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Refer to the OSL documentation for details on their usage.  You can read more about the current version of OSL by visiting OpenShadingLanguage.

Utilizing the trace() shadeop:

Limited support for the trace() shadeop is included.  The trace() shadeop cannot be called during displacement, presence, and opacity shading.  The trace() shadeop is also limited to retrieving geometric values, as we disallow recursive shading so the optional "shade" parameter is ignored and always assumed to be 0. After a trace(), getmessage() can retrieve the "hit", "hitdist", and "geom:name" values, as well as values for primvars on the hit geometry.

Accessing Shading Contexts

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