is within ... polygon shape?

[Cubist at aol.com]

   It occurs to me that even tho the "intersect" function works with the 
bounding rectangle of an object, and not the actual object itself, "intersect" 
could nonetheless be useful as a sort of initial screen. If "intersect" doesn't 
think the two objects intersect, well, they *can't* intersect, right? Thus, use 
"intersect" to winnow out the wheat (stuff that *might* intersect) from the 
chaff (stuff that *can't* intersect), and then use your *real* 
intersection-finding function on the wheat. Like so:

function WhatIntersectz DaList, DerObject
  # DerObject is the thing you want to find out what intersects with it
  # DaList is a return-delimited list of all the objects that *might* 
intersect with DerObject

  put "" into NuList
  repeat for each line LL in DaList
    if intersect (the rect of LL, the rect of DerObject) then
      put LL into line (1 + the number of lines in NuList) of NuList
    end if
  end repeat
  put NuList into DaList

  # now we've got a list of all the objects which *might* intersect
  # which are the real deal?
  put "" into NuList
  repeat for each line LL in DaList
    if ReallyIntersect (the rect of LL, the rect of DerObject) then
      put LL into line (1 + the number of lines in NuList) of NuList
    end if
  end repeat
  return NuList
end WhatIntersectz

   "ReallyIntersect" is, of course, a separate handler which takes the actual 
points of a polygon into account when determining what does or doesn't 
intersect. What's the point of going thru all this rigamarole in the first place? It 
depends how fast the "ReallyIntersect" code is, as compared to the 
"intersect" function. I'm assuming that "ReallyIntersect" is going to be appreciably 
slower than "intersect", in which case it makes sense to use "ReallyIntersect" as 
little as possible.

   Hope this helps...