path: root/crawl-ref/source/mon-movetarget.cc

#include "AppHdr.h"

#include "mon-movetarget.h"

#include "coord.h"
#include "coordit.h"
#include "env.h"
#include "fprop.h"
#include "mon-behv.h"
#include "mon-pathfind.h"
#include "mon-place.h"
#include "mon-stuff.h"
#include "monster.h"
#include "player.h"
#include "random.h"
#include "stuff.h"
#include "terrain.h"
#include "traps.h"

// Check all grids in LoS and mark lava and/or water as seen if the
// appropriate grids are encountered, so we later only need to do the
// visibility check for monsters that can't pass a feature potentially in
// the way. We don't care about shallow water as most monsters can safely
// cross that, and fire elementals alone aren't really worth the extra
// hassle. :)
static void _check_lava_water_in_sight()
{
    you.lava_in_sight = you.water_in_sight = 0;
    for (radius_iterator ri(you.pos(), LOS_RADIUS); ri; ++ri)
    {
        const dungeon_feature_type feat = grd(*ri);
        if (feat == DNGN_LAVA)
        {
            you.lava_in_sight = 1;
            if (you.water_in_sight > 0)
                break;
        }
        else if (feat == DNGN_DEEP_WATER)
        {
            you.water_in_sight = 1;
            if (you.lava_in_sight > 0)
                break;
        }
    }
}

// If a monster can see but not directly reach the target, and then fails to
// find a path to get there, mark all surrounding (in a radius of 2) monsters
// of the same (or greater) movement restrictions as also being unable to
// find a path, so we won't need to calculate again.
// Should there be a direct path to the target for a monster thus marked, it
// will still be able to come nearer (and the mark will then be cleared).
static void _mark_neighbours_target_unreachable(monsters *mon)
{
    // Highly intelligent monsters are perfectly capable of pathfinding
    // and don't need their neighbour's advice.
    const mon_intel_type intel = mons_intel(mon);
    if (intel > I_NORMAL)
        return;

    const bool flies         = mons_flies(mon);
    const bool amphibious    = mons_amphibious(mon);
    const habitat_type habit = mons_primary_habitat(mon);

    for (radius_iterator ri(mon->pos(), 2, true, false); ri; ++ri)
    {
        if (*ri == mon->pos())
            continue;

        // Don't alert monsters out of sight (e.g. on the other side of
        // a wall).
        if (!mon->see_cell(*ri))
            continue;

        monsters* const m = monster_at(*ri);
        if (m == NULL)
            continue;

        // Don't restrict smarter monsters as they might find a path
        // a dumber monster wouldn't.
        if (mons_intel(m) > intel)
            continue;

        // Monsters of differing habitats might prefer different routes.
        if (mons_primary_habitat(m) != habit)
            continue;

        // A flying monster has an advantage over a non-flying one.
        if (!flies && mons_flies(m))
            continue;

        // Same for a swimming one, around water.
        if (you.water_in_sight > 0 && !amphibious && mons_amphibious(m))
            continue;

        if (m->travel_target == MTRAV_NONE)
            m->travel_target = MTRAV_UNREACHABLE;
    }
}

static void _set_no_path_found(monsters *mon)
{
#ifdef DEBUG_PATHFIND
    mpr("No path found!");
#endif

    mon->travel_target = MTRAV_UNREACHABLE;
    // Pass information on to nearby monsters.
    _mark_neighbours_target_unreachable(mon);
}

static bool _target_is_unreachable(monsters *mon)
{
    return (mon->travel_target == MTRAV_UNREACHABLE
            || mon->travel_target == MTRAV_KNOWN_UNREACHABLE);
}

//#define DEBUG_PATHFIND

// The monster is trying to get to the player (MHITYOU).
// Check whether there's an unobstructed path to the player (in sight!),
// either by using an existing travel_path or calculating a new one.
// Returns true if no further handling necessary, else false.
bool try_pathfind(monsters *mon, const dungeon_feature_type can_move,
                          bool potentially_blocking)
{
    // Just because we can *see* the player, that doesn't mean
    // we can actually get there. To find about that, we first
    // check for transparent walls. If there are transparent
    // walls in the way we'll need pathfinding, no matter what.
    // (Though monsters with a los attack don't need to get any
    // closer to hurt the player.)
    // If no walls are detected, there could still be a river
    // or a pool of lava in the way. So we check whether there
    // is water or lava in LoS (boolean) and if so, try to find
    // a way around it. It's possible that the player can see
    // lava but it actually has no influence on the monster's
    // movement (because it's lying in the opposite direction)
    // but if so, we'll find that out during path finding.
    // In another attempt of optimization, don't bother with
    // path finding if the monster in question has no trouble
    // travelling through water or flying across lava.
    // Also, if no path is found (too far away, perhaps) set a
    // flag, so we don't directly calculate the whole thing again
    // next turn, and even extend that flag to neighbouring
    // monsters of similar movement restrictions.

    // Smart monsters that can fire through walls won't use
    // pathfinding, and it's also not necessary if the monster
    // is already adjacent to you.
    if (potentially_blocking && mons_intel(mon) >= I_NORMAL
           && !mon->friendly() && mons_has_los_ability(mon->type)
        || grid_distance(mon->pos(), you.pos()) == 1)
    {
        potentially_blocking = false;
    }
    else
    {
        // If we don't already know whether there's water or lava
        // in LoS of the player, find out now.
        if (you.lava_in_sight == -1 || you.water_in_sight == -1)
            _check_lava_water_in_sight();

        // Flying monsters don't see water/lava as obstacle.
        // Also don't use pathfinding if the monster can shoot
        // across the blocking terrain, and is smart enough to
        // realise that.
        if (!potentially_blocking && !mons_flies(mon)
            && (mons_intel(mon) < I_NORMAL
                || mon->friendly()
                || (!mons_has_ranged_spell(mon, true)
                    && !mons_has_ranged_attack(mon))))
        {
            const habitat_type habit = mons_primary_habitat(mon);
            if (you.lava_in_sight > 0 && habit != HT_LAVA
                || you.water_in_sight > 0 && habit != HT_WATER
                   && can_move != DNGN_DEEP_WATER)
            {
                potentially_blocking = true;
            }
        }
    }

    if (!potentially_blocking
        || can_go_straight(mon->pos(), you.pos(), can_move))
    {
        // The player is easily reachable.
        // Clear travel path and target, if necessary.
        if (mon->travel_target != MTRAV_PATROL
            && mon->travel_target != MTRAV_NONE)
        {
            if (mon->is_travelling())
                mon->travel_path.clear();
            mon->travel_target = MTRAV_NONE;
        }
        return (false);
    }

    // Even if the target has been to "unreachable" (the monster already tried,
    // and failed, to find a path) there's a chance of trying again.
    if (!_target_is_unreachable(mon) || one_chance_in(12))
    {
#ifdef DEBUG_PATHFIND
        mprf("%s: Player out of reach! What now?",
             mon->name(DESC_PLAIN).c_str());
#endif
        // If we're already on our way, do nothing.
        if (mon->is_travelling() && mon->travel_target == MTRAV_PLAYER)
        {
            const int len = mon->travel_path.size();
            const coord_def targ = mon->travel_path[len - 1];

            // Current target still valid?
            if (can_go_straight(targ, you.pos(), can_move))
            {
                // Did we reach the target?
                if (mon->pos() == mon->travel_path[0])
                {
                    // Get next waypoint.
                    mon->travel_path.erase( mon->travel_path.begin() );

                    if (!mon->travel_path.empty())
                    {
                        mon->target = mon->travel_path[0];
                        return (true);
                    }
                }
                else if (can_go_straight(mon->pos(), mon->travel_path[0],
                                       can_move))
                {
                    mon->target = mon->travel_path[0];
                    return (true);
                }
            }
        }

        // Use pathfinding to find a (new) path to the player.
        const int dist = grid_distance(mon->pos(), you.pos());

#ifdef DEBUG_PATHFIND
        mprf("Need to calculate a path... (dist = %d)", dist);
#endif
        const int range = mons_tracking_range(mon);
        if (range > 0 && dist > range)
        {
            mon->travel_target = MTRAV_UNREACHABLE;
#ifdef DEBUG_PATHFIND
            mprf("Distance too great, don't attempt pathfinding! (%s)",
                 mon->name(DESC_PLAIN).c_str());
#endif
            return (false);
        }

#ifdef DEBUG_PATHFIND
        mprf("Need a path for %s from (%d, %d) to (%d, %d), max. dist = %d",
             mon->name(DESC_PLAIN).c_str(), mon->pos(), you.pos(), range);
#endif
        monster_pathfind mp;
        if (range > 0)
            mp.set_range(range);

        if (mp.init_pathfind(mon, you.pos()))
        {
            mon->travel_path = mp.calc_waypoints();
            if (!mon->travel_path.empty())
            {
                // Okay then, we found a path.  Let's use it!
                mon->target = mon->travel_path[0];
                mon->travel_target = MTRAV_PLAYER;
                return (true);
            }
            else
                _set_no_path_found(mon);
        }
        else
            _set_no_path_found(mon);
    }

    // We didn't find a path.
    return (false);
}

static bool _is_level_exit(const coord_def& pos)
{
    // All types of stairs.
    if (feat_is_stair(grd(pos)))
        return (true);

    // Teleportation and shaft traps.
    const trap_type tt = get_trap_type(pos);
    if (tt == TRAP_TELEPORT || tt == TRAP_SHAFT)
        return (true);

    return (false);
}

// Returns true if a monster left the level.
bool pacified_leave_level(monsters *mon, std::vector<level_exit> e,
                          int e_index)
{
    // If a pacified monster is leaving the level, and has reached an
    // exit (whether that exit was its target or not), handle it here.
    // Likewise, if a pacified monster is far enough away from the
    // player, make it leave the level.
    if (_is_level_exit(mon->pos())
        || (e_index != -1 && mon->pos() == e[e_index].target)
        || grid_distance(mon->pos(), you.pos()) >= LOS_RADIUS * 4)
    {
        make_mons_leave_level(mon);
        return (true);
    }

    return (false);
}

// Counts deep water twice.
static int _count_water_neighbours(coord_def p)
{
    int water_count = 0;
    for (adjacent_iterator ai(p); ai; ++ai)
    {
        if (grd(*ai) == DNGN_SHALLOW_WATER)
            water_count++;
        else if (grd(*ai) == DNGN_DEEP_WATER)
            water_count += 2;
    }
    return (water_count);
}

// Pick the nearest water grid that is surrounded by the most
// water squares within LoS.
bool find_siren_water_target(monsters *mon)
{
    ASSERT(mon->type == MONS_SIREN);

    // Moving away could break the entrancement, so don't do this.
    if ((mon->pos() - you.pos()).rdist() >= 6)
        return (false);

    // Already completely surrounded by deep water.
    if (_count_water_neighbours(mon->pos()) >= 16)
        return (true);

    if (mon->travel_target == MTRAV_SIREN)
    {
        coord_def targ_pos(mon->travel_path[mon->travel_path.size() - 1]);
#ifdef DEBUG_PATHFIND
        mprf("siren target is (%d, %d), dist = %d",
             targ_pos.x, targ_pos.y, (int) (mon->pos() - targ_pos).rdist());
#endif
        if ((mon->pos() - targ_pos).rdist() > 2)
            return (true);
    }

    int best_water_count = 0;
    coord_def best_target;
    bool first = true;

    while (true)
    {
        int best_num = 0;
        for (radius_iterator ri(mon->pos(), LOS_RADIUS, true, false);
             ri; ++ri)
        {
            if (!feat_is_water(grd(*ri)))
                continue;

            // In the first iteration only count water grids that are
            // not closer to the player than to the siren.
            if (first && (mon->pos() - *ri).rdist() > (you.pos() - *ri).rdist())
                continue;

            // Counts deep water twice.
            const int water_count = _count_water_neighbours(*ri);
            if (water_count < best_water_count)
                continue;

            if (water_count > best_water_count)
            {
                best_water_count = water_count;
                best_target = *ri;
                best_num = 1;
            }
            else // water_count == best_water_count
            {
                const int old_dist = (mon->pos() - best_target).rdist();
                const int new_dist = (mon->pos() - *ri).rdist();
                if (new_dist > old_dist)
                    continue;

                if (new_dist < old_dist)
                {
                    best_target = *ri;
                    best_num = 1;
                }
                else if (one_chance_in(++best_num))
                    best_target = *ri;
            }
        }

        if (!first || best_water_count > 0)
            break;

        // Else start the second iteration.
        first = false;
    }

    if (!best_water_count)
        return (false);

    // We're already optimally placed.
    if (best_target == mon->pos())
        return (true);

    monster_pathfind mp;
#ifdef WIZARD
    // Remove old highlighted areas to make place for the new ones.
    for (rectangle_iterator ri(1); ri; ++ri)
        env.pgrid(*ri) &= ~(FPROP_HIGHLIGHT);
#endif

    if (mp.init_pathfind(mon, best_target))
    {
        mon->travel_path = mp.calc_waypoints();

        if (!mon->travel_path.empty())
        {
#ifdef WIZARD
            for (unsigned int i = 0; i < mon->travel_path.size(); i++)
                env.pgrid(mon->travel_path[i]) |= FPROP_HIGHLIGHT;
#endif
#ifdef DEBUG_PATHFIND
            mprf("Found a path to (%d, %d) with %d surrounding water squares",
                 best_target.x, best_target.y, best_water_count);
#endif
            // Okay then, we found a path.  Let's use it!
            mon->target = mon->travel_path[0];
            mon->travel_target = MTRAV_SIREN;
            return (true);
        }
    }

    return (false);
}

bool find_wall_target(monsters *mon)
{
    ASSERT(mons_wall_shielded(mon));

    if (mon->travel_target == MTRAV_WALL)
    {
        coord_def targ_pos(mon->travel_path[mon->travel_path.size() - 1]);

        // Target grid might have changed since we started, like if the
        // player destroys the wall the monster wants to hide in.
        if (cell_is_solid(targ_pos)
            && monster_habitable_grid(mon, grd(targ_pos)))
        {
            // Wall is still good.
#ifdef DEBUG_PATHFIND
            mprf("%s target is (%d, %d), dist = %d",
                 mon->name(DESC_PLAIN, true).c_str(),
                 targ_pos.x, targ_pos.y, (int) (mon->pos() - targ_pos).rdist());
#endif
            return (true);
        }

        mon->travel_path.clear();
        mon->travel_target = MTRAV_NONE;
    }

    int       best_dist             = INT_MAX;
    bool      best_closer_to_player = false;
    coord_def best_target;

    for (radius_iterator ri(mon->pos(), LOS_RADIUS, true, false);
         ri; ++ri)
    {
        if (!cell_is_solid(*ri)
            || !monster_habitable_grid(mon, grd(*ri)))
        {
            continue;
        }

        int  dist = (mon->pos() - *ri).rdist();
        bool closer_to_player = false;
        if (dist > (you.pos() - *ri).rdist())
            closer_to_player = true;

        if (dist < best_dist)
        {
            best_dist             = dist;
            best_closer_to_player = closer_to_player;
            best_target           = *ri;
        }
        else if (best_closer_to_player && !closer_to_player
                 && dist == best_dist)
        {
            best_closer_to_player = false;
            best_target           = *ri;
        }
    }

    if (best_dist == INT_MAX || !in_bounds(best_target))
        return (false);

    monster_pathfind mp;
#ifdef WIZARD
    // Remove old highlighted areas to make place for the new ones.
    for (rectangle_iterator ri(1); ri; ++ri)
        env.pgrid(*ri) &= ~(FPROP_HIGHLIGHT);
#endif

    if (mp.init_pathfind(mon, best_target))
    {
        mon->travel_path = mp.calc_waypoints();

        if (!mon->travel_path.empty())
        {
#ifdef WIZARD
            for (unsigned int i = 0; i < mon->travel_path.size(); i++)
                env.pgrid(mon->travel_path[i]) |= FPROP_HIGHLIGHT;
#endif
#ifdef DEBUG_PATHFIND
            mprf("Found a path to (%d, %d)", best_target.x, best_target.y);
#endif
            // Okay then, we found a path.  Let's use it!
            mon->target = mon->travel_path[0];
            mon->travel_target = MTRAV_WALL;
            return (true);
        }
    }
    return (false);
}

// Returns true if further handling neeeded.
static bool _handle_monster_travelling(monsters *mon,
                                       const dungeon_feature_type can_move)
{
#ifdef DEBUG_PATHFIND
    mprf("Monster %s reached target (%d, %d)",
         mon->name(DESC_PLAIN).c_str(), mon->target.x, mon->target.y);
#endif

    // Hey, we reached our first waypoint!
    if (mon->pos() == mon->travel_path[0])
    {
#ifdef DEBUG_PATHFIND
        mpr("Arrived at first waypoint.");
#endif
        mon->travel_path.erase( mon->travel_path.begin() );
        if (mon->travel_path.empty())
        {
#ifdef DEBUG_PATHFIND
            mpr("We reached the end of our path: stop travelling.");
#endif
            mon->travel_target = MTRAV_NONE;
            return (true);
        }
        else
        {
            mon->target = mon->travel_path[0];
#ifdef DEBUG_PATHFIND
            mprf("Next waypoint: (%d, %d)", mon->target.x, mon->target.y);
#endif
            return (false);
        }
    }

    // Can we still see our next waypoint?
    if (!can_go_straight(mon->pos(), mon->travel_path[0], can_move))
    {
#ifdef DEBUG_PATHFIND
        mpr("Can't see waypoint grid.");
#endif
        // Apparently we got sidetracked a bit.
        // Check the waypoints vector backwards and pick the first waypoint
        // we can see.

        // XXX: Note that this might still not be the best thing to do
        // since another path might be even *closer* to our actual target now.
        // Not by much, though, since the original path was optimal (A*) and
        // the distance between the waypoints is rather small.

        int erase = -1;  // Erase how many waypoints?
        const int size = mon->travel_path.size();
        for (int i = size - 1; i >= 0; --i)
        {
            if (can_go_straight(mon->pos(), mon->travel_path[i], can_move))
            {
                mon->target = mon->travel_path[i];
                erase = i;
                break;
            }
        }

        if (erase > 0)
        {
#ifdef DEBUG_PATHFIND
            mprf("Need to erase %d of %d waypoints.",
                 erase, size);
#endif
            // Erase all waypoints that came earlier:
            // we don't need them anymore.
            while (0 < erase--)
                mon->travel_path.erase( mon->travel_path.begin() );
        }
        else
        {
            // We can't reach our old path from our current
            // position, so calculate a new path instead.
            monster_pathfind mp;

            // The last coordinate in the path vector is our destination.
            const int len = mon->travel_path.size();
            if (mp.init_pathfind(mon, mon->travel_path[len-1]))
            {
                mon->travel_path = mp.calc_waypoints();
                if (!mon->travel_path.empty())
                {
                    mon->target = mon->travel_path[0];
#ifdef DEBUG_PATHFIND
                    mprf("Next waypoint: (%d, %d)",
                         mon->target.x, mon->target.y);
#endif
                }
                else
                {
                    mon->travel_target = MTRAV_NONE;
                    return (true);
                }
            }
            else
            {
                // Or just forget about the whole thing.
                mon->travel_path.clear();
                mon->travel_target = MTRAV_NONE;
                return (true);
            }
        }
    }

    // Else, we can see the next waypoint and are making good progress.
    // Carry on, then!
    return (false);
}

static bool _choose_random_patrol_target_grid(monsters *mon)
{
    const int intel = mons_intel(mon);

    // Zombies will occasionally just stand around.
    // This does not mean that they don't move every second turn. Rather,
    // once they reach their chosen target, there's a 50% chance they'll
    // just remain there until next turn when this function is called
    // again.
    if (intel == I_PLANT && coinflip())
        return (true);

    // If there's no chance we'll find the patrol point, quit right away.
    if (grid_distance(mon->pos(), mon->patrol_point) > 2 * LOS_RADIUS)
        return (false);

    // Can the monster see the patrol point from its current position?
    const bool patrol_seen = mon->mon_see_cell(mon->patrol_point,
                                 habitat2grid(mons_primary_habitat(mon)));

    if (intel == I_PLANT && !patrol_seen)
    {
        // Really stupid monsters won't even try to get back into the
        // patrol zone.
        return (false);
    }

    // While the patrol point is in easy reach, monsters of insect/plant
    // intelligence will only use a range of 5 (distance from the patrol point).
    // Otherwise, try to get back using the full LOS.
    const int  rad      = (intel >= I_ANIMAL || !patrol_seen) ? LOS_RADIUS : 5;
    const bool is_smart = (intel >= I_NORMAL);

    los_def patrol(mon->patrol_point, opacity_monmove(*mon),
                   circle_def(rad, C_ROUND));
    patrol.update();
    los_def lm(mon->pos(), opacity_monmove(*mon));
    if (is_smart || !patrol_seen)
    {
        // For stupid monsters, don't bother if the patrol point is in sight.
        lm.update();
    }

    int count_grids = 0;
    for (radius_iterator ri(mon->patrol_point, LOS_RADIUS, true, false);
         ri; ++ri)
    {
        // Don't bother for the current position. If everything fails,
        // we'll stay here anyway.
        if (*ri == mon->pos())
            continue;

        if (!mon->can_pass_through_feat(grd(*ri)))
            continue;

        // Don't bother moving to squares (currently) occupied by a
        // monster. We'll usually be able to find other target squares
        // (and if we're not, we couldn't move anyway), and this avoids
        // monsters trying to move onto a grid occupied by a plant or
        // sleeping monster.
        if (monster_at(*ri))
            continue;

        if (patrol_seen)
        {
            // If the patrol point can be easily (within LOS) reached
            // from the current position, it suffices if the target is
            // within reach of the patrol point OR the current position:
            // we can easily get there.
            // Only smart monsters will even attempt to move out of the
            // patrol area.
            // NOTE: Either of these can take us into a position where the
            // target cannot be easily reached (e.g. blocked by a wall)
            // and the patrol point is out of sight, too. Such a case
            // will be handled below, though it might take a while until
            // a monster gets out of a deadlock. (5% chance per turn.)
            if (!patrol.see_cell(*ri)
                && (!is_smart || !lm.see_cell(*ri)))
            {
                continue;
            }
        }
        else
        {
            // If, however, the patrol point is out of reach, we have to
            // make sure the new target brings us into reach of it.
            // This means that the target must be reachable BOTH from
            // the patrol point AND the current position.
            if (!patrol.see_cell(*ri)
                || !lm.see_cell(*ri))
            {
                continue;
            }

            // If this fails for all surrounding squares (probably because
            // we're too far away), we fall back to heading directly for
            // the patrol point.
        }

        bool set_target = false;
        if (intel == I_PLANT && *ri == mon->patrol_point)
        {
            // Slightly greater chance to simply head for the centre.
            count_grids += 3;
            if (x_chance_in_y(3, count_grids))
                set_target = true;
        }
        else if (one_chance_in(++count_grids))
            set_target = true;

        if (set_target)
            mon->target = *ri;
    }

    return (count_grids);
}// Returns true if further handling neeeded.
static bool _handle_monster_patrolling(monsters *mon)
{
    if (!_choose_random_patrol_target_grid(mon))
    {
        // If we couldn't find a target that is within easy reach
        // of the monster and close to the patrol point, depending
        // on monster intelligence, do one of the following:
        //  * set current position as new patrol point
        //  * forget about patrolling
        //  * head back to patrol point

        if (mons_intel(mon) == I_PLANT)
        {
            // Really stupid monsters forget where they're supposed to be.
            if (mon->friendly())
            {
                // Your ally was told to wait, and wait it will!
                // (Though possibly not where you told it to.)
                mon->patrol_point = mon->pos();
            }
            else
            {
                // Stop patrolling.
                mon->patrol_point.reset();
                mon->travel_target = MTRAV_NONE;
                return (true);
            }
        }
        else
        {
            // It's time to head back!
            // Other than for tracking the player, there's currently
            // no distinction between smart and stupid monsters when
            // it comes to travelling back to the patrol point. This
            // is in part due to the flavour of e.g. bees finding
            // their way back to the Hive (and patrolling should
            // really be restricted to cases like this), and for the
            // other part it's not all that important because we
            // calculate the path once and then follow it home, and
            // the player won't ever see the orderly fashion the
            // bees will trudge along.
            // What he will see is them swarming back to the Hive
            // entrance after some time, and that is what matters.
            monster_pathfind mp;
            if (mp.init_pathfind(mon, mon->patrol_point))
            {
                mon->travel_path = mp.calc_waypoints();
                if (!mon->travel_path.empty())
                {
                    mon->target = mon->travel_path[0];
                    mon->travel_target = MTRAV_PATROL;
                }
                else
                {
                    // We're so close we don't even need a path.
                    mon->target = mon->patrol_point;
                }
            }
            else
            {
                // Stop patrolling.
                mon->patrol_point.reset();
                mon->travel_target = MTRAV_NONE;
                return (true);
            }
        }
    }
    else
    {
#ifdef DEBUG_PATHFIND
        mprf("Monster %s (pp: %d, %d) is now patrolling to (%d, %d)",
             mon->name(DESC_PLAIN).c_str(),
             mon->patrol_point.x, mon->patrol_point.y,
             mon->target.x, mon->target.y);
#endif
    }

    return (false);
}

void set_random_target(monsters* mon)
{
    mon->target = random_in_bounds(); // If we don't find anything better.
    for (int tries = 0; tries < 150; ++tries)
    {
        coord_def delta = coord_def(random2(13), random2(13)) - coord_def(6, 6);
        if (delta.origin())
            continue;

        const coord_def newtarget = delta + mon->pos();
        if (!in_bounds(newtarget))
            continue;

        mon->target = newtarget;
        break;
    }
}

void check_wander_target(monsters *mon, bool isPacified,
                         dungeon_feature_type can_move)
{
    // default wander behaviour
    if (mon->pos() == mon->target
        || mons_is_batty(mon) || !isPacified && one_chance_in(20))
    {
        bool need_target = true;

        if (!can_move)
        {
            can_move = (mons_amphibious(mon) ? DNGN_DEEP_WATER
                                             : DNGN_SHALLOW_WATER);
        }

        if (mon->is_travelling())
            need_target = _handle_monster_travelling(mon, can_move);

        // If we still need a target because we're not travelling
        // (any more), check for patrol routes instead.
        if (need_target && mon->is_patrolling())
            need_target = _handle_monster_patrolling(mon);

        // XXX: This is really dumb wander behaviour... instead of
        // changing the goal square every turn, better would be to
        // have the monster store a direction and have the monster
        // head in that direction for a while, then shift the
        // direction to the left or right.  We're changing this so
        // wandering monsters at least appear to have some sort of
        // attention span.  -- bwr
        if (need_target)
            set_random_target(mon);
    }
}

static void _find_all_level_exits(std::vector<level_exit> &e)
{
    e.clear();

    for (rectangle_iterator ri(1); ri; ++ri)
    {
        if (!in_bounds(*ri))
            continue;

        if (_is_level_exit(*ri))
            e.push_back(level_exit(*ri, false));
    }
}

int mons_find_nearest_level_exit(const monsters *mon,
                                 std::vector<level_exit> &e,
                                 bool reset)
{
    if (e.empty() || reset)
        _find_all_level_exits(e);

    int retval = -1;
    int old_dist = -1;

    for (unsigned int i = 0; i < e.size(); ++i)
    {
        if (e[i].unreachable)
            continue;

        int dist = grid_distance(mon->pos(), e[i].target);

        if (old_dist == -1 || old_dist >= dist)
        {
            // Ignore teleportation and shaft traps that the monster
            // shouldn't know about.
            if (!mons_is_native_in_branch(mon)
                && grd(e[i].target) == DNGN_UNDISCOVERED_TRAP)
            {
                continue;
            }

            retval = i;
            old_dist = dist;
        }
    }

    return (retval);
}

void set_random_slime_target(monsters* mon)
{
    // Strictly neutral slimes will go for the nearest item.
    int item_idx;
    coord_def orig_target = mon->target;

    for (radius_iterator ri(mon->pos(), LOS_RADIUS, true, false); ri; ++ri)
    {
        item_idx = igrd(*ri);
        if (item_idx != NON_ITEM)
        {
            for (stack_iterator si(*ri); si; ++si)
            {
                item_def& item(*si);

                if (is_item_jelly_edible(item))
                {
                    mon->target = *ri;
                    break;
                }
            }
        }
    }

    if (mon->target == mon->pos() || mon->target == you.pos())
        set_random_target(mon);
}