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/*************************************************************************
* Copyright (C) 2010 Tavian Barnes <tavianator@gmail.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/>. *
*************************************************************************/
#include "dimension.h"
#include <stdlib.h> /* For malloc */
#include <math.h> /* For sqrt */
/*
* Sphere
*/
/* Sphere object callbacks */
static dmnsn_intersection *
dmnsn_sphere_intersection_fn(const dmnsn_object *sphere, dmnsn_line line);
static int dmnsn_sphere_inside_fn(const dmnsn_object *sphere,
dmnsn_vector point);
/* Allocate a new sphere */
dmnsn_object *
dmnsn_new_sphere()
{
dmnsn_object *sphere = dmnsn_new_object();
if (sphere) {
sphere->intersection_fn = &dmnsn_sphere_intersection_fn;
sphere->inside_fn = &dmnsn_sphere_inside_fn;
sphere->min = dmnsn_new_vector(-1.0, -1.0, -1.0);
sphere->max = dmnsn_new_vector(1.0, 1.0, 1.0);
}
return sphere;
}
/* Returns the closest intersection of `line' with `sphere' */
static dmnsn_intersection *
dmnsn_sphere_intersection_fn(const dmnsn_object *sphere, dmnsn_line line)
{
double a, b, c, t;
dmnsn_intersection *intersection = NULL;
/* Solve (x0 + nx*t)^2 + (y0 + ny*t)^2 + (z0 + nz*t)^2 == 1 */
a = line.n.x*line.n.x + line.n.y*line.n.y + line.n.z*line.n.z;
b = 2.0*(line.n.x*line.x0.x + line.n.y*line.x0.y + line.n.z*line.x0.z);
c = line.x0.x*line.x0.x + line.x0.y*line.x0.y + line.x0.z*line.x0.z - 1.0;
if (b*b - 4.0*a*c >= 0) {
t = (-b - sqrt(b*b - 4.0*a*c))/(2*a);
if (t < 0.0) {
t = (-b + sqrt(b*b - 4.0*a*c))/(2*a);
}
if (t >= 0.0) {
intersection = dmnsn_new_intersection();
intersection->ray = line;
intersection->t = t;
intersection->normal = dmnsn_line_point(line, t);
intersection->texture = sphere->texture;
/* Flip the normal if we're inside the sphere */
if (dmnsn_vector_dot(line.n, intersection->normal) > 0.0)
intersection->normal = dmnsn_vector_negate(intersection->normal);
}
}
return intersection;
}
/* Return whether a point is inside a sphere (x**2 + y**2 + z**2 < 1.0) */
static int
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;
}
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