This interface contains information that is shared among all the built-in rendering entities.

• string "processors", int number
  Specify the number of CPUs to be used for the computations.
  The default value is 1.
• string "caching", int size, int cells, float minradius, float maxradius
  Specify the use of a spatial caching mechanism that speeds up ray-tracing. It is usefult to produce preview images.
  The size parameter is the number of cell clusters that is used in the cache. The number of cells in each cluster is given by cell.
  A cached value is reused if its distance from the current sample is less than a fixed radius, that is always between minradius and maxradius. In particular minradius is used when the tracing depth is low and the sample is directly visible from the eye, maxradius is used when the sample is only visible after many reflections.
• string "displacement", int switch
  Specify if displacement-mapping is 'on' or 'off'. A switch value of 0 means 'off', other values mean 'on'.
• string "shadows", int switch
  Specify if shadowing is 'on' or 'off'. A switch value of 0 means 'off', other values mean 'on'.
• string "volumes", int switch
  Specify if volumetric shading is 'on' or 'off'. A switch value of 0 means 'off', other values mean 'on'.
• string "trace-depth", int depth
  Specify the maximum tracing depth, that is to say the number of specular bounces the light is allowed to do before reaching the eye. This parameter strongly affects rendering times in scenes with reflecting and transmitting materials. The default is 4.
• string "radiosity-depth", int diffuse, int specular
  Specify the number of diffuse and specular bounces the light is allowed to do from surface to surface. This number is used only when the scene method radiosity() is called. Note that the term radiosity is used only for convention, but the evaluation mechanism really computes radiance, that is to say it takes care of all the global illumination transfers. The default is 0, 4, that is to say radiosity is off, caustics are on.
• string "radiosity-sampling", string type
  Specify the type of sampling that is used for radiosity computations. The valid types are "default" and "stratified", the second being much more precise, but slower, than the first.
• string "radiosity-samples", int samples
  Specify the number of sampling rays that are used to determine the radiosity at each spatial location. This value strongly affects the rendering times.
• string "radiosity-threshold", float threshold
  Specify the maximum allowed error in the radiosity computation. This number controls the physical accuracy of the final radiance estimate.
  The default is 0.2 (that is to say 20%).
• string "radiosity-reuse-distance", (float screen, float max, float min
  ) | (float max, float min
  ) Specify the screen, maximum and minimum distances between different sampling locations. The screen distance is a expressed as a fraction of the screen space. Good values range from 0 to 0.5. A value of 0 means that each pixel is sampled. The other values should be determined considering the size of the visible objects. In particular a good maximum value should be less than a fifth of the longest edge, while the minimum distance should be about an order of magnitude less.
• string "radiosity-patch-edge", float max, float min
  During the radiosity computation emitting surfaces are discretized into patches. Two subdivisions are considered, one is coarse and one is fine. These values are the maximum lengths for the patch edges, in the coarse and in the fine subdivision respectively.
• string "radiosity-file", string file, string flag
  Specify the use of a radiosity file.
  flag may be either "save" or "load". If flag is set to "save", the file will be used to store data resulting from the radiosity computations, otherwise the file will be used to load precomputed values.
  This feature may be used to create an incremental rendering system, where the user modifies the same scene many times and re-renders it frequently. In this case, it should be noted that the radiosity values strictly depend on each scene parameter, so that if anything is modified they suddenly become physically wrong. If the variations are small, however, the difference from the real values might be almost invisible.
• string "lighting-accuracy", float accuracy
  Specify the accuracy of lighting computations. This value strongly affects rendering times when many lights are present. The default is 0.98, that is to say 98%.
• string "lighting-count", int count
  Specify the minimum number of lights that are taken into account for each shading location. The default is 1.
• string "lighting-depth", int depth
  Specify the maximum tracing depth at which correct lighting is performed. At higher depths different heuristic strategies may be used to make an estimate of the real shadowing ratio. The default is 5.
• string "lighting-threshold", float threshold
  Specify the maximum allowed error in the computation of shadows from area lights. The default is 0.05.
• string "lighting-patch-edge", float max, float min
  Specify the maximum and minimum lengths of light patch edges.
  Each area light is discretized into patches. If a light patch has an edge longer than max it is subdivided. Then shadowing is computed and if the error is higher than the lighting-threshold the patch edge is subdivided again until the error is acceptable. When the edge is smaller than min the iteration stops, no matter what the error is.
• string "lighting-angle", float max, float min
  Specify the maximum and minimum angles under which a light patch is viewed by the shading location.
  Each area light is discretized into patches. If a light patch is seen under an angle greater than max it is subdivided. Then shadowing is computed and if the error is higher than the lighting-threshold the patch is subdivided again until the error is acceptable. When the angle is smaller than min the iteration stops, no matter what the error is.
• string "photon-count", int photons
  Specify the number of photons that are spread into the scene to estimate the global illumination. The default is 300000.
• string "photon-clustering-count", int diffuse, int caustic
  Specify the size of each cluster of photons. Once that the photons are spread into the scene, they are clustered together to minimize memory occupancy and to make an estimate of final radiosity. There are actually two groups of clusters: one with low frequency is used to sample light coming from diffuse reflections, and another with high frequency is used to sample light coming from specular reflections, that is to say caustics. By default diffuse is set to 1000 and caustic is set to 50. If the caustics appear too uniform you should decrease the last value, while if they show many artifacts you should increase it.

This interface controls data relative to the surface-engine, an advanced geometry manager that handles complex 3d parametric surfaces.
The surface-engine is highly optimized to handle quantities of geometry that exceed the physical memory. To do this it implements a powerful caching mechanism, which can be controlled using this interface.
The surface-engine can be used both explicitly, by creating an instance of the "surface-engine" object type, and implicitly, when using instances of the "nurbs" and "bspline" object types.
Note that only one surface-engine interface is active at any time.

• string "caching", int memory
  Specify the memory occupancy of the geometry cache in Kb.
  This is the maximum quantity of memory used to handle the surface resulting from the final tessellation.
  Obviously, the smaller is the cache the slower the rendering.
  The default value is 32768, but greater values are highly recommended for larger scenes.

This interface controls data relative to the volumetric-engine, an advanced volumetric renderer.
The volumetric-engine serves to cache huge amounts of shading computations that may eventually exceed the physical memory. To do this it implements a powerful on-disk caching mechanism, which can be controlled using this interface.
The volumetric-engine is used by those interiors that provide a "shadow-caching" parameter.
Note that only one volumetric-engine interface is active at any time.

• string "caching", int memory
  Specify the memory occupancy of the geometry cache in Kb.
  This is the maximum quantity of memory used to handle the volumetric data resulting from shading computations.
  Obviously, the smaller is the cache the slower the rendering.
  The default value is 32768, but greater values are highly recommended for scenes that use intensively this type of volumetric rendering.