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

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

Additional Progress Towards the Unification of Microfacet and Microflake Theories