RENDERMAN 22 DOCUMENTATION

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Comment: wikit macro-replace (build 4280ad5-2021.10.08.115947) run by cwalker

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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 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 A period will match any relevant LPE event<.D> where the period represents R or T
Scattering Types  
R
ReflectionC<R[DS]>[DS]*[LO] matches all reflected light paths
T
Transmission or refractionC<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 eventsCDSL, C(DS)L, and CD(SL) are all functionally the same
Alternatives  
|A vertical bar separates alternativesCD|(SD)L matches direct diffuse or specular-diffuse light paths
[ ]Square brackets will that match any one of the enclosed LPE eventsC[D2D3]L matches direct diffuse2 or diffuse3 light paths
[^ ]
Match Square brackets that 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 An asterisk will match the preceding event zero or more timesC[DS]*[LO] includes matches all light paths (, including emissive)
+
Match A plus sign will match the preceding event one or more timesC[DS]+[LO] includes all matches direct and indirect light paths, but not emissive
{n}
Match Curly brackets that match the preceding event exactly n timesC<T[DS]>{2}[LO] includes all matches double transmission light paths
{min,}
Match Curly brackets that match the preceding event min or more timesC[DS]{2,}[LO] includes matches all indirect light paths
{min,max}
Match Curly brackets that match the preceding event at least min, but not more than max times.C[DS]{40,41}[LO] gives the fourth bounce of light from the camera matches direct and emissive light paths

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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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 
Anchor
commonLPE
commonLPE

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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Carousel Image Slider
dotsfalse
infinitefalse
sliderHeight175
arrowsfalse
labelsFilterlpeBasiclpeBasic1
slidesToScroll01
captionstrue

Carousel Image Slider
dotsfalse
infinitefalse
sliderHeight175
arrowsfalse
labelsFilterlpeBasic2
slidesToScroll01
captionstrue

Carousel Image Slider
dotsfalse
infinitefalse
sliderHeight175
arrowsfalse
labelsFilterlpeBasic3
slidesToScroll01
captionstrue

Per-Lobe LPEs

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Caustics are not included in the built-in list because they overlap with indirectdiffuse lpe:C<RD>[DS]+[<L.>O] However, you can select caustics with the expression lpe:CDS+[<L.>O]  Below you can find an example of the caustics LPE output, Indirect Diffuse, and the difference between them. Note that the Caustics LPE output doesn't capture indirect lighting from object to object, in this case the red cube. You can create the image on the far right with the indirect diffuse minus the caustic result using the following source: lpe:C<RD>D[DS]*[<L.>O]

 

Image Added

 

 

Carousel Image Slider
dotsfalse
infinitefalse
sliderHeight175
arrowsfalse
labelsFiltercausticpath
slidesToScroll01
captionstrue

 

LPE Macro

If a custom LPE is useful for your shots, you can add your custom LPE by creating a macro in rendermn.ini file. The custom LPE will appear in the RenderMan for Maya (RfM) LPE list after relaunching Maya.  For example:

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An LPE group (lpegroup) allows us to specify which objects we want to be use for an LPE channel. The attributes can be added in RenderMan plugins using the software's menu system such as PrmanObjectSettings in Katana.

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  • unoccluded – returns unoccluded or unshadowed result.
  • noclamp – returns unclamped result.
  • nothruput – does not apply thruput (thruput is the accumulative albedo of the objects hit by rays).
  • shadows – returns collected shadows.
  • holdouts holdout LPE that directs the LPE output to the beauty channel.returns only holdout light paths (light paths with one or more holdout events)
  • overwrite – instead of outputting the accumulated result, overwrite it. One example of using this is for the albedo output where we do not want an accumulated result.
  • noinfinitecheck – do not do any infinite check.

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Code Block
/prman/lpe/user2                 Albedo,DiffuseAlbedo,SubsurfaceAlbedo,HairAlbedo

Examples

  • In the documentation examples we often use <L.> means Light scattering type with all scattering events. For light group AOVs, using <L.> is required instead of Lin place of L. There's no functional difference.
  • lpe:CD<L.> means camera with diffuse scattering event for light scattering type.
  • lpe:CO means camera with emissive objection (since emissive does not need any light, there is no L).