"Marc-Hendrik Bremer" wrote:
>There is an isosurface cache already, isn't it?

Yes, there is an isosurface cache.   But that is not for hidden isosurfaces.
That is for non-intersecting rays.  The cache is especially effective to
small(or thin) isosurfaces in a large isosurface container.
For example,
  isosurface{
    function{f_torus(x,y,z,0.9,0.05)}
    contained_by{ box{-<1,0.1,1>, <1,0.1,1>}}
  }

The statistics is
----------------------------------------------------------------------------
Ray->Shape Intersection          Tests       Succeeded  Percentage
----------------------------------------------------------------------------
Isosurface                       37426            4648     12.42
Isosurface Bound                80874           37434     46.29
Isosurface Cache                 28748           24664     85.79
----------------------------------------------------------------------------
In this case, the cache hit ratio is 66% (24664/37426).

This cache technique uses a function value of the previous ray and eliminates
unnecessary calculation.  Maybe I will to explain that technique with figures...

R. Suzuki

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