/* NetHack 3.6	display.c	$NHDT-Date: 1524780381 2018/04/26 22:06:21 $  $NHDT-Branch: NetHack-3.6.0 $:$NHDT-Revision: 1.90 $ */
/* Copyright (c) Dean Luick, with acknowledgements to Kevin Darcy */
/* and Dave Cohrs, 1990.                                          */
/* NetHack may be freely redistributed.  See license for details. */

/*
 *                      THE NEW DISPLAY CODE
 *
 * The old display code has been broken up into three parts: vision, display,
 * and drawing.  Vision decides what locations can and cannot be physically
 * seen by the hero.  Display decides _what_ is displayed at a given location.
 * Drawing decides _how_ to draw a monster, fountain, sword, etc.
 *
 * The display system uses information from the vision system to decide
 * what to draw at a given location.  The routines for the vision system
 * can be found in vision.c and vision.h.  The routines for display can
 * be found in this file (display.c) and display.h.  The drawing routines
 * are part of the window port.  See doc/window.doc for the drawing
 * interface.
 *
 * The display system deals with an abstraction called a glyph.  Anything
 * that could possibly be displayed has a unique glyph identifier.
 *
 * What is seen on the screen is a combination of what the hero remembers
 * and what the hero currently sees.  Objects and dungeon features (walls
 * doors, etc) are remembered when out of sight.  Monsters and temporary
 * effects are not remembered.  Each location on the level has an
 * associated glyph.  This is the hero's _memory_ of what he or she has
 * seen there before.
 *
 * Display rules:
 *
 *      If the location is in sight, display in order:
 *              visible (or sensed) monsters
 *              visible objects
 *              known traps
 *              background
 *
 *      If the location is out of sight, display in order:
 *              sensed monsters (telepathy)
 *              memory
 *
 *
 *
 * Here is a list of the major routines in this file to be used externally:
 *
 * newsym
 *
 * Possibly update the screen location (x,y).  This is the workhorse routine.
 * It is always correct --- where correct means following the in-sight/out-
 * of-sight rules.  **Most of the code should use this routine.**  This
 * routine updates the map and displays monsters.
 *
 *
 * map_background
 * map_object
 * map_trap
 * map_invisible
 * unmap_object
 *
 * If you absolutely must override the in-sight/out-of-sight rules, there
 * are two possibilities.  First, you can mess with vision to force the
 * location in sight then use newsym(), or you can  use the map_* routines.
 * The first has not been tried [no need] and the second is used in the
 * detect routines --- detect object, magic mapping, etc.  The map_*
 * routines *change* what the hero remembers.  All changes made by these
 * routines will be sticky --- they will survive screen redraws.  Do *not*
 * use these for things that only temporarily change the screen.  These
 * routines are also used directly by newsym().  unmap_object is used to
 * clear a remembered object when/if detection reveals it isn't there.
 *
 *
 * show_glyph
 *
 * This is direct (no processing in between) buffered access to the screen.
 * Temporary screen effects are run through this and its companion,
 * flush_screen().  There is yet a lower level routine, print_glyph(),
 * but this is unbuffered and graphic dependent (i.e. it must be surrounded
 * by graphic set-up and tear-down routines).  Do not use print_glyph().
 *
 *
 * see_monsters
 * see_objects
 * see_traps
 *
 * These are only used when something affects all of the monsters or
 * objects or traps.  For objects and traps, the only thing is hallucination.
 * For monsters, there are hallucination and changing from/to blindness, etc.
 *
 *
 * tmp_at
 *
 * This is a useful interface for displaying temporary items on the screen.
 * Its interface is different than previously, so look at it carefully.
 *
 *
 *
 * Parts of the rm structure that are used:
 *
 *      typ     - What is really there.
 *      glyph   - What the hero remembers.  This will never be a monster.
 *                Monsters "float" above this.
 *      lit     - True if the position is lit.  An optimization for
 *                lit/unlit rooms.
 *      waslit  - True if the position was *remembered* as lit.
 *      seenv   - A vector of bits representing the directions from which the
 *                hero has seen this position.  The vector's primary use is
 *                determining how walls are seen.  E.g. a wall sometimes looks
 *                like stone on one side, but is seen as wall from the other.
 *                Other uses are for unmapping detected objects and felt
 *                locations, where we need to know if the hero has ever
 *                seen the location.
 *      flags   - Additional information for the typ field.  Different for
 *                each typ.
 *      horizontal - Indicates whether the wall or door is horizontal or
 *                vertical.
 */
#include "hack.h"

STATIC_DCL void FDECL(display_monster,
                      (XCHAR_P, XCHAR_P, struct monst *, int, XCHAR_P));
STATIC_DCL int FDECL(swallow_to_glyph, (int, int));
STATIC_DCL void FDECL(display_warning, (struct monst *));

STATIC_DCL int FDECL(check_pos, (int, int, int));
STATIC_DCL int FDECL(get_bk_glyph, (XCHAR_P, XCHAR_P));

/*#define WA_VERBOSE*/ /* give (x,y) locations for all "bad" spots */
#ifdef WA_VERBOSE
STATIC_DCL boolean FDECL(more_than_one, (int, int, int, int, int));
#endif

STATIC_DCL int FDECL(set_twall, (int, int, int, int, int, int, int, int));
STATIC_DCL int FDECL(set_wall, (int, int, int));
STATIC_DCL int FDECL(set_corn, (int, int, int, int, int, int, int, int));
STATIC_DCL int FDECL(set_crosswall, (int, int));
STATIC_DCL void FDECL(set_seenv, (struct rm *, int, int, int, int));
STATIC_DCL void FDECL(t_warn, (struct rm *));
STATIC_DCL int FDECL(wall_angle, (struct rm *));

#define remember_topology(x, y) (lastseentyp[x][y] = levl[x][y].typ)

/*
 * magic_map_background()
 *
 * This function is similar to map_background (see below) except we pay
 * attention to and correct unexplored, lit ROOM and CORR spots.
 */
void
magic_map_background(x, y, show)
xchar x, y;
int show;
{
    int glyph = back_to_glyph(x, y); /* assumes hero can see x,y */
    struct rm *lev = &levl[x][y];

    /*
     * Correct for out of sight lit corridors and rooms that the hero
     * doesn't remember as lit.
     */
    if (!cansee(x, y) && !lev->waslit) {
        /* Floor spaces are dark if unlit.  Corridors are dark if unlit. */
        if (lev->typ == ROOM && glyph == cmap_to_glyph(S_room))
            glyph = cmap_to_glyph((flags.dark_room && iflags.use_color)
                                      ? (DARKROOMSYM)
                                      : S_stone);
        else if (lev->typ == CORR && glyph == cmap_to_glyph(S_litcorr))
            glyph = cmap_to_glyph(S_corr);
    }
    if (level.flags.hero_memory)
        lev->glyph = glyph;
    if (show)
        show_glyph(x, y, glyph);

    remember_topology(x, y);
}

/*
 * The routines map_background(), map_object(), and map_trap() could just
 * as easily be:
 *
 *      map_glyph(x,y,glyph,show)
 *
 * Which is called with the xx_to_glyph() in the call.  Then I can get
 * rid of 3 routines that don't do very much anyway.  And then stop
 * having to create fake objects and traps.  However, I am reluctant to
 * make this change.
 */
/* FIXME: some of these use xchars for x and y, and some use ints.  Make
 * this consistent.
 */

/*
 * map_background()
 *
 * Make the real background part of our map.  This routine assumes that
 * the hero can physically see the location.  Update the screen if directed.
 */
void
map_background(x, y, show)
register xchar x, y;
register int show;
{
    register int glyph = back_to_glyph(x, y);

    if (level.flags.hero_memory)
        levl[x][y].glyph = glyph;
    if (show)
        show_glyph(x, y, glyph);
}

/*
 * map_trap()
 *
 * Map the trap and print it out if directed.  This routine assumes that the
 * hero can physically see the location.
 */
void
map_trap(trap, show)
register struct trap *trap;
register int show;
{
    register int x = trap->tx, y = trap->ty;
    register int glyph = trap_to_glyph(trap);

    if (level.flags.hero_memory)
        levl[x][y].glyph = glyph;
    if (show)
        show_glyph(x, y, glyph);
}

/*
 * map_object()
 *
 * Map the given object.  This routine assumes that the hero can physically
 * see the location of the object.  Update the screen if directed.
 */
void
map_object(obj, show)
register struct obj *obj;
register int show;
{
    register int x = obj->ox, y = obj->oy;
    register int glyph = obj_to_glyph(obj);

    if (level.flags.hero_memory) {
        /* MRKR: While hallucinating, statues are seen as random monsters */
        /*       but remembered as random objects.                        */

        if (Hallucination && obj->otyp == STATUE) {
            levl[x][y].glyph = random_obj_to_glyph();
        } else {
            levl[x][y].glyph = glyph;
        }
    }
    if (show)
        show_glyph(x, y, glyph);
}

/*
 * map_invisible()
 *
 * Make the hero remember that a square contains an invisible monster.
 * This is a special case in that the square will continue to be displayed
 * this way even when the hero is close enough to see it.  To get rid of
 * this and display the square's actual contents, use unmap_object() followed
 * by newsym() if necessary.
 */
void
map_invisible(x, y)
register xchar x, y;
{
    if (x != u.ux || y != u.uy) { /* don't display I at hero's location */
        if (level.flags.hero_memory)
            levl[x][y].glyph = GLYPH_INVISIBLE;
        show_glyph(x, y, GLYPH_INVISIBLE);
    }
}

boolean
unmap_invisible(x, y)
int x, y;
{
    if (isok(x,y) && glyph_is_invisible(levl[x][y].glyph)) {
        unmap_object(x, y);
        newsym(x, y);
        return TRUE;
    }
    return FALSE;
}


/*
 * unmap_object()
 *
 * Remove something from the map when the hero realizes it's not there any
 * more.  Replace it with background or known trap, but not with any other
 * If this is used for detection, a full screen update is imminent anyway;
 * if this is used to get rid of an invisible monster notation, we might have
 * to call newsym().
 */
void
unmap_object(x, y)
register int x, y;
{
    register struct trap *trap;

    if (!level.flags.hero_memory)
        return;

    if ((trap = t_at(x, y)) != 0 && trap->tseen && !covers_traps(x, y))
        map_trap(trap, 0);
    else if (levl[x][y].seenv) {
        struct rm *lev = &levl[x][y];

        map_background(x, y, 0);

        /* turn remembered dark room squares dark */
        if (!lev->waslit && lev->glyph == cmap_to_glyph(S_room)
            && lev->typ == ROOM)
            lev->glyph = cmap_to_glyph(S_stone);
    } else
        levl[x][y].glyph = cmap_to_glyph(S_stone); /* default val */
}

/*
 * map_location()
 *
 * Make whatever at this location show up.  This is only for non-living
 * things.  This will not handle feeling invisible objects correctly.
 *
 * Internal to display.c, this is a #define for speed.
 */
#define _map_location(x, y, show)                                           \
    {                                                                       \
        register struct obj *obj;                                           \
        register struct trap *trap;                                         \
                                                                            \
        if ((obj = vobj_at(x, y)) && !covers_objects(x, y))                 \
            map_object(obj, show);                                          \
        else if ((trap = t_at(x, y)) && trap->tseen && !covers_traps(x, y)) \
            map_trap(trap, show);                                           \
        else                                                                \
            map_background(x, y, show);                                     \
                                                                            \
        remember_topology(x, y);                                            \
    }

void
map_location(x, y, show)
int x, y, show;
{
    _map_location(x, y, show);
}

#define DETECTED 2
#define PHYSICALLY_SEEN 1
#define is_worm_tail(mon) ((mon) && ((x != (mon)->mx) || (y != (mon)->my)))

/*
 * display_monster()
 *
 * Note that this is *not* a map_XXXX() function!  Monsters sort of float
 * above everything.
 *
 * Yuck.  Display body parts by recognizing that the display position is
 * not the same as the monster position.  Currently the only body part is
 * a worm tail.
 *
 */
STATIC_OVL void
display_monster(x, y, mon, sightflags, worm_tail)
register xchar x, y;        /* display position */
register struct monst *mon; /* monster to display */
int sightflags;             /* 1 if the monster is physically seen;
                               2 if detected using Detect_monsters */
xchar worm_tail;            /* mon is actually a worm tail */
{
    boolean mon_mimic = (mon->m_ap_type != M_AP_NOTHING);
    int sensed = (mon_mimic && (Protection_from_shape_changers
                                || sensemon(mon)));
    /*
     * We must do the mimic check first.  If the mimic is mimicing something,
     * and the location is in sight, we have to change the hero's memory
     * so that when the position is out of sight, the hero remembers what
     * the mimic was mimicing.
     */

    if (mon_mimic && (sightflags == PHYSICALLY_SEEN)) {
        switch (mon->m_ap_type) {
        default:
            impossible("display_monster:  bad m_ap_type value [ = %d ]",
                       (int) mon->m_ap_type);
            /*FALLTHRU*/
        case M_AP_NOTHING:
            show_glyph(x, y, mon_to_glyph(mon));
            break;

        case M_AP_FURNITURE: {
            /*
             * This is a poor man's version of map_background().  I can't
             * use map_background() because we are overriding what is in
             * the 'typ' field.  Maybe have map_background()'s parameters
             * be (x,y,glyph) instead of just (x,y).
             *
             * mappearance is currently set to an S_ index value in
             * makemon.c.
             */
            int sym = mon->mappearance, glyph = cmap_to_glyph(sym);

            levl[x][y].glyph = glyph;
            if (!sensed) {
                show_glyph(x, y, glyph);
                /* override real topology with mimic's fake one */
                lastseentyp[x][y] = cmap_to_type(sym);
            }
            break;
        }

        case M_AP_OBJECT: {
            /* Make a fake object to send to map_object(). */
            struct obj obj;

            obj = zeroobj;
            obj.ox = x;
            obj.oy = y;
            obj.otyp = mon->mappearance;
            /* might be mimicing a corpse or statue */
            obj.corpsenm = has_mcorpsenm(mon) ? MCORPSENM(mon) : PM_TENGU;
            map_object(&obj, !sensed);
            break;
        }

        case M_AP_MONSTER:
            show_glyph(x, y,
                       monnum_to_glyph(what_mon((int) mon->mappearance)));
            break;
        }
    }

    /* If the mimic is unsuccessfully mimicing something, display the monster.
     */
    if (!mon_mimic || sensed) {
        int num;

        /* [ALI] Only use detected glyphs when monster wouldn't be
         * visible by any other means.
         *
         * There are no glyphs for "detected pets" so we have to
         * decide whether to display such things as detected or as tame.
         * If both are being highlighted in the same way, it doesn't
         * matter, but if not, showing them as pets is preferrable.
         */
        if (mon->mtame && !Hallucination) {
            if (worm_tail)
                num = petnum_to_glyph(PM_LONG_WORM_TAIL);
            else
                num = pet_to_glyph(mon);
        } else if (sightflags == DETECTED) {
            if (worm_tail)
                num = detected_monnum_to_glyph(what_mon(PM_LONG_WORM_TAIL));
            else
                num = detected_mon_to_glyph(mon);
        } else {
            if (worm_tail)
                num = monnum_to_glyph(what_mon(PM_LONG_WORM_TAIL));
            else
                num = mon_to_glyph(mon);
        }
        show_glyph(x, y, num);
    }
}

/*
 * display_warning()
 *
 * This is also *not* a map_XXXX() function!  Monster warnings float
 * above everything just like monsters do, but only if the monster
 * is not showing.
 *
 * Do not call for worm tails.
 */
STATIC_OVL void
display_warning(mon)
register struct monst *mon;
{
    int x = mon->mx, y = mon->my;
    int glyph;

    if (mon_warning(mon)) {
        int wl = Hallucination ? rn1(WARNCOUNT - 1, 1) : warning_of(mon);
        glyph = warning_to_glyph(wl);
    } else if (MATCH_WARN_OF_MON(mon)) {
        glyph = mon_to_glyph(mon);
    } else {
        impossible("display_warning did not match warning type?");
        return;
    }
    /* warning glyph is drawn on the monster layer; unseen
       monster glyph is drawn on the object/trap/floor layer;
       if we see a 'warning' move onto 'remembered, unseen' we
       need to explicitly remove that in order for it to not
       reappear when the warned-of monster moves off that spot */
    if (glyph_is_invisible(levl[x][y].glyph))
        unmap_object(x, y);
    show_glyph(x, y, glyph);
}

int
warning_of(mon)
struct monst *mon;
{
    int wl = 0, tmp = 0;
    if (mon_warning(mon)) {
        tmp = (int) (mon->m_lev / 4);    /* match display.h */
        wl = (tmp > WARNCOUNT - 1) ? WARNCOUNT - 1 : tmp;
    }
    return wl;
}


/*
 * feel_newsym()
 *
 * When hero knows what happened to location, even when blind.
 */
void
feel_newsym(x, y)
xchar x, y;
{
    if (Blind)
        feel_location(x, y);
    else
        newsym(x, y);
}


/*
 * feel_location()
 *
 * Feel the given location.  This assumes that the hero is blind and that
 * the given position is either the hero's or one of the eight squares
 * adjacent to the hero (except for a boulder push).
 * If an invisible monster has gone away, that will be discovered.  If an
 * invisible monster has appeared, this will _not_ be discovered since
 * searching only finds one monster per turn so we must check that separately.
 */
void
feel_location(x, y)
xchar x, y;
{
    struct rm *lev;
    struct obj *boulder;
    register struct monst *mon;

    if (!isok(x, y))
        return;
    lev = &(levl[x][y]);
    /* If hero's memory of an invisible monster is accurate, we want to keep
     * him from detecting the same monster over and over again on each turn.
     * We must return (so we don't erase the monster).  (We must also, in the
     * search function, be sure to skip over previously detected 'I's.)
     */
    if (glyph_is_invisible(lev->glyph) && m_at(x, y))
        return;

    /* The hero can't feel non pool locations while under water
       except for lava and ice. */
    if (Underwater && !Is_waterlevel(&u.uz)
        && !is_pool_or_lava(x, y) && !is_ice(x, y))
        return;

    /* Set the seen vector as if the hero had seen it.
       It doesn't matter if the hero is levitating or not. */
    set_seenv(lev, u.ux, u.uy, x, y);

    if (!can_reach_floor(FALSE)) {
        /*
         * Levitation Rules.  It is assumed that the hero can feel the state
         * of the walls around herself and can tell if she is in a corridor,
         * room, or doorway.  Boulders are felt because they are large enough.
         * Anything else is unknown because the hero can't reach the ground.
         * This makes things difficult.
         *
         * Check (and display) in order:
         *
         *      + Stone, walls, and closed doors.
         *      + Boulders.  [see a boulder before a doorway]
         *      + Doors.
         *      + Room/water positions
         *      + Everything else (hallways!)
         */
        if (IS_ROCK(lev->typ)
            || (IS_DOOR(lev->typ)
                && (lev->doormask & (D_LOCKED | D_CLOSED)))) {
            map_background(x, y, 1);
        } else if ((boulder = sobj_at(BOULDER, x, y)) != 0) {
            map_object(boulder, 1);
        } else if (IS_DOOR(lev->typ)) {
            map_background(x, y, 1);
        } else if (IS_ROOM(lev->typ) || IS_POOL(lev->typ)) {
            boolean do_room_glyph;

            /*
             * An open room or water location.  Normally we wouldn't touch
             * this, but we have to get rid of remembered boulder symbols.
             * This will only occur in rare occasions when the hero goes
             * blind and doesn't find a boulder where expected (something
             * came along and picked it up).  We know that there is not a
             * boulder at this location.  Show fountains, pools, etc.
             * underneath if already seen.  Otherwise, show the appropriate
             * floor symbol.
             *
             * Similarly, if the hero digs a hole in a wall or feels a
             * location
             * that used to contain an unseen monster.  In these cases,
             * there's no reason to assume anything was underneath, so
             * just show the appropriate floor symbol.  If something was
             * embedded in the wall, the glyph will probably already
             * reflect that.  Don't change the symbol in this case.
             *
             * This isn't quite correct.  If the boulder was on top of some
             * other objects they should be seen once the boulder is removed.
             * However, we have no way of knowing that what is there now
             * was there then.  So we let the hero have a lapse of memory.
             * We could also just display what is currently on the top of the
             * object stack (if anything).
             */
            do_room_glyph = FALSE;
            if (lev->glyph == objnum_to_glyph(BOULDER)
                || glyph_is_invisible(lev->glyph)) {
                if (lev->typ != ROOM && lev->seenv)
                    map_background(x, y, 1);
                else
                    do_room_glyph = TRUE;
            } else if (lev->glyph >= cmap_to_glyph(S_stone)
                       && lev->glyph < cmap_to_glyph(S_darkroom)) {
                do_room_glyph = TRUE;
            }
            if (do_room_glyph) {
                lev->glyph = (flags.dark_room && iflags.use_color
                              && !Is_rogue_level(&u.uz))
                                 ? cmap_to_glyph(S_darkroom)
                                 : (lev->waslit ? cmap_to_glyph(S_room)
                                                : cmap_to_glyph(S_stone));
                show_glyph(x, y, lev->glyph);
            }
        } else {
            /* We feel it (I think hallways are the only things left). */
            map_background(x, y, 1);
            /* Corridors are never felt as lit (unless remembered that way) */
            /* (lit_corridor only).                                         */
            if (lev->typ == CORR && lev->glyph == cmap_to_glyph(S_litcorr)
                && !lev->waslit)
                show_glyph(x, y, lev->glyph = cmap_to_glyph(S_corr));
            else if (lev->typ == ROOM && flags.dark_room && iflags.use_color
                     && lev->glyph == cmap_to_glyph(S_room))
                show_glyph(x, y, lev->glyph = cmap_to_glyph(S_darkroom));
        }
    } else {
        _map_location(x, y, 1);

        if (Punished) {
            /*
             * A ball or chain is only felt if it is first on the object
             * location list.  Otherwise, we need to clear the felt bit ---
             * something has been dropped on the ball/chain.  If the bit is
             * not cleared, then when the ball/chain is moved it will drop
             * the wrong glyph.
             */
            if (uchain->ox == x && uchain->oy == y) {
                if (level.objects[x][y] == uchain)
                    u.bc_felt |= BC_CHAIN;
                else
                    u.bc_felt &= ~BC_CHAIN; /* do not feel the chain */
            }
            if (!carried(uball) && uball->ox == x && uball->oy == y) {
                if (level.objects[x][y] == uball)
                    u.bc_felt |= BC_BALL;
                else
                    u.bc_felt &= ~BC_BALL; /* do not feel the ball */
            }
        }

        /* Floor spaces are dark if unlit.  Corridors are dark if unlit. */
        if (lev->typ == ROOM && lev->glyph == cmap_to_glyph(S_room)
            && (!lev->waslit || (flags.dark_room && iflags.use_color)))
            show_glyph(x, y, lev->glyph = cmap_to_glyph(
                                 flags.dark_room ? S_darkroom : S_stone));
        else if (lev->typ == CORR && lev->glyph == cmap_to_glyph(S_litcorr)
                 && !lev->waslit)
            show_glyph(x, y, lev->glyph = cmap_to_glyph(S_corr));
    }
    /* draw monster on top if we can sense it */
    if ((x != u.ux || y != u.uy) && (mon = m_at(x, y)) != 0 && sensemon(mon))
        display_monster(x, y, mon,
                        (tp_sensemon(mon) || MATCH_WARN_OF_MON(mon))
                            ? PHYSICALLY_SEEN
                            : DETECTED,
                        is_worm_tail(mon));
}

/*
 * newsym()
 *
 * Possibly put a new glyph at the given location.
 */
void
newsym(x, y)
register int x, y;
{
    register struct monst *mon;
    register struct rm *lev = &(levl[x][y]);
    register int see_it;
    register xchar worm_tail;

    if (in_mklev)
        return;
#ifdef HANGUPHANDLING
    if (program_state.done_hup)
        return;
#endif

    /* only permit updating the hero when swallowed */
    if (u.uswallow) {
        if (x == u.ux && y == u.uy)
            display_self();
        return;
    }
    if (Underwater && !Is_waterlevel(&u.uz)) {
        /* when underwater, don't do anything unless <x,y> is an
           adjacent water or lava or ice position */
        if (!(is_pool_or_lava(x, y) || is_ice(x, y)) || distu(x, y) > 2)
            return;
    }

    /* Can physically see the location. */
    if (cansee(x, y)) {
        NhRegion *reg = visible_region_at(x, y);
        /*
         * Don't use templit here:  E.g.
         *
         *      lev->waslit = !!(lev->lit || templit(x,y));
         *
         * Otherwise we have the "light pool" problem, where non-permanently
         * lit areas just out of sight stay remembered as lit.  They should
         * re-darken.
         *
         * Perhaps ALL areas should revert to their "unlit" look when
         * out of sight.
         */
        lev->waslit = (lev->lit != 0); /* remember lit condition */

        /* normal region shown only on accessible positions, but poison clouds
         * also shown above lava, pools and moats.
         */
        if (reg != NULL && (ACCESSIBLE(lev->typ)
                            || (reg->glyph == cmap_to_glyph(S_poisoncloud)
                                && (lev->typ == LAVAPOOL || lev->typ == POOL
                                    || lev->typ == MOAT)))) {
            show_region(reg, x, y);
            return;
        }
        if (x == u.ux && y == u.uy) {
            if (canspotself()) {
                _map_location(x, y, 0); /* map *under* self */
                display_self();
            } else
                /* we can see what is there */
                _map_location(x, y, 1);
        } else {
            mon = m_at(x, y);
            worm_tail = is_worm_tail(mon);
            see_it =
                mon && (worm_tail ? (!mon->minvis || See_invisible)
                                  : (mon_visible(mon)) || tp_sensemon(mon)
                                        || MATCH_WARN_OF_MON(mon));
            if (mon && (see_it || (!worm_tail && Detect_monsters))) {
                if (mon->mtrapped) {
                    struct trap *trap = t_at(x, y);
                    int tt = trap ? trap->ttyp : NO_TRAP;

                    /* if monster is in a physical trap, you see the trap too
                     */
                    if (tt == BEAR_TRAP || tt == PIT || tt == SPIKED_PIT
                        || tt == WEB) {
                        trap->tseen = TRUE;
                    }
                }
                _map_location(x, y, 0); /* map under the monster */
                /* also gets rid of any invisibility glyph */
                display_monster(x, y, mon,
                                see_it ? PHYSICALLY_SEEN : DETECTED,
                                worm_tail);
            } else if (mon && mon_warning(mon) && !is_worm_tail(mon)) {
                display_warning(mon);
            } else if (glyph_is_invisible(levl[x][y].glyph)) {
                map_invisible(x, y);
            } else
                _map_location(x, y, 1); /* map the location */\
        }

    /* Can't see the location. */
    } else {
        if (x == u.ux && y == u.uy) {
            feel_location(u.ux, u.uy); /* forces an update */

            if (canspotself())
                display_self();
        } else if ((mon = m_at(x, y))
                   && ((see_it = (tp_sensemon(mon) || MATCH_WARN_OF_MON(mon)
                                  || (see_with_infrared(mon)
                                      && mon_visible(mon))))
                       || Detect_monsters)) {
            /* Monsters are printed every time. */
            /* This also gets rid of any invisibility glyph */
            display_monster(x, y, mon, see_it ? 0 : DETECTED,
                            is_worm_tail(mon) ? TRUE : FALSE);
        } else if ((mon = m_at(x, y)) && mon_warning(mon)
                   && !is_worm_tail(mon)) {
            display_warning(mon);
        }

        /*
         * If the location is remembered as being both dark (waslit is false)
         * and lit (glyph is a lit room or lit corridor) then it was either:
         *
         *      (1) A dark location that the hero could see through night
         *          vision.
         *
         *      (2) Darkened while out of the hero's sight.  This can happen
         *          when cursed scroll of light is read.
         *
         * In either case, we have to manually correct the hero's memory to
         * match waslit.  Deciding when to change waslit is non-trivial.
         *
         *  Note:  If flags.lit_corridor is set, then corridors act like room
         *         squares.  That is, they light up if in night vision range.
         *         If flags.lit_corridor is not set, then corridors will
         *         remain dark unless lit by a light spell and may darken
         *         again, as discussed above.
         *
         * These checks and changes must be here and not in back_to_glyph().
         * They are dependent on the position being out of sight.
         */
        else if (Is_rogue_level(&u.uz)) {
            if (lev->glyph == cmap_to_glyph(S_litcorr) && lev->typ == CORR)
                show_glyph(x, y, lev->glyph = cmap_to_glyph(S_corr));
            else if (lev->glyph == cmap_to_glyph(S_room) && lev->typ == ROOM
                     && !lev->waslit)
                show_glyph(x, y, lev->glyph = cmap_to_glyph(S_stone));
            else
                goto show_mem;
        }
        else if (!lev->waslit || (flags.dark_room && iflags.use_color)) {
            if (lev->glyph == cmap_to_glyph(S_litcorr) && lev->typ == CORR)
                show_glyph(x, y, lev->glyph = cmap_to_glyph(S_corr));
            else if (lev->glyph == cmap_to_glyph(S_room) && lev->typ == ROOM)
                show_glyph(x, y, lev->glyph = cmap_to_glyph(DARKROOMSYM));
            else
                goto show_mem;
        } else {
        show_mem:
            show_glyph(x, y, lev->glyph);
        }
    }
}

#undef is_worm_tail

/*
 * shieldeff()
 *
 * Put magic shield pyrotechnics at the given location.  This *could* be
 * pulled into a platform dependent routine for fancier graphics if desired.
 */
void
shieldeff(x, y)
xchar x, y;
{
    register int i;

    if (!flags.sparkle)
        return;
    if (cansee(x, y)) { /* Don't see anything if can't see the location */
        for (i = 0; i < SHIELD_COUNT; i++) {
            show_glyph(x, y, cmap_to_glyph(shield_static[i]));
            flush_screen(1); /* make sure the glyph shows up */
            delay_output();
        }
        newsym(x, y); /* restore the old information */
    }
}

/*
 * tmp_at()
 *
 * Temporarily place glyphs on the screen.  Do not call delay_output().  It
 * is up to the caller to decide if it wants to wait [presently, everyone
 * but explode() wants to delay].
 *
 * Call:
 *      (DISP_BEAM,   glyph)    open, initialize glyph
 *      (DISP_FLASH,  glyph)    open, initialize glyph
 *      (DISP_ALWAYS, glyph)    open, initialize glyph
 *      (DISP_CHANGE, glyph)    change glyph
 *      (DISP_END,    0)        close & clean up (second argument doesn't
 *                              matter)
 *      (DISP_FREEMEM, 0)       only used to prevent memory leak during
 *                              exit)
 *      (x, y)                  display the glyph at the location
 *
 * DISP_BEAM  - Display the given glyph at each location, but do not erase
 *              any until the close call.
 * DISP_FLASH - Display the given glyph at each location, but erase the
 *              previous location's glyph.
 * DISP_ALWAYS- Like DISP_FLASH, but vision is not taken into account.
 */

#define TMP_AT_MAX_GLYPHS (COLNO * 2)

static struct tmp_glyph {
    coord saved[TMP_AT_MAX_GLYPHS]; /* previously updated positions */
    int sidx;                       /* index of next unused slot in saved[] */
    int style; /* either DISP_BEAM or DISP_FLASH or DISP_ALWAYS */
    int glyph; /* glyph to use when printing */
    struct tmp_glyph *prev;
} tgfirst;

void
tmp_at(x, y)
int x, y;
{
    static struct tmp_glyph *tglyph = (struct tmp_glyph *) 0;
    struct tmp_glyph *tmp;

    switch (x) {
    case DISP_BEAM:
    case DISP_ALL:
    case DISP_FLASH:
    case DISP_ALWAYS:
        if (!tglyph)
            tmp = &tgfirst;
        else /* nested effect; we need dynamic memory */
            tmp = (struct tmp_glyph *) alloc(sizeof(struct tmp_glyph));
        tmp->prev = tglyph;
        tglyph = tmp;
        tglyph->sidx = 0;
        tglyph->style = x;
        tglyph->glyph = y;
        flush_screen(0); /* flush buffered glyphs */
        return;

    case DISP_FREEMEM: /* in case game ends with tmp_at() in progress */
        while (tglyph) {
            tmp = tglyph->prev;
            if (tglyph != &tgfirst)
                free((genericptr_t) tglyph);
            tglyph = tmp;
        }
        return;

    default:
        break;
    }

    if (!tglyph)
        panic("tmp_at: tglyph not initialized");

    switch (x) {
    case DISP_CHANGE:
        tglyph->glyph = y;
        break;

    case DISP_END:
        if (tglyph->style == DISP_BEAM || tglyph->style == DISP_ALL) {
            register int i;

            /* Erase (reset) from source to end */
            for (i = 0; i < tglyph->sidx; i++)
                newsym(tglyph->saved[i].x, tglyph->saved[i].y);
        } else {              /* DISP_FLASH or DISP_ALWAYS */
            if (tglyph->sidx) /* been called at least once */
                newsym(tglyph->saved[0].x, tglyph->saved[0].y);
        }
        /* tglyph->sidx = 0; -- about to be freed, so not necessary */
        tmp = tglyph->prev;
        if (tglyph != &tgfirst)
            free((genericptr_t) tglyph);
        tglyph = tmp;
        break;

    default: /* do it */
        if (!isok(x, y))
            break;
        if (tglyph->style == DISP_BEAM || tglyph->style == DISP_ALL) {
            if (tglyph->style != DISP_ALL && !cansee(x, y))
                break;
            if (tglyph->sidx >= TMP_AT_MAX_GLYPHS)
                break; /* too many locations */
            /* save pos for later erasing */
            tglyph->saved[tglyph->sidx].x = x;
            tglyph->saved[tglyph->sidx].y = y;
            tglyph->sidx += 1;
        } else {                /* DISP_FLASH/ALWAYS */
            if (tglyph->sidx) { /* not first call, so reset previous pos */
                newsym(tglyph->saved[0].x, tglyph->saved[0].y);
                tglyph->sidx = 0; /* display is presently up to date */
            }
            if (!cansee(x, y) && tglyph->style != DISP_ALWAYS)
                break;
            tglyph->saved[0].x = x;
            tglyph->saved[0].y = y;
            tglyph->sidx = 1;
        }

        show_glyph(x, y, tglyph->glyph); /* show it */
        flush_screen(0);                 /* make sure it shows up */
        break;
    } /* end case */
}

/*
 * swallowed()
 *
 * The hero is swallowed.  Show a special graphics sequence for this.  This
 * bypasses all of the display routines and messes with buffered screen
 * directly.  This method works because both vision and display check for
 * being swallowed.
 */
void
swallowed(first)
int first;
{
    static xchar lastx, lasty; /* last swallowed position */
    int swallower, left_ok, rght_ok;

    if (first) {
        cls();
        bot();
    } else {
        register int x, y;

        /* Clear old location */
        for (y = lasty - 1; y <= lasty + 1; y++)
            for (x = lastx - 1; x <= lastx + 1; x++)
                if (isok(x, y))
                    show_glyph(x, y, cmap_to_glyph(S_stone));
    }

    swallower = monsndx(u.ustuck->data);
    /* assume isok(u.ux,u.uy) */
    left_ok = isok(u.ux - 1, u.uy);
    rght_ok = isok(u.ux + 1, u.uy);
    /*
     *  Display the hero surrounded by the monster's stomach.
     */
    if (isok(u.ux, u.uy - 1)) {
        if (left_ok)
            show_glyph(u.ux - 1, u.uy - 1,
                       swallow_to_glyph(swallower, S_sw_tl));
        show_glyph(u.ux, u.uy - 1, swallow_to_glyph(swallower, S_sw_tc));
        if (rght_ok)
            show_glyph(u.ux + 1, u.uy - 1,
                       swallow_to_glyph(swallower, S_sw_tr));
    }

    if (left_ok)
        show_glyph(u.ux - 1, u.uy, swallow_to_glyph(swallower, S_sw_ml));
    display_self();
    if (rght_ok)
        show_glyph(u.ux + 1, u.uy, swallow_to_glyph(swallower, S_sw_mr));

    if (isok(u.ux, u.uy + 1)) {
        if (left_ok)
            show_glyph(u.ux - 1, u.uy + 1,
                       swallow_to_glyph(swallower, S_sw_bl));
        show_glyph(u.ux, u.uy + 1, swallow_to_glyph(swallower, S_sw_bc));
        if (rght_ok)
            show_glyph(u.ux + 1, u.uy + 1,
                       swallow_to_glyph(swallower, S_sw_br));
    }

    /* Update the swallowed position. */
    lastx = u.ux;
    lasty = u.uy;
}

/*
 * under_water()
 *
 * Similar to swallowed() in operation.  Shows hero when underwater
 * except when in water level.  Special routines exist for that.
 */
void
under_water(mode)
int mode;
{
    static xchar lastx, lasty;
    static boolean dela;
    register int x, y;

    /* swallowing has a higher precedence than under water */
    if (Is_waterlevel(&u.uz) || u.uswallow)
        return;

    /* full update */
    if (mode == 1 || dela) {
        cls();
        dela = FALSE;

    /* delayed full update */
    } else if (mode == 2) {
        dela = TRUE;
        return;

    /* limited update */
    } else {
        for (y = lasty - 1; y <= lasty + 1; y++)
            for (x = lastx - 1; x <= lastx + 1; x++)
                if (isok(x, y))
                    show_glyph(x, y, cmap_to_glyph(S_stone));
    }

    /*
     * TODO?  Should this honor Xray radius rather than force radius 1?
     */

    for (x = u.ux - 1; x <= u.ux + 1; x++)
        for (y = u.uy - 1; y <= u.uy + 1; y++)
            if (isok(x, y) && (is_pool_or_lava(x, y) || is_ice(x, y))) {
                if (Blind && !(x == u.ux && y == u.uy))
                    show_glyph(x, y, cmap_to_glyph(S_stone));
                else
                    newsym(x, y);
            }
    lastx = u.ux;
    lasty = u.uy;
}

/*
 *      under_ground()
 *
 *      Very restricted display.  You can only see yourself.
 */
void
under_ground(mode)
int mode;
{
    static boolean dela;

    /* swallowing has a higher precedence than under ground */
    if (u.uswallow)
        return;

    /* full update */
    if (mode == 1 || dela) {
        cls();
        dela = FALSE;

    /* delayed full update */
    } else if (mode == 2) {
        dela = TRUE;
        return;

    /* limited update */
    } else {
        newsym(u.ux, u.uy);
    }
}

/* =========================================================================
 */

/*
 * Loop through all of the monsters and update them.  Called when:
 *      + going blind & telepathic
 *      + regaining sight & telepathic
 *      + getting and losing infravision
 *      + hallucinating
 *      + doing a full screen redraw
 *      + see invisible times out or a ring of see invisible is taken off
 *      + when a potion of see invisible is quaffed or a ring of see
 *        invisible is put on
 *      + gaining telepathy when blind [givit() in eat.c, pleased() in pray.c]
 *      + losing telepathy while blind [xkilled() in mon.c, attrcurse() in
 *        sit.c]
 */
void
see_monsters()
{
    register struct monst *mon;
    int new_warn_obj_cnt = 0;

    if (defer_see_monsters)
        return;

    for (mon = fmon; mon; mon = mon->nmon) {
        if (DEADMONSTER(mon))
            continue;
        newsym(mon->mx, mon->my);
        if (mon->wormno)
            see_wsegs(mon);
        if (Warn_of_mon && (context.warntype.obj & mon->data->mflags2) != 0L)
            new_warn_obj_cnt++;
    }
    /*
     * Make Sting glow blue or stop glowing if required.
     */
    if (new_warn_obj_cnt != warn_obj_cnt) {
        Sting_effects(new_warn_obj_cnt);
        warn_obj_cnt = new_warn_obj_cnt;
    }

    /* when mounted, hero's location gets caught by monster loop */
    if (!u.usteed)
        newsym(u.ux, u.uy);
}

/*
 * Block/unblock light depending on what a mimic is mimicing and if it's
 * invisible or not.  Should be called only when the state of See_invisible
 * changes.
 */
void
set_mimic_blocking()
{
    register struct monst *mon;

    for (mon = fmon; mon; mon = mon->nmon) {
        if (DEADMONSTER(mon))
            continue;
        if (mon->minvis && is_lightblocker_mappear(mon)) {
            if (See_invisible)
                block_point(mon->mx, mon->my);
            else
                unblock_point(mon->mx, mon->my);
        }
    }
}

/*
 * Loop through all of the object *locations* and update them.  Called when
 *      + hallucinating.
 */
void
see_objects()
{
    register struct obj *obj;
    for (obj = fobj; obj; obj = obj->nobj)
        if (vobj_at(obj->ox, obj->oy) == obj)
            newsym(obj->ox, obj->oy);
}

/*
 * Update hallucinated traps.
 */
void
see_traps()
{
    struct trap *trap;
    int glyph;

    for (trap = ftrap; trap; trap = trap->ntrap) {
        glyph = glyph_at(trap->tx, trap->ty);
        if (glyph_is_trap(glyph))
            newsym(trap->tx, trap->ty);
    }
}

/*
 * Put the cursor on the hero.  Flush all accumulated glyphs before doing it.
 */
void
curs_on_u()
{
    flush_screen(1); /* Flush waiting glyphs & put cursor on hero */
}

int
doredraw()
{
    docrt();
    return 0;
}

void
docrt()
{
    register int x, y;
    register struct rm *lev;

    if (!u.ux)
        return; /* display isn't ready yet */

    if (u.uswallow) {
        swallowed(1);
        return;
    }
    if (Underwater && !Is_waterlevel(&u.uz)) {
        under_water(1);
        return;
    }
    if (u.uburied) {
        under_ground(1);
        return;
    }

    /* shut down vision */
    vision_recalc(2);

    /*
     * This routine assumes that cls() does the following:
     *      + fills the physical screen with the symbol for rock
     *      + clears the glyph buffer
     */
    cls();

    /* display memory */
    for (x = 1; x < COLNO; x++) {
        lev = &levl[x][0];
        for (y = 0; y < ROWNO; y++, lev++)
            if (lev->glyph != cmap_to_glyph(S_stone))
                show_glyph(x, y, lev->glyph);
    }

    /* see what is to be seen */
    vision_recalc(0);

    /* overlay with monsters */
    see_monsters();

    context.botlx = 1; /* force a redraw of the bottom line */
}

/* =========================================================================
 */
/* Glyph Buffering (3rd screen) ============================================
 */

typedef struct {
    xchar new; /* perhaps move this bit into the rm structure. */
    int glyph;
} gbuf_entry;

static gbuf_entry gbuf[ROWNO][COLNO];
static char gbuf_start[ROWNO];
static char gbuf_stop[ROWNO];

/* FIXME: This is a dirty hack, because newsym() doesn't distinguish
 * between object piles and single objects, it doesn't mark the location
 * for update. */
void
newsym_force(x, y)
register int x, y;
{
    newsym(x,y);
    gbuf[y][x].new = 1;
    if (gbuf_start[y] > x)
        gbuf_start[y] = x;
    if (gbuf_stop[y] < x)
        gbuf_stop[y] = x;
}

/*
 * Store the glyph in the 3rd screen for later flushing.
 */
void
show_glyph(x, y, glyph)
int x, y, glyph;
{
    /*
     * Check for bad positions and glyphs.
     */
    if (!isok(x, y)) {
        const char *text;
        int offset;

        /* column 0 is invalid, but it's often used as a flag, so ignore it */
        if (x == 0)
            return;

        /*
         *  This assumes an ordering of the offsets.  See display.h for
         *  the definition.
         */

        if (glyph >= GLYPH_WARNING_OFF
            && glyph < GLYPH_STATUE_OFF) { /* a warning */
            text = "warning";
            offset = glyph - GLYPH_WARNING_OFF;
        } else if (glyph >= GLYPH_SWALLOW_OFF) { /* swallow border */
            text = "swallow border";
            offset = glyph - GLYPH_SWALLOW_OFF;
        } else if (glyph >= GLYPH_ZAP_OFF) { /* zap beam */
            text = "zap beam";
            offset = glyph - GLYPH_ZAP_OFF;
        } else if (glyph >= GLYPH_EXPLODE_OFF) { /* explosion */
            text = "explosion";
            offset = glyph - GLYPH_EXPLODE_OFF;
        } else if (glyph >= GLYPH_CMAP_OFF) { /* cmap */
            text = "cmap_index";
            offset = glyph - GLYPH_CMAP_OFF;
        } else if (glyph >= GLYPH_OBJ_OFF) { /* object */
            text = "object";
            offset = glyph - GLYPH_OBJ_OFF;
        } else if (glyph >= GLYPH_RIDDEN_OFF) { /* ridden mon */
            text = "ridden mon";
            offset = glyph - GLYPH_RIDDEN_OFF;
        } else if (glyph >= GLYPH_BODY_OFF) { /* a corpse */
            text = "corpse";
            offset = glyph - GLYPH_BODY_OFF;
        } else if (glyph >= GLYPH_DETECT_OFF) { /* detected mon */
            text = "detected mon";
            offset = glyph - GLYPH_DETECT_OFF;
        } else if (glyph >= GLYPH_INVIS_OFF) { /* invisible mon */
            text = "invisible mon";
            offset = glyph - GLYPH_INVIS_OFF;
        } else if (glyph >= GLYPH_PET_OFF) { /* a pet */
            text = "pet";
            offset = glyph - GLYPH_PET_OFF;
        } else { /* a monster */
            text = "monster";
            offset = glyph;
        }

        impossible("show_glyph:  bad pos %d %d with glyph %d [%s %d].", x, y,
                   glyph, text, offset);
        return;
    }

    if (glyph >= MAX_GLYPH) {
        impossible("show_glyph:  bad glyph %d [max %d] at (%d,%d).", glyph,
                   MAX_GLYPH, x, y);
        return;
    }

    if (gbuf[y][x].glyph != glyph || iflags.use_background_glyph) {
        gbuf[y][x].glyph = glyph;
        gbuf[y][x].new = 1;
        if (gbuf_start[y] > x)
            gbuf_start[y] = x;
        if (gbuf_stop[y] < x)
            gbuf_stop[y] = x;
    }
}

/*
 * Reset the changed glyph borders so that none of the 3rd screen has
 * changed.
 */
#define reset_glyph_bbox()             \
    {                                  \
        int i;                         \
                                       \
        for (i = 0; i < ROWNO; i++) {  \
            gbuf_start[i] = COLNO - 1; \
            gbuf_stop[i] = 0;          \
        }                              \
    }

static gbuf_entry nul_gbuf = { 0, cmap_to_glyph(S_stone) };
/*
 * Turn the 3rd screen into stone.
 */
void
clear_glyph_buffer()
{
    register int x, y;
    register gbuf_entry *gptr;

    for (y = 0; y < ROWNO; y++) {
        gptr = &gbuf[y][0];
        for (x = COLNO; x; x--) {
            *gptr++ = nul_gbuf;
        }
    }
    reset_glyph_bbox();
}

/*
 * Assumes that the indicated positions are filled with S_stone glyphs.
 */
void
row_refresh(start, stop, y)
int start, stop, y;
{
    register int x;

    for (x = start; x <= stop; x++)
        if (gbuf[y][x].glyph != cmap_to_glyph(S_stone))
            print_glyph(WIN_MAP, x, y, gbuf[y][x].glyph, get_bk_glyph(x,y));
}

void
cls()
{
    static boolean in_cls = 0;

    if (in_cls)
        return;
    in_cls = TRUE;
    display_nhwindow(WIN_MESSAGE, FALSE); /* flush messages */
    context.botlx = 1;                    /* force update of botl window */
    clear_nhwindow(WIN_MAP);              /* clear physical screen */

    clear_glyph_buffer(); /* this is sort of an extra effort, but OK */
    in_cls = FALSE;
}

/*
 * Synch the third screen with the display.
 */
void
flush_screen(cursor_on_u)
int cursor_on_u;
{
    /* Prevent infinite loops on errors:
     *      flush_screen->print_glyph->impossible->pline->flush_screen
     */
    static boolean flushing = 0;
    static boolean delay_flushing = 0;
    register int x, y;

    if (cursor_on_u == -1)
        delay_flushing = !delay_flushing;
    if (delay_flushing)
        return;
    if (flushing)
        return; /* if already flushing then return */
    flushing = 1;
#ifdef HANGUPHANDLING
    if (program_state.done_hup)
        return;
#endif

    for (y = 0; y < ROWNO; y++) {
        register gbuf_entry *gptr = &gbuf[y][x = gbuf_start[y]];
        for (; x <= gbuf_stop[y]; gptr++, x++)
            if (gptr->new) {
                print_glyph(WIN_MAP, x, y, gptr->glyph, get_bk_glyph(x, y));
                gptr->new = 0;
            }
    }

    if (cursor_on_u)
        curs(WIN_MAP, u.ux, u.uy); /* move cursor to the hero */
    display_nhwindow(WIN_MAP, FALSE);
    reset_glyph_bbox();
    flushing = 0;
    if (context.botl || context.botlx)
        bot();
}

/* =========================================================================
 */

/*
 * back_to_glyph()
 *
 * Use the information in the rm structure at the given position to create
 * a glyph of a background.
 *
 * I had to add a field in the rm structure (horizontal) so that we knew
 * if open doors and secret doors were horizontal or vertical.  Previously,
 * the screen symbol had the horizontal/vertical information set at
 * level generation time.
 *
 * I used the 'ladder' field (really doormask) for deciding if stairwells
 * were up or down.  I didn't want to check the upstairs and dnstairs
 * variables.
 */
int
back_to_glyph(x, y)
xchar x, y;
{
    int idx;
    struct rm *ptr = &(levl[x][y]);

    switch (ptr->typ) {
    case SCORR:
    case STONE:
        idx = level.flags.arboreal ? S_tree : S_stone;
        break;
    case ROOM:
        idx = S_room;
        break;
    case CORR:
        idx = (ptr->waslit || flags.lit_corridor) ? S_litcorr : S_corr;
        break;
    case HWALL:
    case VWALL:
    case TLCORNER:
    case TRCORNER:
    case BLCORNER:
    case BRCORNER:
    case CROSSWALL:
    case TUWALL:
    case TDWALL:
    case TLWALL:
    case TRWALL:
    case SDOOR:
        idx = ptr->seenv ? wall_angle(ptr) : S_stone;
        break;
    case DOOR:
        if (ptr->doormask) {
            if (ptr->doormask & D_BROKEN)
                idx = S_ndoor;
            else if (ptr->doormask & D_ISOPEN)
                idx = (ptr->horizontal) ? S_hodoor : S_vodoor;
            else /* else is closed */
                idx = (ptr->horizontal) ? S_hcdoor : S_vcdoor;
        } else
            idx = S_ndoor;
        break;
    case IRONBARS:
        idx = S_bars;
        break;
    case TREE:
        idx = S_tree;
        break;
    case POOL:
    case MOAT:
        idx = S_pool;
        break;
    case STAIRS:
        idx = (ptr->ladder & LA_DOWN) ? S_dnstair : S_upstair;
        break;
    case LADDER:
        idx = (ptr->ladder & LA_DOWN) ? S_dnladder : S_upladder;
        break;
    case FOUNTAIN:
        idx = S_fountain;
        break;
    case SINK:
        idx = S_sink;
        break;
    case ALTAR:
        idx = S_altar;
        break;
    case GRAVE:
        idx = S_grave;
        break;
    case THRONE:
        idx = S_throne;
        break;
    case LAVAPOOL:
        idx = S_lava;
        break;
    case ICE:
        idx = S_ice;
        break;
    case AIR:
        idx = S_air;
        break;
    case CLOUD:
        idx = S_cloud;
        break;
    case WATER:
        idx = S_water;
        break;
    case DBWALL:
        idx = (ptr->horizontal) ? S_hcdbridge : S_vcdbridge;
        break;
    case DRAWBRIDGE_UP:
        switch (ptr->drawbridgemask & DB_UNDER) {
        case DB_MOAT:
            idx = S_pool;
            break;
        case DB_LAVA:
            idx = S_lava;
            break;
        case DB_ICE:
            idx = S_ice;
            break;
        case DB_FLOOR:
            idx = S_room;
            break;
        default:
            impossible("Strange db-under: %d",
                       ptr->drawbridgemask & DB_UNDER);
            idx = S_room; /* something is better than nothing */
            break;
        }
        break;
    case DRAWBRIDGE_DOWN:
        idx = (ptr->horizontal) ? S_hodbridge : S_vodbridge;
        break;
    default:
        impossible("back_to_glyph:  unknown level type [ = %d ]", ptr->typ);
        idx = S_room;
        break;
    }

    return cmap_to_glyph(idx);
}

/*
 * swallow_to_glyph()
 *
 * Convert a monster number and a swallow location into the correct glyph.
 * If you don't want a patchwork monster while hallucinating, decide on
 * a random monster in swallowed() and don't use what_mon() here.
 */
STATIC_OVL int
swallow_to_glyph(mnum, loc)
int mnum;
int loc;
{
    if (loc < S_sw_tl || S_sw_br < loc) {
        impossible("swallow_to_glyph: bad swallow location");
        loc = S_sw_br;
    }
    return ((int) (what_mon(mnum) << 3) | (loc - S_sw_tl)) + GLYPH_SWALLOW_OFF;
}

/*
 * zapdir_to_glyph()
 *
 * Change the given zap direction and beam type into a glyph.  Each beam
 * type has four glyphs, one for each of the symbols below.  The order of
 * the zap symbols [0-3] as defined in rm.h are:
 *
 *      |  S_vbeam      ( 0, 1) or ( 0,-1)
 *      -  S_hbeam      ( 1, 0) or (-1, 0)
 *      \  S_lslant     ( 1, 1) or (-1,-1)
 *      /  S_rslant     (-1, 1) or ( 1,-1)
 */
int
zapdir_to_glyph(dx, dy, beam_type)
register int dx, dy;
int beam_type;
{
    if (beam_type >= NUM_ZAP) {
        impossible("zapdir_to_glyph:  illegal beam type");
        beam_type = 0;
    }
    dx = (dx == dy) ? 2 : (dx && dy) ? 3 : dx ? 1 : 0;

    return ((int) ((beam_type << 2) | dx)) + GLYPH_ZAP_OFF;
}

/*
 * Utility routine for dowhatis() used to find out the glyph displayed at
 * the location.  This isn't necessarily the same as the glyph in the levl
 * structure, so we must check the "third screen".
 */
int
glyph_at(x, y)
xchar x, y;
{
    if (x < 0 || y < 0 || x >= COLNO || y >= ROWNO)
        return cmap_to_glyph(S_room); /* XXX */
    return gbuf[y][x].glyph;
}

/*
 * This will be used to get the glyph for the background so that
 * it can potentially be merged into graphical window ports
 * to improve the appearance of stuff on dark room
 * squares and the plane of air etc.
 *
 * Until that is working correctly in the branch, however, for now
 * we just return NO_GLYPH as an indicator to ignore it.
 */

STATIC_OVL int
get_bk_glyph(x,y)
xchar x, y;
{
    int idx, bkglyph = NO_GLYPH;
    struct rm *lev = &levl[x][y];

    if (iflags.use_background_glyph && lev->seenv != 0
            && gbuf[y][x].glyph != cmap_to_glyph(S_stone)) {
        switch (lev->typ) {
        case SCORR:
        case STONE:
            idx = level.flags.arboreal ? S_tree : S_stone;
            break;
        case ROOM:
           idx = S_room;
           break;
        case CORR:
           idx = (lev->waslit || flags.lit_corridor) ? S_litcorr : S_corr;
           break;
        case ICE:
           idx = S_ice;
           break;
        case AIR:
           idx = S_air;
           break;
        case CLOUD:
           idx = S_cloud;
           break;
        case POOL:
        case MOAT:
           idx = S_pool;
           break;
        case WATER:
           idx = S_water;
           break;
        case LAVAPOOL:
           idx = S_lava;
           break;
        default:
           idx = S_room;
           break;
        }

        if (!cansee(x, y) && (!lev->waslit || flags.dark_room)) {
            /* Floor spaces are dark if unlit.  Corridors are dark if unlit. */
            if (lev->typ == CORR && idx == S_litcorr)
                idx = S_corr;
            else if (idx == S_room)
                idx = (flags.dark_room && iflags.use_color)
                         ? DARKROOMSYM : S_stone;
        }

        if (idx != S_room)
            bkglyph = cmap_to_glyph(idx);
    }
    return bkglyph;
}

/* -------------------------------------------------------------------------
 */
/* Wall Angle --------------------------------------------------------------
 */

#ifdef WA_VERBOSE

static const char *FDECL(type_to_name, (int));
static void FDECL(error4, (int, int, int, int, int, int));

static int bad_count[MAX_TYPE]; /* count of positions flagged as bad */
static const char *type_names[MAX_TYPE] = {
    "STONE", "VWALL", "HWALL", "TLCORNER", "TRCORNER", "BLCORNER", "BRCORNER",
    "CROSSWALL", "TUWALL", "TDWALL", "TLWALL", "TRWALL", "DBWALL", "TREE",
    "SDOOR", "SCORR", "POOL", "MOAT", "WATER", "DRAWBRIDGE_UP", "LAVAPOOL",
    "IRON_BARS", "DOOR", "CORR", "ROOM", "STAIRS", "LADDER", "FOUNTAIN",
    "THRONE", "SINK", "GRAVE", "ALTAR", "ICE", "DRAWBRIDGE_DOWN", "AIR",
    "CLOUD"
};

static const char *
type_to_name(type)
int type;
{
    return (type < 0 || type >= MAX_TYPE) ? "unknown" : type_names[type];
}

static void
error4(x, y, a, b, c, dd)
int x, y, a, b, c, dd;
{
    pline("set_wall_state: %s @ (%d,%d) %s%s%s%s",
          type_to_name(levl[x][y].typ), x, y,
          a ? "1" : "", b ? "2" : "", c ? "3" : "", dd ? "4" : "");
    bad_count[levl[x][y].typ]++;
}
#endif /* WA_VERBOSE */

/*
 * Return 'which' if position is implies an unfinished exterior.  Return
 * zero otherwise.  Unfinished implies outer area is rock or a corridor.
 *
 * Things that are ambiguous: lava
 */
STATIC_OVL int
check_pos(x, y, which)
int x, y, which;
{
    int type;
    if (!isok(x, y))
        return which;
    type = levl[x][y].typ;
    if (IS_ROCK(type) || type == CORR || type == SCORR)
        return which;
    return 0;
}

/* Return TRUE if more than one is non-zero. */
/*ARGSUSED*/
#ifdef WA_VERBOSE
STATIC_OVL boolean
more_than_one(x, y, a, b, c)
int x, y, a, b, c;
{
    if ((a && (b | c)) || (b && (a | c)) || (c && (a | b))) {
        error4(x, y, a, b, c, 0);
        return TRUE;
    }
    return FALSE;
}
#else
#define more_than_one(x, y, a, b, c) \
    (((a) && ((b) | (c))) || ((b) && ((a) | (c))) || ((c) && ((a) | (b))))
#endif

/* Return the wall mode for a T wall. */
STATIC_OVL int
set_twall(x0, y0, x1, y1, x2, y2, x3, y3)
int x0, y0; /* used #if WA_VERBOSE */
int x1, y1, x2, y2, x3, y3;
{
    int wmode, is_1, is_2, is_3;

    nhUse(x0);
    nhUse(y0);

    is_1 = check_pos(x1, y1, WM_T_LONG);
    is_2 = check_pos(x2, y2, WM_T_BL);
    is_3 = check_pos(x3, y3, WM_T_BR);
    if (more_than_one(x0, y0, is_1, is_2, is_3)) {
        wmode = 0;
    } else {
        wmode = is_1 + is_2 + is_3;
    }
    return wmode;
}

/* Return wall mode for a horizontal or vertical wall. */
STATIC_OVL int
set_wall(x, y, horiz)
int x, y, horiz;
{
    int wmode, is_1, is_2;

    if (horiz) {
        is_1 = check_pos(x, y - 1, WM_W_TOP);
        is_2 = check_pos(x, y + 1, WM_W_BOTTOM);
    } else {
        is_1 = check_pos(x - 1, y, WM_W_LEFT);
        is_2 = check_pos(x + 1, y, WM_W_RIGHT);
    }
    if (more_than_one(x, y, is_1, is_2, 0)) {
        wmode = 0;
    } else {
        wmode = is_1 + is_2;
    }
    return wmode;
}

/* Return a wall mode for a corner wall. (x4,y4) is the "inner" position. */
STATIC_OVL int
set_corn(x1, y1, x2, y2, x3, y3, x4, y4)
int x1, y1, x2, y2, x3, y3, x4, y4;
{
    int wmode, is_1, is_2, is_3, is_4;

    is_1 = check_pos(x1, y1, 1);
    is_2 = check_pos(x2, y2, 1);
    is_3 = check_pos(x3, y3, 1);
    is_4 = check_pos(x4, y4, 1); /* inner location */

    /*
     * All 4 should not be true.  So if the inner location is rock,
     * use it.  If all of the outer 3 are true, use outer.  We currently
     * can't cover the case where only part of the outer is rock, so
     * we just say that all the walls are finished (if not overridden
     * by the inner section).
     */
    if (is_4) {
        wmode = WM_C_INNER;
    } else if (is_1 && is_2 && is_3)
        wmode = WM_C_OUTER;
    else
        wmode = 0; /* finished walls on all sides */

    return wmode;
}

/* Return mode for a crosswall. */
STATIC_OVL int
set_crosswall(x, y)
int x, y;
{
    int wmode, is_1, is_2, is_3, is_4;

    is_1 = check_pos(x - 1, y - 1, 1);
    is_2 = check_pos(x + 1, y - 1, 1);
    is_3 = check_pos(x + 1, y + 1, 1);
    is_4 = check_pos(x - 1, y + 1, 1);

    wmode = is_1 + is_2 + is_3 + is_4;
    if (wmode > 1) {
        if (is_1 && is_3 && (is_2 + is_4 == 0)) {
            wmode = WM_X_TLBR;
        } else if (is_2 && is_4 && (is_1 + is_3 == 0)) {
            wmode = WM_X_BLTR;
        } else {
#ifdef WA_VERBOSE
            error4(x, y, is_1, is_2, is_3, is_4);
#endif
            wmode = 0;
        }
    } else if (is_1)
        wmode = WM_X_TL;
    else if (is_2)
        wmode = WM_X_TR;
    else if (is_3)
        wmode = WM_X_BR;
    else if (is_4)
        wmode = WM_X_BL;

    return wmode;
}

/* Called from mklev.  Scan the level and set the wall modes. */
void
set_wall_state()
{
    int x, y;
    int wmode;
    struct rm *lev;

#ifdef WA_VERBOSE
    for (x = 0; x < MAX_TYPE; x++)
        bad_count[x] = 0;
#endif

    for (x = 0; x < COLNO; x++)
        for (lev = &levl[x][0], y = 0; y < ROWNO; y++, lev++) {
            switch (lev->typ) {
            case SDOOR:
                wmode = set_wall(x, y, (int) lev->horizontal);
                break;
            case VWALL:
                wmode = set_wall(x, y, 0);
                break;
            case HWALL:
                wmode = set_wall(x, y, 1);
                break;
            case TDWALL:
                wmode = set_twall(x, y, x, y - 1, x - 1, y + 1, x + 1, y + 1);
                break;
            case TUWALL:
                wmode = set_twall(x, y, x, y + 1, x + 1, y - 1, x - 1, y - 1);
                break;
            case TLWALL:
                wmode = set_twall(x, y, x + 1, y, x - 1, y - 1, x - 1, y + 1);
                break;
            case TRWALL:
                wmode = set_twall(x, y, x - 1, y, x + 1, y + 1, x + 1, y - 1);
                break;
            case TLCORNER:
                wmode =
                    set_corn(x - 1, y - 1, x, y - 1, x - 1, y, x + 1, y + 1);
                break;
            case TRCORNER:
                wmode =
                    set_corn(x, y - 1, x + 1, y - 1, x + 1, y, x - 1, y + 1);
                break;
            case BLCORNER:
                wmode =
                    set_corn(x, y + 1, x - 1, y + 1, x - 1, y, x + 1, y - 1);
                break;
            case BRCORNER:
                wmode =
                    set_corn(x + 1, y, x + 1, y + 1, x, y + 1, x - 1, y - 1);
                break;
            case CROSSWALL:
                wmode = set_crosswall(x, y);
                break;

            default:
                wmode = -1; /* don't set wall info */
                break;
            }

            if (wmode >= 0)
                lev->wall_info = (lev->wall_info & ~WM_MASK) | wmode;
        }

#ifdef WA_VERBOSE
    /* check if any bad positions found */
    for (x = y = 0; x < MAX_TYPE; x++)
        if (bad_count[x]) {
            if (y == 0) {
                y = 1; /* only print once */
                pline("set_wall_type: wall mode problems with: ");
            }
            pline("%s %d;", type_names[x], bad_count[x]);
        }
#endif /* WA_VERBOSE */
}

/* -------------------------------------------------------------------------
 */
/* This matrix is used here and in vision.c. */
unsigned char seenv_matrix[3][3] = { { SV2, SV1, SV0 },
                                     { SV3, SVALL, SV7 },
                                     { SV4, SV5, SV6 } };

#define sign(z) ((z) < 0 ? -1 : ((z) > 0 ? 1 : 0))

/* Set the seen vector of lev as if seen from (x0,y0) to (x,y). */
STATIC_OVL void
set_seenv(lev, x0, y0, x, y)
struct rm *lev;
int x0, y0, x, y; /* from, to */
{
    int dx = x - x0, dy = y0 - y;

    lev->seenv |= seenv_matrix[sign(dy) + 1][sign(dx) + 1];
}

/* Called by blackout(vault.c) when vault guard removes temporary corridor,
   turning spot <x0,y0> back into stone; <x1,y1> is an adjacent spot. */
void
unset_seenv(lev, x0, y0, x1, y1)
struct rm *lev;     /* &levl[x1][y1] */
int x0, y0, x1, y1; /* from, to; abs(x1-x0)==1 && abs(y0-y1)==1 */
{
    int dx = x1 - x0, dy = y0 - y1;

    lev->seenv &= ~seenv_matrix[dy + 1][dx + 1];
}

/* -------------------------------------------------------------------------
 */

/* T wall types, one for each row in wall_matrix[][]. */
#define T_d 0
#define T_l 1
#define T_u 2
#define T_r 3

/*
 * These are the column names of wall_matrix[][].  They are the "results"
 * of a tdwall pattern match.  All T walls are rotated so they become
 * a tdwall.  Then we do a single pattern match, but return the
 * correct result for the original wall by using different rows for
 * each of the wall types.
 */
#define T_stone 0
#define T_tlcorn 1
#define T_trcorn 2
#define T_hwall 3
#define T_tdwall 4

static const int wall_matrix[4][5] = {
    { S_stone, S_tlcorn, S_trcorn, S_hwall, S_tdwall }, /* tdwall */
    { S_stone, S_trcorn, S_brcorn, S_vwall, S_tlwall }, /* tlwall */
    { S_stone, S_brcorn, S_blcorn, S_hwall, S_tuwall }, /* tuwall */
    { S_stone, S_blcorn, S_tlcorn, S_vwall, S_trwall }, /* trwall */
};

/* Cross wall types, one for each "solid" quarter.  Rows of cross_matrix[][].
 */
#define C_bl 0
#define C_tl 1
#define C_tr 2
#define C_br 3

/*
 * These are the column names for cross_matrix[][].  They express results
 * in C_br (bottom right) terms.  All crosswalls with a single solid
 * quarter are rotated so the solid section is at the bottom right.
 * We pattern match on that, but return the correct result depending
 * on which row we'ere looking at.
 */
#define C_trcorn 0
#define C_brcorn 1
#define C_blcorn 2
#define C_tlwall 3
#define C_tuwall 4
#define C_crwall 5

static const int cross_matrix[4][6] = {
    { S_brcorn, S_blcorn, S_tlcorn, S_tuwall, S_trwall, S_crwall },
    { S_blcorn, S_tlcorn, S_trcorn, S_trwall, S_tdwall, S_crwall },
    { S_tlcorn, S_trcorn, S_brcorn, S_tdwall, S_tlwall, S_crwall },
    { S_trcorn, S_brcorn, S_blcorn, S_tlwall, S_tuwall, S_crwall },
};

/* Print out a T wall warning and all interesting info. */
STATIC_OVL void
t_warn(lev)
struct rm *lev;
{
    static const char warn_str[] = "wall_angle: %s: case %d: seenv = 0x%x";
    const char *wname;

    if (lev->typ == TUWALL)
        wname = "tuwall";
    else if (lev->typ == TLWALL)
        wname = "tlwall";
    else if (lev->typ == TRWALL)
        wname = "trwall";
    else if (lev->typ == TDWALL)
        wname = "tdwall";
    else
        wname = "unknown";
    impossible(warn_str, wname, lev->wall_info & WM_MASK,
               (unsigned int) lev->seenv);
}

/*
 * Return the correct graphics character index using wall type, wall mode,
 * and the seen vector.  It is expected that seenv is non zero.
 *
 * All T-wall vectors are rotated to be TDWALL.  All single crosswall
 * blocks are rotated to bottom right.  All double crosswall are rotated
 * to W_X_BLTR.  All results are converted back.
 *
 * The only way to understand this is to take out pen and paper and
 * draw diagrams.  See rm.h for more details on the wall modes and
 * seen vector (SV).
 */
STATIC_OVL int
wall_angle(lev)
struct rm *lev;
{
    register unsigned int seenv = lev->seenv & 0xff;
    const int *row;
    int col, idx;

#define only(sv, bits) (((sv) & (bits)) && !((sv) & ~(bits)))
    switch (lev->typ) {
    case TUWALL:
        row = wall_matrix[T_u];
        seenv = (seenv >> 4 | seenv << 4) & 0xff; /* rotate to tdwall */
        goto do_twall;
    case TLWALL:
        row = wall_matrix[T_l];
        seenv = (seenv >> 2 | seenv << 6) & 0xff; /* rotate to tdwall */
        goto do_twall;
    case TRWALL:
        row = wall_matrix[T_r];
        seenv = (seenv >> 6 | seenv << 2) & 0xff; /* rotate to tdwall */
        goto do_twall;
    case TDWALL:
        row = wall_matrix[T_d];
    do_twall:
        switch (lev->wall_info & WM_MASK) {
        case 0:
            if (seenv == SV4) {
                col = T_tlcorn;
            } else if (seenv == SV6) {
                col = T_trcorn;
            } else if (seenv & (SV3 | SV5 | SV7)
                       || ((seenv & SV4) && (seenv & SV6))) {
                col = T_tdwall;
            } else if (seenv & (SV0 | SV1 | SV2)) {
                col = (seenv & (SV4 | SV6) ? T_tdwall : T_hwall);
            } else {
                t_warn(lev);
                col = T_stone;
            }
            break;
        case WM_T_LONG:
            if (seenv & (SV3 | SV4) && !(seenv & (SV5 | SV6 | SV7))) {
                col = T_tlcorn;
            } else if (seenv & (SV6 | SV7) && !(seenv & (SV3 | SV4 | SV5))) {
                col = T_trcorn;
            } else if ((seenv & SV5)
                       || ((seenv & (SV3 | SV4)) && (seenv & (SV6 | SV7)))) {
                col = T_tdwall;
            } else {
                /* only SV0|SV1|SV2 */
                if (!only(seenv, SV0 | SV1 | SV2))
                    t_warn(lev);
                col = T_stone;
            }
            break;
        case WM_T_BL:
#if 0  /* older method, fixed */
            if (only(seenv, SV4|SV5)) {
                col = T_tlcorn;
            } else if ((seenv & (SV0|SV1|SV2))
                       && only(seenv, SV0|SV1|SV2|SV6|SV7)) {
                col = T_hwall;
            } else if ((seenv & SV3)
                       || ((seenv & (SV0|SV1|SV2)) && (seenv & (SV4|SV5)))) {
                col = T_tdwall;
            } else {
                if (seenv != SV6)
                    t_warn(lev);
                col = T_stone;
            }
#endif /* 0 */
            if (only(seenv, SV4 | SV5))
                col = T_tlcorn;
            else if ((seenv & (SV0 | SV1 | SV2 | SV7))
                     && !(seenv & (SV3 | SV4 | SV5)))
                col = T_hwall;
            else if (only(seenv, SV6))
                col = T_stone;
            else
                col = T_tdwall;
            break;
        case WM_T_BR:
#if 0  /* older method, fixed */
            if (only(seenv, SV5|SV6)) {
                col = T_trcorn;
            } else if ((seenv & (SV0|SV1|SV2))
                       && only(seenv, SV0|SV1|SV2|SV3|SV4)) {
                col = T_hwall;
            } else if ((seenv & SV7)
                       || ((seenv & (SV0|SV1|SV2)) && (seenv & (SV5|SV6)))) {
                col = T_tdwall;
            } else {
                if (seenv != SV4)
                    t_warn(lev);
                col = T_stone;
            }
#endif /* 0 */
            if (only(seenv, SV5 | SV6))
                col = T_trcorn;
            else if ((seenv & (SV0 | SV1 | SV2 | SV3))
                     && !(seenv & (SV5 | SV6 | SV7)))
                col = T_hwall;
            else if (only(seenv, SV4))
                col = T_stone;
            else
                col = T_tdwall;

            break;
        default:
            impossible("wall_angle: unknown T wall mode %d",
                       lev->wall_info & WM_MASK);
            col = T_stone;
            break;
        }
        idx = row[col];
        break;

    case SDOOR:
        if (lev->horizontal)
            goto horiz;
    /* fall through */
    case VWALL:
        switch (lev->wall_info & WM_MASK) {
        case 0:
            idx = seenv ? S_vwall : S_stone;
            break;
        case 1:
            idx = seenv & (SV1 | SV2 | SV3 | SV4 | SV5) ? S_vwall : S_stone;
            break;
        case 2:
            idx = seenv & (SV0 | SV1 | SV5 | SV6 | SV7) ? S_vwall : S_stone;
            break;
        default:
            impossible("wall_angle: unknown vwall mode %d",
                       lev->wall_info & WM_MASK);
            idx = S_stone;
            break;
        }
        break;

    case HWALL:
    horiz:
        switch (lev->wall_info & WM_MASK) {
        case 0:
            idx = seenv ? S_hwall : S_stone;
            break;
        case 1:
            idx = seenv & (SV3 | SV4 | SV5 | SV6 | SV7) ? S_hwall : S_stone;
            break;
        case 2:
            idx = seenv & (SV0 | SV1 | SV2 | SV3 | SV7) ? S_hwall : S_stone;
            break;
        default:
            impossible("wall_angle: unknown hwall mode %d",
                       lev->wall_info & WM_MASK);
            idx = S_stone;
            break;
        }
        break;

#define set_corner(idx, lev, which, outer, inner, name)    \
    switch ((lev)->wall_info & WM_MASK) {                  \
    case 0:                                                \
        idx = which;                                       \
        break;                                             \
    case WM_C_OUTER:                                       \
        idx = seenv & (outer) ? which : S_stone;           \
        break;                                             \
    case WM_C_INNER:                                       \
        idx = seenv & ~(inner) ? which : S_stone;          \
        break;                                             \
    default:                                               \
        impossible("wall_angle: unknown %s mode %d", name, \
                   (lev)->wall_info &WM_MASK);             \
        idx = S_stone;                                     \
        break;                                             \
    }

    case TLCORNER:
        set_corner(idx, lev, S_tlcorn, (SV3 | SV4 | SV5), SV4, "tlcorn");
        break;
    case TRCORNER:
        set_corner(idx, lev, S_trcorn, (SV5 | SV6 | SV7), SV6, "trcorn");
        break;
    case BLCORNER:
        set_corner(idx, lev, S_blcorn, (SV1 | SV2 | SV3), SV2, "blcorn");
        break;
    case BRCORNER:
        set_corner(idx, lev, S_brcorn, (SV7 | SV0 | SV1), SV0, "brcorn");
        break;

    case CROSSWALL:
        switch (lev->wall_info & WM_MASK) {
        case 0:
            if (seenv == SV0)
                idx = S_brcorn;
            else if (seenv == SV2)
                idx = S_blcorn;
            else if (seenv == SV4)
                idx = S_tlcorn;
            else if (seenv == SV6)
                idx = S_trcorn;
            else if (!(seenv & ~(SV0 | SV1 | SV2))
                     && (seenv & SV1 || seenv == (SV0 | SV2)))
                idx = S_tuwall;
            else if (!(seenv & ~(SV2 | SV3 | SV4))
                     && (seenv & SV3 || seenv == (SV2 | SV4)))
                idx = S_trwall;
            else if (!(seenv & ~(SV4 | SV5 | SV6))
                     && (seenv & SV5 || seenv == (SV4 | SV6)))
                idx = S_tdwall;
            else if (!(seenv & ~(SV0 | SV6 | SV7))
                     && (seenv & SV7 || seenv == (SV0 | SV6)))
                idx = S_tlwall;
            else
                idx = S_crwall;
            break;

        case WM_X_TL:
            row = cross_matrix[C_tl];
            seenv = (seenv >> 4 | seenv << 4) & 0xff;
            goto do_crwall;
        case WM_X_TR:
            row = cross_matrix[C_tr];
            seenv = (seenv >> 6 | seenv << 2) & 0xff;
            goto do_crwall;
        case WM_X_BL:
            row = cross_matrix[C_bl];
            seenv = (seenv >> 2 | seenv << 6) & 0xff;
            goto do_crwall;
        case WM_X_BR:
            row = cross_matrix[C_br];
        do_crwall:
            if (seenv == SV4)
                idx = S_stone;
            else {
                seenv = seenv & ~SV4; /* strip SV4 */
                if (seenv == SV0) {
                    col = C_brcorn;
                } else if (seenv & (SV2 | SV3)) {
                    if (seenv & (SV5 | SV6 | SV7))
                        col = C_crwall;
                    else if (seenv & (SV0 | SV1))
                        col = C_tuwall;
                    else
                        col = C_blcorn;
                } else if (seenv & (SV5 | SV6)) {
                    if (seenv & (SV1 | SV2 | SV3))
                        col = C_crwall;
                    else if (seenv & (SV0 | SV7))
                        col = C_tlwall;
                    else
                        col = C_trcorn;
                } else if (seenv & SV1) {
                    col = seenv & SV7 ? C_crwall : C_tuwall;
                } else if (seenv & SV7) {
                    col = seenv & SV1 ? C_crwall : C_tlwall;
                } else {
                    impossible("wall_angle: bottom of crwall check");
                    col = C_crwall;
                }

                idx = row[col];
            }
            break;

        case WM_X_TLBR:
            if (only(seenv, SV1 | SV2 | SV3))
                idx = S_blcorn;
            else if (only(seenv, SV5 | SV6 | SV7))
                idx = S_trcorn;
            else if (only(seenv, SV0 | SV4))
                idx = S_stone;
            else
                idx = S_crwall;
            break;

        case WM_X_BLTR:
            if (only(seenv, SV0 | SV1 | SV7))
                idx = S_brcorn;
            else if (only(seenv, SV3 | SV4 | SV5))
                idx = S_tlcorn;
            else if (only(seenv, SV2 | SV6))
                idx = S_stone;
            else
                idx = S_crwall;
            break;

        default:
            impossible("wall_angle: unknown crosswall mode");
            idx = S_stone;
            break;
        }
        break;

    default:
        impossible("wall_angle: unexpected wall type %d", lev->typ);
        idx = S_stone;
    }
    return idx;
}

/*display.c*/
