Open Shading Language (OSL)
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This document provides an introduction to Open Shading Language (OSL), including: - OSL was developed at Sony Imageworks to describe shaders for use in rendering pipelines for movies. It uses the LLVM infrastructure. - OSL allows accurately replicating measured surface properties like BRDFs to flexibly represent surface properties in rendered scenes. - In OSL, shaders define functions that return surface, displacement, volume properties or new shaders, rather than directly calculating pixel colors. Reflectance and transmittance are modeled as functions called "closures". - OSL closures compute an explicit symbolic description of how surfaces or volumes scatter light, which can be evaluated, sampled
![Example Surface Shader
● A sample surface shader looks like below:
surface
test (string noisename = "gabor", float freq = 5, output color Cout =
0)
{
point p = P*freq * (1.0+10*v*v) * (1.0+10*u*u);
float n = noise(noisename, p[0], p[1]);
cout = n * 0.5 + 0.5;
}](https://image.slidesharecdn.com/osl-151222134400/85/Open-Shading-Language-OSL-6-320.jpg)
Open Shading Language (OSL)
- 1. Introduction to Open Shading Language Prabindh Sundareson
- 2. Introduction ●OSL was developed at Sony Imageworks, for use in its rendering pipelines for movies. ●It is a shader description language, built out of LLVM infrastructure.
- 3. Why OSL ● To be able to replicate the behaviour of pre-recorded BRDF using instruments like the Gonioreflectometer. ● Once recorded, these BRDFs can be replicated almost accurately in the rendered scene ● More flexible representation of properties of surfaces
- 4. The OSL shader ● In OSL, shaders do not calculate color output per pixel, but define a function that returns a surface, displacement, volume or define a new generic shader ● Reflectance and Transmittance of surfaces are modelled as functions, or "Closures" ● These shaders are evaluated during the rendering phase
- 5. Open Shading Language ● OSL's surface and volume shaders compute an explicit symbolic description, called a "closure", of the way a surface or volume scatters light, in units of radiance ● These radiance closures may be evaluated in particular directions, sampled to find important directions, or saved for later evaluation and re-evaluation (by component blocks called as "Integrators") – From "Larry Gritz, OSL_Introduction"
- 6. Example Surface Shader ● A sample surface shader looks like below: surface test (string noisename = "gabor", float freq = 5, output color Cout = 0) { point p = P*freq * (1.0+10*v*v) * (1.0+10*u*u); float n = noise(noisename, p[0], p[1]); cout = n * 0.5 + 0.5; }
- 7. Sample Scenes built out of OSL ● Some examples are to be found in chocofur.com (http://store.chocofur.com/exterior-scene-01), that look amazingly realistic
- 8. Source Code and More Details ● The source code for OSL is provided under a liberal New BSD license, at, ● https://github.com/imageworks/OpenShadingLangua ge