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Clarisse 4.0 User Guide

Light Path Expressions or LPEs are regular expressions describing light transport paths. They define paths initiated from camera that are bouncing all around the scene until they reach light sources. LPEs are extremely powerful as it is a mean to extract specific paths to output their results in custom AOVs without of relying on specific AOVs predefined by materials. This is extremely useful to extract all per light AOVs to relight in compositing for example or to output specific AOVs that are not available by materials.

 

Since the syntax of the expressions are based on regex, they can be very daunting at first. However, even if LPE syntax seems really painful to learn, "you should not underestimate the power of LPEs". They are definitely worth the extra effort. This is why we created a special guide to help you understand LPEs. Make sure to read Introduction to Light Path Expressions

 

LPEs in Clarisse are based upon Open Shading Language (OSL) implementation. For more information on LPEs and their syntax, we strongly advise you to refer to https://github.com/imageworks/OpenShadingLanguage/wiki/OSL-Light-Path-Expressions. Please note that Clarisse implementation extends the original specifications by introducing some new useful events: W, U, _, K, M

Event Types

Event Type

Description

C

Camera

R

Surface Reflection

T

Surface Transmission

M

Material (Clarisse specific used to identify a material in order to extract its specific constants. Useful for baking)

V

Volume

W

Sub Surface Scattering (Clarisse specific)

L

Emitting Light

O

Emitting Object

B

Background Emission

U

Unoccluded (Clarisse specific)

_

Clamped (Clarisse specific)

K

Constant (Clarisse specific used to extract lobe or material constants. Useful for baking)

Events Scattering Types

Event Scattering Type

Description

D

Diffuse

G

Glossy

S

Singular (specular reflection or refraction (non glossy))

s

special case of S (note the lower case) for cases when the ray passes through the surface without changing direction (transparency)

 

Note

Scattering events only apply to R, T, W, V event types.

Material Lobes

Clarisse extends the LPE intermediate event tokens notation by pushing a 4th component for materials such as: <EventTypeScatteringType'MaterialLabel''LobeLabel'>

Label

Description

'coat'

Identify the coat lobe for Standard (Specular2) and Disney (Clear Coat) material. For example C<R..'coat'><K.'albedo'>

'hair_r'

Identify the primary highlight of the Physical Hair material.

'hair_trt'

Identify the secondary highlight of the Physical Hair material.

'hair_tt'

Identify the transmission highlight of the Physical Hair material.

'hair_glints'

Identify the glint of the Physical Hair material.

Lobes Common Constants

Constant Label

Description

'albedo'

Output the albedo of the surface. For example CD<K.'albedo'> to extract the albedo of the diffuse reflection

'roughness'

Output the roughness of the surface. For example CG<K.'roughness'> to extract the roughness of the glossy reflection

Disney Material Constants

Label

Description

'base_color'

Output the base color value of the material. For example CM<K.'base_color'> to extract the base color value of the material

'roughness'

Output the roughness value of the material

'metalness'

Output the metallic value of the material

'specular'

Output the specular value of the material

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