1 files changed, 91 insertions, 0 deletions
diff --git a/libdimension/sphere.c b/libdimension/sphere.c
new file mode 100644
index 0000000..c61a46f
--- /dev/null
+++ b/libdimension/sphere.c
@@ -0,0 +1,91 @@
+/*************************************************************************
+ * 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;
+}