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Precomputed Shadow Fields for Dynamic ScenesPrecomputed Shadow Fields for Dynamic Scenes

Kun Zhou Yaohua Hu Stephen Lin Baining Guo Heung-Yeung Shum

Microsoft Research Asia

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Outline

• Introduction

• Method Overview

• Detail

• Results

• Introduction

• Method Overview

• Detail

• Results

Introduction

Soft Shadow:multiple shadow maps -[Heckbert and Herf] 1997

Exntnd shadow volume -[Assarsson and Akenine-Moller] 2003

Fake approach -[Chan and Durand] 2003

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Introduction

Why this is not good?

For a dynamic scene: -scene complexity -recomputed for each frame

For illuminants: -point-like or small light source

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Introduction

PRT (Precomputed Radiance Transfer):

based on two main assumptions: 1.all objects in the scene are non-emitters2.the incoming light direction is independent with the position of a point x

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Introduction

PRT (Precomputed Radiance Transfer):These spherical functions can be compressed by using some basis functions:

Spherical harmonics Wavelet

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Introduction

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• Introduction

• Method Overview

• Detail

• Results

Method Overview

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Method Overview

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Compute Incoming radiance of each point

Method Overview

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Compute Occlusion Field for each Object

Method Overview

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Compute Occlusion Field for each Object

Method Overview

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Compute Occlusion Field for each Object

Method Overview

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Compute Occlusion Field for each Object

Method Overview

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Compute radiance field for each Light Source

Method Overview

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Compute Radiance Field for each Light Source

Method Overview

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multiply these and self-visibility at the point together

=> Incident radiance distribution

Method Overview

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Combine with the BRDF to get the final radiance at the point

Method Overview

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Combine with the BRDF to get the final radiance at the point

• Introduction

• Method Overview

• Detail

• Results

Detail

SRF and OOF Precomputation

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Detail

Data SamplingFor low frequency shadow: 16 concentric spheresFor all frequency shadow: 32 concentric spheres

Intermediate points: trilinear interpolation with 8 nearest samples

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Detail

Data CompressionHow?approximate the function using basis functions

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Detail

Data CompressionFor low frequency shadow: Spherical harmonics

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Detail

Data CompressionSpherical harmonics reconstruction

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Detail

Data CompressionSpherical harmonics has two properties:1.Rotationaly invariant

2.Integrating the product of two SH functions = a dot product of their coefficients.

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Detail

Data CompressionFor all frequency shadow: Wavelet Basis

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Detail

Data CompressionSpherical harmonics VS Wavelet

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Detail

Incident Radiance Computation

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Detail

Soft Shadow Rendering

Acceleration -Culling

-Lazy Occlusion Updating occluders for a specific light source remain unchanged, the

cached visibility can be reused

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• Introduction

• Method Overview

• Detail

• Results

Results

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