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When a ray hits a surface, it can reflect, refract (transmit), or pass through a volume. These are the ray spawn events which we can record with LPE symbols.

We use the R symbol for reflection and T for refraction and sub-surface scattering.

They can be used directly, e.g. R captures reflections of any scattering type and is also equivalent to <R.>.

We can further specify the kind of hit we want to trace by combining R and T with one or more scattering types - diffuse (D), glossy (G), or singular (S). If we don’t specify that, all scattering types are assumed for our R or T events.

This allows us to filter the results only from diffuse reflection, for example with <RD> or combine glossy and singular reflection <R[GS]> .

By using ray spawn events and scattering types, we can recreate some familiar render elements or create custom single or multiple event expressions.