/*
Copyright (C) 2001-2006, William Joseph.
All Rights Reserved.

This file is part of GtkRadiant.

GtkRadiant is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

GtkRadiant 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 General Public License for more details.

You should have received a copy of the GNU General Public License
along with GtkRadiant; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include "mathlib.h"
#include <float.h>

vec3_t identity = { 0,0,0 };

void ray_construct_for_vec3(ray_t *ray, const vec3_t origin, const vec3_t direction)
{
  VectorCopy(origin, ray->origin);
  VectorCopy(direction, ray->direction);
}
  
void ray_transform(ray_t *ray, const m4x4_t matrix)
{
  m4x4_transform_point(matrix, ray->origin);
  m4x4_transform_normal(matrix, ray->direction);
}

vec_t ray_intersect_point(const ray_t *ray, const vec3_t point, vec_t epsilon, vec_t divergence)
{
  vec3_t displacement;
  vec_t depth;

  // calc displacement of test point from ray origin
  VectorSubtract(point, ray->origin, displacement);
  // calc length of displacement vector along ray direction
	depth = DotProduct(displacement, ray->direction);
  if(depth < 0.0f) return (vec_t)FLT_MAX;
  // calc position of closest point on ray to test point
  VectorMA (ray->origin, depth, ray->direction, displacement);
  // calc displacement of test point from closest point
	VectorSubtract(point, displacement, displacement);
  // calc length of displacement, subtract depth-dependant epsilon
  if (VectorLength(displacement) - (epsilon + (depth * divergence)) > 0.0f) return (vec_t)FLT_MAX;
  return depth;
}

// Tomas Moller and Ben Trumbore. Fast, minimum storage ray-triangle intersection. Journal of graphics tools, 2(1):21-28, 1997

#define EPSILON 0.000001

vec_t ray_intersect_triangle(const ray_t *ray, qboolean bCullBack, const vec3_t vert0, const vec3_t vert1, const vec3_t vert2)
{
  float edge1[3], edge2[3], tvec[3], pvec[3], qvec[3];
  float det,inv_det;
  float u, v;
  vec_t depth = (vec_t)FLT_MAX;
  
  /* find vectors for two edges sharing vert0 */
  VectorSubtract(vert1, vert0, edge1);
  VectorSubtract(vert2, vert0, edge2);
  
  /* begin calculating determinant - also used to calculate U parameter */
  CrossProduct(ray->direction, edge2, pvec);
  
  /* if determinant is near zero, ray lies in plane of triangle */
  det = DotProduct(edge1, pvec);
  
  if (bCullBack == qtrue)
  {
    if (det < EPSILON)
      return depth;
    
    // calculate distance from vert0 to ray origin
    VectorSubtract(ray->origin, vert0, tvec);
    
    // calculate U parameter and test bounds
    u = DotProduct(tvec, pvec);
    if (u < 0.0 || u > det)
      return depth;
    
    // prepare to test V parameter
    CrossProduct(tvec, edge1, qvec);
    
    // calculate V parameter and test bounds
    v = DotProduct(ray->direction, qvec);
    if (v < 0.0 || u + v > det)
      return depth;
    
    // calculate t, scale parameters, ray intersects triangle
    depth = DotProduct(edge2, qvec);
    inv_det = 1.0f / det;
    depth *= inv_det;
    //u *= inv_det;
    //v *= inv_det;
  }
  else
  {
    /* the non-culling branch */
    if (det > -EPSILON && det < EPSILON)
      return depth;
    inv_det = 1.0f / det;
    
    /* calculate distance from vert0 to ray origin */
    VectorSubtract(ray->origin, vert0, tvec);
    
    /* calculate U parameter and test bounds */
    u = DotProduct(tvec, pvec) * inv_det;
    if (u < 0.0 || u > 1.0)
      return depth;
    
    /* prepare to test V parameter */
    CrossProduct(tvec, edge1, qvec);
    
    /* calculate V parameter and test bounds */
    v = DotProduct(ray->direction, qvec) * inv_det;
    if (v < 0.0 || u + v > 1.0)
      return depth;
    
    /* calculate t, ray intersects triangle */
    depth = DotProduct(edge2, qvec) * inv_det;
  }
  return depth;
}

vec_t ray_intersect_plane(const ray_t* ray, const vec3_t normal, vec_t dist)
{
  return -(DotProduct(normal, ray->origin) - dist) / DotProduct(ray->direction, normal);
}