Additional Progress Towards the Unification of Microfacet and Microflake Theories

Jonathan Dupuy	Eric Heitz	Eugene d'Eon
Unity Technologies	Unity Technologies	8i

(Press the 's' key to display the annoted version)

Follow-up on Heitz et al.

Single

Photo

Multiple

Problem

Surface $\overset{?}{\longrightarrow}$ Volume

Our approach: preserve light transport
using microfacet and microflake theories

Outline

What is responsible for surface light transport ?

A:	microfacet NDF + geometric profile (e.g., Smith)

What is responsible for volume light transport ?

A:	microflake NDF + microflake density

How to make a volume act as a surface ?

A:	microfacet NDF + semi-infinite homogeneous density

Discussion

Before diving into the details of our contribution, I must mention that our paper is purely experimental, which means we haven't solved our problem entirely; but we did make some progress. Our paper is mostly about sharing this progress along with the insights/ideas we investigated. In the remainder of this presentation, I am going to introduce microfacet and microflake theories, and point out the components they designate as responsible for light transport. Once these components identified, I will show how we related both theories in our paper by building a volume that produces surface-like light transport. Finally, since this is a work-in-progress, I will point out the remaining open problems we think need to be solved to arrive at a unified object representation.

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Microfacet Surface

Definition

BSDF framework
BSDF = facets

Components

µBSDF
NDF

Outline

What is responsible for surface light transport ?

A:	microfacet NDF

What is responsible for volume light transport ?

A:	microflake NDF + microflake density

How to make a volume act as a surface ?

A:	microfacet NDF + semi-infinite homogeneous density

Discussion

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Microflake Volume

Definition

medium framework
medium = flakes

Components

density
µBSDF
NDF

Outline

What is responsible for surface light transport ?

A:	microfacet NDF

What is responsible for volume light transport ?

A:	microflake NDF + microflake density

How to make a volume act as a surface ?

A:	microfacet NDF + semi-infinite homogeneous density

Discussion

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
microfacet NDF

Properties

monosided flakes
surface-like LT

Outline

What is responsible for surface light transport ?

A:	microfacet NDF

What is responsible for volume light transport ?

A:	microflake NDF + microflake density

How to make a volume act as a surface ?

A:	microfacet NDF + semi-infinite homogeneous density

Discussion

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

$\Rightarrow$ How to support both types of microflakes inside a single medium ?

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Chandrasekhar $$\boxed{f_r = \frac{a}{4\pi} \frac{H(\cos \theta_i) \, H(\cos \theta_o)}{\cos \theta_i + \cos \theta_o}}$$

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Chandrasekhar $$\boxed{f_r = \frac{a}{4\pi} \frac{H(\cos \theta_i) \, H(\cos \theta_o)}{\cos \theta_i + \cos \theta_o}}$$
$\Rightarrow$ Can we generalize to other NDFs ?

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Semiporous Materials

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

close
1 voxel/pixel

2000MB

far
8 voxels/pixel

2000MB

far
1 voxel/pixel

16MB

Discussion

Topics

unified theory
multiscattering BSDFs
closed-form LT
semiporous materials
level-of-detail

close
1 voxel/pixel

2000MB

far
8 voxels/pixel

2000MB

far
1 voxel/pixel

16MB

Questions

Backup Slides

Surface-Like Microflake Volume

Geometry

semi-infinite
homogeneous
exponential free paths
microfacet NDF

Properties

monosided flakes
surface-like LT