Vrije Universiteit Brussel, Brussels, Belgium, April, 3-4 2017}, editor = {Alberto Riva,}, publisher = {ACM}, address = {New York, NY, USA}, isbn = {978-2-9557474-1-4}, pages = {72 -- 79}, abstract = {In earlier work we described C-Mera, an S-Expression to C-style code transformator, and how it can be used to provide high-level abstractions to the C-family of programming languages. In this paper we provide an in-depth description of its internals that would have been out of the scope of the earlier presentations. Œese implementation details are presented as a toolkit of general techniques for implementing similar meta languages on top of Common Lisp and illustrated on the example of C-Mera, with the goal of making our experience in implementing them more broadly available.}, language = {en} } @inproceedings{SelgradLierWittmannetal., author = {Selgrad, Kai and Lier, Alexander and Wittmann, Markus and Lohmann, Daniel and Stamminger, Marc}, title = {Defmacro for C: Lightweight, Ad Hoc Code Generation}, series = {Proceedings of ELS 2014 7th European Lisp Symposium ; May 5 - 6 2014, IRCAM, Paris, France}, booktitle = {Proceedings of ELS 2014 7th European Lisp Symposium ; May 5 - 6 2014, IRCAM, Paris, France}, issn = {2677-3465}, pages = {80 -- 87}, abstract = {We describe the design and implementation of CGen, a C code generator with support for Common Lisp-style macro expansion. Our code generator supports the simple and efficient management of variants, ad hoc code generation to capture reoccurring patterns, composable abstractions as well as the implementation of embedded domain specific languages by using the Common Lisp macro system. We demonstrate the applicability of our approach by numerous examples from small scale convenience macros over embedded languages to real-world applications in high-performance computing.}, language = {en} } @inproceedings{LierStammingerSelgrad, author = {Lier, Alexander and Stamminger, Marc and Selgrad, Kai}, title = {CPU-Style SIMD Ray Traversal on GPUs}, series = {Proceedings of the Conference on High-Performance Graphics}, booktitle = {Proceedings of the Conference on High-Performance Graphics}, publisher = {Association for Computing Machinery}, address = {New York, NY, USA}, isbn = {9781450358965}, doi = {10.1145/3231578.3231583}, pages = {1 -- 4}, abstract = {In this paper we describe and evaluate an implementation of CPU-style SIMD ray traversal on the GPU. We show how spreading moderately wide BVHs (up to a branching factor of eight) across multiple threads in a warp can improve performance while not requiring expensive pre-processing. The presented ray-traversal method exhibits improved traversal performance especially for increasingly incoherent rays.}, language = {en} } @inproceedings{LauxErdődiSelgrad, author = {Laux, Lea and Erdődi, L{\´a}szl{\´o} and Selgrad, Kai}, title = {Trust as the Elephant in the Room: Security Evaluation of Decentralized Online Social Networks with Mastodon}, series = {Norsk IKT-konferanse for forskning og utdanning}, booktitle = {Norsk IKT-konferanse for forskning og utdanning}, number = {3}, abstract = {Federated online social networks are an alternative to centralized and often profit-driven social networks. Instead of providing exactly one main platform, federated and decentralized approaches consist of multiple platforms, nodes or instances, leading to new challenges for guaranteeing confidentiality, integrity and availability. In addition, privacy is taken into close consideration due to the sensitive nature of processed personal data and the purpose of online social networks as well as the user behavior on social media. The recent popularity and broad use of the federated micro-blogging platform Mastodon issues the matter of security and privacy challenges for this type of architecture and the specific platform as well. Mastodon is part of a larger network called Fediverse with several platforms with different purposes. Communication and interoperability between Fediverse platforms is mostly achieved by ActivityPub protocol as standard for decentralized social networking, defined by W3C. We analyze Mastodon as the currently most prominent and largest example of a Fediverse platform. Therefore, we perform tests for typical types of software vulnerabilities as well as evaluate common security challenges built into its design. As a result, we identify trust as security principle as critical issue, leading to multiple weak points such as enabling attackers and malicious actors to spread misleading information as well as network availability impacts. We suggest possible solutions customized to our findings as well as general security recommendations when building a federated online social network such as the Fediverse}, language = {en} } @inproceedings{BaumannPohlSelgrad, author = {Baumann, Timo and Pohl, Martin and Selgrad, Kai}, title = {Einf{\"u}hrung und erste Evaluation des Selbstlernkonzepts CodeClinic an der OTH Regensburg}, series = {Tagungsband MINT Symposium 2025. Zukunft MINT Lehre: Was bleibt? Was kommt? Was wirkt?}, booktitle = {Tagungsband MINT Symposium 2025. Zukunft MINT Lehre: Was bleibt? Was kommt? Was wirkt?}, editor = {Sch{\"a}fle, Claudia and D{\"o}lling, Hanna}, publisher = {BayZiel - Bayerisches Zentrum f{\"u}r Innovative Lehre}, address = {M{\"u}nchen}, issn = {1612-4537}, doi = {10.35096/othr/pub-8613}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-86138}, pages = {9}, abstract = {Mit der CodeClinic wollen wir das Programmieren-Lernen - eine der großen Einstiegsh{\"u}rden in Informatik- und informatiknahen Studieng{\"a}ngen - in einen Prozess {\"u}berf{\"u}hren, der das gemeinschaftliche Lernen in der Hochschullehre st{\"a}rker als bisher in den Vordergrund r{\"u}ckt. Davon profitieren Studierende in ihrer fachlichen und pers{\"o}nlichen Entwicklung, und das Lernumfeld spiegelt die tats{\"a}chliche Realit{\"a}t der beruflichen Praxis besser wider. Wir unterst{\"u}tzen dieses Konzept durch einen f{\"u}r selbstgesteuertes und gemeinschaftliches Lernen ausgelegten SCALE-UP-Raum, den wir an der OTH Regensburg eingerichtet haben. In unserem Beitrag erl{\"a}utern wir Konzept und Raum und liefern eine erste Evaluation zum Erfolg unserer Maßnahmen.}, subject = {Hochschuldidaktik}, language = {de} }