My foolish attempt at a new primitive has finally paid off. After much
compiling and bug fixing, and yet finished far sooner than I thought,
the first version of the isoblob patch is working.
The isoblob, for those who haven't been following the project (i.e.,
probably most of you), combines the traits of a blob and an isosurface,
allowing blob-like components to be specified with user-supplied density
functions. The result isn't *perfect*, and nowhere near as good-looking
as a regular blob is where simple shapes are involved, but it's not
half-bad.
I've posted a test scene I made in povray.binaries.images, under the
subject "Behold the isoblob!", if you want to see an example scene file
and its output.
Here's what the syntax looks like (so far):

isoblob
  {
  /* similar to blob threshold, not to isosurface */
  threshold <THRESHOLD>
  [accuracy <ACCURACY>]
  /* maximum intersections per interval--default is quite high */
  [max_trace <MAX_TRACE>]

  /*  Functions
   *  <x,y,z> -- coordinates in component space
   *  <r,s,t> -- coordinates in isoblob space
   *
   *  Functions should generally return a value from 0 to 1.
   */
  function { ... }          /* function 1--at least one is required */
  [function { ... } ...]    /* functions 2 and up */

  /*  Components
   *
   *  Strength is multipled by the density function to yield true
   *  density, just as in blobs.
   *
   *  Function numbers start at 1, and go in order of definition.
   */

  /* Translated so that component space is centered at <0,0,0> */
  sphere
    {
    <CENTER>, <RADIUS>, [strength] <STRENGTH>
    [function] <FUNCTION NUMBER>
    /* Insert any other blob-component modifiers here. */
    }
  /* Transformed so that component space is centered around axis from
   * <0,0,0> to <0,0,length> */
  cylinder
    {
    <END1>, <END2>, <RADIUS>, [strength] <STRENGTH>
    [function] <FUNCTION NUMBER>
    /* Insert any other blob-component modifiers here. */
    }
  }

Lummox JR

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