Bob Hughes wrote:

> To get openings into planes you have to use 'clipped_by' instead of
> difference since the plane is considered infinitely deep and no box
> could ever difference all the way through.

Historical Point of Order:

   A minor correction to your staement concerning planes being treated as
infinetly deep. If you construct a box using a csg of 6 planes and have
their normals correctly oriented then there is no issue of infinite
depth. The interior of the csg construct will become the bounding limits
of the plane objects. This is evidenced by the way a clipped by shows
only a shell of the clipped object when so treated rather than a true
solid object as you would expect.
  Something that many users are not aware too is that the box object
is really nothing more than an internaly constructed object using
a cgs of 6 plane objects. Originaly when Pov grew from DKBTrace the
box object was used by way of the original shapes.inc file. They
thought is wise in later versions to instead make these declared
objects primitaves internal to the program rather than through the
repeated use of predeclared declared shapes accessed through the use
of include files. The memory hit was substantualy less and this was
a major issue as most users had at most 1 - 4 megs of memory on their
systems at that time. A 386 with 8 megs of ram was considered
a very well equipped system and those who owned systems with 16 megs
were gods amoung the rest.
   Take a look a the file shapes.old for methods of creating most of
the common predefined primitaves using spheres, planes, quartics,
and quadrics. Things have been simplified since the early days but
you can still find evidence of these older times if you look hard
enough.

-- 
Ken Tyler

mailto://tylereng@pacbell.net

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