Ron Parker wrote:
> if you shoot a ray "tangent" to a vertex or
> edge, you don't want to count the intersection.  If you shoot it "through"
> a vertex or edge, you want to count it, but only once (more than one
> triangle could be hit at such a point, but you only want to count one.)

I think I know what you mean, but just in case.....

Consider a prism of vertices

<0,  -1, 0>
<-1, -1, 1>
<-2, -1, 0>
<-1, -1, -1>
<0,   1, 0>
<-1,  1, 1>
<-2,  1, 0>
<-1,  1, -1>

A ray along the z axis is perpendicular to an edge (not tangent),
yet the intersection must be counted either 0 or 2 times, as
the ray never penetrates the object surface.

Further, I am not sure what you mean by tangent to a
vertex, as a vertex is just a single point, and thus all
intersections are equivalent.

But your general point is excellent -- the intersection determination
is highly non-trivial.

Furthermore, open objects don't have a well-defined interior,
so care is needed to make sure the object is a "solid" object....
if it is formed by nondegenerate CSG, this is of course
guaranteed.

Dan



-- 
http://www.flash.net/~djconnel/

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