/* plane.c */

#include "ray.h"


/**/
/* Determine if a vector projected from location *base  */
/* in direction *dir hits the plane.. If so the return */
/* value is the distance from the base to the point of  */
/* contact.                                             */

double  plane_hits(
object_t  *obj,
vec_t     base,      /* ray base              */
vec_t     dir)       /* unit direction vector */
{
   plane_t *pln;

   assert(obj->cookie == OBJ_COOKIE);

/* extract pln pointer from object structure */


-------------------


/* We will use the following notation in the comments below */
/*  Q = point on the plane  (plane attribute )              */
/*  N = normal to the plane (plane attribute )              */
/*  B = base of ray (input parameter )                      */
/*  D = direction of ray                                    */

/*  ndotd = N dot D */
/*  ndotb = N dot B */
/*  ndotq = N dot Q --- which was precomputed in plane_init */
/*  dist  = signed distance from base to hitpoint location  */


/* Compute ndotd and if 0 return(-1.0); /*

------------------


/* Compute ndotb */


--------------------

/* Compute dist = (ndotq - ndotb) / ndotd;  */

--------------------


/* If dist <= 0.0 return(-1.0); */



--------------------


/* Compute location of hit point by scaling dir by dist and */
/* adding to base                                           */

--------------------

/* if hitpoint_location[Z]  is postive  return(-1).         */

--------------------

/* Copy hitpoint_location to obj->last_hit                 */
/* and  pln->normal to obj->last_normal                    */

   return(dist);
}

void plane_print(
object_t *obj,
FILE *out)
{
   plane_t *pln;

   -------------
}

int plane_load_attributes(
FILE    *in,
plane_t *pln)
{

  --------------
}

/**/
/* Create a new plane object and initialize it */

void plane_init(
FILE *in,
model_t *model,
int  attrmax)
{
   plane_t  *pln;
   object_t *obj;

  int       count;

/* Call the object_init()function to create the object_t */
/* and process the "material" attribute                  */

   ----------------

/* Use list_get_entity() to make obj point to the newly  */
/* created object_t structure.Your  list_add() function */
/* MUST set current to the last element in the list for */
/* this to work correctly.                              */

   -----------------

/* malloc a plane_t structure and set the priv pointer */
/* in the object_t structure to point to the plane_t   */

   -----------------

/* Store the word "plane" in the object_type field of   */
/* the object_t structure. Use the strcpy() function    */

   -----------------

/* Ask plane_load_attributes to load the attributes */
/* Attributes are normal and point                  */

   count = plane_load_attributes(in, pln);
   assert(count == 2);

/* Setup polymorphic function pointers in object_t */

   ----------------

/* pre-compute ndotq                                 */

   -----------------
}