The VRayOSL texture can be used to load OSL shader code files (.osl) or OSL object code files (.oso) and render them directly with V-Ray. The VRayOSL node can be used with shaders that have simple color and float output parameters. These parameters are considered respectively as texture RGB and alpha outputs.

If the shader file describes a material (rather than a texture) and writes its result in an output closure color parameter, it is advised to use the V-Ray OSL material. Otherwise the texture map would not evaluate the materials and would be rendered black. 

UI Path: Texture > plugins > V-Ray > VRayOSL

Shader File – Specifies the .osl or .oso file which contains the shader code.

Color output –  Specifies the color source for the texture's RGB output. If None is selected the texture renders black.

Alpha output – Specifies the float source for the texture's alpha output. If None is selected the texture is considered fully opaque.

Reload Shader – Reloads the shader.

Recreate Attributes – Reloads the shader and recreates its parameters.

Default Output – Determines which channel is included in the output.

Default – Outputs all the channels of the OSL shader.
Out Alpha – Only outputs the Alpha channel of the OSL shader.
Color – Only outputs the Color channel of the OSL shader.
Out Transparency – Only outputs the transparency channel of the OSL shader.
Out Intensity – Only outputs the intensity channel of the OSL shader.