Optional rendering parameters

Optional rendering parameters

Note

When you specify a texture, such as with the "environment" keyword, you can also use the image filtering keyword arguments.

Keyword	Functions	Description
“scope”, string spec	all	Allows an override of the scope for ray-intersections. A special scope argument, scope:self, will match the currently shading object.
“bias”, float value	irradiance occlusion	The irradiance and occlusion functions take an optional bias parameter which gives control over self-intersection.
“maxdist”, float value	all	Allows an override of the maximum distance the ray can travel when testing for intersections. Some functions (i.e. fastshadow()) have the maximum distance implicitly defined (by the length of the ray) and should probably avoid using this option. However, this option can be used effectively when computing reflections, global illumination, refraction etc.
“variance”, float value	reflectlight refractlight fastshadow filtershadow trace	Overrides the global variance control (mantra’s -v option) which is used to determine anti-aliasing quality of ray tracing. For more information please refer to the documentation on mantra.
“angle”, float value	reflectlight refractlight fastshadow filtershadow trace	Specifies a cone angle over which samples will be distributed. To be effective, the samples parameter should also be specified. The value is specified in radians.
“samples”, int value	reflectlight refractlight fastshadow filtershadow trace irradiance occlusion	How many samples should be sent out to filter rays. For the irradiance and occlusion functions, specifying a samples parameter will override the default irradiance sampling.
“environment”, string map	reflectlight refractlight trace irradiance occlusion	If the ray sent out to the scene misses everything, then it’s possible to specify an environment map to evaluate. Using the ray’s direction, the environment map specified will be evaluated and the resulting color will be returned. Most likely, it will be necessary to specify a transform space for the environment map evaluations. In the case of refractlight and trace the Of and Af variables will be set to 0 regardless of the background color specified. the resulting color. When an environment map is specified, the filtering options from texture() are also supported. See how to create an environment/reflection map.
“envobject”, string objectname “envlight”, string lightname “envfog”, string fogname	reflectlight refractlight trace irradiance occlusion	If an environment map is used, the orientation of the environment map can be specified by transforming the ray into the space of another object, light or fog object in the scene. In Houdini, null objects can be used to specify the orientation. For example: Cf = R*reflectlight(bias, max(R), "environment", "map.rat", "envobject", "null_object_name");
“envtint”, vector color	reflectlight refractlight trace irradiance occlusion	If an environment map is used, it’s possible to “tint” the resulting color.
“background”, vector color	reflectlight refractlight trace irradiance occlusion	If a ray misses all objects, it’s possible to specify the background color of the scene. In the case of refractlight and trace the Of and Af variables will be set to 0 regardless of the background color specified.
“distribution”, string style	irradiance occlusion	Distribution for computing irradiance. The default is to use a cosine distribution (diffuse illumination). The possible values for the style are: nonweighted - Uniform sampling cosine - Cosine weighted sampling See irradiance and occlusion for issues related to this keyword.