🚀 go-pugleaf

danielbt@cs.curtin.edu.au (Brett Daniel) writes:

> Can you describe a convex polygon that intersects all six clipping planes?
> I can only think of a 3D convex polygon intersecting a maximum of four planes.
> Unless you count the polygon intersecting with the edges and corners 
> of the clipping planes. But even in this case one point would be clipped away
> and only two vertices added.

Its quite possible to cut all 6 planes; imagine a plane that cuts the
parallelpipe in a bit like the way the ribbons on a christmas present
might be arranged.  I mean the ones that are wrapped in a shop..  The
plane cuts through the corner of the top face and continues to the
diagonally opposite corner cutting the bottom face in a similar manner. 

  i.e.
                ----------------
                \               \
                |\               \
                | \               \
                |  \              /\
                |   \            /  \
                |    ---------==-----
                |    |   ===        |
                |====|===           |
                \    |              |
                 \   |              |
                  \  |              |
                   \ |              |
                    \----------------

[Cube rendered with backface culling=ON, edges=ON, projection type=PARALLEL and
 14 area light sources]

	Adam

-------------
Adam Billyard, Graphics Division,
Canon Research Centre Europe,
17/20 Frederick Sanger Rd, Surrey Research Park, Guildford, Surrey, GU25YD, UK.
ads@canon.co.uk, ads@canon.uucp, ..!ukc!canon!ads
Tel: +44 (0) 483 574325 Fax: +44 (0) 483 574360
 



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