Ray-Plane intersection

  
// Start = start of ray

// Dir = direction of ray (normalized)

// Normal = plane normal (normalized)

// D = Distance of plane from origin along normal (D in the plane equation)

// IntPoint = final pointof intersection

// returns true if an intersection was found, or false if not.

bool RayPlaneIntersect(const fvector3 &Start, const fvector3 &Dir, const fvector3 &Normal, float D, fvector3 *IntPoint)
{
        float hd = 0;
	float i = Normal * Dir;               // dotproduct


	if( i==0 ) return( false );           // ray is parallel to plane, no hit


        float j = -(Normal * Start + D);
	hd = j/i;                             // compute distance along ray to intersection point

	if( hd < EPSILON ) return( false );   // Hit is behind start of ray, no hit

        *IntPoint = Start + hd*Dir;           // compute the point of intersection, using the ray equation


        return( true );
};
  

  
#define EPSILON 0.000001
#define CROSS(dest,v1,v2) \
          dest[0]=v1[1]*v2[2]-v1[2]*v2[1]; \
          dest[1]=v1[2]*v2[0]-v1[0]*v2[2]; \
          dest[2]=v1[0]*v2[1]-v1[1]*v2[0];
#define DOT(v1,v2) (v1[0]*v2[0]+v1[1]*v2[1]+v1[2]*v2[2])
#define SUB(dest,v1,v2)
          dest[0]=v1[0]-v2[0]; \
          dest[1]=v1[1]-v2[1]; \
          dest[2]=v1[2]-v2[2]; 
/*
We present a clean algorithm for determining whether a ray intersects a triangle. 
The algorithm translates the origin of the ray and then changes the base to yield a vector (t u v)T, where t is the 
distance to the plane in which the triangle lies and (u,v) represents the coordinates inside the triangle.
*/
int
intersect_triangle(double orig[3], double dir[3],
                   double vert0[3], double vert1[3], double vert2[3],
                   double *t, double *u, double *v)
{
   double edge1[3], edge2[3], tvec[3], pvec[3], qvec[3];
   double det,inv_det;

   /* find vectors for two edges sharing vert0 */
   SUB(edge1, vert1, vert0);
   SUB(edge2, vert2, vert0);

   /* begin calculating determinant - also used to calculate U parameter */
   CROSS(pvec, dir, edge2);

   /* if determinant is near zero, ray lies in plane of triangle */
   det = DOT(edge1, pvec);

#ifdef TEST_CULL           /* define TEST_CULL if culling is desired */
   if (det < EPSILON)
      return 0;

   /* calculate distance from vert0 to ray origin */
   SUB(tvec, orig, vert0);

   /* calculate U parameter and test bounds */
   *u = DOT(tvec, pvec);
   if (*u < 0.0 || *u > det)
      return 0;

   /* prepare to test V parameter */
   CROSS(qvec, tvec, edge1);

    /* calculate V parameter and test bounds */
   *v = DOT(dir, qvec);
   if (*v < 0.0 || *u + *v > det)
      return 0;

   /* calculate t, scale parameters, ray intersects triangle */
   *t = DOT(edge2, qvec);
   inv_det = 1.0 / det;
   *t *= inv_det;
   *u *= inv_det;
   *v *= inv_det;
#else                    /* the non-culling branch */
   if (det > -EPSILON && det < EPSILON)
     return 0;
   inv_det = 1.0 / det;

   /* calculate distance from vert0 to ray origin */
   SUB(tvec, orig, vert0);

   /* calculate U parameter and test bounds */
   *u = DOT(tvec, pvec) * inv_det;
   if (*u < 0.0 || *u > 1.0)
     return 0;

   /* prepare to test V parameter */
   CROSS(qvec, tvec, edge1);

   /* calculate V parameter and test bounds */
   *v = DOT(dir, qvec) * inv_det;
   if (*v < 0.0 || *u + *v > 1.0)
     return 0;

   /* calculate t, ray intersects triangle */
   *t = DOT(edge2, qvec) * inv_det;
#endif
   return 1;
}