virtualx-engine/core/math/dynamic_bvh.cpp

/*************************************************************************/
/*  dynamic_bvh.cpp                                                      */
/*************************************************************************/
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#include "dynamic_bvh.h"

void DynamicBVH::_delete_node(Node *p_node) {
	node_allocator.free(p_node);
}

void DynamicBVH::_recurse_delete_node(Node *p_node) {
	if (!p_node->is_leaf()) {
		_recurse_delete_node(p_node->childs[0]);
		_recurse_delete_node(p_node->childs[1]);
	}
	if (p_node == bvh_root) {
		bvh_root = nullptr;
	}
	_delete_node(p_node);
}

DynamicBVH::Node *DynamicBVH::_create_node(Node *p_parent, void *p_data) {
	Node *node = node_allocator.alloc();
	node->parent = p_parent;
	node->data = p_data;
	return (node);
}

DynamicBVH::Node *DynamicBVH::_create_node_with_volume(Node *p_parent, const Volume &p_volume, void *p_data) {
	Node *node = _create_node(p_parent, p_data);
	node->volume = p_volume;
	return node;
}

void DynamicBVH::_insert_leaf(Node *p_root, Node *p_leaf) {
	if (!bvh_root) {
		bvh_root = p_leaf;
		p_leaf->parent = nullptr;
	} else {
		if (!p_root->is_leaf()) {
			do {
				p_root = p_root->childs[p_leaf->volume.select_by_proximity(
						p_root->childs[0]->volume,
						p_root->childs[1]->volume)];
			} while (!p_root->is_leaf());
		}
		Node *prev = p_root->parent;
		Node *node = _create_node_with_volume(prev, p_leaf->volume.merge(p_root->volume), nullptr);
		if (prev) {
			prev->childs[p_root->get_index_in_parent()] = node;
			node->childs[0] = p_root;
			p_root->parent = node;
			node->childs[1] = p_leaf;
			p_leaf->parent = node;
			do {
				if (!prev->volume.contains(node->volume)) {
					prev->volume = prev->childs[0]->volume.merge(prev->childs[1]->volume);
				} else {
					break;
				}
				node = prev;
			} while (nullptr != (prev = node->parent));
		} else {
			node->childs[0] = p_root;
			p_root->parent = node;
			node->childs[1] = p_leaf;
			p_leaf->parent = node;
			bvh_root = node;
		}
	}
}

DynamicBVH::Node *DynamicBVH::_remove_leaf(Node *leaf) {
	if (leaf == bvh_root) {
		bvh_root = nullptr;
		return (nullptr);
	} else {
		Node *parent = leaf->parent;
		Node *prev = parent->parent;
		Node *sibling = parent->childs[1 - leaf->get_index_in_parent()];
		if (prev) {
			prev->childs[parent->get_index_in_parent()] = sibling;
			sibling->parent = prev;
			_delete_node(parent);
			while (prev) {
				const Volume pb = prev->volume;
				prev->volume = prev->childs[0]->volume.merge(prev->childs[1]->volume);
				if (pb.is_not_equal_to(prev->volume)) {
					prev = prev->parent;
				} else {
					break;
				}
			}
			return (prev ? prev : bvh_root);
		} else {
			bvh_root = sibling;
			sibling->parent = nullptr;
			_delete_node(parent);
			return (bvh_root);
		}
	}
}

void DynamicBVH::_fetch_leaves(Node *p_root, LocalVector<Node *> &r_leaves, int p_depth) {
	if (p_root->is_internal() && p_depth) {
		_fetch_leaves(p_root->childs[0], r_leaves, p_depth - 1);
		_fetch_leaves(p_root->childs[1], r_leaves, p_depth - 1);
		_delete_node(p_root);
	} else {
		r_leaves.push_back(p_root);
	}
}

// Partitions leaves such that leaves[0, n) are on the
// left of axis, and leaves[n, count) are on the right
// of axis. returns N.
int DynamicBVH::_split(Node **leaves, int p_count, const Vector3 &p_org, const Vector3 &p_axis) {
	int begin = 0;
	int end = p_count;
	for (;;) {
		while (begin != end && leaves[begin]->is_left_of_axis(p_org, p_axis)) {
			++begin;
		}

		if (begin == end) {
			break;
		}

		while (begin != end && !leaves[end - 1]->is_left_of_axis(p_org, p_axis)) {
			--end;
		}

		if (begin == end) {
			break;
		}

		// swap out of place nodes
		--end;
		Node *temp = leaves[begin];
		leaves[begin] = leaves[end];
		leaves[end] = temp;
		++begin;
	}

	return begin;
}

DynamicBVH::Volume DynamicBVH::_bounds(Node **leaves, int p_count) {
	Volume volume = leaves[0]->volume;
	for (int i = 1, ni = p_count; i < ni; ++i) {
		volume = volume.merge(leaves[i]->volume);
	}
	return (volume);
}

void DynamicBVH::_bottom_up(Node **leaves, int p_count) {
	while (p_count > 1) {
		real_t minsize = INFINITY;
		int minidx[2] = { -1, -1 };
		for (int i = 0; i < p_count; ++i) {
			for (int j = i + 1; j < p_count; ++j) {
				const real_t sz = leaves[i]->volume.merge(leaves[j]->volume).get_size();
				if (sz < minsize) {
					minsize = sz;
					minidx[0] = i;
					minidx[1] = j;
				}
			}
		}
		Node *n[] = { leaves[minidx[0]], leaves[minidx[1]] };
		Node *p = _create_node_with_volume(nullptr, n[0]->volume.merge(n[1]->volume), nullptr);
		p->childs[0] = n[0];
		p->childs[1] = n[1];
		n[0]->parent = p;
		n[1]->parent = p;
		leaves[minidx[0]] = p;
		leaves[minidx[1]] = leaves[p_count - 1];
		--p_count;
	}
}

DynamicBVH::Node *DynamicBVH::_top_down(Node **leaves, int p_count, int p_bu_threshold) {
	static const Vector3 axis[] = { Vector3(1, 0, 0), Vector3(0, 1, 0), Vector3(0, 0, 1) };

	ERR_FAIL_COND_V(p_bu_threshold <= 1, nullptr);
	if (p_count > 1) {
		if (p_count > p_bu_threshold) {
			const Volume vol = _bounds(leaves, p_count);
			const Vector3 org = vol.get_center();
			int partition;
			int bestaxis = -1;
			int bestmidp = p_count;
			int splitcount[3][2] = { { 0, 0 }, { 0, 0 }, { 0, 0 } };
			int i;
			for (i = 0; i < p_count; ++i) {
				const Vector3 x = leaves[i]->volume.get_center() - org;
				for (int j = 0; j < 3; ++j) {
					++splitcount[j][x.dot(axis[j]) > 0 ? 1 : 0];
				}
			}
			for (i = 0; i < 3; ++i) {
				if ((splitcount[i][0] > 0) && (splitcount[i][1] > 0)) {
					const int midp = (int)Math::abs(real_t(splitcount[i][0] - splitcount[i][1]));
					if (midp < bestmidp) {
						bestaxis = i;
						bestmidp = midp;
					}
				}
			}
			if (bestaxis >= 0) {
				partition = _split(leaves, p_count, org, axis[bestaxis]);
				ERR_FAIL_COND_V(partition == 0 || partition == p_count, nullptr);
			} else {
				partition = p_count / 2 + 1;
			}

			Node *node = _create_node_with_volume(nullptr, vol, nullptr);
			node->childs[0] = _top_down(&leaves[0], partition, p_bu_threshold);
			node->childs[1] = _top_down(&leaves[partition], p_count - partition, p_bu_threshold);
			node->childs[0]->parent = node;
			node->childs[1]->parent = node;
			return (node);
		} else {
			_bottom_up(leaves, p_count);
			return (leaves[0]);
		}
	}
	return (leaves[0]);
}

DynamicBVH::Node *DynamicBVH::_node_sort(Node *n, Node *&r) {
	Node *p = n->parent;
	ERR_FAIL_COND_V(!n->is_internal(), nullptr);
	if (p > n) {
		const int i = n->get_index_in_parent();
		const int j = 1 - i;
		Node *s = p->childs[j];
		Node *q = p->parent;
		ERR_FAIL_COND_V(n != p->childs[i], nullptr);
		if (q) {
			q->childs[p->get_index_in_parent()] = n;
		} else {
			r = n;
		}
		s->parent = n;
		p->parent = n;
		n->parent = q;
		p->childs[0] = n->childs[0];
		p->childs[1] = n->childs[1];
		n->childs[0]->parent = p;
		n->childs[1]->parent = p;
		n->childs[i] = p;
		n->childs[j] = s;
		SWAP(p->volume, n->volume);
		return (p);
	}
	return (n);
}

void DynamicBVH::clear() {
	if (bvh_root) {
		_recurse_delete_node(bvh_root);
	}
	lkhd = -1;
	opath = 0;
}

void DynamicBVH::optimize_bottom_up() {
	if (bvh_root) {
		LocalVector<Node *> leaves;
		_fetch_leaves(bvh_root, leaves);
		_bottom_up(&leaves[0], leaves.size());
		bvh_root = leaves[0];
	}
}

void DynamicBVH::optimize_top_down(int bu_threshold) {
	if (bvh_root) {
		LocalVector<Node *> leaves;
		_fetch_leaves(bvh_root, leaves);
		bvh_root = _top_down(&leaves[0], leaves.size(), bu_threshold);
	}
}

void DynamicBVH::optimize_incremental(int passes) {
	if (passes < 0) {
		passes = total_leaves;
	}
	if (passes > 0) {
		do {
			if (!bvh_root) {
				break;
			}
			Node *node = bvh_root;
			unsigned bit = 0;
			while (node->is_internal()) {
				node = _node_sort(node, bvh_root)->childs[(opath >> bit) & 1];
				bit = (bit + 1) & (sizeof(unsigned) * 8 - 1);
			}
			_update(node);
			++opath;
		} while (--passes);
	}
}

DynamicBVH::ID DynamicBVH::insert(const AABB &p_box, void *p_userdata) {
	Volume volume;
	volume.min = p_box.position;
	volume.max = p_box.position + p_box.size;

	Node *leaf = _create_node_with_volume(nullptr, volume, p_userdata);
	_insert_leaf(bvh_root, leaf);
	++total_leaves;

	ID id;
	id.node = leaf;

	return id;
}

void DynamicBVH::_update(Node *leaf, int lookahead) {
	Node *root = _remove_leaf(leaf);
	if (root) {
		if (lookahead >= 0) {
			for (int i = 0; (i < lookahead) && root->parent; ++i) {
				root = root->parent;
			}
		} else {
			root = bvh_root;
		}
	}
	_insert_leaf(root, leaf);
}

bool DynamicBVH::update(const ID &p_id, const AABB &p_box) {
	ERR_FAIL_COND_V(!p_id.is_valid(), false);
	Node *leaf = p_id.node;

	Volume volume;
	volume.min = p_box.position;
	volume.max = p_box.position + p_box.size;

	if (leaf->volume.min.is_equal_approx(volume.min) && leaf->volume.max.is_equal_approx(volume.max)) {
		// noop
		return false;
	}

	Node *base = _remove_leaf(leaf);
	if (base) {
		if (lkhd >= 0) {
			for (int i = 0; (i < lkhd) && base->parent; ++i) {
				base = base->parent;
			}
		} else {
			base = bvh_root;
		}
	}
	leaf->volume = volume;
	_insert_leaf(base, leaf);
	return true;
}

void DynamicBVH::remove(const ID &p_id) {
	ERR_FAIL_COND(!p_id.is_valid());
	Node *leaf = p_id.node;
	_remove_leaf(leaf);
	_delete_node(leaf);
	--total_leaves;
}

void DynamicBVH::_extract_leaves(Node *p_node, List<ID> *r_elements) {
	if (p_node->is_internal()) {
		_extract_leaves(p_node->childs[0], r_elements);
		_extract_leaves(p_node->childs[1], r_elements);
	} else {
		ID id;
		id.node = p_node;
		r_elements->push_back(id);
	}
}

void DynamicBVH::set_index(uint32_t p_index) {
	ERR_FAIL_COND(bvh_root != nullptr);
	index = p_index;
}

uint32_t DynamicBVH::get_index() const {
	return index;
}

void DynamicBVH::get_elements(List<ID> *r_elements) {
	if (bvh_root) {
		_extract_leaves(bvh_root, r_elements);
	}
}

int DynamicBVH::get_leaf_count() const {
	return total_leaves;
}
int DynamicBVH::get_max_depth() const {
	if (bvh_root) {
		int depth = 1;
		int max_depth = 0;
		bvh_root->get_max_depth(depth, max_depth);
		return max_depth;
	} else {
		return 0;
	}
}

DynamicBVH::~DynamicBVH() {
	clear();
}