To better understand how an LPE is constructed, the below tokens are used to define interactions. For most users, the pre-built LPE are easily selected and explained below.
<type event 'group'>
|Scattering event specified by scattering type, scattering event, or lpe group|
|Light, i.e. analytic and geometric lights|
|Emissive object, i.e. camera visible lights and material glow|
|Match any relevant LPE event|
|Transmission or refraction|
|Diffuse lobes (D1 to D4)|
|Specular/Glossy lobes (S1 to S8)|
|User lobes used to output material properties (U1 to U12)|
|( )||Parentheses allow grouping of a sequence of LPE events|
||||A vertical bar separates alternatives|
|[ ]||Square brackets will match any one of the enclosed LPE events|
|Match any one LPE event that is not contained within the brackets|
|Match preceding event zero or more times|
|Match one or more times|
|Match exactly n times|
|Match min or more times|
|Match at least min, but not more than max times.|
LPE tokens are not necessarily the most artist-friendly things. For this reason, we provide a list of LPEs in our plugins that can be easily selected and output. We also provide options on how specific you want to be when it comes to output; from outputting all your direct or indirect interactions at once per type or outputting them per-lobe which provides greater control for advanced workflows.
For basic workflows, the following LPE are recommended. Note that we are specifying the DisplayChannel and a name (which can be most anything). Note that these LPE will collect the light interaction from different lobes of materials and store them in the same AOV. For example: reflections from the Glass Lobe in PxrSurface will be combined with other specular reflections in the direct and indirectSpecular AOVs. This can simplify the outputs.