/*************************************************************************
 * Copyright (C) 2009-2011 Tavian Barnes <tavianator@tavianator.com>     *
 *                                                                       *
 * This file is part of The Dimension Library.                           *
 *                                                                       *
 * The Dimension Library is free software; you can redistribute it and/  *
 * or modify it under the terms of the GNU Lesser General Public License *
 * as published by the Free Software Foundation; either version 3 of the *
 * License, or (at your option) any later version.                       *
 *                                                                       *
 * The Dimension 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  *
 * Lesser General Public License for more details.                       *
 *                                                                       *
 * You should have received a copy of the GNU Lesser General Public      *
 * License along with this program.  If not, see                         *
 * <http://www.gnu.org/licenses/>.                                       *
 *************************************************************************/

/**
 * @file
 * Spheres.
 */

#include "dimension-internal.h"

/** Sphere intersection callback. */
static bool
dmnsn_sphere_intersection_fn(const dmnsn_object *sphere, dmnsn_line l,
                             dmnsn_intersection *intersection)
{
  /* Solve (x0 + nx*t)^2 + (y0 + ny*t)^2 + (z0 + nz*t)^2 == 1 */
  double poly[3], x[2];
  poly[2] = dmnsn_vector_dot(l.n, l.n);
  poly[1] = 2.0*dmnsn_vector_dot(l.n, l.x0);
  poly[0] = dmnsn_vector_dot(l.x0, l.x0) - 1.0;

  size_t n = dmnsn_polynomial_solve(poly, 2, x);
  if (n == 0) {
    return false;
  } else {
    double t = x[0];
    /* Optimize for the case where we're outside the sphere */
    if (dmnsn_likely(n == 2))
      t = dmnsn_min(t, x[1]);

    intersection->t      = t;
    intersection->normal = dmnsn_line_point(l, t);
    return true;
  }
}

/** Sphere inside callback. */
static bool
dmnsn_sphere_inside_fn(const dmnsn_object *sphere, dmnsn_vector point)
{
  return point.x*point.x + point.y*point.y + point.z*point.z < 1.0;
}

/* Allocate a new sphere */
dmnsn_object *
dmnsn_new_sphere(void)
{
  dmnsn_object *sphere = dmnsn_new_object();
  sphere->intersection_fn  = dmnsn_sphere_intersection_fn;
  sphere->inside_fn        = dmnsn_sphere_inside_fn;
  sphere->bounding_box.min = dmnsn_new_vector(-1.0, -1.0, -1.0);
  sphere->bounding_box.max = dmnsn_new_vector(1.0, 1.0, 1.0);
  return sphere;
}