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diff --git a/libdimension/bvh.h b/libdimension/bvh.h
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+/*************************************************************************
+ * Copyright (C) 2012 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.
+ * Bounding volume hierarchy.  This generic interface allows different data
+ * structures to be represented in the same way, thus sharing code for their
+ * traversal algorithm.
+ */
+
+#include <stdbool.h>
+
+/** A bounding volume hierarchy. */
+typedef struct dmnsn_bvh dmnsn_bvh;
+
+/** Available BVH implementations. */
+typedef enum dmnsn_bvh_kind {
+  DMNSN_BVH_NONE,
+  DMNSN_BVH_PRTREE,
+} dmnsn_bvh_kind;
+
+/** Create a BVH. */
+DMNSN_INTERNAL dmnsn_bvh *dmnsn_new_bvh(const dmnsn_array *objects,
+                                        dmnsn_bvh_kind kind);
+/** Delete a BVH. */
+DMNSN_INTERNAL void dmnsn_delete_bvh(dmnsn_bvh *bvh);
+
+/** Find the closest ray-object intersection in the tree. */
+DMNSN_INTERNAL bool dmnsn_bvh_intersection(const dmnsn_bvh *bvh,
+                                           dmnsn_line ray,
+                                           dmnsn_intersection *intersection,
+                                           bool reset);
+/** Determine whether a point is inside any object in the tree. */
+DMNSN_INTERNAL bool dmnsn_bvh_inside(const dmnsn_bvh *bvh, dmnsn_vector point);
+/** Return the bounding box of the whole hierarchy. */
+DMNSN_INTERNAL dmnsn_bounding_box dmnsn_bvh_bounding_box(const dmnsn_bvh *bvh);
+
+/** A non-flat BVH representation, used by BVH implementations. */
+typedef struct dmnsn_bvh_node {
+  dmnsn_bounding_box bounding_box;   /** The bounding box of this node. */
+  dmnsn_object *object;              /** The object, for leaf nodes. */
+  int data;                          /** Extra field for implementation use. */
+  size_t nchildren;                  /** How many children this node has. */
+  size_t max_children;               /** Maximum number of children. */
+  struct dmnsn_bvh_node *children[]; /** Flexible array of children. */
+} dmnsn_bvh_node;
+
+/** Create a BVH node. */
+DMNSN_INTERNAL dmnsn_bvh_node *dmnsn_new_bvh_node(size_t max_children);
+
+/** Create a BVH leaf node. */
+DMNSN_INTERNAL dmnsn_bvh_node *dmnsn_new_bvh_leaf_node(dmnsn_object *object);
+
+/** Delete a BVH node. */
+DMNSN_INTERNAL void dmnsn_delete_bvh_node(dmnsn_bvh_node *node);
+
+/** Add a child to a BVH node. */
+DMNSN_INTERNAL void dmnsn_bvh_node_add(dmnsn_bvh_node *parent,
+                                       dmnsn_bvh_node *child);