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Local, Deformable Precomputed Radiance Transfer Peter-Pike Sloan, Ben Luna Microsoft Corporation John Snyder Microsoft Research.

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Presentation on theme: "Local, Deformable Precomputed Radiance Transfer Peter-Pike Sloan, Ben Luna Microsoft Corporation John Snyder Microsoft Research."— Presentation transcript:

1 Local, Deformable Precomputed Radiance Transfer Peter-Pike Sloan, Ben Luna Microsoft Corporation John Snyder Microsoft Research

2 Local Global Illumination Renders GI effects on local details Neglects gross shadowing Rotates transfer model

3 Local Global Illumination OriginalRay TracedRotated

4 Bat Demo

5 illuminateresponse Transfer Vector Precomputed Radiance Transfer (PRT)

6 Related Work: Area Lighting [Kautz2004] [James2003] [Ramamoorthi2001] [Sloan2002] [Ng2003] [Liu2004;Wang2004] [Sloan2003] [Muller2004] [Zhou2005]

7 Other Related Work Directional Lighting – [Malzbender2001],[Ashikhmin2002] – [Heidrich2000] – [Max1988],[Dana1999] Ambient Occlusion – [Miller1994],[Phar2004] – [Kontkanen2005],[Bunnel2005] Environmental Lighting – [McCallister2002]

8 Spherical Harmonics (SH) Spherical Analog to the Fourier basis Used extensively in graphics – [Kajiya84;Cabral87;Sillion91;Westin92;Stam95] Polynomials in R 3 restricted to sphere projection reconstruction

9 Spherical Harmonics (SH) Spherical Analog to the Fourier basis Used extensively in graphics – [Kajiya84;Cabral87;Sillion91;Westin92;Stam95] Polynomials in R 3 restricted to sphere projection reconstruction

10 Low Frequency Lighting order 1 order 2 order 4 order 8order 16order 32original

11 SH Rotational Invariance rotate SH

12 Spherical Harmonics (SH) n th order, n 2 coefficients Evaluation O(n 2 )

13 Zonal Harmonics (ZH) Polynomials in Z Circular Symmetry

14 SH Rotation Structure O(n 3 ) Too Slow!

15 ZH Rotation Structure O(n 2 )

16 Whats that column? Rotate delta function so that z z : Evaluate delta function at z = (0,0,1) Rotating scales column C by d l – Equals y(z ) due to rotation invariance z z

17 Whats that column? Rotate delta function so that z z : Evaluate delta function at z = (0,0,1) Rotating scales column C by d l – Equals y(z ) due to rotation invariance z z

18 Efficient ZH Rotation z g(s)g(s)

19 z g(s)g(s)

20 z z g(s)g(s) g (s)

21 Efficient ZH Rotation z z g(s)g(s) g (s)

22 Efficient ZH Rotation z z g(s)g(s) g (s)

23 Transfer Approx. Using ZH Approximate transfer vector t by sum of N lobes +++

24 Transfer Approx. Using ZH Approximate transfer vector t by sum of N lobes

25 Transfer Approx. Using ZH Approximate transfer vector t by sum of N lobes Minimize squared error over the sphere

26 Single Lobe Solution For known direction s*, closed form solution Optimal linear direction is often good – Reproduces linear, formed by gradient of linear terms – Well behaved under interpolation – Cosine weighted direction of maximal visibility in AO

27 Multiple Lobes

28 Random vs. PRT Signals

29 Energy Distribution of Transfer Signals

30 Energy Distribution and Subsurface Scatter

31 Rendering Rotate lobe axis, reconstruct transfer and dot with lighting Care must be taken when interpolating – Non-linear parameters – Lobe correspondence with multiple-lobes

32 Light Specialized Rendering

33

34

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36 O(N n 2 ) O(N n) Quadratic QuinticQuartic Cubic

37 Generating LDPRT Models PRT simulation over mesh – texture: specify patch (a) – per-vertex: specify mesh (b) Parameterized models – ad-hoc using intuitive parameters (c) – fit to simulation data (d) (a) LDPRT texture (b) LDPRT mesh (c) thin-membrane model (d) wrinkle model

38 LDPRT Texture Pipeline Start with tileable heightmap Simulate 3x3 grid Extract and fit LDPRT Store in texture maps

39 Thin Membrane Model Single degree of freedom (DOF) – optical thickness: light bleed in negative normal direction

40 Wrinkle Model Two DOF – Phase, position along canonical wrinkle

41 Wrinkle Model Two DOF – Phase, position along canonical wrinkle – Amplitude, max magnitude of wrinkle

42 Wrinkle Model Fit Compute several simulations – 64 discrete amplitudes – 255 unique points in phase Fit 32x32 textures – One optimization for all DOF simultaneously – Optimized for bi-linear reconstruction – 3 lobes

43 Glossy LDPRT Use separable BRDF Encode each row of transfer matrix using multiple lobes (3 lobes, 4 th order lighting) See paper for details

44 Demo

45 Conclusions/Future Work local global illumination effects – soft shadows, inter-reflections, translucency easy-to-rotate rep. for spherical functions – sums of rotated zonal harmonics – allows dynamic geometry, real-time performance – may be useful in other applications [Zhou2005] future work: non-local effects – articulated characters

46 Acknowledgements Demos/Art: John Steed, Shanon Drone, Jason Sandlin Video: David Thiel Graphics Cards: Matt Radeki Light Probes: Paul Debevec


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