Upgrading from mental ray 3.5 to 3.6
What's new in Version 3.6
Scene Description Language
Shader Writing and Integration
Incompatible Changes

What's new in Version 3.6

Here is a summary of some of the new features and feature improvements in version 3.6 of mental ray. Please refer to the release notes for more details and for other changes which are not mentioned here.


An assembly is a subscene attached to a bounding box, which is loaded on demand when the bounding box is hit by a ray, or is contained and not completely occluded in a rendering tile, if the rasterizer is used. In cases of insufficient memory, assemblies are unloaded automatically and reloaded the next time they are required.
An assembly may contain all scene DAG elements, such as objects, instances and groups, as well as textures, materials, shaders, phenomena, lightprofiles and other scene elements. Lights and cameras can be contained in an assembly, but they will be ignored in the rendering process. An assembly can be created procedurally as a result of geometry shadercall, or loaded from a .mi file. See also Known Limitations.

New BSP Acceleration Technique

A new BSP acceleration technique (BSP2) has been developed for efficient rendering of large BSP trees. The new technique does not require manual tuning for BSP traversal performance and memory consumption improvements. The memory requirements are much lower compared to the traditional BSP. Thus, the new BSP2 is recommended for rendering of large scenes, like those which do not fit into the physical memory of a machine, and scenes containing assemblies.

New Subdivision Surface Support

This completely new subdivision surface implementation is based on a mixed triangle-quad subdivision scheme. The new implementation is several times faster than the previous one, at a reduced feature set compared to the full hierarchical subdivision surface support. The new code path is used for triangle-quad ccmesh input objects not containing features listed below:

For objects containing containing one of the above features or other types of approximations, the mental ray 3.5-based subdivision surface implementation is used.
The following approximation types are supported by the new implementation:

See also Known Limitations.


Importons are "particles" similar to photons. However, they are shot from the camera and traverse the scene in the opposite order. Instead of "energy", they hold a quality which is an importance of the contribution to the final image. The information from importons is used by the kernel for distribution of rendering efforts according to the final contribution to the rendered image, i.e. so-called importance-driven sampling. Importons are thus a foundation for new view-dependent indirect illumination techniques. As a first of them, mental ray 3.6 adds an importance-driven photon map described below.

Importance-driven Photon Maps

A new technique based on the importon map described above has been implemented. This technique is superior to the photon merging introduced in mental ray 3.5. If importons are enabled, they are used to control the density of the globillum photon maps and to improve the lookup time.

Native Ambient Occlusion with Caching

A native implementation of ambient occlusion has been added, which can be used by shaders to replace custom probe ray tracing solutions and benefit from advanced features like caching. See also Known Limitations.

MetaSL Support

MetaSL is a powerful shading language targeting current and future shading requirements. mental ray shading functionality has been extended to allow efficient support for the MetaSL shaders. It is possible to use a mixture of native and MetaSL shaders in the same scene. It is also possible to combine "native" software mental ray shaders and MetaSL shaders in a shader tree or in a mental ray Phenomena at rendering time. See also Known Limitations.

Exact Final Gathering

Added new finalgather mode "force", where finalgather map creation and interpolation will be disabled. A set of finalgather ray will be shot each time mi_compute_irradiance or mi_compute_avg_radiance is called. The rendering speed would be much slower than in other finalgather modes, delivering a superior image quality.

Other improvements

Scene Description Language

The following changes were made in the .mi scene description syntax:

Shader Writing and Integration

The following changes were made in the shader and integration interfaces.

Note: All shaders and integrations should be recompiled for mental ray version 3.6. Common data structures in the shader interface and integration API have been changed, especially with regard to assemblies. Shaders compiled for an earlier version of mental ray may crash without error indication if they access changed data structures in the shader interface.

Incompatible Changes

The following changes were made in mental ray 3.6 which are not backwards compatible or which may cause different results than previous versions of mental ray:

Copyright © 1986-2011 by mental images GmbH