An Introduction To Open Shading Language

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From	Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups	comp.graphics.animation, comp.graphics.rendering.misc
Subject	An Introduction To Open Shading Language
Date	Wed, 30 Jul 2025 00:14:24 -0000 (UTC)
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Been watching the video from this course
<https://dl.acm.org/doi/10.1145/3664475.3664534> that was presented by
a certain Mitch Prater at SIGGRAPH 2024 on writing OSL shaders. OSL is
supported nowadays by a bunch of 3D tools, among them RenderMan and
Blender. It seems the only one of these the presenter is familiar with
is RenderMan.

What struck me is, in a two-hour talk, he didn’t once go into the
concept of the “closure color”, which is the special OSL type that
encapsulates the totality of the interaction between light and the
material. He gives example shaders that compute elaborate textures
and transform between coordinate systems, but nothing on closures.
Without these, what kind of renderer would you have?

Could it be that RenderMan does not support that feature of OSL?

In OSL (at least the current version), you do not construct closure
values from scratch. Instead, you start with the builtin closure
functions that represent elemental material characteristics like
diffuse, glossy etc
<https://open-shading-language.readthedocs.io/en/v1.13.12.0/stdlib.html#material-closures>,
and compose these into expressions that evaluate to the desired
overall material behaviour.

If you want a renderer that does integrate the totality of OSL,
including closures, have a look at Blender Cycles.

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An Introduction To Open Shading Language Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-07-30 00:14 +0000

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