Walter Course Sig 11 v 2

7/29/2019 Walter Course Sig 11 v 2

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Automatic Shader Bounding fEfficient Global Illumination

Bruce WalterCornell University

Course: Compiler Techniques for

Thursday August 11, 20


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Credit Based on group project:

Automatic Bounding of Programmable Shaders for EfficieGlobal Illumination, SIGGRAPH 2009 Edgar Velzquez-Armendriz

Shuang Zhao

Milo Haan

Bruce Walter Kavita Bala


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Motivation

Programmable shading Physically-based rend

Artistic control, flexibility

Manual lighting design

The Pumpkin Factory 2008

Limited material mod

Global illumination

Veach and


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About the Shaders

surface matte(colorKd) {

return Kd * max(dot(N,L),0);

}

Shader

Simple RenderMan-like example language

Material (surface) shader that implements a BRDFAllows arbitrary code within shader

Extensible to new material models


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Challenge

shade (point, light) color

sample (point) direction and probability

bound (points, lights) max color

G.I. needs additional related functions

surface matte(colorKd) {


}

Shader


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Contributions First step towards closing the gap

InterfaceProvides the functions G.I. needsInterval arithmetic

Automated compilerConverts the shaders to interval form

DemonstrationPhoton mapping

Multidimensional lightcuts


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Result PreviewPhoton mapping Multidimensional lightcu

Procedural Textures

Procedural varyingmaterial

Environment map lightingIndirect Illumination

Measured materiaPCA Reconstruc

Procedural varyingnormal


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Outline Introduction

Background and related work Interface between shaders and G.I.

Compiler

Results

Conclusions and future work


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Related Work Production shaders

Simplified G.I. [Tabellion and Lamorlette 2004]

Automatic simplification [Pellacini 2005]

GPU translation for relighting

[Pellacini et al. 2005, Ragan-Kelley et al. 2007]


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Related Work Interval methods

Ray Tracing [Synder 1992, Bala et al. 1999, Heidrich and Seidel 1998]

Tesselation [Moule and McCool 2002]

Culling

[Hasselgren and Akenine-Mller 2007,Hasselgren et al. 2009]

Affine Arithmetic [Comba and Stolfi 1993]


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Related Work Heidrich et al. 1998

High quality rasterization of textures

Hasselgren et al. 2009Subdivison surfaces pre-tessellation culling

Compiler with type propagation

Clarberg et al. 2010Performance optimization of interval code

Our focus is on enabling global illumination

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Background and related work Interface between shaders and G.I.

Compiler

Results



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Interface Functions needed

shade (point, viewDir, lightDir)

colorsample (point, viewDir) direction

bound (points, viewDirs, lightDirs) max color

Covers most Monte Carlo global illumination algorithneed versions for both eye and light tracing

multiple importance sampling needs related prob f


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Interface Shade (point, viewDir, lightDir)

Evaluate shading for single point and lightWritten by the user as shader program

Sample (point, viewDir)

Select outgoing direction with low noise

Needed by virtually all Monte Carlo rendering algo Bound (points, viewDirs, lightDirs)

Compute upper bound on shade for range of input

Used to construct our sample function and by Ligh


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Importance Sampling

Importance sampling needed for:

Distribution Ray TracingPath tracing

Bidirectional path tracing

Metropolis

Photon Mappingand many more


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Importance Sampling Generate directions with probability related to shade

Minimize weights (f/p ratio) to reduce noise


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Importance Sampling Shader is an unknown function


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Importance Sampling Shader is an unknown function

Construct piecewise-constant bounding function


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Importance Sampling Use bound to obtain piecewise values

Subdivide regions for better approximation


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Importance Sampling Use bound to obtain piecewise values

Subdivide regions for better approximation


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Guaranteed sampling quality

f/p ratio


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Multidimensional Lightcuts Scalable rendering [Walter et al. 2006]

Works on clusters of lights and shading points

Uses bounding functions (S2 and S3)

Bound direction (S2) Bound direction and location

D i


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Design

Compiler

ImportSamp

Runtime

shade bound sam

O tli


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Background and related work

Interface between shaders and G.I.

Compiler

Results


I t l A ith ti R i


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Interval Arithmetic Review

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

1

4

5

+

=

I t l A ith ti R i


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Interval Arithmetic Review

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

0 1 2 3 4 5 6 7

[0,2]

[3,6]

[3,8]

+

=

I t l A ith ti


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Interval Arithmetic Define interval versions of basic operations

+, -, *, /, sqrt, pow, etc.

Composable for compound operationsSuch as f(x) = sqrt(x*x - x)

Replace each basic operation with interval version

I t l A ith ti


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Interval Arithmetic Simple and general

Simple conversion even for complex functions

Cost typically 2-4x more than original non-interval version

Result intervals are often larger than necesaryIntervals are conservative

always contain all possible outputs but may also include other vDoes not track correlation among values

Interval for x*x can contain negative values

Worse with large starting intervals Subdividing initial intervals can help

I t l A ith ti


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Interval Arithmetic Higher order variants can track value correlation

Affine and Taylor Interval Methods

Tighter result intervals

More expensive to compute

Not cost effective in our testsYour milage may vary

Lifting the Shaders


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Lifting the Shaderssurface matte(colorKd) {


}

Kd

N

L

dot(N,L)

max(dot(N,L),0)

Kd*max()

vector3

vector3

vector3

real

real

vector3

shade

vector3

vector3

interval3

interval

interval

interval3

bound s2

interva

interva

interva

interva

interva

interva

bound

Static Single Assignment For


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Static Single Assignment For

Standard compiler technique

[Cytron et al. 1991] Simplifies analysis and control flow

y = 1.0;y = 2.0;

x = y;x = x + 1.0;

y1 = 1.0;y2 = 2.0;

x1 = y2;x2 = x1 + 1.0;

Convert to SSA

Translating Branches


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if(x > 0.0)

y = 0.0;elsey = 1.0;

return y;

y1 = 0.0;y2 = 1.0;y3 = Psi(Greater(x,0.0), y1, y2);return y3;

? -1 0 1x =

-1 0 1y =



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Translating Branchesy = z = 0.0;

if(x > 0.0)y = 1.0;else

z = 1.0;

y1 = 0.0;y2 = 1.0;z1 = 0.0;z2 = 1.0;y3 = Psi(Greater(x,0.0), y2, y1);z3 = Psi(Greater(x,0.0), z1, z2);

-1 0 1x =

-1 0 1y =

-1 0 1z =

Using the Interface


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Using the Interface

Photon Mapp

MultidimensioLightcuts

Compiler

Runtime API

shader

Outline


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Background and related work

Interface between shaders and G.I.

Compiler

Results


Results


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Results Highlight complex shading

SystemMostly unoptimized Java implementation

Dual quad-core Xeon E5440 2.83 GHz, 16 GB RAM

Sun Java 1.6.0-11 64 bit

Bounds Comparison


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Bounds Comparison Compare our bounds with hand-crafted

ones

Use multidimensional lightcuts asreferenceAnalytic materials

Depth of field

Antialiasing

Environment map lighting[Walter et a

Bounds Comparison


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Bounds Comparison

Our automatic bounds Hand-crafted bounds

Time: 459 s Time: 176 s

640x480 images, 256 eye rays per pixel, 55,000 lights

Importance Sampling


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Importance Sampling

Automatic Importance sampling Cosine-weighted (equal tim

Time: 1,830 s Time: 2,031 s

Importance Sampling


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Importance Sampling

Cosine-weighted (3x time)

Time: 6,134 s

Automatic Importance sampling

Time: 1,830 s

Results Big Buck Bunny


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Results Big Buck Bunny bershader

32 eye rays per pixel55,000 lights

10+ M triangles

Time: 648 sSize: 852x480


Results Big Buck Bunny


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Results Big Buck Bunny bershader Blender materials

Multiple branches 86 lines of code

Kajiya-Kay hair shader

Environment map andsun lighting

32 eye rays per pixel55,000 lights

10+ M triangles



Results Elephants Dream


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Results Elephants Dream

bershaderFully automated G.I.Multidimensional lightcuts

852x432 eye rays

55,

Results Pillow


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Results Pillow Measured material shader

PCA Decompression

83 data textures 243 lines of code

Time: 2,413 s

Results Pillow


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Results Pillow

Lightcuts vs Brute Force


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Lightcuts vs Brute Force

Scene Time Speed-up

Tableau 459.2 s 601 x

Big Buck Bunny 647.6 s 311 x

Chinchilla 516.3 s 282 x

Elephants Dream 464.0 s 834 x

Pillow 2,412.5 s 8 x

Conclusions


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Conclusions First step to automatically combine

programmable shading and physically

based rendering

Compiler generates interval versions ofshaders

Prototype enables multiple Monte Carloglobal illumination algorithms

Limitations and Future Work


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Limitations and Future Work Expensive importance function creation

Use known good sampling when possible

Improve tightness of the bounds

Higher level primitives in language

Generalize shading language

Arbitrary loops

Port to other languages, OpenSL?

Support other types of shadersLight, displacement, etc.

Acknowledgements


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Acknowledgements NSF

CAREER 0644175, CPA 0811680, CNS 0403340

Intel Microsoft

CONACYT-Mexico 228785

NVIDIA

Autodesk

The End


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Walter Course Sig 11 v 2

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