Rendering Algorithms

Introduced detail shadowmaps that can multisample shadowmap pixels, and also call shadow shaders on shadow-casting geometry to obtain and store transparent shadows.
Shadowmaps can now specify a shadowmap bias to replace the standard Woo trick, which stores the halfway distance between the first two shadow-casting objects, with a fixed distance. The bias can also be set in the options. Although Woo shadowmaps are generally superior, they are not compatible with shadowmap merging, which was also added to mental ray 3.3 to support shadows cast from one rendering pass on another. Note that mental ray 3.3 will read shadowmap files created with older versions of mental ray, but older versions cannot read the new 3.3 format.
Shadowmaps also support extra fields supplied by a camera attached to the light source.
Uncompressed HDR (High Dynamic Range) images are now supported in addition to compressed HDR images.
Performance improvements: Light emitter shaders now work several times faster. Raytracing motion-blurred hair geometry, and hair rendering in general, is also several times faster. Significantly improved final gathering performance for surfaces with very strong bump mapping; for extreme bump mapping, performance can increase by a factor of 10. Scenes with very large numbers of instances are rendered much faster with far reduced memory overhead. Frame buffers now take about half as much space.
Large finely displaced objects of which only a very small part is in the viewing frustum, and the bulk of the object to the side or behind the camera, are now handled much more efficiently. Much less subdivision effort is expended on invisible portions of such objects.
For hyperthreaded Intel CPUs and Linux, the -threads command-line option now includes hyperthreaded pseudo CPUs. These pseudo-CPUs will not consume licenses.
Autovolume mode no longer requires ray tracing.
Multihosted rendering could get wedged in mental ray 3.2 under certain circumstances. mental ray 3.3 has a new networking algorithm that is completely stable, and also much faster, permitting more slave hosts to contribute efficiently.
The multipass rendering file format was changed. Old files can be imported, but older versions of mental ray cannot read the new format.
mental ray is now much more frugal with stack allocations. The default stack size was reduced from 4 MB to 512 KB. This reduces memory requirements and the risk of being unable to start another thread. If 512 KB is insufficient, it can be overridden with the MI_STACKSIZE environment variable.

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