Moving Frostbite to Physically Based Rendering

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Moving to PBR
Sébastien Lagarde & Charles de Rousiers

Acknowledgments
• Contributions from *many* people
• This talk and the course notes are about:
1. Summarizing all of the s...

Disclaimer
• This presentation is about:
 A high level overview
 Steps to move to PBR
• Courses notes come with full
det...

What is the scope of PBR?

What is the scope of PBR?

What is the scope of PBR?
Environment

What is the scope of PBR?
Environment

What is the scope of PBR?
Environment
1 Materials
2 Lighting
3 Camera

What is the scope of PBR?
Environment
1 Materials
2 Lighting
3 Camera

What is the scope of PBR?
Environment
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
...

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
DielectricMetal

Material – Specular
Height-correlated Smith G Term
DielectricMetal

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
Metal...

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 bot...

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 power
Lumens Lux
Illuminance Luminous intensity
Candela
Luminance
Candela/m...

Lighting – Units & Frame of Reference
Luminous power (lm), Luminance (cd/m2), or EVArea
Luminous power (lm)Punctual
Photom...

Lighting – Analytical Lights
• Parameterization
1,000 k 10,000 k

Lighting – Units & Frame of Reference

Lighting – Analytical Lights

Lighting – Analytical Lights
Point
Sphere
Line
Tube
Spot
Disk
Frustum
Rectangle
Punctual Area

Lighting – Analytical Lights
• Punctual lights
 Unit: Lum. power (lm) or Lum. intensity (cd)
 Use smooth attenuation [Ka...

Lighting – Analytical Lights
• Photometric lights
 Unit: luminous intensity (cd)
 Applied to point and spot lights
Simpl...

Lighting – Analytical Lights
• Area lights
 Unit: Luminous power (lm), Luminance (cd/m2 or EV)
 Separate diffuse and spe...

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 ...

Lighting – Analytical lights
• Area lights: Diffuse term
Sphere
Tube
Disk
Rectangle
View factor
Mix of sphere and rectangl...

Lighting – Analytical Lights
• Specular area lights
 No satisfying method
 Shortest distance to reflection ray
with ener...

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 e...

Lighting – Image-Based Lights
• Types of IBLs
 Distant light probe
 Local light probes
 Screen-space reflections
 Plan...

Lighting – Image-Based Lights
• Types of IBLs
 Distant light probe
 Local light probes
 Screen-space reflections
 Plan...

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:
• In...

Lighting – Image-Based Lights
• Light probe lighting: Integral[Env. lighting x BRDF]
• Pre-integration by separating:
• In...

Lighting – Image-Based Lights
• Light probe lighting: pre-integration
Isotropic approximation Reference
Error due to LD pr...

Lighting – Image-Based Lights
• Light probe lighting: pre-integration
 LD needs to be computed each time the lighting cha...

Lighting – Image-Based Lights
• Light probe lighting: pre-integration
 LD needs to be computed each time the lighting cha...

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 sampling
Filtered...

Lighting – Image-Based Lights
Light probe
• Runtime evaluation
N

Lighting – Image-Based Lights
Light probe
• Runtime evaluation
N

Lighting – Image-Based Lights
Light probe
• Runtime evaluation
N

Lighting – Image-Based Lights
Light probe
• Runtime evaluation
N

Lighting – Image-Based Lights
Mirror Direction
DielectricMetal

Lighting – Image-Based Lights
Dominant Direction
DielectricMetal

Lighting – Image-Based Lights
Main Direction
DominantReferenceMirrorReference

Lighting – Image-Based Lights
• Local light probes
 Acquire surrounding geometry
 Approximate local parallax: box & sphe...

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...

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/1.4
1/125s
ISO 100
f/2.8
1/125s
ISO 100
f/5.6
1/125s
...

Camera – Exposure
Scene luminance
Sensor illumiance
CCD ADC FilmStock
Sensor exposure
Quantized
value
Pixel
value
Normaliz...

Camera – Exposure
Incident Luminance
Camerarange
1
0 Camera range
Pixelvalue
1
0
1. Film stock / tone map
2. Style (LUT / ...

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 automati...

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

QUESTIONS?
Sébastien Lagarde
Lagardese@hotmail.fr
Twitter: @seblagarde
Charles de Rousiers
Charles.derousiers@frostbite.co...

References
• [Burley12] Brent Burley, “Physically Based Shading at Disney”, SIGGRAPH’12,
PBR Course
• [Karis13] Brian Kari...

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