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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.
| LPE Events | Description | Example |
|---|---|---|
C | Camera | |
<type event 'group'> | Scattering event specified by scattering type, scattering event, or lpe group | C<.[DS]'floor'>[LO] matches all light paths from the floor lpe group |
<L'group'> | Light, i.e. analytic and geometric lights | C[DS]*<L'key'> matches all light paths from the key light group |
O | Emissive object, i.e. camera visible lights and material glow | C[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 | Reflection | C<R[DS]>[DS]*[LO] matches all reflected light paths |
T | Transmission or refraction | C<T[DS]>[DS]*[LO] matches all transmitted light paths |
| Scattering Events | ||
D | Diffuse lobes (D1 to D4) | CD[DS]*[LO] matches all diffuse light paths |
S | Specular/Glossy lobes (S1 to S8) | CS[DS]*[LO] matches all specular light paths |
U | User 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 events | CDSL, C(DS)L, and CD(SL) are all functionally the same |
| Alternatives | ||
| | | A vertical bar separates alternatives | CD|(SD)L matches direct diffuse or specular-diffuse light paths |
| [ ] | Square brackets will match any one of the enclosed LPE events | C[D2D3]L matches direct diffuse2 or diffuse3 light paths |
[^ ] | Match any one LPE event that is not contained within the brackets | C[^D2D3]L matches all light paths besides diffuse2 and diffuse3 (including specular and user) |
| Qualifiers | ||
* | Match preceding event zero or more times | C[DS]*[LO] includes all light paths (including emissive) |
+ | Match one or more times | C[DS]+[LO] includes all direct and indirect light paths, but not emissive |
{n} | Match exactly n times | C<T[DS]>{2}[LO] includes all double transmission light paths |
{min,} | Match min or more times | C[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 fourth bounce of light from the camera |
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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.
Basic
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LPEs
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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.
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