Stephen <mcavoys_at@aoldotcom> wrote:
> PovRay gives a warning when Patch objects are used in a Difference or 
> Intersection. (Ver 3.6 & 3.7)
> Parse Warning: Patch objects not allowed in intersection.

> 3.4.2  Finite Patch Primitives
> There are six totally thin, finite objects which have no well-defined 
> inside. They are bicubic patch, disc, smooth triangle, triangle, polygon 
> and mesh / mesh2. They may be combined in CSG union but cannot be used 
> in other types of CSG (or inside a clipped_by statement).

> I???ve found that all four operations work well with the Bicubic_Patch, 
> except for differencing a patch from a primitive when the use of the 
> inverse keyword in the CSG helps.

  I don't understand how it could work ok with a bicubic patch, because
a bicubic patch has no well-defined interior.

  (Meshes don't have one either, by default, but an interior calculation
for closed meshes can be turned on with the 'inside_vector' feature.
IIRC discs work like planes in that they divide the space into two parts:
the outside and the inside. However, because the visible surface does not
cover the entire partition, they will cause odd behavior when used in CSG.)

-- 
                                                          - Warp

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