moving frostbite to physically based rendering

Moving to PBRSébastien Lagarde & Charles de Rousiers

Acknowledgments

• Contributions from *many* people

• This talk and the course notes are about:1. Summarizing all of the steps to move an engine to

PBR2. Using the state of the art in our base

implementation3. Small improvements in quality

Disclaimer

• This presentation is about: A high level overview Steps to move to PBR

• Courses notes come with full details and code …

What is the scope of PBR?

What is the scope of PBR?

Light

What is the scope of PBR?

Light

Environment

What is the scope of PBR?

Light Camera

Environment

What is the scope of PBR?

Light

Camera

Environment

1 Materials

2 Lighting

3 Camera

What is the scope of PBR?

CameraLight

Environment

1 Materials

2 Lighting

3 Camera

What is the scope of PBR?

Light

Environment

Camera

1 Materials

2 Lighting

3 Camera

Reference framework

• Need good reference Export to offline path-tracer In-engine reference

Materials

Material – Standard Model

• Standard material 80% of appearance types Model• Specular: Microfacet model with GGX NDF• Diffuse: Disney’s model

• Other material types Subsurface material Single layer coated material

Die

lectr

icC

on

du

cto

r

Material – Specular

4 (n.v)

F(v, h, f0)G(v, l, h )D(h, ɑ)

(n.l)Fs(v, l) =

Schlick GGX

Height-Correlated Smith[Heitz14]

Material – Specular

Standard (uncorrelated) Smith G Term

Die

lectr

icM

eta

l

Material – Specular

Height-correlated Smith G Term

Die

lectr

icM

eta

l

Material - Specular

Height-correlated Smith G Term

Correlated Standard

Material – Diffuse

• Disney Diffuse [Burley12] Coupled roughness between diffuse and specular Retro-reflection

Material – Diffuse

Lambertian Diffuse

RoughSmooth

Material – Diffuse

Disney Diffuse

RoughSmooth

Material - Diffuse

Disney’s Diffuse

Disney LambertDisney Lambert

Smooth Roughness

Material – Diffuse

Original Disney Diffuse Renormalized Disney Diffuse Diffuse + Specular

Material – Diffuse

Disney Diffuse

Material – Diffuse

Renormalized Disney Diffuse

Material – Parameterization

Normal

BaseColor

Smoothness

Metallic

Reflectance

Normal

BaseColor

Reflectance

Smoothness

Metallic

Material – Parameterization

(1 –Smoothness)

(1 –Smoothness)2

(1 –Smoothness)3

(1 –Smoothness)4

Burley12

Smoothness

Material – Parameterization

Fresnel0

Reflectance

0

255

ConductorsDielectrics

CommonMicro occlusion Gem stones

0

1

128

Material – Parameterization

LIGHTING

Lighting

Lighting

Lighting

Lighting

Lighting

• Lighting coherence All BRDFs must be integrated properly with all light

types All lights need to manage both direct and indirect

lighting All lighting is composed properly (SSR/local IBL/…) All lights have the correct ratio between each other

Lighting – Units & Frame of Reference

Light Power

Lighting – Units & Frame of Reference

Light Power

15 lm 1 200 lm 2 600 lm 64 000 lux

Lighting – Units & Frame of Reference

Luminous powerLumens Lux

Illuminance Luminous intensityCandela

LuminanceCandela/m2

Photometric Unit System

Lighting – Units & Frame of Reference

Luminous power (lm), Luminance (cd/m2), or EV

Area

Luminous power (lm)Punctual

Photometric

Emissive

Sun

Luminous intensity (cd)

Luminance (cd/m2) or EV

Illuminance (lux)

Lighting – Analytical Lights

• Parameterization

1,000 k 10,000 k

Lighting – Units & Frame of Reference

Lighting – Analytical Lights

Lighting – Analytical Lights

Point Sphere

LineTube

SpotDisk

FrustumRectangle

Punctual Area

Lighting – Analytical Lights

• Punctual lights Unit: Lum. power (lm) or Lum. intensity (cd) Use smooth attenuation [Karis13]

Inverse squareKaris13

Distance

Falloff

AttenuationRadius

Lighting – Analytical Lights

• Photometric lights Unit: luminous intensity (cd) Applied to point and spot lights

Simple / IsotropicProfile

IES photometricProfile

Artists

Measured

Lighting – Analytical Lights

• Area lights Unit: Luminous power (lm), Luminance (cd/m2 or

EV) Separate diffuse and specular evaluation

Lighting – Analytical Lights

• Area lights

Without horizon handling With horizon handling

Large area light Horizon handling

Lighting – Analytical Lights

• Diffuse area lights 3 integration techniques:• Analytic

Form factors (radiosity) / view factors (heat transfer)

• MRPSolid angles x Most Representative Point lighting [Drobot14]

• Structured sampling of light shapeSolid angles x average cos

Lighting – Analytical lights

• Area lights: Diffuse term

Sphere

Tube

Disk

Rectangle

View factor

Mix of sphere and rectangle

View factor

Structured sampling

Lighting – Analytical Lights

• Specular area lights No satisfying method Shortest distance to reflection

ray with energy conservation [Karis13]

Lighting – Analytical Lights

• Sun light Units: Illuminance (lux) Facing disk with non-null solid angle

Lighting – Analytical Lights

• Emissive surfaces Units: Luminance (cd/m2 or EV) ”Visible part” of a light Does not emit light

Lighting – Image-Based Lights

• Types of IBLs Distant light probe Local light probes Screen-space reflections Planar reflections

Lighting – Image-Based Lights

• Types of IBLs Distant light probe Local light probes Screen-space reflections Planar reflections

Focus

Lighting – Image-Based Lights

• Units: Luminance (cd/m2 or EV) • Source for the distant light probe

HDRI Procedural sky

Lighting – Image-Based Lights

• Light probe lighting: Integral[Env. lighting x BRDF]

• Pre-integration by separating:• Integral of Lighting x NDF, for V = N• Integral of BRDF, for all V & roughness values

Specular[Karis13]

& Diffuse

Lighting – Image-Based Lights

• Light probe lighting: Integral[Env. lighting x BRDF]

• Pre-integration by separating:• Integral of Lighting x NDF, for V = N• Integral of BRDF, for all V & roughness values

Specular[Karis13]

& Diffuse

LDDFG

Lighting – Image-Based Lights

• Light probe lighting: pre-integration

Isotropic approximation Reference

Error due to LD pre-integration with V = N

Lighting – Image-Based Lights

• Light probe lighting: pre-integration LD needs to be computed each time the lighting changes Needs to be fast (real-time capture / refresh) Deals with HDR source

• Integration method for LD Importance sampling Multiple importance sampling Filtered importance sampling

Lighting – Image-Based Lights

• Light probe lighting: pre-integration LD needs to be computed each time the lighting changes Needs to be fast (real-time capture / refresh) Deals with HDR source

• Integration method for LD Importance sampling Multiple importance sampling Filtered importance samplingFaster convergence

Lighting – Image-Based Lights

• Light probe: pre-integration

Filtered importance sampling

Importance sampling

Lighting – Image-based lights

• Light probe: pre-integration

Pre-Filtered importance sampling

Importance samplingFiltered ISSimple IS

Lighting – Image-Based LightsLight probe• Runtime evaluation

N

Lighting – Image-Based LightsLight probe• Runtime evaluation

N

Lighting – Image-Based LightsLight probe• Runtime evaluation

N

Lighting – Image-Based LightsLight probe• Runtime evaluation

N

Lighting – Image-Based Lights

Mirror Direction

Die

lectr

icM

eta

l

Lighting – Image-Based Lights

Dominant Direction

Die

lectr

icM

eta

l

Lighting – Image-Based Lights

Main Direction

DominantReferenceMirrorReference

Lighting – Image-Based Lights

• Local light probes Acquire surrounding geometry Approximate local parallax: box & sphere proxy

[Lagarde12]

RGB

Dielectric

Conductor

Sky is handled by distant light probe

ConductorDielectric

Lighting – Image-Based Lights

• Distant & local light probes composition Lots of local light probes across level Local light probes can overlap each other Distant light probe contains sky information

RGB Alpha

Probe

Lighting – Image-Based Lights

• Distance-based roughness

Probe

Probe

Lighting – Image-Based Lights

• Distance-based roughness

Probe

Probe

Lighting – Image-Based Lights

• Distance-based roughness

Probe

Probe

Lighting – Image-Based Lights

• Distance-based roughness

Probe

Probe

Lighting – Image-Based Lights

• Distance-based roughness

Probe

CAMERA

Camera – Physically Based Camera

• Transforming scene luminance to pixel value

Camera – Settings

Sensor (Sensitivity)

Aperture

Lens

Shutter Speed f/1.41/125s

ISO 100

f/2.81/125s

ISO 100

f/5.61/125s

ISO 100

f-Stop 1/s

ISO

Camera – Exposure Scene luminance

Sensor illumiance

CCD ADC FilmStock

Sensor exposure

Quantized value

Pixel value

Normalizedvalue

lux

lux.scd/m2

Camera – Exposure

Incident Luminance

Cam

era

ran

ge 1

0 Camera range

Pix

el valu

e

1

0

1. Film stock / tone map 2. Style (LUT / grading)3. sRGB / Rec709

1

Exposure computationbased on HSBS sensitivity

Camera – Exposure

• Sunny 16 rule as validation Sky 20,000 lux Sun 100,000 lux

f/16 1/125s ISO 100

TRANSITION TO PBR

Transition – Steps

1. Standard material + viewer first + educating key artists

2. PBR / non-PBR in parallel, with automatic conversion

3. Evangelize PBR to game teams + validation tools

Fresnel0 Diffuse Albedo Illuminance

Acknowledgements

• EA Frostbite - Alex Fry, Christian Bense, Noah Klabunde, Henrik Fernlund, the rendering team

• EA DICE - Yasin Uludag, Arne Schober

• Lucasfilm: Lutz Latta, Cliff Ramshaw, Rodney Huff, Rogers Cordes

• Graphics community: Michał Drobot, Benjamin Rouveyrol, Eric Heitz, Juan Cañada, Ondra Karlík, Tomasz Stachowiak, Brian Karis

• Stephen Hill & Stephen McAuley

QUESTIONS?

Sébastien LagardeLagardese@hotmail.frTwitter: @seblagarde

Charles de RousiersCharles.derousiers@frostbite.comTwitter: @kiwaiii

References

• [Burley12] Brent Burley, “Physically Based Shading at Disney”, SIGGRAPH’12, PBR Course

• [Karis13] Brian Karis, “Real Shading in Unreal Engine 4”, SIGRRAPH’13, PBR Course

• [Drobot14] Michal Drobot, ”Physically Based Area Lights”, GPU Pro 5

• [Heitz14] Eric Heitz, ”Understanding the Masking-Shadowing Function in Microfacet-Based BRDFs”, JCGT, 2014

• [Lagarde12] Sébastien Lagarde, “Local Image-based Lighting With Parallax-Corrected Cubemaps”, SIGGRAPH’12