/*
 *  Ray++ - Object-oriented ray tracing library
 *  Copyright (C) 1998-2001 Martin Reinecke and others.
 *  See the AUTHORS file for more information.
 *
 *  This library is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU Library General Public
 *  License as published by the Free Software Foundation; either
 *  version 2 of the License, or (at your option) any later version.
 *
 *  This library is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 *  Library General Public License for more details.
 *
 *  You should have received a copy of the GNU Library General Public
 *  License along with this library; if not, write to the Free
 *  Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 *  See the README file for more information.
 */

/* 
 * A two-sided triangle (no backface culling)
 *
 * See 
 *   Moeller, Trumbore: "Fast, Minimum Storage Ray/Triangle Intersection",
 *   Journal of Graphics Tools, 2(1):21-28, 1997. 
 * for details.
 */

#include "shapes/triangle.h"

namespace RAYPP {

inline bool TRIANGLE::Find_Intersection (const GEOM_RAY &Ray,
  float8 &dist) const
  {
  VECTOR TVec, PVec, QVec;
  float8 det, inv_det;
  float8 u, v;

  /* begin calculating determinant - also used to calculate U parameter */
  PVec = Cross (Ray.dir, Edge2);

  /* if determinant is near zero, ray lies in plane of triangle */
  det = Dot (Edge1, PVec);

  if (abs (det) < Small_float4)
    return false;
   
  inv_det = 1.0 / det;

  /* calculate distance from vert1 to ray origin */
  TVec = Ray.start - Vert1;

  /* calculate U parameter and test bounds */
  u = Dot (TVec, PVec) * inv_det;
  if (u < 0.0 || u > 1.0)
    return false;

  /* prepare to test V parameter */
  QVec = Cross (TVec, Edge1);

  /* calculate V parameter and test bounds */
  v = Dot (Ray.dir, QVec) * inv_det;
  if (v < 0.0 || u + v > 1.0)
    return false;

  /* calculate t, ray intersects triangle */
  dist = Dot (Edge2, QVec) * inv_det;

  return ((dist > Ray.mindist) && (dist < Ray.maxdist));
  }

TRIANGLE::TRIANGLE (const VECTOR &Vertex1,
                    const VECTOR &Vertex2,
                    const VECTOR &Vertex3)
  : Vert1 (Vertex1), Edge1 (Vertex2-Vertex1), Edge2 (Vertex3-Vertex1)
  {}

//virtual
void TRIANGLE::Init ()
  {
  if (initialized) return;

  Normal_Vector = Cross (Edge1, Edge2).Norm();

  initialized = true;
  }

//virtual
void TRIANGLE::Transform (const TRANSFORM &Trans)
  {
  cni();

  Vert1 = Trans.TransPoint (Vert1);
  Edge1 = Trans.TransDirection (Edge1);
  Edge2 = Trans.TransDirection (Edge2);
  }

//virtual
AXISBOX TRIANGLE::BBox () const
  {
  ci();

  AXISBOX Box;
  Box.Include(Vert1);
  Box.Include(Vert1+Edge1);
  Box.Include(Vert1+Edge2);
  return Box;
  }

//virtual
bool TRIANGLE::Test 
  (const GEOM_RAY &Ray, float8 &dist, bool &realhit) const
  {
  ci();
  realhit = true;
  return Find_Intersection (Ray, dist);
  }

//virtual
bool TRIANGLE::Intersect 
  (const GEOM_RAY &Ray, float8 &dist, VECTOR &Normal) const
  {
  ci();
  Normal = Normal_Vector;
  return Find_Intersection (Ray, dist);
  }

//virtual
void TRIANGLE::All_Intersections 
  (const GEOM_RAY &Ray, vector<INTER> &Inter) const
  {
  ci();
  float8 depth;
  if (Find_Intersection (Ray, depth))
    Inter.push_back (INTER (depth, Normal_Vector));
  }

} // namespace RAYPP