1 implicit visibility and antiradiance for interactive global illumination carsten dachsbacher 1,...

Implicit Visibility and Implicit Visibility and Antiradiance for Interactive Antiradiance for Interactive

Global IlluminationGlobal Illumination

Carsten DachsbacherCarsten Dachsbacher11, Marc Stamminger, Marc Stamminger22, , George DrettakisGeorge Drettakis11, Frédo Durand, Frédo Durand33

11 REVES/INRIA Sophia-Antipolis, REVES/INRIA Sophia-Antipolis, 22 University of Erlangen, University of Erlangen,

33 MIT CSAIL MIT CSAIL

MotivationMotivation

global illuminationimportant for realistic image synthesisinteractivity is desirablevisibility is expensive

global illuminationimportant for realistic image synthesisinteractivity is desirablevisibility is expensive

direct illuminationdirect illumination global illuminationglobal illumination

Previous WorkPrevious Work

off-line vs. precomputed vs. real-time

radiosity / finite element methodsamount of transport: form factors

computation involves visibility, most expensive partdynamic scenes make global updates necessary

off-line vs. precomputed vs. real-time

radiosity / finite element methodsamount of transport: form factors

computation involves visibility, most expensive partdynamic scenes make global updates necessary

[Cohen88][Cohen88] [Sloan02][Sloan02] [Keller97][Keller97]

Previous Work - negative lightPrevious Work - negative lightstill using visibility

incremental updates for dynamic radiosity [Chen90]complex data structures, “negative light”

photon mapping (shadow photons) [Jensen95]

alleviating visibility ambient occlusion [Bunnell05]“how to avoid explicit visibility” [Pellegrini99]

purely theoretical discussiondoes not address directional discretization, iterative solutions

still using visibilityincremental updates for dynamic radiosity [Chen90]

complex data structures, “negative light”

photon mapping (shadow photons) [Jensen95]

alleviating visibility ambient occlusion [Bunnell05]“how to avoid explicit visibility” [Pellegrini99]

purely theoretical discussiondoes not address directional discretization, iterative solutions

BRDFBRDF geometry termgeometry termincident radianceincident radiancevisibility functionvisibility function

Light TransportLight Transport

rendering equation [Kajiya86]rendering equation [Kajiya86]

Rendering EquationRendering Equationlinear operators [Arvo94]global transport operator G

computes incident radiance from other surfacesdetermines visibility

linear operators [Arvo94]global transport operator G

computes incident radiance from other surfacesdetermines visibility

GG

transportwith occlusion


Rendering EquationRendering Equationreflection operator K

local operator, computes reflected radiance

rendering equation

reflection operator K local operator, computes reflected radiance

rendering equation

GG



KK

reflectionreflection

radiance L

emission E

radiance L

emission E

Goal: alleviate visibility computationGoal: alleviate visibility computation

replace Guse operator U for unoccluded transport

problem: excessive light transportsolution: compensate with “negative light”

replace Guse operator U for unoccluded transport

problem: excessive light transportsolution: compensate with “negative light”

UU

transportwithout occlusion


generatenegative light

generatenegative light

New operatorNew operator

additional local operatorgo-through operator J

lets radiance pass through surfaceno change in direction or magnitude

additional local operatorgo-through operator J

lets radiance pass through surfaceno change in direction or magnitude

UU



KK


JJ

go-throughoperator

go-throughoperator

From occluded to unoccluded transportFrom occluded to unoccluded transport

LLGLGL JGL

JGL

ULUL

Antiradiance

Antiradiance

inputinputoccludedoccluded unoccludedunoccludedradianceradiancetransporttransport transporttransport

go-throughgo-throughoperator Joperator J

problem:problem:extraneousextraneous

UAUA

negativenegativelightlight

lightlight

what we wantwhat we want what we can

do cheaply

what we can

do cheaply

what we needto remove

what we needto remove

From occluded to unoccluded transportFrom occluded to unoccluded transport

GLGL

occludedoccludedtransporttransport

ULUL

unoccludedunoccludedtransporttransport

UAUA

negativenegativelightlight

== --

occluded and unoccluded transport

antiradiance

radiance

occluded and unoccluded transport

antiradiance

radiance

AntiradianceAntiradiance

UAUAULULGLGL

BB

Occluded vs. unoccluded transportOccluded vs. unoccluded transport

GLGL

AA

ULUL

CC

antiradiance

exchange from C to B

antiradiance

exchange from C to B

GL: light is blocked at C, no transport A to BGL: light is blocked at C, no transport A to BUL: transport A to BUL: transport A to Bantiradiance generated at Cantiradiance generated at C

new rendering equation

avoids explicit visibility new quantity antiradiance propagate

new rendering equation

avoids explicit visibility new quantity antiradiance propagate

RecapRecap

UU



KK


JJ

go-throughoperator

go-throughoperator

Practical implementationPractical implementation

finite element approach

iterative strategies and convergence

using the GPUimplicit visibility makes is feasible

finite element approach

iterative strategies and convergence

using the GPUimplicit visibility makes is feasible

Finite ElementsFinite Elementsspatial and directional discretizationhierarchical radiosity with clustering

energy transport over linksform factors: energy transport between two patchesdirectional quantities: uniform discretization

spatial and directional discretizationhierarchical radiosity with clustering

energy transport over linksform factors: energy transport between two patchesdirectional quantities: uniform discretization

ComputationComputation

UU



KK


JJ

go-throughoperator

go-throughoperator


UU



global passpropagate energyhierarchical solver: links

global passpropagate energyhierarchical solver: links


KK


JJ

go-throughoperator

go-throughoperator

local passtransform incident energy into new exitant energy

local passtransform incident energy into new exitant energy

Iterative SolutionIterative Solution

symmetric iterationsymmetric iteration

Symmetric IterationSymmetric Iteration

1st iteration1st iteration 2nd iteration2nd iteration 3rd iteration3rd iteration

4th iteration4th iteration 8th iteration8th iterationpath tracingpath tracingreferencereference


symmetric iteration

shadows are one step behindfast convergence

it can diverge in contrived scenesconverged in allscenes tested

symmetric iteration

shadows are one step behindfast convergence

it can diverge in contrived scenesconverged in allscenes tested


asymmetric iterationone step of radiance propagation

multiple steps for antiradiance

#iterations = depth complexity

“emulate” one step of GL

asymmetric iterationone step of radiance propagation

multiple steps for antiradiance

#iterations = depth complexity

“emulate” one step of GL

ULUL UAUA

ConvergenceConvergenceoffice scene

symmetric: faster in the beginningasymmetric: better >90 stepsvisually: 10 iterations suffice

office scenesymmetric: faster in the beginningasymmetric: better >90 stepsvisually: 10 iterations suffice

Data structuresData structures

exitant energyexitant energy incident energyincident energy emission+total reflectionemission+total reflection

spatial and directional discretizationsimple 2D data structurestextures/render targets on GPUs

each table stores L and AK and J operate on separate hemispheres

spatial and directional discretizationsimple 2D data structurestextures/render targets on GPUs

each table stores L and AK and J operate on separate hemispheres

ele

men

tsele

men

ts

directionsdirections

Data structures (global pass)Data structures (global pass)

directionsdirections

receiver

patch

receiver

patch

sender

patch

sender

patch

formfactorformfactor

PPQQ FPQFPQ

link tablelink table


**

**

direction maskdirection maskcheap, because

no visibilitycheap, because

no visibility

store radiance and antiradiance for next iterationstore radiance and antiradiance for next iterationaccumulate reflected radiance for displayaccumulate reflected radiance for display

Data structures (local pass)Data structures (local pass)


KKJJ

new antiradiancenew antiradiance new radiancenew radiance

apply local operators to incident energy of each patchapply local operators to incident energy of each patch

separate direct and indirect illuminationinitialize from environment mapsevaluate direct light with shadow maps

separate direct and indirect illuminationinitialize from environment mapsevaluate direct light with shadow maps

ResultsResults

ResultsResults

glossy materialscomparison to path tracing

glossy materialscomparison to path tracing

GPU (11 fps) GPU (11 fps) path tracingpath tracing

Dynamic ScenesDynamic Scenesmoving or deforming objects

only update directly affected linksoptimal link hierarchy changes

moving or deforming objectsonly update directly affected linksoptimal link hierarchy changes

meshing and linking excessive subdivision for dynamic scenesdirectional quantities

memoryaccuracy, main approximation

meshing and linking excessive subdivision for dynamic scenesdirectional quantities

memoryaccuracy, main approximation

DiscussionDiscussion

rendering equation with implicit visibilitydirectional quantity antiradiancereorganized global illumination computation

interactive updatesmoving objects, lightsglossy surfaces

rendering equation with implicit visibilitydirectional quantity antiradiancereorganized global illumination computation

interactive updatesmoving objects, lightsglossy surfaces

ConclusionConclusion

Thank you for your attention!

Questions?

Thank you for your attention!

Questions?

Acknowledgements: DFG (project “Interaktive Visualisierung Prozeduraler Modelle”)Marie-Curie Postdoctoral Fellowship “Scalable-GlobIllum” (MEIF-CT-2006-

041306)Microsoft Research New Faculty Fellowship, Sloan FellowshipNSF CAREER award 0447561Autodesk, A. Olivier, F. Firsching, P. Richard, P. Green

Acknowledgements: DFG (project “Interaktive Visualisierung Prozeduraler Modelle”)Marie-Curie Postdoctoral Fellowship “Scalable-GlobIllum” (MEIF-CT-2006-

041306)Microsoft Research New Faculty Fellowship, Sloan FellowshipNSF CAREER award 0447561Autodesk, A. Olivier, F. Firsching, P. Richard, P. Green

1 implicit visibility and antiradiance for interactive global illumination carsten dachsbacher 1,...

Documents

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