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Willard Marriott Digital Library MODULAR RADIANCE TRANSFER by Bradford J Loos A dissertation submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Computing School of Computing The University of Utah May 2015 Copyright © Bradford J Loos 2015 All Rights Reserved T h e U n i v e r s i t y o f U t a h G r a d u a t e S c h o o l STATEMENT OF DISSERTATION APPROVAL The dissertation of Bradford J Loos has been approved by the following supervisory committee members: Peter-Pike Sloan Co-Chair 1 1 /2 5 /2 0 1 4 Date Approved Charles Hansen Co-Chair 1 1 /2 5 /2 0 1 4 Date Approved Adam Bargteil Member 1 1 /2 5 /2 0 1 4 Date Approved Peter Shirley Member 1 1 /2 5 /2 0 1 4 Date Approved C em Y uksel Member 1 1 /2 5 /2 0 1 4 Date Approved and by Ross Whitaker Chair /Dean of the Department/College/School of C om p u tin g and by David B. Kieda, Dean of The Graduate School. ABSTRACT Real-time global illumination is the next frontier in real-time rendering. In an attempt to generate realistic images, games have followed the film industry into physically based shading and will soon begin integrating global illumination techniques. Traditional methods require too much memory and too much time to compute for real-time use. With Modular and Delta Radiance Transfer we precompute a scene-independent, low-frequency basis that allows us to calculate complex indirect lighting calculations in a much lower dimensional subspace with a reduced memory footprint and real-time execution. The results are then applied as a light map on many different scenes. To improve the low frequency results, we also introduce a novel screen space ambient occlusion technique that allows us to generate a smoother result with fewer samples. These three techniques, low and high frequency used together, provide a viable indirect lighting solution that can be run in milliseconds on today's hardware, providing a useful new technique for indirect lighting in real-time graphics. CONTENTS A B S T R A C T ................................................................................................................................ iii A C K N O W L E D G M E N T S .................................................................................................... vi C H A P T E R S 1......I N T R O D U C T I O N ........................................................................................................... 1 2. B A C K G R O U N D .............................................................................................................. 3 2.1 R adiom etry.................................................................................................................... 3 2.2 The Rendering Equation............................................................................................. 5 2.3 The First Global Illumination M e th o d .................................................................... 6 2.4 Traditional Global Illumination M eth od s............................................................... 7 2.5 Real-Time Global Illum ination.................................................................................. 9 2.6 Issues ................................................................................................................................ 16 3. M O D U L A R R A D IA N C E T R A N S F E R ............................................................... 17 3.1 Introduction .................................................................................................................. 17 3.2 Preliminaries .................................................................................................................. 19 3.3 Reduced Direct-to-Indirect Transfer ........................................................................ 21 3.4 Direct-to-Indirect Transfer Between Shapes .......................................................... 23 3.5 Direct-to-Indirect Transfer on Real Scenes ............................................................. 25 3.6 Implementation and R esu lts...................................................................................... 28 3.7 Discussion ....................................................................................................................... 34 4. M R T R U N T IM E IM P L E M E N T A T IO N ............................................................... 38 4.1 U Basis Functions......................................................................................................... 38 4.2 Interface F unctions....................................................................................................... 40 4.3 Mapping MRT to L evels............................................................................................. 43 4.4 b-coefficients.................................................................................................................. 44 4.5 r-coefficients .................................................................................................................. 46 4.6 Lightmap Padding ......................................................................................................... 48 4.7 Results .............................................................................................................................. 48 5. D E L TA R A D IA N C E T R A N S F E R ........................................................................... 50 5.1 Introduction .................................................................................................................. 50 5.2 Background - Modular Radiance Transport.......................................................... 52 5.3 Indirect Occlusions and Interreflections ................................................................. 55 5.4 Implementation D etails............................................................................................... 59 5.5 D iscussion....................................................................................................................... 62 6. V O L U M E T R IC O B S C U R A N C E ............................................................................. 63 6.1 Introduction .................................................................................................................. 63 6.2 Obscurance and Ambient O cclu sion ........................................................................ 64 6.3 Volumetric Obscurance............................................................................................... 65 6.4 Results.............................................................................................................................. 70 7. F U T U R E W O R K .............................................................................................................. 72 7.1 Modeling T o o ls .............................................................................................................. 72 7.2 Directability .................................................................................................................. 72 7.3 Real-time AO and Global Illumination.................................................................... 73 7.4 High Frequency Indirect Lighting............................................................................. 73 8. C O N C L U S IO N .................................................................................................................. 74 APPENDICES A . B A S IS E N R I C H M E N T ............................................................................................... 76 B. Q U A D R A T IC SH T O H E M IS P H E R IC A L L IN E A R S H ............................ 78 R E F E R E N C E S ......................................................................................................................... 79 v ACKNOWLEDGMENTS There are many people I’d like to thank for helping me in my long journey to this point. Kathy Loos, who always strove to introduce me to new technology as it came out, from our first VCR to our first Macintosh. Brandon Anderson, who explained to me why DB2 was different than actually program­ ming a computer, resulting in my first programming class. Craig Snow, for introducing me to a debugger, and many, many conversations on software engineering practice over the years. Pete Shirley, who, many years before I started my graduate studies, introduced me to the idea of research programming and graphics research in general. And last, but not least, my advisor Peter-Pike Sloan, whose tireless dedication to the field has given me limitless sources of inspiration and without whom, this work would have never come to fruition. CHAPTER 1 INTRODUCTION Indirection illumination is a highly desirable feature of realism in computer generated imagery. However, its global nature makes it difficult to compute in real-time. Despite the difficulty, many games are currently attempting to produce global illumination solutions using varying techniques. Most are simple techniques, unlike the fully dynamic systems talked about in academia. Games generally use precomputed global illumination stored in light maps (otherwise known as static baked global lighting) or ambient occlusion as well as placing nonshadowing static lights to fill in areas of shadow. In live-action films, reflectors and bounce cards are used to reflect