To reduce the amount of memory being used by the RayTracer, at the expense of some speed. With all of the recursive subdivision in the RayTracer, a large amount of memory can be used up in storing grids which undergo heavy use at the start of a ray trace, but are not used at all later on in the process. These grids and their associated memory may be reused to reduce the amount of memory required by the ray tracer.
The ray tracer keeps an time ordered list of all the grids in the scene, based on a Least Recently Used criteria. If grid_cache is set to some small integer (say 600), then after 600 grids have been allocated, the Least Recently used grid will be freed and that memory will be reused to store the next grid created. This is not a data destructive process; the triangles in the freed grid are simply placed back into the larger voxel which held the grid. That voxel may be subdivided again should another ray enter that voxel in the future of the ray trace.
This option is ignored by the PowerTracer, RayCaster, and PowerCaster.
