[ggt-devel] Bug in LineSeg/Box intersection

[Sebastian M. <seb...@gm...>]

Hi folks,

After solving some other problems not directly related to GMTL, I think 
I have found a bug in the line segment vs. Box intersection.


The problem are the tests of tIn and tOut.
In my understanding, the should be between 0 and 1 for a line segment.
What is done here is completely wrong, or do I misunderstand something?

In my opinion, there has to be a test of
tIn < 0.0 || tOut > 1.0 for early rejection.

Any comments?

<snip>
   template<class DATA_TYPE>
   bool intersect(const AABox<DATA_TYPE>& box, const LineSeg<DATA_TYPE>& 
seg,
                  unsigned int& numHits, DATA_TYPE& tIn, DATA_TYPE& tOut)
   {
      numHits = 0;
      bool result = intersectAABoxRay(box, seg, tIn, tOut);

      if ( result )
      {
         // If tIn is less than 0, then the origin of the line segment is
         // inside the bounding box (not on an edge)but the endpoint is
         // outside.
         if ( tIn < DATA_TYPE(0))
         {
            numHits = 1;
            tIn = tOut;
         }
         // If tIn is less than 0, then the origin of the line segment is
         // outside the bounding box but the endpoint is inside (not on an
         // edge).
         else if ( tOut > DATA_TYPE(1) )
         {
            numHits = 1;
            tOut = tIn;
         }
         // Otherwise, the line segement intersects the bounding box in two
         // places. tIn and tOut reflect those points of intersection.
         else
         {
            numHits = 2;
         }
      }

      return result;
   }
</snip>

cheers Sebastian