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To better understand how an LPE is constructed, the below tokens are used to define interactions.

Qualifiers
LPE EventsDescriptionExample
C
Camera 
<type event 'group'>
Scattering event specified by scattering type, scattering event, or lpe groupC<.[DS]'floor'>[LO] matches all light paths from the floor lpe group
<L'group'>
Light, i.e. analytic and geometric lightsC[DS]*<L'key'> matches all light paths from the key light group
O
Emissive object, i.e. camera visible lights and material glowC[DS]*O matches all emissive object light paths
Wildcard  
.
Match any relevant LPE event<.D> where the period represents R or T
Scattering Types  
R
ReflectionC<R[DS]>[DS]*[LO] matches all diffuse light paths
T
Transmission or refractionC<T[DS]>[DS]*[LO] matches all transmitted light paths
Scattering Events  
D
Diffuse lobes (includes D1 ... to D4)CD[DS]*[LO] matches all diffuse light paths
S
Specular/Glossy lobes (includes S1 ... to S8)CS[DS]*[LO] matches all specular light paths
U
User signal (includes U1 ... U12)lobes used to output material properties (U1 to U12)CU2L matches the camera visible user2 lobe, typically albedo
Grouping  
( )Parentheses allow grouping of a sequence of LPE eventsCDSL, C(DS)L, and CD(SL) are all functionally the same
Alternatives  
|A vertical bar separates alternatives. For example CD|(SD)L matches direct diffuse or specular-diffuse lighting.light paths
[ ]Square brackets will match any one of the enclosed LPE events. For example C[D1D2D2D3]L will match matches direct diffuse1 or diffuse2 lighting.diffuse2 or diffuse3 light paths
[^ ]
Match any one LPE event that is not contained within the bracketsC[^D2D3]L matches all light paths besides diffuse2 and diffuse3 (including specular and user)
Qualifiers  
*
Match preceding event zero or more times. For example C[DS]*[LO] includes all light paths.
+
Match one or more times. For example C[DS]+[LO] includes all direct and indirect lightinglight paths, but not missive.emissive
{n}
Match exactly n timesC<T[DS]>{2}[LO] includes all double transmission light paths
{min,}
Match min or more timesC[DS]{2,}[LO] includes all indirect light paths
{min,max}
Match at least min, but not more than max times.C[DS]{4,4}[LO] gives the forth bounce of light from the camera

In RIB

To specify an LPE in RIB, reference a DisplayChannel in the Display. This is the most basic way to view what's being output.

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