Neural Two-Level Monte Carlo Real-Time Rendering.

Johannes Hanika Johannes Schudeiske Karlsruhe Institute of Technology, Germany Ulm University, Germany https://jo.dreggn.org/home/ https://cg.ivd.kit.edu/english/staff_649.php https://orcid.org/0000-0002-7648-1782 https://gepris.dfg.de/gepris/person/431478107

Mikhail Dereviannykh Dmitrii Klepikov Johannes Hanika Carsten Dachsbacher Neural Two-Level Monte Carlo Real-Time Rendering. 2025 44 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.70050 db/journals/cgf/cgf44.html#DereviannykhKHD25 streams/journals/cgf

Lucas Domingo Alber Johannes Hanika Carsten Dachsbacher Real-Time Markov Chain Path Guiding for Global Illumination and Single Scattering. 15:1-15:18 2025 May 8 Proc. ACM Comput. Graph. Interact. Tech. 1 https://doi.org/10.1145/3728296 db/journals/pacmcgit/pacmcgit8.html#AlberHD25 streams/journals/pacmcgit

Moritz Grauer Johannes Hanika Carsten Dachsbacher Minimizing Ray Tracing Memory Traffic through Quantized Structures and Ray Stream Tracing. 2025 May abs/2505.24653 CoRR https://doi.org/10.48550/arXiv.2505.24653 db/journals/corr/corr2505.html#abs-2505-24653 streams/journals/corr

Vincent Schüßler Johannes Hanika Carsten Dachsbacher Bridge Sampling for Connections via Multiple Scattering Events. i-x 2024 July 43 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.15160 db/journals/cgf/cgf43.html#SchusslerHD24 streams/journals/cgf

Reiner Dolp Johannes Hanika Carsten Dachsbacher A Fast GPU Schedule For À-Trous Wavelet-Based Denoisers. 15:1-15:18 2024 May 7 Proc. ACM Comput. Graph. Interact. Tech. 1 https://doi.org/10.1145/3651299 db/journals/pacmcgit/pacmcgit7.html#DolpHD24 streams/journals/pacmcgit

Luca Fascione Johannes Hanika A Study of Observer Metamerism for Reflectance-induced Stimuli. 2024 MAM/MANER@ESGR https://doi.org/10.2312/mam.20241176 conf/mam/2024 db/conf/mam/mam2024.html#FascioneH24

Hisanari Otsu Killian Herveau Johannes Hanika Derek Nowrouzezahrai Carsten Dachsbacher Regional Adaptive Metropolis Light Transport. 2024 abs/2402.08273 CoRR https://doi.org/10.48550/arXiv.2402.08273 db/journals/corr/corr2402.html#abs-2402-08273

Mikhail Dereviannykh Dmitrii Klepikov Johannes Hanika Carsten Dachsbacher Neural Two-Level Monte Carlo Real-Time Rendering. 2024 abs/2412.04634 CoRR https://doi.org/10.48550/arXiv.2412.04634 db/journals/corr/corr2412.html#abs-2412-04634 streams/journals/corr

Addis Dittebrandt Vincent Schüssler Johannes Hanika Sebastian Herholz Carsten Dachsbacher Markov Chain Mixture Models for Real-Time Direct Illumination. i-x 2023 July 42 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.14881 db/journals/cgf/cgf42.html#DittebrandtSHHD23

Marc Droske Johannes Hanika Jirí Vorba Andrea Weidlich Manuele Sabbadin Path tracing in Production: The Path of Water. 12:1-12:66 2023 SIGGRAPH Courses https://doi.org/10.1145/3587423.3595519 conf/siggraph/2023courses db/conf/siggraph/siggraph2023courses.html#DroskeHVWS23

Vincent Schüssler Johannes Hanika Alisa Jung Carsten Dachsbacher Path Guiding with Vertex Triplet Distributions. 1-15 2022 41 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.14582 db/journals/cgf/cgf41.html#SchusslerHJD22

Johannes Hanika Andrea Weidlich Marc Droske Once-more scattered next event estimation for volume rendering. 17-28 2022 41 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.14583 db/journals/cgf/cgf41.html#HanikaWD22

Weizhen Huang Matthias B. Hullin Johannes Hanika A Microfacet-based Hair Scattering Model. 79-91 2022 41 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.14588 https://www.wikidata.org/entity/Q113389148 db/journals/cgf/cgf41.html#HuangHH22

Weizhen Huang Matthias B. Hullin Johannes Hanika Scattering from Elliptical Hair Fibers Based on Microfacet Theory. 43:1-43:2 2022 SIGGRAPH Posters https://doi.org/10.1145/3532719.3543236 conf/siggraph/2022posters db/conf/siggraph/siggraph2022posters.html#HuangHH22

Philippe Weier Marc Droske Johannes Hanika Andrea Weidlich Jirí Vorba Optimised Path Space Regularisation. 139-151 2021 40 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.14347 db/journals/cgf/cgf40.html#WeierDHWV21

Andrea Weidlich Alex Forsythe Scott Dyer Thomas Mansencal Johannes Hanika Alexander Wilkie Luke Emrose Anders Langlands Spectral imaging in production: course notes Siggraph 2021. 14:1-14:90 2021 SIGGRAPH Courses https://doi.org/10.1145/3450508.3464582 conf/siggraph/2021courses db/conf/siggraph/siggraph2021courses.html#WeidlichFDMHWEL21

Alisa Jung Johannes Hanika Carsten Dachsbacher Spectral Mollification for Bidirectional Fluorescence. 373-384 2020 39 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.13937 db/journals/cgf/cgf39.html#JungHD20

Lorenzo Tessari Johannes Hanika Carsten Dachsbacher Marc Droske Temporal Normal Distribution Functions. 1-12 2020 EGSR (DL) https://doi.org/10.2312/sr.20201132 conf/rt/2020dl db/conf/rt/dl2020.html#TessariHDD20 Addis Dittebrandt Johannes Hanika Carsten Dachsbacher Temporal Sample Reuse for Next Event Estimation and Path Guiding for Real-Time Path Tracing. 39-51 2020 EGSR (DL) https://doi.org/10.2312/sr.20201135 conf/rt/2020dl db/conf/rt/dl2020.html#DittebrandtHD20 Hisanari Otsu Johannes Hanika Carsten Dachsbacher Portal-Based Path Perturbation for Metropolis Light Transport. 19-27 2020 VMV https://doi.org/10.2312/vmv.20201184 conf/vmv/2020 db/conf/vmv/vmv2020.html#OtsuHD20

Wenzel Jakob Johannes Hanika A Low-Dimensional Function Space for Efficient Spectral Upsampling. 147-155 2019 38 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.13626 https://www.wikidata.org/entity/Q127750921 db/journals/cgf/cgf38.html#JakobH19

Alisa Jung Alexander Wilkie Johannes Hanika Wenzel Jakob Carsten Dachsbacher Wide Gamut Spectral Upsampling with Fluorescence. 87-96 2019 38 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.13773 db/journals/cgf/cgf38.html#JungWHJD19

Christoph Peters 0002 Sebastian Merzbach Johannes Hanika Carsten Dachsbacher Using moments to represent bounded signals for spectral rendering. 136:1-136:14 2019 38 ACM Trans. Graph. 4 https://doi.org/10.1145/3306346.3322964 db/journals/tog/tog38.html#PetersMHD19

Christoph Peters 0002 Sebastian Merzbach Johannes Hanika Carsten Dachsbacher Spectral Rendering with the Bounded MESE and sRGB Data. 1-5 2019 MAM@EGSR https://doi.org/10.2312/mam.20191304 conf/mam/2019 db/conf/mam/mam2019.html#PetersMHD19 Jirí Vorba Johannes Hanika Sebastian Herholz Thomas Müller 0013 Jaroslav Krivánek Alexander Keller 0001 Path guiding in production. 18:1-18:77 2019 SIGGRAPH Courses https://doi.org/10.1145/3305366.3328091 conf/siggraph/2019courses db/conf/siggraph/siggraph2019courses.html#VorbaHHMKK19 Luca Fascione Johannes Hanika Daniel Heckenberg Christopher D. Kulla Marc Droske Jorge Schwarzhaupt Path tracing in production: part 1: modern path tracing. 19:1-19:113 2019 SIGGRAPH Courses https://doi.org/10.1145/3305366.3328079 conf/siggraph/2019courses db/conf/siggraph/siggraph2019courses.html#FascioneHHKDS19 Wenzel Jakob Andrea Weidlich Andrew Beddini Rob Pieké Hanzhi Tang Luca Fascione Johannes Hanika Path tracing in production: part 2: making movies. 20:1-20:41 2019 SIGGRAPH Courses https://doi.org/10.1145/3305366.3328085 https://www.wikidata.org/entity/Q131109911 conf/siggraph/2019courses db/conf/siggraph/siggraph2019courses.html#JakobWBPTFH19

Jan Novák Iliyan Georgiev Johannes Hanika Wojciech Jarosz Monte Carlo Methods for Volumetric Light Transport Simulation. 551-576 2018 37 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.13383 https://www.wikidata.org/entity/Q129799592 db/journals/cgf/cgf37.html#NovakGHJ18

Tobias Zirr Johannes Hanika Carsten Dachsbacher Re-Weighting Firefly Samples for Improved Finite-Sample Monte Carlo Estimates. 410-421 2018 37 Comput. Graph. Forum 6 https://doi.org/10.1111/cgf.13335 db/journals/cgf/cgf37.html#ZirrHD18

Luca Fascione Johannes Hanika Mark Leone Marc Droske Jorge Schwarzhaupt Tomás Davidovic Andrea Weidlich Johannes Meng Manuka: A Batch-Shading Architecture for Spectral Path Tracing in Movie Production. 31 2018 37 ACM Trans. Graph. 3 https://doi.org/10.1145/3182161 db/journals/tog/tog37.html#FascioneHLDSDWM18

Florian Reibold Johannes Hanika Alisa Jung Carsten Dachsbacher Selective guided sampling with complete light transport paths. 223 2018 37 ACM Trans. Graph. 6 https://doi.org/10.1145/3272127.3275030 https://www.wikidata.org/entity/Q128853707 db/journals/tog/tog37.html#ReiboldHJD18

Hisanari Otsu Johannes Hanika Toshiya Hachisuka Carsten Dachsbacher Geometry-aware metropolis light transport. 278 2018 37 ACM Trans. Graph. 6 https://doi.org/10.1145/3272127.3275106 https://www.wikidata.org/entity/Q128852448 db/journals/tog/tog37.html#OtsuHHD18

Alisa Jung Johannes Hanika Steve Marschner Carsten Dachsbacher A Simple Diffuse Fluorescent BBRRDF Model. 15-18 2018 MAM@EGSR https://doi.org/10.2312/mam.20181193 https://dl.acm.org/citation.cfm?id=3297784 conf/rt/2018mam db/conf/rt/mam2018.html#JungHMD18 Jan Novák Iliyan Georgiev Johannes Hanika Jaroslav Krivánek Wojciech Jarosz Monte Carlo methods for physically based volume rendering. 14:1 2018 SIGGRAPH Courses https://doi.org/10.1145/3214834.3214880 conf/siggraph/2018courses db/conf/siggraph/siggraph2018courses.html#NovakGHKJ18 Luca Fascione Johannes Hanika Rob Pieké Ryusuke Villemin Christophe Hery Manuel N. Gamito Luke Emrose André Mazzone Path tracing in production. 15:1-15:79 2018 SIGGRAPH Courses https://doi.org/10.1145/3214834.3214864 conf/siggraph/2018courses db/conf/siggraph/siggraph2018courses.html#FascioneHPVHGEM18

Pascal Weber Johannes Hanika Carsten Dachsbacher Multiple Vertex Next Event Estimation for Lighting in dense, forward-scattering Media. 21-30 2017 36 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.13103 db/journals/cgf/cgf36.html#WeberHD17

Florian Simon Johannes Hanika Tobias Zirr Carsten Dachsbacher Line Integration for Rendering Heterogeneous Emissive Volumes. 101-110 2017 36 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.13228 db/journals/cgf/cgf36.html#SimonHZD17

Hisanari Otsu Anton S. Kaplanyan Johannes Hanika Carsten Dachsbacher Toshiya Hachisuka Fusing state spaces for markov chain Monte Carlo rendering. 74:1-74:10 2017 36 ACM Trans. Graph. 4 https://doi.org/10.1145/3072959.3073691 db/journals/tog/tog36.html#OtsuKHDH17

Vincent Schüssler Eric Heitz Johannes Hanika Carsten Dachsbacher Microfacet-based normal mapping for robust Monte Carlo path tracing. 205:1-205:12 2017 36 ACM Trans. Graph. 6 https://doi.org/10.1145/3130800.3130806 db/journals/tog/tog36.html#SchusslerHHD17

Lorenzo Tessari Johannes Hanika Carsten Dachsbacher Local Quasi-Monte Carlo Exploration. 71-81 2017 EGSR (EI&I) https://doi.org/10.2312/sre.20171196 conf/rt/2017eii db/conf/rt/eii2017.html#TessariHD17 Luca Fascione Johannes Hanika Marcos Fajardo Per H. Christensen Brent Burley Brian Green Path tracing in production - part 1: production renderers. 13:1-13:39 2017 SIGGRAPH Courses https://doi.org/10.1145/3084873.3084904 conf/siggraph/2017courses db/conf/siggraph/siggraph2017courses.html#FascioneHFCBG17 Luca Fascione Johannes Hanika Rob Pieké Christophe Hery Ryusuke Villemin Thorsten-Walther Schmidt Christopher D. Kulla Daniel Heckenberg André Mazzone Path tracing in production - part 2: making movies. 15:1-15:32 2017 SIGGRAPH Courses https://doi.org/10.1145/3084873.3084906 conf/siggraph/2017courses db/conf/siggraph/siggraph2017courses.html#FascioneHPHVSKH17

Johannes Meng Johannes Hanika Carsten Dachsbacher Improving the Dwivedi Sampling Scheme. 37-44 2016 35 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.12947 db/journals/cgf/cgf35.html#MengHD16

Emanuel Schrade Johannes Hanika Carsten Dachsbacher Sparse high-degree polynomials for wide-angle lenses. 89-97 2016 35 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.12952 db/journals/cgf/cgf35.html#SchradeHD16

Eric Heitz Johannes Hanika Eugene d'Eon Carsten Dachsbacher Multiple-scattering microfacet BSDFs with the Smith model. 58:1-58:14 2016 35 ACM Trans. Graph. 4 https://doi.org/10.1145/2897824.2925943 db/journals/tog/tog35.html#HeitzHdD16

Nicolas Holzschuch Anton Kaplanyan Johannes Hanika Carsten Dachsbacher Estimating local Beckmann roughness for complex BSDFs. 66:1-66:2 2016 SIGGRAPH Talks https://doi.org/10.1145/2897839.2927416 conf/siggraph/2016talks db/conf/siggraph/siggraph2016talks.html#HolzschuchKHD16

Florian Simon Johannes Hanika Carsten Dachsbacher Rich-VPLs for Improving the Versatility of Many-Light Methods. 575-584 2015 34 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.12585 db/journals/cgf/cgf34.html#SimonHD15

Johannes Meng Florian Simon Johannes Hanika Carsten Dachsbacher Physically Meaningful Rendering using Tristimulus Colours. 31-40 2015 34 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.12676 db/journals/cgf/cgf34.html#MengSHD15

Johannes Hanika Anton Kaplanyan Carsten Dachsbacher Improved Half Vector Space Light Transport. 65-74 2015 34 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.12679 db/journals/cgf/cgf34.html#HanikaKD15

Johannes Hanika Marc Droske Luca Fascione Manifold Next Event Estimation. 87-97 2015 34 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.12681 db/journals/cgf/cgf34.html#HanikaDF15

Alexander Keller 0001 Luca Fascione Marcos Fajardo Iliyan Georgiev Per H. Christensen Johannes Hanika Christian Eisenacher Gregory Nichols The path tracing revolution in the movie industry. 24:1-24:7 2015 SIGGRAPH Courses https://doi.org/10.1145/2776880.2792699 conf/siggraph/2015courses db/conf/siggraph/siggraph2015courses.html#KellerFFGCHEN15

Johannes Hanika Carsten Dachsbacher Efficient Monte Carlo rendering with realistic lenses. 323-332 2014 33 Comput. Graph. Forum 2 https://doi.org/10.1111/cgf.12301 db/journals/cgf/cgf33.html#HanikaD14

Alexander Wilkie S. Nawaz Marc Droske Andrea Weidlich Johannes Hanika Hero Wavelength Spectral Sampling. 123-131 2014 33 Comput. Graph. Forum 4 https://doi.org/10.1111/cgf.12419 db/journals/cgf/cgf33.html#WilkieNDWH14

Anton S. Kaplanyan Johannes Hanika Carsten Dachsbacher The natural-constraint representation of the path space for efficient light transport simulation. 102:1-102:13 2014 33 ACM Trans. Graph. 4 https://doi.org/10.1145/2601097.2601108 db/journals/tog/tog33.html#KaplanyanHD14

Eugene d'Eon Steve Marschner Johannes Hanika A fiber scattering model with non-separable lobes. 46:1 2014 SIGGRAPH Talks https://doi.org/10.1145/2614106.2614161 conf/siggraph/2014talks db/conf/siggraph/siggraph2014talks.html#dEonMH14 Eugene d'Eon Steve Marschner Johannes Hanika Importance sampling for physically-based hair fiber models. 25:1-25:4 2013 SIGGRAPH ASIA Technical Briefs https://doi.org/10.1145/2542355.2542386 conf/siggraph/2013asiatb db/conf/siggraph/siggraph2013asiatb.html#dEonMH13

Christoph Rößing Johannes Hanika Hendrik P. A. Lensch Real-Time Disparity Map-Based Pictorial Depth Cue Enhancement. 275-284 2012 31 Comput. Graph. Forum 2pt1 https://doi.org/10.1111/j.1467-8659.2012.03006.x db/journals/cgf/cgf31.html#RossingHL12

Matthias B. Hullin Johannes Hanika Wolfgang Heidrich Polynomial Optics: A Construction Kit for Efficient Ray-Tracing of Lens Systems. 1375-1383 2012 31 Comput. Graph. Forum 4 https://doi.org/10.1111/j.1467-8659.2012.03132.x db/journals/cgf/cgf31.html#HullinHH12

Johannes Hanika Peter Hillman 0001 Martin Hill Luca Fascione Camera space volumetric shadows. 7-14 2012 DigiPro https://doi.org/10.1145/2370919.2370921 conf/digipro/2012 db/conf/digipro/digipro2012.html#HanikaHHF12

B. Steinert Holger Dammertz Johannes Hanika Hendrik P. A. Lensch General Spectral Camera Lens Simulation. 1643-1654 2011 30 Comput. Graph. Forum 6 https://doi.org/10.1111/j.1467-8659.2011.01851.x db/journals/cgf/cgf30.html#SteinertDHL11

Johannes Hanika Holger Dammertz Hendrik P. A. Lensch Edge-Optimized À-Trous Wavelets for Local Contrast Enhancement with Robust Denoising. 1879-1886 2011 30 Comput. Graph. Forum 7 https://doi.org/10.1111/j.1467-8659.2011.02054.x db/journals/cgf/cgf30.html#HanikaDL11

Johannes Hanika Spectral light transport simulation using a precision-based ray tracing architecture. 2010 University of Ulm 1-153 http://vts.uni-ulm.de/docs/2011/7539/vts_7539_10763.pdf https://nbn-resolving.org/urn:nbn:de:bsz:289-vts-75394 https://d-nb.info/1010436449 https://d-nb.info/1016626142

Matthias B. Hullin Johannes Hanika Boris Ajdin Hans-Peter Seidel Jan Kautz Hendrik P. A. Lensch Acquisition and analysis of bispectral bidirectional reflectance and reradiation distribution functions. 2010 29 ACM Trans. Graph. 4 https://doi.org/10.1145/1778765.1778834 https://doi.org/10.1145/1833349.1778834 https://doi.org/10.1145/1833351.1778834 db/journals/tog/tog29.html#HullinHASKL10 97:1-97:7

Holger Dammertz Daniel Sewtz Johannes Hanika Hendrik P. A. Lensch Edge-avoiding À-Trous wavelet transform for fast global illumination filtering. 67-75 2010 High Performance Graphics https://doi.org/10.2312/EGGH/HPG10/067-075 http://dl.acm.org/citation.cfm?id=1921491 conf/egh/2010 db/conf/egh/hpg2010.html#DammertzSHL10 Johannes Hanika Alexander Keller 0001 Hendrik P. A. Lensch Two-level ray tracing with reordering for highly complex scenes. 145-152 2010 Graphics Interface http://portal.acm.org/citation.cfm?id=1839241&CFID=37966912&CFTOKEN=40351478 conf/graphicsinterface/2010 db/conf/graphicsinterface/graphicsinterface2010.html#HanikaKL10 Stefan Menz Holger Dammertz Johannes Hanika Michael Weber 0001 Hendrik P. A. Lensch Graphical Interface Models for Procedural Mesh Growing. 17-24 2010 VMV https://doi.org/10.2312/PE/VMV/VMV10/017-024 conf/vmv/2010 db/conf/vmv/vmv2010.html#MenzDHWL10

Holger Dammertz Johannes Hanika Plane Sampling for Light Paths from the Environment Map. 25-31 2009 14 J. Graphics, GPU, & Game Tools 2 https://doi.org/10.1080/2151237X.2009.10129280 db/journals/jgtools/jgtools14.html#DammertzH09

Holger Dammertz Johannes Hanika Alexander Keller 0001 Shallow Bounding Volume Hierarchies for Fast SIMD Ray Tracing of Incoherent Rays. 1225-1233 2008 27 Comput. Graph. Forum 4 https://doi.org/10.1111/j.1467-8659.2008.01261.x db/journals/cgf/cgf27.html#DammertzHK08

Boris Ajdin Lucas Domingo Alber Andrew Beddini Brent Burley Per H. Christensen Carsten Dachsbacher Holger Dammertz Tomás Davidovic Eugene d'Eon Mikhail Dereviannykh Addis Dittebrandt Reiner Dolp Marc Droske Scott Dyer Christian Eisenacher Luke Emrose Marcos Fajardo Luca Fascione Alex Forsythe Manuel N. Gamito Iliyan Georgiev Moritz Grauer Brian Green Toshiya Hachisuka Daniel Heckenberg Wolfgang Heidrich Eric Heitz Sebastian Herholz Killian Herveau Christophe Hery Martin Hill Peter Hillman 0001 Nicolas Holzschuch Weizhen Huang Matthias B. Hullin Wenzel Jakob Wojciech Jarosz Alisa Jung Anton KaplanyanAnton S. Kaplanyan Jan Kautz Alexander Keller 0001 Dmitrii Klepikov Jaroslav Krivánek Christopher D. Kulla Anders Langlands Hendrik P. A. Lensch Mark Leone Thomas Mansencal Steve Marschner André Mazzone Johannes Meng Stefan Menz Sebastian Merzbach Thomas Müller 0013 S. Nawaz Gregory Nichols Jan Novák Derek Nowrouzezahrai Hisanari Otsu Christoph Peters 0002 Rob Pieké Florian Reibold Christoph Rößing Manuele Sabbadin Thorsten-Walther Schmidt Emanuel Schrade Vincent SchüsslerVincent Schüßler Jorge Schwarzhaupt Hans-Peter Seidel Daniel Sewtz Florian Simon B. Steinert Hanzhi Tang Lorenzo Tessari Ryusuke Villemin Jirí Vorba Michael Weber 0001 Pascal Weber Andrea Weidlich Philippe Weier Alexander Wilkie Tobias Zirr