Light Path Expressions

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Download: Builds for Windows, Linux and MacOSX
Source Code: LPE_Rif.cpp

Related Links
    Cutter & Light Path Expressions
    LPE Tool


The RifPlugin presented here is intended to help artists experiment with LPE's. When using the RifPlugin there is no need to use the RenderMan Controls window to assign a custom LPE. Instead, LPEs can be saved as a text document in Maya's current project directory. For example, a text file named "trial.lpe" might contain the following text.

lpe:C<RD[^'floor']><L.> # not_floor
lpe:C<RD['floor']><L.>  # floor

When rendering a scene that uses the LPE_Rif plugin adds the appropriate DisplayChannel and secondary Display statements to the output rib stream as a result of reading the lpes contained in "trial.lpe". Any other AOVs that have been assigned via the RenderMan Controls window or the Render Setting "Passes" tab are not effected by the rif.

AOV outputs can be named by providing a comment on the same line as the lpe. For example, this lpe would be named "diffuse_foo_light" in the "it" window or as a channel in an openexr file.

lpe:C<RD><L.'foo'> # diffuse_foo_light

Figure 1

Another advantage of using the rif is that only is it easier to experiment with LPEs in order to learn about the tokens they use but shot-specific custom LPEs do not have to be added to the rendermn.ini file.

Step 1 - get the Rif plugin

Pre-built versions of the plugin are available for downloading from the link at the top of this page. Alternatively, save the source code in the,
directory. Open the file in Cutter and press control + e, or alt + e, or Apple + e to build the plugin.

Step 2 - create a LPE text file

Save the following text as trial.lpe in the Maya project directory that you intend to use for your LPE experiments, say,

Listing 1 (trial.lpe)

# Examples from Pixar's "LPE" doc
# specular
# diffuse

Step 3 - assign the plugin

Go to the Render Settings Advanced tab and assign the plugin and the trial.lpe file.

Figure 1

Step 4 - edit 'r' edit 'r' etc...

Experimentation with one or more LPE's can proceed quickly by editing the trial.lpe document in Cutter (or any other text editor) and pressing 'r' in the "it" window to re-render. There is no need to keep Maya as a "front" window.

Figure 2

© 2002- Malcolm Kesson. All rights reserved.