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-rw-r--r--libdimension/sphere.c91
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diff --git a/libdimension/sphere.c b/libdimension/sphere.c
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+/*************************************************************************
+ * Copyright (C) 2009 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;
+}