/****************************************************************************
*                spheres.c
*
*  This module implements the sphere primitive.
*
*  from Persistence of Vision Raytracer 
*  Copyright 1992 Persistence of Vision Team
*---------------------------------------------------------------------------
*  Copying, distribution and legal info is in the file povlegal.doc which
*  should be distributed with this file. If povlegal.doc is not available
*  or for more info please contact:
*
*       Drew Wells [POV-Team Leader] 
*       CIS: 73767,1244  Internet: 73767.1244@compuserve.com
*       Phone: (213) 254-4041
* 
* This program is based on the popular DKB raytracer version 2.12.
* DKBTrace was originally written by David K. Buck.
* DKBTrace Ver 2.0-2.12 were written by David K. Buck & Aaron A. Collins.
*
*****************************************************************************/

#include "frame.h"
#include "vector.h"
#include "povproto.h"

METHODS Sphere_Methods =
{ Object_Intersect, All_Sphere_Intersections,
   Inside_Sphere, Sphere_Normal,
   Copy_Sphere,
   Translate_Sphere, Rotate_Sphere,
   Scale_Sphere, Invert_Sphere};

extern SPHERE *Get_Sphere_Shape();

extern RAY *VP_Ray;
extern long Ray_Sphere_Tests, Ray_Sphere_Tests_Succeeded;

int All_Sphere_Intersections (Object, Ray, Depth_Queue)
OBJECT *Object;
RAY *Ray;
PRIOQ *Depth_Queue;
{
   DBL Depth1, Depth2;
   VECTOR Intersection_Point;
   INTERSECTION Local_Element;
   register int Intersection_Found;
   SPHERE *Shape = (SPHERE *) Object;

   Intersection_Found = FALSE;
   if (Intersect_Sphere (Ray, Shape, &Depth1, &Depth2))
   {
      Local_Element.Depth = Depth1;
      Local_Element.Object = Shape -> Parent_Object;
      VScale (Intersection_Point, Ray -> Direction, Depth1);
      VAdd (Intersection_Point, Intersection_Point, Ray -> Initial);
      Local_Element.Point = Intersection_Point;
      Local_Element.Shape = (SHAPE *)Shape;
      pq_add (Depth_Queue, &Local_Element);
      Intersection_Found = TRUE;

      if (Depth2 != Depth1)
      {
         Local_Element.Depth = Depth2;
         Local_Element.Object = Shape -> Parent_Object;
         VScale (Intersection_Point, Ray -> Direction, Depth2);
         VAdd (Intersection_Point, Intersection_Point, Ray -> Initial);
         Local_Element.Point = Intersection_Point;
         Local_Element.Shape = (SHAPE *) Shape;
         pq_add (Depth_Queue, &Local_Element);
         Intersection_Found = TRUE;
      }
   }
   return (Intersection_Found);
}

int Intersect_Sphere (Ray, Sphere, Depth1, Depth2)
RAY *Ray;
SPHERE *Sphere;
DBL *Depth1, *Depth2;
{
   VECTOR Origin_To_Center;
   DBL OCSquared, t_Closest_Approach, Half_Chord, t_Half_Chord_Squared;
   short inside;

   Ray_Sphere_Tests++;
   if (Ray == VP_Ray) {
      if (!Sphere->VPCached) {
         VSub (Sphere->VPOtoC, Sphere->Center, Ray->Initial);
         VDot (Sphere->VPOCSquared, Sphere->VPOtoC, Sphere->VPOtoC);
         Sphere->VPinside = (Sphere->VPOCSquared < Sphere->Radius_Squared);
         Sphere->VPCached = TRUE;
      }
      VDot (t_Closest_Approach, Sphere->VPOtoC, Ray->Direction);
      if (!Sphere->VPinside && (t_Closest_Approach < Small_Tolerance))
         return (FALSE);      
      t_Half_Chord_Squared = Sphere->Radius_Squared - Sphere->VPOCSquared +
      (t_Closest_Approach * t_Closest_Approach);
   }
   else {
      VSub (Origin_To_Center, Sphere->Center, Ray->Initial);
      VDot (OCSquared, Origin_To_Center, Origin_To_Center);
      inside = (OCSquared < Sphere->Radius_Squared);
      VDot (t_Closest_Approach, Origin_To_Center, Ray->Direction);
      if (!inside && (t_Closest_Approach < Small_Tolerance))
         return (FALSE);

      t_Half_Chord_Squared = Sphere->Radius_Squared - OCSquared +
      (t_Closest_Approach * t_Closest_Approach);
   }

   if (t_Half_Chord_Squared < Small_Tolerance)
      return (FALSE);

   Half_Chord = sqrt (t_Half_Chord_Squared);
   *Depth1 = t_Closest_Approach + Half_Chord;
   *Depth2 = t_Closest_Approach - Half_Chord;

   if ((*Depth1 < Small_Tolerance) || (*Depth1 > Max_Distance))
      if ((*Depth2 < Small_Tolerance) || (*Depth2 > Max_Distance))
         return (FALSE);
      else
         *Depth1 = *Depth2;
   else
      if ((*Depth2 < Small_Tolerance) || (*Depth2 > Max_Distance))
         *Depth2 = *Depth1;

   Ray_Sphere_Tests_Succeeded++;
   return (TRUE);
}

int Inside_Sphere (Test_Point, Object)
VECTOR *Test_Point;
OBJECT *Object;
{
   VECTOR Origin_To_Center;
   DBL OCSquared;
   SPHERE *Sphere = (SPHERE *) Object;

   VSub (Origin_To_Center, Sphere->Center, *Test_Point);
   VDot (OCSquared, Origin_To_Center, Origin_To_Center);

   if (Sphere->Inverted)
      return (OCSquared - Sphere->Radius_Squared > Small_Tolerance);
   else
      return (OCSquared - Sphere->Radius_Squared < Small_Tolerance);
}

void Sphere_Normal (Result, Object, Intersection_Point)
OBJECT *Object;
VECTOR *Result, *Intersection_Point;
{
   SPHERE *Sphere = (SPHERE *) Object;

   VSub (*Result, *Intersection_Point, Sphere->Center);
   VScale (*Result, *Result, Sphere->Inverse_Radius);
}

void *Copy_Sphere (Object)
OBJECT *Object;
{
   SPHERE *New_Shape;

   New_Shape = Get_Sphere_Shape ();
   *New_Shape = *((SPHERE *) Object);
   New_Shape -> Next_Object = NULL;

   if (New_Shape->Shape_Texture != NULL)
      New_Shape->Shape_Texture = Copy_Texture (New_Shape->Shape_Texture);

   return (New_Shape);
}

void Translate_Sphere (Object, Vector)
OBJECT *Object;
VECTOR *Vector;
{
   VAdd (((SPHERE *) Object)->Center, ((SPHERE *) Object)->Center, *Vector);

   Translate_Texture (&((SPHERE *) Object)->Shape_Texture, Vector);
}

void Rotate_Sphere (Object, Vector)
OBJECT *Object;
VECTOR *Vector;
{
   TRANSFORMATION Transformation;

   Get_Rotation_Transformation (&Transformation, Vector);
   MTransformVector (&((SPHERE *) Object)->Center,
      &((SPHERE *) Object)->Center, &Transformation);

   Rotate_Texture (&((SPHERE *) Object)->Shape_Texture, Vector);
}

void Scale_Sphere (Object, Vector)
OBJECT *Object;
VECTOR *Vector;
{
   SPHERE *Sphere = (SPHERE *) Object;

   if ((Vector->x != Vector->y) ||
      (Vector->x != Vector->z)) {
      fprintf (stderr, "Error - you cannot scale a sphere unevenly\n");
      exit (1);
   }

   VScale (Sphere->Center, Sphere->Center, Vector->x);
   Sphere->Radius *= Vector->x;
   Sphere->Radius_Squared = Sphere->Radius * Sphere->Radius;
   Sphere->Inverse_Radius = 1.0 / Sphere->Radius;


   Scale_Texture (&((SPHERE *) Object)->Shape_Texture, Vector);
}

void Invert_Sphere (Object)
OBJECT *Object;
{
   ((SPHERE *) Object)->Inverted ^= TRUE;
}