Method constructIntersection

Engine/source/math/mPolyhedron.impl.h:85–325

template< typename Base >
U32 PolyhedronImpl< Base >::constructIntersection( const PlaneF& plane, Point3F* outPoints, U32 maxOutPoints ) const
{
   // The assumption here is that the polyhedron is entirely composed
   // of convex polygons implicitly described by the edges, points, and planes.
   // So, any polygon can only have one of three relations to the given plane
   //
   // 1) None of its edges intersect with the plane, i.e. the polygon can be ignored.
   // 2) One of its edges lies on the plane.
   // 2) Two of its edges intersect with the plane.
   //
   // Conceptually, we need to find the first face with an intersecting edge, then find
   // another edge on the same face that is also intersecting, and then continue with the
   // face on the opposite side of the edge.

   const U32 numEdges = this->getNumEdges();
   const typename Base::EdgeType* edges = this->getEdges();
   const typename Base::PointType* points = this->getPoints();
   U32 numOutPoints = 0;

   #define ADD_POINT( p ) \
      if( numOutPoints >= maxOutPoints ) \
         return 0; \
      outPoints[ numOutPoints ++ ] = p;

   Point3F intersection;

   S32 firstEdge = -1;
   S32 firstFace = -1;

   U32 v1 = 0;
   U32 v2 = 0;

   PlaneF::Side v1Side = PlaneF::Front;
   PlaneF::Side v2Side = PlaneF::Front;

   // Find an edge to start with.  This is the first edge
   // in the polyhedron that intersects the plane.

   for( U32 i = 0; i < numEdges; ++ i )
   {
      const typename Base::EdgeType& edge = edges[ i ];

      v1 = edge.vertex[ 0 ];
      v2 = edge.vertex[ 1 ];

      const Point3F& p1 = points[ v1 ];
      const Point3F& p2 = points[ v2 ];

      v1Side = plane.whichSide( p1 );
      v2Side = plane.whichSide( p2 );

      if( v1Side == PlaneF::On || v2Side == PlaneF::On ||
          plane.clipSegment( p1, p2, intersection ) )
      {
         firstEdge = i;
         firstFace = edge.face[ 0 ];
         break;
      }