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

#include "AppHdr.h"

#include "mon-pathfind.h"

#include "coord.h"
#include "directn.h"
#include "env.h"
#include "mon-place.h"
#include "mon-stuff.h"
#include "mon-util.h"
#include "monster.h"
#include "terrain.h"
#include "traps.h"

/////////////////////////////////////////////////////////////////////////////
// monster_pathfind

// The pathfinding is an implementation of the A* algorithm. Beginning at the
// destination square we check all neighbours of a given grid, estimate the
// distance needed for any shortest path including this grid and push the
// result into a hash. We can then easily access all points with the shortest
// distance estimates and then check _their_ neighbours and so on.
// The algorithm terminates once we reach the monster position since - because
// of the sorting of grids by shortest distance in the hash - there can be no
// path between start and target that is shorter than the current one. There
// could be other paths that have the same length but that has no real impact.
// If the hash has been cleared and the start grid has not been encountered,
// then there's no path that matches the requirements fed into monster_pathfind.
// (These requirements are usually preference of habitat of a specific monster
// or a limit of the distance between start and any grid on the path.)

int mons_tracking_range(const monsters *mon)
{

    int range = 0;
    switch (mons_intel(mon))
    {
    case I_PLANT:
        range = 2;
        break;
    case I_INSECT:
        range = 4;
        break;
    case I_ANIMAL:
        range = 5;
        break;
    case I_NORMAL:
        range = LOS_RADIUS;
        break;
    default:
        // Highly intelligent monsters can find their way
        // anywhere. (range == 0 means no restriction.)
        break;
    }

    if (range)
    {
        if (mons_is_native_in_branch(mon))
            range += 3;
        else if (mons_class_flag(mon->type, M_BLOOD_SCENT))
            range++;
    }

    return (range);
}

//#define DEBUG_PATHFIND
monster_pathfind::monster_pathfind()
    : mons(NULL), start(), target(), pos(), allow_diagonals(true),
      traverse_unmapped(false), range(0), min_length(0), max_length(0),
      dist(), prev(), hash()
{
}

monster_pathfind::~monster_pathfind()
{
}

void monster_pathfind::set_range(int r)
{
    if (r >= 0)
        range = r;
}

coord_def monster_pathfind::next_pos(const coord_def &c) const
{
    return c + Compass[prev[c.x][c.y]];
}

// The main method in the monster_pathfind class.
// Returns true if a path was found, else false.
bool monster_pathfind::init_pathfind(const monsters *mon, coord_def dest,
                                     bool diag, bool msg, bool pass_unmapped)
{
    mons   = mon;

    // We're doing a reverse search from target to monster.
    start  = dest;
    target = mon->pos();
    pos    = start;
    allow_diagonals   = diag;
    traverse_unmapped = pass_unmapped;

    // Easy enough. :P
    if (start == target)
    {
        if (msg)
            mpr("The monster is already there!");

        return (true);
    }

    return start_pathfind(msg);
}

bool monster_pathfind::init_pathfind(coord_def src, coord_def dest, bool diag,
                                     bool msg)
{
    start  = src;
    target = dest;
    pos    = start;
    allow_diagonals = diag;

    // Easy enough. :P
    if (start == target)
        return (true);

    return start_pathfind(msg);
}

bool monster_pathfind::start_pathfind(bool msg)
{
    // NOTE: We never do any traversable() check for the starting square
    //       (target). This means that even if the target cannot be reached
    //       we may still find a path leading adjacent to this position, which
    //       is desirable if e.g. the player is hovering over deep water
    //       surrounded by shallow water or floor, or if a foe is hiding in
    //       a wall.
    //       If the surrounding squares also are not traversable, we return
    //       early that no path could be found.

    max_length = min_length = grid_distance(pos.x, pos.y, target.x, target.y);
    for (int i = 0; i < GXM; i++)
        for (int j = 0; j < GYM; j++)
            dist[i][j] = INFINITE_DISTANCE;

    dist[pos.x][pos.y] = 0;

    bool success = false;
    do
    {
        // Calculate the distance to all neighbours of the current position,
        // and add them to the hash, if they haven't already been looked at.
        success = calc_path_to_neighbours();
        if (success)
            return (true);

        // Pull the position with shortest distance estimate to our target grid.
        success = get_best_position();

        if (!success)
        {
            if (msg)
            {
                mprf("Couldn't find a path from (%d,%d) to (%d,%d).",
                     target.x, target.y, start.x, start.y);
            }
            return (false);
        }
    }
    while (true);
}

// Returns true as soon as we encounter the target.
bool monster_pathfind::calc_path_to_neighbours()
{
    coord_def npos;
    int distance, old_dist, total;

    // For each point, we look at all neighbour points. Check the orthogonals
    // last, so that, should an orthogonal and a diagonal direction have the
    // same total travel cost, the orthogonal will be picked first, and thus
    // zigzagging will be significantly reduced.
    //
    //      1  0  3       This means directions are looked at, in order,
    //       \ | /        1, 3, 5, 7 (diagonals) followed by 0, 2, 4, 6
    //      6--.--2       (orthogonals). This is achieved by the assignment
    //       / | \        of (dir = 0) once dir has passed 7.
    //      7  4  5
    //
    for (int dir = 1; dir < 8; (dir += 2) == 9 && (dir = 0))
    {
        // Skip diagonal movement.
        if (!allow_diagonals && (dir % 2))
            continue;

        npos = pos + Compass[dir];

#ifdef DEBUG_PATHFIND
        mprf("Looking at neighbour (%d,%d)", npos.x, npos.y);
#endif
        if (!in_bounds(npos))
            continue;

        if (!traversable(npos))
            continue;

        // Ignore this grid if it takes us above the allowed distance.
        if (range && estimated_cost(npos) > range)
            continue;

        distance = dist[pos.x][pos.y] + travel_cost(npos);
        old_dist = dist[npos.x][npos.y];
#ifdef DEBUG_PATHFIND
        mprf("old dist: %d, new dist: %d, infinite: %d", old_dist, distance,
             INFINITE_DISTANCE);
#endif
        // If the new distance is better than the old one (initialised with
        // INFINITE), update the position.
        if (distance < old_dist)
        {
            // Calculate new total path length.
            total = distance + estimated_cost(npos);
            if (old_dist == INFINITE_DISTANCE)
            {
#ifdef DEBUG_PATHFIND
                mprf("Adding (%d,%d) to hash (total dist = %d)",
                     npos.x, npos.y, total);
#endif
                add_new_pos(npos, total);
                if (total > max_length)
                    max_length = total;
            }
            else
            {
#ifdef DEBUG_PATHFIND
                mprf("Improving (%d,%d) to total dist %d",
                     npos.x, npos.y, total);
#endif

                update_pos(npos, total);
            }

            // Update distance start->pos.
            dist[npos.x][npos.y] = distance;

            // Set backtracking information.
            // Converts the Compass direction to its counterpart.
            //      0  1  2         4  5  6
            //      7  .  3   ==>   3  .  7       e.g. (3 + 4) % 8          = 7
            //      6  5  4         2  1  0            (7 + 4) % 8 = 11 % 8 = 3

            prev[npos.x][npos.y] = (dir + 4) % 8;

            // Are we finished?
            if (npos == target)
            {
#ifdef DEBUG_PATHFIND
                mpr("Arrived at target.");
#endif
                return (true);
            }
        }
    }
    return (false);
}

// Starting at known min_length (minimum total estimated path distance), check
// the hash for existing vectors, then pick the last entry of the first vector
// that matches. Update min_length, if necessary.
bool monster_pathfind::get_best_position()
{
    for (int i = min_length; i <= max_length; i++)
    {
        if (!hash[i].empty())
        {
            if (i > min_length)
                min_length = i;

            std::vector<coord_def> &vec = hash[i];
            // Pick the last position pushed into the vector as it's most
            // likely to be close to the target.
            pos = vec[vec.size()-1];
            vec.pop_back();

#ifdef DEBUG_PATHFIND
            mprf("Returning (%d, %d) as best pos with total dist %d.",
                 pos.x, pos.y, min_length);
#endif

            return (true);
        }
#ifdef DEBUG_PATHFIND
        mprf("No positions for path length %d.", i);
#endif
    }

    // Nothing found? Then there's no path! :(
    return (false);
}

// Using the prev vector backtrack from start to target to find all steps to
// take along the shortest path.
std::vector<coord_def> monster_pathfind::backtrack()
{
#ifdef DEBUG_PATHFIND
    mpr("Backtracking...");
#endif
    std::vector<coord_def> path;
    pos = target;
    path.push_back(pos);

    if (pos == start)
        return path;

    int dir;
    do
    {
        dir = prev[pos.x][pos.y];
        pos = pos + Compass[dir];
        ASSERT(in_bounds(pos));
#ifdef DEBUG_PATHFIND
        mprf("prev: (%d, %d), pos: (%d, %d)", Compass[dir].x, Compass[dir].y,
                                              pos.x, pos.y);
#endif
        path.push_back(pos);

        if (pos.x == 0 && pos.y == 0)
            break;
    }
    while (pos != start);
    ASSERT(pos == start);

    return (path);
}

// Reduces the path coordinates to only a couple of key waypoints needed
// to reach the target. Waypoints are chosen such that from one waypoint you
// can see (and, more importantly, reach) the next one. Note that
// can_go_straight() is probably rather too conservative in these estimates.
// This is done because Crawl's pathfinding - once a target is in sight and easy
// reach - is both very robust and natural, especially if we want to flexibly
// avoid plants and other monsters in the way.
std::vector<coord_def> monster_pathfind::calc_waypoints()
{
    std::vector<coord_def> path = backtrack();

    // If no path found, nothing to be done.
    if (path.empty())
        return path;

    dungeon_feature_type can_move;
    if (mons_amphibious(mons))
        can_move = DNGN_DEEP_WATER;
    else
        can_move = DNGN_SHALLOW_WATER;

    std::vector<coord_def> waypoints;
    pos = path[0];

#ifdef DEBUG_PATHFIND
    mpr(EOL "Waypoints:");
#endif
    for (unsigned int i = 1; i < path.size(); i++)
    {
        if (can_go_straight(pos, path[i], can_move))
            continue;
        else
        {
            pos = path[i-1];
            waypoints.push_back(pos);
#ifdef DEBUG_PATHFIND
            mprf("waypoint: (%d, %d)", pos.x, pos.y);
#endif
        }
    }

    // Add the actual target to the list of waypoints, so we can later check
    // whether a tracked enemy has moved too much, in case we have to update
    // the path.
    if (pos != path[path.size() - 1])
        waypoints.push_back(path[path.size() - 1]);

    return (waypoints);
}

bool monster_pathfind::traversable(const coord_def p)
{
    if (traverse_unmapped && grd(p) == DNGN_UNSEEN)
        return (true);

    if (mons)
        return mons_traversable(p);

    return feat_has_solid_floor(grd(p));
}

// Checks whether a given monster can pass over a certain position, respecting
// its preferred habit and capability of flight or opening doors.
bool monster_pathfind::mons_traversable(const coord_def p)
{
    const monster_type montype = mons_is_zombified(mons) ? mons_zombie_base(mons)
                                                         : mons->type;
    const dungeon_feature_type feat = grd(p);
    // Monsters that can't open doors won't be able to pass them, and
    // only monsters of normal or greater intelligence can pathfind through
    // secret doors.
    if (feat == DNGN_CLOSED_DOOR ||
        (mons_intel(mons) >= I_NORMAL &&
         (feat == DNGN_DETECTED_SECRET_DOOR || feat == DNGN_SECRET_DOOR)))
    {
        if (mons->is_habitable_feat(DNGN_FLOOR))
        {
            if (mons_eats_items(mons))
                return (true);
            else if (mons_is_zombified(mons))
            {
                if (mons_class_itemuse(montype) >= MONUSE_OPEN_DOORS)
                    return (true);
            }
            else if (mons_itemuse(mons) >= MONUSE_OPEN_DOORS)
                return (true);
        }
    }

    if (!mons->is_habitable_feat(grd(p)))
        return (false);

    // Your friends only know about doors you know about, unless they feel
    // at home in this branch.
    if (grd(p) == DNGN_SECRET_DOOR && mons->friendly()
        && (mons_intel(mons) < I_NORMAL || !mons_is_native_in_branch(mons)))
    {
        return (false);
    }

    const trap_def* ptrap = find_trap(p);
    if (ptrap)
    {
        const trap_type tt = ptrap->type;

        // Don't allow allies to pass over known (to them) Zot traps.
        if (tt == TRAP_ZOT
            && ptrap->is_known(mons)
            && mons->friendly())
        {
            return (false);
        }

        // Monsters cannot travel over teleport traps.
        if (!can_place_on_trap(montype, tt))
            return (false);
    }

    return (true);
}

int monster_pathfind::travel_cost(coord_def npos)
{
    if (mons)
        return mons_travel_cost(npos);

    return (1);
}

// Assumes that grids that really cannot be entered don't even get here.
// (Checked by traversable().)
int monster_pathfind::mons_travel_cost(coord_def npos)
{
    ASSERT(grid_distance(pos, npos) <= 1);

    // Doors need to be opened.
    if (feat_is_closed_door(grd(npos)) || grd(npos) == DNGN_SECRET_DOOR)
        return 2;

    const int montype = mons_is_zombified(mons) ? mons_zombie_base(mons)
                                                : mons->type;

    const bool airborne = mons_airborne(montype, -1, false);

    // Travelling through water, entering or leaving water is more expensive
    // for non-amphibious monsters, so they'll avoid it where possible.
    // (The resulting path might not be optimal but it will lead to a path
    // a monster of such habits is likely to prefer.)
    // Only tested for shallow water since they can't enter deep water anyway.
    if (!airborne && !mons_class_amphibious(montype)
        && (grd(pos) == DNGN_SHALLOW_WATER || grd(npos) == DNGN_SHALLOW_WATER))
    {
        return 2;
    }

    // Try to avoid (known) traps.
    const trap_def* ptrap = find_trap(npos);
    if (ptrap)
    {
        const bool knows_trap = ptrap->is_known(mons);
        const trap_type tt = ptrap->type;
        if (tt == TRAP_ALARM || tt == TRAP_ZOT)
        {
            // Your allies take extra precautions to avoid known alarm traps.
            // Zot traps are considered intraversable.
            if (knows_trap && mons->friendly())
                return (3);

            // To hostile monsters, these traps are completely harmless.
            return 1;
        }

        // Mechanical traps can be avoided by flying, as can shafts, and
        // tele traps are never traversable anyway.
        if (knows_trap && !airborne)
            return 2;
    }

    return 1;
}

// The estimated cost to reach a grid is simply max(dx, dy).
int monster_pathfind::estimated_cost(coord_def p)
{
    return (grid_distance(p, target));
}

void monster_pathfind::add_new_pos(coord_def npos, int total)
{
    hash[total].push_back(npos);
}

void monster_pathfind::update_pos(coord_def npos, int total)
{
    // Find hash position of old distance and delete it,
    // then call_add_new_pos.
    int old_total = dist[npos.x][npos.y] + estimated_cost(npos);

    std::vector<coord_def> &vec = hash[old_total];
    for (unsigned int i = 0; i < vec.size(); i++)
    {
        if (vec[i] == npos)
        {
            vec.erase(vec.begin() + i);
            break;
        }
    }

    add_new_pos(npos, total);
}