filter.cpp

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/*
    Copyright (C) 2003 - 2022
    by David White <dave@whitevine.net>
    Part of the Battle for Wesnoth Project https://www.wesnoth.org/

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY.

    See the COPYING file for more details.
*/

#define GETTEXT_DOMAIN "wesnoth-lib"

#include "config.hpp"
#include "display_context.hpp"
#include "filter_context.hpp"
#include "game_board.hpp"
#include "game_data.hpp"
#include "log.hpp"
#include "map/map.hpp"
#include "side_filter.hpp"
#include "team.hpp"
#include "terrain/filter.hpp"
#include "tod_manager.hpp"
#include "units/unit.hpp"
#include "units/filter.hpp"
#include "variable.hpp"
#include "formula/callable_objects.hpp"
#include "formula/formula.hpp"
#include "formula/function_gamestate.hpp"
#include "scripting/game_lua_kernel.hpp"
#include "units/unit_alignments.hpp"

#include <boost/range/adaptor/transformed.hpp>

static lg::log_domain log_engine("engine");
#define ERR_NG LOG_STREAM(err, log_engine)
#define WRN_NG LOG_STREAM(warn, log_engine)

static lg::log_domain log_wml("wml");
#define ERR_WML LOG_STREAM(err, log_wml)

terrain_filter::~terrain_filter()
{
}

terrain_filter::terrain_filter(const vconfig& cfg, const filter_context * fc, const bool flat_tod) :
    cfg_(cfg),
    fc_(fc),
    cache_(),
    max_loop_(game_config::max_loop),
    flat_(flat_tod)
{
}

terrain_filter::terrain_filter(const vconfig& cfg, const terrain_filter& original) :
    cfg_(cfg),
    fc_(original.fc_),
    cache_(),
    max_loop_(original.max_loop_),
    flat_(original.flat_)
{
}

terrain_filter::terrain_filter(const terrain_filter& other) :
    xy_pred(), // We should construct this too, since it has no datamembers
               // use the default constructor.
    cfg_(other.cfg_),
    fc_(other.fc_),
    cache_(),
    max_loop_(other.max_loop_),
    flat_(other.flat_)
{
}

terrain_filter& terrain_filter::operator=(const terrain_filter& other)
{
    // Use copy constructor to make sure we are coherent
    if (this != &other) {
        this->~terrain_filter();
        new (this) terrain_filter(other) ;
    }
    return *this ;
}

terrain_filter::terrain_filter_cache::terrain_filter_cache() :
    parsed_terrain(nullptr),
    adjacent_matches(nullptr),
    adjacent_match_cache(),
    ufilter_()
{}

bool terrain_filter::match_internal(const map_location& loc, const unit* ref_unit, const bool ignore_xy) const
{
    if (!this->fc_->get_disp_context().map().on_board_with_border(loc)) {
        return false;
    }

    std::string lua_function = cfg_["lua_function"];
    if (!lua_function.empty() && fc_->get_lua_kernel()) {
        if (!fc_->get_lua_kernel()->run_filter(lua_function.c_str(), loc)) {
            return false;
        }
    }

    //Filter Areas
    if (cfg_.has_attribute("area") &&
        fc_->get_tod_man().get_area_by_id(cfg_["area"]).count(loc) == 0)
        return false;

    if(cfg_.has_attribute("gives_income") &&
        cfg_["gives_income"].to_bool() != fc_->get_disp_context().map().is_village(loc))
        return false;

    if(cfg_.has_attribute("terrain")) {
        if(cache_.parsed_terrain == nullptr) {
            cache_.parsed_terrain.reset(new t_translation::ter_match(std::string_view(cfg_["terrain"].str())));
        }
        if(!cache_.parsed_terrain->is_empty) {
            const t_translation::terrain_code letter = fc_->get_disp_context().map().get_terrain_info(loc).number();
            if(!t_translation::terrain_matches(letter, *cache_.parsed_terrain)) {
                return false;
            }
        }
    }

    //Allow filtering on location ranges
    if (!ignore_xy) {
        if (!loc.matches_range(cfg_["x"], cfg_["y"])) {
            return false;
        }
        //allow filtering by searching a stored variable of locations
        if (cfg_.has_attribute("find_in")) {
            if (const game_data * gd = fc_->get_game_data()) {
                try
                {
                    variable_access_const vi = gd->get_variable_access_read(cfg_["find_in"]);

                    bool found = false;
                    for (const config &cfg : vi.as_array()) {
                        if (map_location(cfg, nullptr) == loc) {
                            found = true;
                            break;
                        }
                    }
                    if (!found) return false;
                }
                catch (const invalid_variablename_exception&)
                {
                    return false;
                }
            }
        }
        if (cfg_.has_attribute("location_id")) {
            std::set<map_location> matching_locs;
            for(const auto& id : utils::split(cfg_["location_id"])) {
                map_location test_loc = fc_->get_disp_context().map().special_location(id);
                if(test_loc.valid()) {
                    matching_locs.insert(test_loc);
                }
            }
            if (matching_locs.count(loc) == 0) {
                return false;
            }
        }
    }
    //Allow filtering on unit
    if(cfg_.has_child("filter")) {
        const unit_map::const_iterator u = fc_->get_disp_context().units().find(loc);
        if (!u.valid())
            return false;
        if (!cache_.ufilter_) {
            cache_.ufilter_.reset(new unit_filter(cfg_.child("filter").make_safe()));
            cache_.ufilter_->set_use_flat_tod(flat_);
        }
        if (!cache_.ufilter_->matches(*u, loc))
            return false;
    }

    // Allow filtering on visibility to a side
    if (cfg_.has_child("filter_vision")) {
        const vconfig::child_list& vis_filt = cfg_.get_children("filter_vision");
        vconfig::child_list::const_iterator i, i_end = vis_filt.end();
        for (i = vis_filt.begin(); i != i_end; ++i) {
            bool visible = (*i)["visible"].to_bool(true);
            bool respect_fog = (*i)["respect_fog"].to_bool(true);

            side_filter ssf(*i, fc_);
            std::vector<int> sides = ssf.get_teams();

            bool found = false;
            for (const int side : sides) {
                const team &viewing_team = fc_->get_disp_context().get_team(side);
                bool viewer_sees = respect_fog ? !viewing_team.fogged(loc) : !viewing_team.shrouded(loc);
                if (visible == viewer_sees) {
                    found = true;
                    break;
                }
            }
            if (!found) {return false;}
        }
    }

    //Allow filtering on adjacent locations
    if(cfg_.has_child("filter_adjacent_location")) {
        const auto adjacent = get_adjacent_tiles(loc);
        const vconfig::child_list& adj_cfgs = cfg_.get_children("filter_adjacent_location");
        vconfig::child_list::const_iterator i, i_end, i_begin = adj_cfgs.begin();
        for (i = i_begin, i_end = adj_cfgs.end(); i != i_end; ++i) {
            int match_count = 0;
            vconfig::child_list::difference_type index = i - i_begin;
            std::vector<map_location::DIRECTION> dirs = (*i).has_attribute("adjacent")
                ? map_location::parse_directions((*i)["adjacent"]) : map_location::default_dirs();
            std::vector<map_location::DIRECTION>::const_iterator j, j_end = dirs.end();
            for (j = dirs.begin(); j != j_end; ++j) {
                const map_location &adj = adjacent[*j];
                if (fc_->get_disp_context().map().on_board(adj)) {
                    if(cache_.adjacent_matches == nullptr) {
                        while(index >= std::distance(cache_.adjacent_match_cache.begin(), cache_.adjacent_match_cache.end())) {
                            const vconfig& adj_cfg = adj_cfgs[cache_.adjacent_match_cache.size()];
                            std::pair<terrain_filter, std::map<map_location,bool>> amc_pair(
                                terrain_filter(adj_cfg, *this),
                                std::map<map_location,bool>());
                            cache_.adjacent_match_cache.push_back(amc_pair);
                        }
                        terrain_filter &amc_filter = cache_.adjacent_match_cache[index].first;
                        std::map<map_location,bool> &amc = cache_.adjacent_match_cache[index].second;
                        std::map<map_location,bool>::iterator lookup = amc.find(adj);
                        if(lookup == amc.end()) {
                            if(amc_filter(adj)) {
                                amc[adj] = true;
                                ++match_count;
                            } else {
                                amc[adj] = false;
                            }
                        } else if(lookup->second) {
                            ++match_count;
                        }
                    } else {
                        assert(index < std::distance(cache_.adjacent_matches->begin(), cache_.adjacent_matches->end()));
                        std::set<map_location> &amc = (*cache_.adjacent_matches)[index];
                        if(amc.find(adj) != amc.end()) {
                            ++match_count;
                        }
                    }
                }
            }
            static std::vector<std::pair<int,int>> default_counts = utils::parse_ranges("1-6");
            std::vector<std::pair<int,int>> counts = (*i).has_attribute("count")
                ? utils::parse_ranges((*i)["count"]) : default_counts;
            if(!in_ranges(match_count, counts)) {
                return false;
            }
        }
    }

    const t_string& t_tod_type = cfg_["time_of_day"];
    const t_string& t_tod_id = cfg_["time_of_day_id"];
    const std::string& tod_type = t_tod_type;
    const std::string& tod_id = t_tod_id;
    if(!tod_type.empty() || !tod_id.empty()) {
        // creating a time_of_day is expensive, only do it if we will use it
        time_of_day tod;

        if(flat_) {
            tod = fc_->get_tod_man().get_time_of_day(loc);
        } else {
            tod = fc_->get_tod_man().get_illuminated_time_of_day(fc_->get_disp_context().units(), fc_->get_disp_context().map(),loc);
        }

        if(!tod_type.empty()) {
            const std::vector<std::string>& vals = utils::split(tod_type);
            if(tod.lawful_bonus<0) {
                if(std::find(vals.begin(),vals.end(), unit_alignments::chaotic) == vals.end()) {
                    return false;
                }
            } else if(tod.lawful_bonus>0) {
                if(std::find(vals.begin(),vals.end(), unit_alignments::lawful) == vals.end()) {
                    return false;
                }
            } else if(std::find(vals.begin(),vals.end(), unit_alignments::neutral) == vals.end() &&
                std::find(vals.begin(),vals.end(), unit_alignments::liminal) == vals.end()) {
                return false;
            }
        }

        if(!tod_id.empty()) {
            if(tod_id != tod.id) {
                if(std::find(tod_id.begin(),tod_id.end(),',') != tod_id.end() &&
                    std::search(tod_id.begin(),tod_id.end(),
                    tod.id.begin(),tod.id.end()) != tod_id.end()) {
                    const std::vector<std::string>& vals = utils::split(tod_id);
                    if(std::find(vals.begin(),vals.end(),tod.id) == vals.end()) {
                        return false;
                    }
                } else {
                    return false;
                }
            }
        }
    }

    //allow filtering on owner (for villages)
    const config::attribute_value &owner_side = cfg_["owner_side"];
    const vconfig& filter_owner = cfg_.child("filter_owner");
    if(!filter_owner.null()) {
        if(!owner_side.empty()) {
            WRN_NG << "duplicate side information in a SLF, ignoring inline owner_side=";
        }
        if(!fc_->get_disp_context().map().is_village(loc))
            return false;
        side_filter ssf(filter_owner, fc_);
        const std::vector<int>& sides = ssf.get_teams();
        bool found = false;
        if(sides.empty() && fc_->get_disp_context().village_owner(loc) == 0)
            found = true;
        for(const int side : sides) {
            if(fc_->get_disp_context().get_team(side).owns_village(loc)) {
                found = true;
                break;
            }
        }
        if(!found)
            return false;
    }
    else if(!owner_side.empty()) {
        const int side_num = owner_side.to_int(0);
        if(fc_->get_disp_context().village_owner(loc) != side_num) {
            return false;
        }
    }

    if(cfg_.has_attribute("formula")) {
        try {
            const wfl::terrain_callable main(fc_->get_disp_context(), loc);
            wfl::map_formula_callable callable(main.fake_ptr());
            if(ref_unit) {
                auto ref = std::make_shared<wfl::unit_callable>(*ref_unit);
                callable.add("teleport_unit", wfl::variant(ref));
                // It's not destroyed upon scope exit because the variant holds a reference
            }
            wfl::gamestate_function_symbol_table symbols;
            const wfl::formula form(cfg_["formula"], &symbols);
            if(!form.evaluate(callable).as_bool()) {
                return false;
            }
            return true;
        } catch(const wfl::formula_error& e) {
            lg::log_to_chat() << "Formula error in location filter: " << e.type << " at " << e.filename << ':' << e.line << ")\n";
            ERR_WML << "Formula error in location filter: " << e.type << " at " << e.filename << ':' << e.line << ")";
            // Formulae with syntax errors match nothing
            return false;
        }
    }

    return true;
}

class filter_with_unit : public xy_pred {
    const terrain_filter& filt_;
    const unit& ref_;
public:
    filter_with_unit(const terrain_filter& filt, const unit& ref) : filt_(filt), ref_(ref) {}
    bool operator()(const map_location& loc) const override {
        return filt_.match(loc, ref_);
    }
};

bool terrain_filter::match_impl(const map_location& loc, const unit* ref_unit) const
{
    if(cfg_["x"] == "recall" && cfg_["y"] == "recall") {
        return !fc_->get_disp_context().map().on_board(loc);
    }
    std::set<map_location> hexes;
    std::vector<map_location> loc_vec(1, loc);

    std::unique_ptr<scoped_wml_variable> ref_unit_var;
    if(ref_unit) {
        if(fc_->get_disp_context().map().on_board(ref_unit->get_location())) {
            ref_unit_var.reset(new scoped_xy_unit("teleport_unit", ref_unit->get_location(), fc_->get_disp_context().units()));
        } else {
            // Possible TODO: Support recall list units?
        }
    }

    //handle radius
    std::size_t radius = cfg_["radius"].to_size_t(0);
    if(radius > max_loop_) {
        ERR_NG << "terrain_filter: radius greater than " << max_loop_
        << ", restricting";
        radius = max_loop_;
    }
    if ( radius == 0 )
        hexes.insert(loc_vec.begin(), loc_vec.end());
    else if ( cfg_.has_child("filter_radius") ) {
        terrain_filter r_filter(cfg_.child("filter_radius"), *this);
        if(ref_unit) {
            get_tiles_radius(fc_->get_disp_context().map(), loc_vec, radius, hexes, false, filter_with_unit(r_filter, *ref_unit));
        } else {
            get_tiles_radius(fc_->get_disp_context().map(), loc_vec, radius, hexes, false, r_filter);
        }
    } else {
        get_tiles_radius(fc_->get_disp_context().map(), loc_vec, radius, hexes);
    }

    std::size_t loop_count = 0;
    std::set<map_location>::const_iterator i;
    for(i = hexes.begin(); i != hexes.end(); ++i) {
        bool matches = match_internal(*i, ref_unit, false);

        // Handle [and], [or], and [not] with in-order precedence
        for(const auto& [key, filter] : cfg_.all_ordered()) {
            // Handle [and]
            if(key == "and") {
                matches = matches && terrain_filter(filter, *this).match_impl(*i, ref_unit);
            }
            // Handle [or]
            else if(key == "or") {
                matches = matches || terrain_filter(filter, *this).match_impl(*i, ref_unit);
            }
            // Handle [not]
            else if(key == "not") {
                matches = matches && !terrain_filter(filter, *this).match_impl(*i, ref_unit);
            }
        }

        if(matches) {
            return true;
        }
        if(++loop_count > max_loop_) {
            std::set<map_location>::const_iterator temp = i;
            if(++temp != hexes.end()) {
                ERR_NG << "terrain_filter: loop count greater than " << max_loop_
                << ", aborting";
                break;
            }
        }
    }
    return false;
}
//using a class to be able to firen it in terrain_filter
class terrain_filterimpl
{
public:
    using location_set = std::set<map_location>;
    struct no_start_set_yet {};
    struct no_filter
    {
        bool operator()(const map_location&) const { return true; }
    };

    template<typename T, typename F1, typename F2, typename F3>
    static void filter_final(T&& src, location_set& dest, const terrain_filter&, const F1& f1, const F2& f2, const F3& f3)
    {
        for (map_location loc : src) {
            if (f1(loc) && f2(loc) && f3(loc)) {
                dest.insert(loc);
            }
        }
    }

    template<typename T, typename F1, typename F2>
    static void filter_special_loc(T&& src, location_set& dest, const terrain_filter& filter, const F1& f1, const F2& f2)
    {
        if (filter.cfg_.has_attribute("location_id")) {
            std::set<map_location> matching_locs;
            for(const auto& id : utils::split(filter.cfg_["location_id"])) {
                map_location test_loc = filter.fc_->get_disp_context().map().special_location(id);
                if(test_loc.valid()) {
                    matching_locs.insert(test_loc);
                }
            }
            filter_final(src, dest, filter, f1, f2, [matching_locs](const map_location& loc) { return matching_locs.count(loc) > 0; });
        }
        else {
            filter_final(src, dest, filter, f1, f2, no_filter());
        }
    }

    template<typename T, typename F1>
    static void filter_area(T&& src, location_set& dest, const terrain_filter& filter, const F1& f1)
    {
        if (filter.cfg_.has_attribute("area")) {
            const std::set<map_location>& area = filter.fc_->get_tod_man().get_area_by_id(filter.cfg_["area"]);
            filter_special_loc(src, dest, filter, f1, [&area](const map_location& loc) { return area.find(loc) != area.end(); });
        }
        else {
            filter_special_loc(src, dest, filter, f1, no_filter());
        }
    }

    template<typename T>
    static void filter_xy(T&& src, location_set& dest, const terrain_filter& filter, bool with_border)
    {
        if (filter.cfg_.has_attribute("x") || filter.cfg_.has_attribute("y")) {
            std::vector<map_location> xy_vector = filter.fc_->get_disp_context().map().parse_location_range(filter.cfg_["x"], filter.cfg_["y"], with_border);
            filter_area(src, dest, filter, [&xy_vector](const map_location& loc) { return std::find(xy_vector.begin(), xy_vector.end(), loc) != xy_vector.end(); });
        }
        else {
            filter_area(src, dest, filter, no_filter());
        }
    }
};
//using lambdas with boost transformed gives compile erros on gcc (it works on clang and msvc)
struct cfg_to_loc
{
    map_location operator()(const config& cfg) const { return map_location(cfg, nullptr); }
    typedef map_location result_type;
};
void terrain_filter::get_locs_impl(std::set<map_location>& locs, const unit* ref_unit, bool with_border) const
{
    std::unique_ptr<scoped_wml_variable> ref_unit_var;
    if(ref_unit) {
        if(fc_->get_disp_context().map().on_board(ref_unit->get_location())) {
            ref_unit_var.reset(new scoped_xy_unit("teleport_unit", ref_unit->get_location(), fc_->get_disp_context().units()));
        } else {
            // Possible TODO: Support recall list units?
        }
    }

    std::set<map_location> match_set;

    // See if the caller provided an override to with_border
    with_border = cfg_["include_borders"].to_bool(with_border);

    if (cfg_.has_attribute("find_in")) {

        if (const game_data * gd = fc_->get_game_data()) {
            try
            {
                auto ar = gd->get_variable_access_read(cfg_["find_in"]).as_array();
                terrain_filterimpl::filter_xy(ar | boost::adaptors::transformed(cfg_to_loc()), match_set, *this, with_border);
            }
            catch (const invalid_variablename_exception&)
            {
                //Do nothing
            }
        }
    }
    else if (cfg_.has_attribute("x") || cfg_.has_attribute("y")) {
        std::vector<map_location> xy_vector = fc_->get_disp_context().map().parse_location_range(cfg_["x"], cfg_["y"], with_border);
        terrain_filterimpl::filter_area(xy_vector, match_set, *this, terrain_filterimpl::no_filter());
    }
    else if (cfg_.has_attribute("area")) {
        const std::set<map_location>& area = fc_->get_tod_man().get_area_by_id(cfg_["area"]);
        terrain_filterimpl::filter_special_loc(area, match_set, *this, terrain_filterimpl::no_filter(), terrain_filterimpl::no_filter());
    }
    else if (cfg_.has_attribute("location_id")) {
        for(const auto& id : utils::split(cfg_["location_id"])) {
            map_location test_loc = fc_->get_disp_context().map().special_location(id);
            if(test_loc.valid()) {
                match_set.insert(test_loc);
            }
        }
    }
    else if (cfg_["gives_income"].to_bool()) {
        auto ar = fc_->get_disp_context().map().villages();
        terrain_filterimpl::filter_xy(ar, match_set, *this, with_border);
    }
    else {
        //consider all locations on the map
        int bs = fc_->get_disp_context().map().border_size();
        int w = with_border ? fc_->get_disp_context().map().w() + bs : fc_->get_disp_context().map().w();
        int h = with_border ? fc_->get_disp_context().map().h() + bs : fc_->get_disp_context().map().h();
        for (int x = with_border ? 0 - bs : 0; x < w; ++x) {
            for (int y = with_border ? 0 - bs : 0; y < h; ++y) {
                match_set.insert(map_location(x, y));
            }
        }
    }

    //handle location filter
    if(cfg_.has_child("filter_adjacent_location")) {
        if(cache_.adjacent_matches == nullptr) {
            cache_.adjacent_matches.reset(new std::vector<std::set<map_location>>());
        }
        const vconfig::child_list& adj_cfgs = cfg_.get_children("filter_adjacent_location");
        for (unsigned i = 0; i < adj_cfgs.size(); ++i) {
            std::set<map_location> adj_set;
            /* GCC-3.3 doesn't like operator[] so use at(), which has the same result */
            terrain_filter(adj_cfgs.at(i), *this).get_locations(adj_set, with_border);
            cache_.adjacent_matches->push_back(adj_set);
            if(i >= max_loop_ && i+1 < adj_cfgs.size()) {
                ERR_NG << "terrain_filter: loop count greater than " << max_loop_
                << ", aborting";
                break;
            }
        }
    }
    std::set<map_location>::iterator loc_itor = match_set.begin();
    while(loc_itor != match_set.end()) {
        if(match_internal(*loc_itor, ref_unit, true)) {
            ++loc_itor;
        } else {
            loc_itor = match_set.erase(loc_itor);
        }
    }

    int ors_left = std::count_if(cfg_.ordered_begin(), cfg_.ordered_end(), [](const auto& val) { return val.first == "or"; });

    // Handle [and], [or], and [not] with in-order precedence
    for(const auto& [key, filter] : cfg_.all_ordered()) {
        //if there are no locations or [or] conditions left, go ahead and return empty
        if(match_set.empty() && ors_left <= 0) {
            return;
        }

        // Handle [and]
        if(key == "and") {
            std::set<map_location> intersect_hexes;
            terrain_filter(filter, *this).get_locations(intersect_hexes, with_border);
            std::set<map_location>::iterator intersect_itor = match_set.begin();
            while(intersect_itor != match_set.end()) {
                if(intersect_hexes.find(*intersect_itor) == intersect_hexes.end()) {
                    match_set.erase(*intersect_itor++);
                } else {
                    ++intersect_itor;
                }
            }
        }
        // Handle [or]
        else if(key == "or") {
            std::set<map_location> union_hexes;
            terrain_filter(filter, *this).get_locations(union_hexes, with_border);
            //match_set.insert(union_hexes.begin(), union_hexes.end()); //doesn't compile on MSVC
            std::set<map_location>::iterator insert_itor = union_hexes.begin();
            while(insert_itor != union_hexes.end()) {
                match_set.insert(*insert_itor++);
            }
            --ors_left;
        }
        // Handle [not]
        else if(key == "not") {
            std::set<map_location> removal_hexes;
            terrain_filter(filter, *this).get_locations(removal_hexes, with_border);
            std::set<map_location>::iterator erase_itor = removal_hexes.begin();
            while(erase_itor != removal_hexes.end()) {
                match_set.erase(*erase_itor++);
            }
        }
    }
    if(match_set.empty()) {
        return;
    }

    //handle radius
    std::size_t radius = cfg_["radius"].to_size_t(0);
    if(radius > max_loop_) {
        ERR_NG << "terrain_filter: radius greater than " << max_loop_
        << ", restricting";
        radius = max_loop_;
    }
    if(radius > 0) {
        std::vector<map_location> xy_vector (match_set.begin(), match_set.end());
        if(cfg_.has_child("filter_radius")) {
            terrain_filter r_filter(cfg_.child("filter_radius"), *this);
            get_tiles_radius(fc_->get_disp_context().map(), xy_vector, radius, locs, with_border, r_filter);
        } else {
            get_tiles_radius(fc_->get_disp_context().map(), xy_vector, radius, locs, with_border);
        }
    } else {
        locs.insert(match_set.begin(), match_set.end());
    }
}

config terrain_filter::to_config() const
{
    return cfg_.get_config();
}