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/** @file
* @brief Class for implementing sweepline algorithms
*//*
* Authors:
* Krzysztof Kosiński <tweenk.pl@gmail.com>
*
* Copyright 2015 Authors
*
* This library is free software; you can redistribute it and/or
* modify it either under the terms of the GNU Lesser General Public
* License version 2.1 as published by the Free Software Foundation
* (the "LGPL") or, at your option, under the terms of the Mozilla
* Public License Version 1.1 (the "MPL"). If you do not alter this
* notice, a recipient may use your version of this file under either
* the MPL or the LGPL.
*
* You should have received a copy of the LGPL along with this library
* in the file COPYING-LGPL-2.1; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
* You should have received a copy of the MPL along with this library
* in the file COPYING-MPL-1.1
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.1 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
* OF ANY KIND, either express or implied. See the LGPL or the MPL for
* the specific language governing rights and limitations.
*/
#ifndef LIB2GEOM_SEEN_SWEEPER_H
#define LIB2GEOM_SEEN_SWEEPER_H
#include <2geom/coord.h>
#include <algorithm>
#include <vector>
#include <boost/intrusive/list.hpp>
namespace Geom {
// exposition only
template <typename Item>
class SweepVector {
public:
typedef typename std::vector<Item>::const_iterator ItemIterator;
SweepVector(std::vector<Item> const &v)
: _items(v)
{}
std::vector<Item> const &items() { return _items; }
Interval itemBounds(ItemIterator /*ii*/) { return Interval(); }
void addActiveItem(ItemIterator /*ii*/) {}
void removeActiveItem(ItemIterator /*ii*/) {}
private:
std::vector<Item> const &_items;
};
/** @brief Generic sweepline algorithm.
*
* This class encapsulates an algorithm that sorts the objects according
* to their bounds, then moves an imaginary line (sweepline) over those
* bounds from left to right. Objects are added to the active list when
* the line starts intersecting their bounds, and removed when it completely
* passes over them.
*
* To use this, create a class that exposes the following methods:
* - Range items() - returns a forward iterable range of items that will be swept.
* - Interval itemBounds(iterator i) - given an iterator from the above range,
* compute the bounding interval of the referenced item in the direction of sweep.
* - void addActiveItem(iterator i) - add an item to the active list.
* - void removeActiveItem(iterator i) - remove an item from the active list.
*
* Create the object, then instantiate this template with the above class
* as the template parameter, pass it the constructed object of the class,
* and call the process() method.
*
* A good choice for the active list is a Boost intrusive list, which allows
* you to get an iterator from a value in constant time.
*
* Look in path.cpp for example usage.
*
* @tparam Item The type of items to sweep
* @tparam SweepTraits Traits class that defines the items' bounds,
* how to interpret them and how to sort the events
* @ingroup Utilities
*/
template <typename SweepSet>
class Sweeper {
public:
typedef typename SweepSet::ItemIterator Iter;
explicit Sweeper(SweepSet &set)
: _set(set)
{
std::size_t sz = std::distance(set.items().begin(), set.items().end());
_entry_events.reserve(sz);
_exit_events.reserve(sz);
}
/** @brief Process entry and exit events.
* This will iterate over all inserted items, calling the methods
* addActiveItem and removeActiveItem on the SweepSet passed at construction
* according to the order of the boundaries of each item. */
void process() {
if (_set.items().empty()) return;
Iter last = _set.items().end();
for (Iter i = _set.items().begin(); i != last; ++i) {
Interval b = _set.itemBounds(i);
// guard against NANs
assert(b.min() == b.min() && b.max() == b.max());
_entry_events.push_back(Event(b.max(), i));
_exit_events.push_back(Event(b.min(), i));
}
std::make_heap(_entry_events.begin(), _entry_events.end());
std::make_heap(_exit_events.begin(), _exit_events.end());
Event next_entry = _get_next(_entry_events);
Event next_exit = _get_next(_exit_events);
while (next_entry || next_exit) {
assert(next_exit);
if (!next_entry || next_exit > next_entry) {
// exit event - remove record from active list
_set.removeActiveItem(next_exit.item);
next_exit = _get_next(_exit_events);
} else {
// entry event - add record to active list
_set.addActiveItem(next_entry.item);
next_entry = _get_next(_entry_events);
}
}
}
private:
struct Event
: boost::totally_ordered<Event>
{
Coord coord;
Iter item;
Event(Coord c, Iter const &i)
: coord(c), item(i)
{}
Event()
: coord(nan("")), item()
{}
bool operator<(Event const &other) const { return coord < other.coord; }
bool operator==(Event const &other) const { return coord == other.coord; }
operator bool() const { return !std::isnan(coord); }
};
static Event _get_next(std::vector<Event> &heap) {
if (heap.empty()) {
Event e;
return e;
}
std::pop_heap(heap.begin(), heap.end());
Event ret = heap.back();
heap.pop_back();
return ret;
}
SweepSet &_set;
std::vector<Event> _entry_events;
std::vector<Event> _exit_events;
};
} // namespace Geom
#endif // !LIB2GEOM_SEEN_SWEEPER_H
/*
Local Variables:
mode:c++
c-file-style:"stroustrup"
c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
indent-tabs-mode:nil
fill-column:99
End:
*/
// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :
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