/*	SCCS Id: @(#)vision.c	3.3	99/02/18	*/
/* Copyright (c) Dean Luick, with acknowledgements to Dave Cohrs, 1990.	*/
/* NetHack may be freely redistributed.  See license for details.	*/

#include "hack.h"

/* Circles ==================================================================*/

/*
 * These numbers are limit offsets for one quadrant of a circle of a given
 * radius (the first number of each line) from the source.  The number in
 * the comment is the element number (so pointers can be set up).  Each
 * "circle" has as many elements as its radius+1.  The radius is the number
 * of points away from the source that the limit exists.  The radius of the
 * offset on the same row as the source *is* included so we don't have to
 * make an extra check.  For example, a circle of radius 4 has offsets:
 *
 *				XXX	+2
 *				...X	+3
 *				....X	+4
 *				....X	+4
 *				@...X   +4
 *
 */
char circle_data[] = {
/*  0*/	 1, 1,
/*  2*/	 2, 2, 1,
/*  5*/	 3, 3, 2, 1,
/*  9*/	 4, 4, 4, 3, 2,
/* 14*/	 5, 5, 5, 4, 3, 2,
/* 20*/	 6, 6, 6, 5, 5, 4, 2,
/* 27*/	 7, 7, 7, 6, 6, 5, 4, 2,
/* 35*/	 8, 8, 8, 7, 7, 6, 6, 4, 2,
/* 44*/	 9, 9, 9, 9, 8, 8, 7, 6, 5, 3,
/* 54*/	10,10,10,10, 9, 9, 8, 7, 6, 5, 3,
/* 65*/	11,11,11,11,10,10, 9, 9, 8, 7, 5, 3,
/* 77*/	12,12,12,12,11,11,10,10, 9, 8, 7, 5, 3,
/* 90*/	13,13,13,13,12,12,12,11,10,10, 9, 7, 6, 3,
/*104*/	14,14,14,14,13,13,13,12,12,11,10, 9, 8, 6, 3,
/*119*/	15,15,15,15,14,14,14,13,13,12,11,10, 9, 8, 6, 3,
/*135*/ 16 /* should be MAX_RADIUS+1; used to terminate range loops -dlc */
};

/*
 * These are the starting indexes into the circle_data[] array for a
 * circle of a given radius.
 */
char circle_start[] = {
/*  */	  0,	/* circles of radius zero are not used */
/* 1*/    0,
/* 2*/	  2,
/* 3*/	  5,
/* 4*/	  9,
/* 5*/	 14,
/* 6*/	 20,
/* 7*/	 27,
/* 8*/	 35,
/* 9*/	 44,
/*10*/	 54,
/*11*/	 65,
/*12*/	 77,
/*13*/	 90,
/*14*/	104,
/*15*/	119,
};


/*===========================================================================*/
/* Vision (arbitrary line of sight) =========================================*/

/*------ global variables ------*/

#if 0	/* (moved to decl.c) */
/* True if we need to run a full vision recalculation. */
boolean	vision_full_recalc = 0;

/* Pointers to the current vision array. */
char	**viz_array;
#endif
char	*viz_rmin, *viz_rmax;		/* current vision cs bounds */


/*------ local variables ------*/


static char could_see[2][ROWNO][COLNO];		/* vision work space */
static char *cs_rows0[ROWNO], *cs_rows1[ROWNO];
static char  cs_rmin0[ROWNO],  cs_rmax0[ROWNO];
static char  cs_rmin1[ROWNO],  cs_rmax1[ROWNO];

static char  viz_clear[ROWNO][COLNO];		/* vision clear/blocked map */
static char *viz_clear_rows[ROWNO];

static char  left_ptrs[ROWNO][COLNO];		/* LOS algorithm helpers */
static char right_ptrs[ROWNO][COLNO];

/* Forward declarations. */
STATIC_DCL void FDECL(fill_point, (int,int));
STATIC_DCL void FDECL(dig_point, (int,int));
STATIC_DCL void NDECL(view_init);
STATIC_DCL void FDECL(view_from,(int,int,char **,char *,char *,int,
			     void (*)(int,int,genericptr_t),genericptr_t));
STATIC_DCL void FDECL(get_unused_cs, (char ***,char **,char **));
#ifdef REINCARNATION
STATIC_DCL void FDECL(rogue_vision, (char **,char *,char *));
#endif

/* Macro definitions that I can't find anywhere. */
#define sign(z) ((z) < 0 ? -1 : ((z) ? 1 : 0 ))
#define v_abs(z)  ((z) < 0 ? -(z) : (z))	/* don't use abs -- it may exist */

/*
 * vision_init()
 *
 * The one-time vision initialization routine.
 *
 * This must be called before mklev() is called in newgame() [allmain.c],
 * or before a game restore.   Else we die a horrible death.
 */
void
vision_init()
{
    int i;

    /* Set up the pointers. */
    for (i = 0; i < ROWNO; i++) {
	cs_rows0[i] = could_see[0][i];
	cs_rows1[i] = could_see[1][i];
	viz_clear_rows[i] = viz_clear[i];
    }

    /* Start out with cs0 as our current array */
    viz_array = cs_rows0;
    viz_rmin  = cs_rmin0;
    viz_rmax  = cs_rmax0;

    vision_full_recalc = 0;
    (void) memset((genericptr_t) could_see, 0, sizeof(could_see));

    /* Initialize the vision algorithm (currently C or D). */
    view_init();

#ifdef VISION_TABLES
    /* Note:  this initializer doesn't do anything except guarantee that
	      we're linked properly.
    */
    vis_tab_init();
#endif
}

/*
 * does_block()
 *
 * Returns true if the level feature, object, or monster at (x,y) blocks
 * sight.
 */
int
does_block(x,y,lev)
    int x, y;
    register struct rm    *lev;
{
    struct obj   *obj;
    struct monst *mon;

    /* Features that block . . */
    if (IS_ROCK(lev->typ) || lev->typ == TREE || (IS_DOOR(lev->typ) &&
			    (lev->doormask & (D_CLOSED|D_LOCKED|D_TRAPPED) )))
	return 1;

    if (lev->typ == CLOUD || lev->typ == WATER ||
			(lev->typ == MOAT && Underwater))
	return 1;

    /* Boulders block light. */
    for (obj = level.objects[x][y]; obj; obj = obj->nexthere)
	if (obj->otyp == BOULDER) return 1;

    /* Mimics mimicing a door or boulder block light. */
    if ((mon = m_at(x,y)) && (!mon->minvis || See_invisible) &&
	  ((mon->m_ap_type == M_AP_FURNITURE &&
	  (mon->mappearance == S_hcdoor || mon->mappearance == S_vcdoor)) ||
	  (mon->m_ap_type == M_AP_OBJECT && mon->mappearance == BOULDER)))
	return 1;

    return 0;
}

/*
 * vision_reset()
 *
 * This must be called *after* the levl[][] structure is set with the new
 * level and the level monsters and objects are in place.
 */
void
vision_reset()
{
    int y;
    register int x, i, dig_left, block;
    register struct rm    *lev;

    /* Start out with cs0 as our current array */
    viz_array = cs_rows0;
    viz_rmin  = cs_rmin0;
    viz_rmax  = cs_rmax0;

    (void) memset((genericptr_t) could_see, 0, sizeof(could_see));

    /* Reset the pointers and clear so that we have a "full" dungeon. */
    (void) memset((genericptr_t) viz_clear,        0, sizeof(viz_clear));

    /* Dig the level */
    for (y = 0; y < ROWNO; y++) {
	dig_left = 0;
	block = TRUE;	/* location (0,y) is always stone; it's !isok() */
	lev = &levl[1][y];
	for (x = 1; x < COLNO; x++, lev += ROWNO)
	    if (block != (IS_ROCK(lev->typ) || does_block(x,y,lev))) {
		if(block) {
		    for(i=dig_left; i<x; i++) {
			left_ptrs [y][i] = dig_left;
			right_ptrs[y][i] = x-1;
		    }
		} else {
		    i = dig_left;
		    if(dig_left) dig_left--; /* point at first blocked point */
		    for(; i<x; i++) {
			left_ptrs [y][i] = dig_left;
			right_ptrs[y][i] = x;
			viz_clear[y][i] = 1;
		    }
		}
		dig_left = x;
		block = !block;
	    }
	/* handle right boundary; almost identical for blocked/unblocked */
	i = dig_left;
	if(!block && dig_left) dig_left--; /* point at first blocked point */
	for(; i<COLNO; i++) {
	    left_ptrs [y][i] = dig_left;
	    right_ptrs[y][i] = (COLNO-1);
	    viz_clear[y][i] = !block;
	}
    }

    vision_full_recalc = 1;	/* we want to run vision_recalc() */
}


/*
 * get_unused_cs()
 *
 * Called from vision_recalc() and at least one light routine.  Get pointers
 * to the unused vision work area.
 */
STATIC_OVL void
get_unused_cs(rows, rmin, rmax)
    char ***rows;
    char **rmin, **rmax;
{
    register int  row;
    register char *nrmin, *nrmax;

    if (viz_array == cs_rows0) {
	*rows = cs_rows1;
	*rmin = cs_rmin1;
	*rmax = cs_rmax1;
    } else {
	*rows = cs_rows0;
	*rmin = cs_rmin0;
	*rmax = cs_rmax0;
    }

    /* return an initialized, unused work area */
    nrmin = *rmin;
    nrmax = *rmax;

    (void) memset((genericptr_t)**rows, 0, ROWNO*COLNO);  /* we see nothing */
    for (row = 0; row < ROWNO; row++) {		/* set row min & max */
	*nrmin++ = COLNO-1;
	*nrmax++ = 0;
    }
}


#ifdef REINCARNATION
/*
 * rogue_vision()
 *
 * Set the "could see" and in sight bits so vision acts just like the old
 * rogue game:
 *
 *	+ If in a room, the hero can see to the room boundaries.
 *	+ The hero can always see adjacent squares.
 *
 * We set the in_sight bit here as well to escape a bug that shows up
 * due to the one-sided lit wall hack.
 */
STATIC_OVL void
rogue_vision(next, rmin, rmax)
    char **next;	/* could_see array pointers */
    char *rmin, *rmax;
{
    int rnum = levl[u.ux][u.uy].roomno - ROOMOFFSET; /* no SHARED... */
    int start, stop, in_door, xhi, xlo, yhi, ylo;
    register int zx, zy;

    /* If in a lit room, we are able to see to its boundaries. */
    /* If dark, set COULD_SEE so various spells work -dlc */
    if (rnum >= 0) {
	for (zy = rooms[rnum].ly-1; zy <= rooms[rnum].hy+1; zy++) {
	    rmin[zy] = start = rooms[rnum].lx-1;
	    rmax[zy] = stop  = rooms[rnum].hx+1;

	    for (zx = start; zx <= stop; zx++) {
		if (rooms[rnum].rlit) {
		    next[zy][zx] = COULD_SEE | IN_SIGHT;
		    levl[zx][zy].seenv = SVALL;	/* see the walls */
		} else
		    next[zy][zx] = COULD_SEE;
	    }
	}
    }

    in_door = levl[u.ux][u.uy].typ == DOOR;

    /* Can always see adjacent. */
    ylo = max(u.uy - 1, 0);
    yhi = min(u.uy + 1, ROWNO - 1);
    xlo = max(u.ux - 1, 1);
    xhi = min(u.ux + 1, COLNO - 1);
    for (zy = ylo; zy <= yhi; zy++) {
	if (xlo < rmin[zy]) rmin[zy] = xlo;
	if (xhi > rmax[zy]) rmax[zy] = xhi;

	for (zx = xlo; zx <= xhi; zx++) {
	    next[zy][zx] = COULD_SEE | IN_SIGHT;
	    /*
	     * Yuck, update adjacent non-diagonal positions when in a doorway.
	     * We need to do this to catch the case when we first step into
	     * a room.  The room's walls were not seen from the outside, but
	     * now are seen (the seen bits are set just above).  However, the
	     * positions are not updated because they were already in sight.
	     * So, we have to do it here.
	     */
	    if (in_door && (zx == u.ux || zy == u.uy)) newsym(zx,zy);
	}
    }
}
#endif /* REINCARNATION */

/*#define EXTEND_SPINE*/	/* possibly better looking wall-angle */

#ifdef EXTEND_SPINE

STATIC_DCL int FDECL(new_angle, (struct rm *, unsigned char *, int, int));
/*
 * new_angle()
 *
 * Return the new angle seen by the hero for this location.  The angle
 * bit is given in the value pointed at by sv.
 *
 * For T walls and crosswall, just setting the angle bit, even though
 * it is technically correct, doesn't look good.  If we can see the
 * next position beyond the current one and it is a wall that we can
 * see, then we want to extend a spine of the T to connect with the wall
 * that is beyond.  Example:
 *
 *	 Correct, but ugly			   Extend T spine
 *
 *		| ...					| ...
 *		| ...	<-- wall beyond & floor -->	| ...
 *		| ...					| ...
 * Unseen   -->   ...					| ...
 * spine	+-...	<-- trwall & doorway	-->	+-...
 *		| ...					| ...
 *
 *
 *		   @	<-- hero		-->	   @
 *
 *
 * We fake the above check by only checking if the horizontal &
 * vertical positions adjacent to the crosswall and T wall are
 * unblocked.  Then, _in general_ we can see beyond.  Generally,
 * this is good enough.
 *
 *	+ When this function is called we don't have all of the seen
 *	  information (we're doing a top down scan in vision_recalc).
 *	  We would need to scan once to set all IN_SIGHT and COULD_SEE
 *	  bits, then again to correctly set the seenv bits.
 *	+ I'm trying to make this as cheap as possible.  The display &
 *	  vision eat up too much CPU time.
 *	
 *
 * Note:  Even as I write this, I'm still not convinced.  There are too
 *	  many exceptions.  I may have to bite the bullet and do more
 *	  checks.	- Dean 2/11/93
 */
STATIC_OVL int
new_angle(lev, sv, row, col)
    struct rm *lev;
    unsigned char *sv;
    int row, col;
{
    register int res = *sv;

    /*
     * Do extra checks for crosswalls and T walls if we see them from
     * an angle.
     */
    if (lev->typ >= CROSSWALL && lev->typ <= TRWALL) {
	switch (res) {
	    case SV0:
		if (col > 0	  && viz_clear[row][col-1]) res |= SV7;
		if (row > 0	  && viz_clear[row-1][col]) res |= SV1;
		break;
	    case SV2:
		if (row > 0	  && viz_clear[row-1][col]) res |= SV1;
		if (col < COLNO-1 && viz_clear[row][col+1]) res |= SV3;
		break;
	    case SV4:
		if (col < COLNO-1 && viz_clear[row][col+1]) res |= SV3;
		if (row < ROWNO-1 && viz_clear[row+1][col]) res |= SV5;
		break;
	    case SV6:
		if (row < ROWNO-1 && viz_clear[row+1][col]) res |= SV5;
		if (col > 0	  && viz_clear[row][col-1]) res |= SV7;
		break;
	}
    }
    return res;
}
#else
/*
 * new_angle()
 *
 * Return the new angle seen by the hero for this location.  The angle
 * bit is given in the value pointed at by sv.
 *
 * The other parameters are not used.
 */
#define new_angle(lev, sv, row, col) (*sv)

#endif


/*
 * vision_recalc()
 *
 * Do all of the heavy vision work.  Recalculate all locations that could
 * possibly be seen by the hero --- if the location were lit, etc.  Note
 * which locations are actually seen because of lighting.  Then add to
 * this all locations that be seen by hero due to night vision and x-ray
 * vision.  Finally, compare with what the hero was able to see previously.
 * Update the difference.
 *
 * This function is usually called only when the variable 'vision_full_recalc'
 * is set.  The following is a list of places where this function is called,
 * with three valid values for the control flag parameter:
 *
 * Control flag = 0.  A complete vision recalculation.  Generate the vision
 * tables from scratch.  This is necessary to correctly set what the hero
 * can see.  (1) and (2) call this routine for synchronization purposes, (3)
 * calls this routine so it can operate correctly.
 *
 *	+ After the monster move, before input from the player. [moveloop()]
 *	+ At end of moveloop. [moveloop() ??? not sure why this is here]
 *	+ Right before something is printed. [pline()]
 *	+ Right before we do a vision based operation. [do_clear_area()]
 *	+ screen redraw, so we can renew all positions in sight. [docrt()]
 *
 * Control flag = 1.  An adjacent vision recalculation.  The hero has moved
 * one square.  Knowing this, it might be possible to optimize the vision
 * recalculation using the current knowledge.  This is presently unimplemented
 * and is treated as a control = 0 call.
 *
 *	+ Right after the hero moves. [domove()]
 *
 * Control flag = 2.  Turn off the vision system.  Nothing new will be
 * displayed, since nothing is seen.  This is usually done when you need
 * a newsym() run on all locations in sight, or on some locations but you
 * don't know which ones.
 *
 *	+ Before a screen redraw, so all positions are renewed. [docrt()]
 *	+ Right before the hero arrives on a new level. [goto_level()]
 *	+ Right after a scroll of light is read. [litroom()]
 *	+ After an option has changed that affects vision [parseoptions()]
 *	+ Right after the hero is swallowed. [gulpmu()]
 *	+ Just before bubbles are moved. [movebubbles()]
 */
void
vision_recalc(control)
    int control;
{
    char **temp_array;	/* points to the old vision array */
    char **next_array;	/* points to the new vision array */
    char *next_row;	/* row pointer for the new array */
    char *old_row;	/* row pointer for the old array */
    char *next_rmin;	/* min pointer for the new array */
    char *next_rmax;	/* max pointer for the new array */
    char *ranges;	/* circle ranges -- used for xray & night vision */
    int row;		/* row counter (outer loop)  */
    int start, stop;	/* inner loop starting/stopping index */
    int dx, dy;		/* one step from a lit door or lit wall (see below) */
    register int col;	/* inner loop counter */
    register struct rm *lev;	/* pointer to current pos */
    struct rm *flev;	/* pointer to position in "front" of current pos */
    extern unsigned char seenv_matrix[3][3];	/* from display.c */
    static unsigned char colbump[COLNO+1];	/* cols to bump sv */
    unsigned char *sv;				/* ptr to seen angle bits */
    int oldseenv;				/* previous seenv value */

    vision_full_recalc = 0;			/* reset flag */
    if (in_mklev) return;

#ifdef GCC_WARN
    row = 0;
#endif

    /*
     * Either the light sources have been taken care of, or we must
     * recalculate them here.
     */

    /* Get the unused could see, row min, and row max arrays. */
    get_unused_cs(&next_array, &next_rmin, &next_rmax);

    /* You see nothing, nothing can see you --- if swallowed or refreshing. */
    if (u.uswallow || control == 2) {
	/* do nothing -- get_unused_cs() nulls out the new work area */

    } else if (Blind) {
	/*
	 * Calculate the could_see array even when blind so that monsters
	 * can see you, even if you can't see them.  Note that the current
	 * setup allows:
	 *
	 *	+ Monsters to see with the "new" vision, even on the rogue
	 *	  level.
	 *
	 *	+ Monsters can see you even when you're in a pit.
	 */
	view_from(u.uy, u.ux, next_array, next_rmin, next_rmax,
		0, (void FDECL((*),(int,int,genericptr_t)))0, (genericptr_t)0);

	/*
	 * Our own version of the update loop below.  We know we can't see
	 * anything, so we only need update positions we used to be able
	 * to see.
	 */
	temp_array = viz_array;	/* set viz_array so newsym() will work */
	viz_array = next_array;

	for (row = 0; row < ROWNO; row++) {
	    old_row = temp_array[row];

	    /* Find the min and max positions on the row. */
	    start = min(viz_rmin[row], next_rmin[row]);
	    stop  = max(viz_rmax[row], next_rmax[row]);

	    for (col = start; col <= stop; col++)
		if (old_row[col] & IN_SIGHT) newsym(col,row);
	}

	/* skip the normal update loop */
	goto skip;
    }
#ifdef REINCARNATION
    else if (Is_rogue_level(&u.uz)) {
	rogue_vision(next_array,next_rmin,next_rmax);
    }
#endif
    else {
	int has_night_vision = 1;	/* hero has night vision */

	if (Underwater && !Is_waterlevel(&u.uz)) {
	    /*
	     * The hero is under water.  Only see surrounding locations if
	     * they are also underwater.  This overrides night vision but
	     * does not override x-ray vision.
	     */
	    has_night_vision = 0;

	    for (row = u.uy-1; row <= u.uy+1; row++)
		for (col = u.ux-1; col <= u.ux+1; col++) {
		    if (!isok(col,row) || !is_pool(col,row)) continue;

		    next_rmin[row] = min(next_rmin[row], col);
		    next_rmax[row] = max(next_rmax[row], col);
		    next_array[row][col] = IN_SIGHT;
		}
	}

	/* if in a pit, just update for immediate locations */
	else if (u.utrap && u.utraptype == TT_PIT) {
	    for (row = u.uy-1; row <= u.uy+1; row++) {
		if (row < 0) continue;	if (row >= ROWNO) break;

		next_rmin[row] = max(      0, u.ux - 1);
		next_rmax[row] = min(COLNO-1, u.ux + 1);
		next_row = next_array[row];

		for(col=next_rmin[row]; col <= next_rmax[row]; col++)
		    next_row[col] = IN_SIGHT;
	    }
	} else
	    view_from(u.uy, u.ux, next_array, next_rmin, next_rmax,
		0, (void FDECL((*),(int,int,genericptr_t)))0, (genericptr_t)0);

	/*
	 * Set the IN_SIGHT bit for xray and night vision.
	 */
	if (u.xray_range >= 0) {
	    if (u.xray_range) {
		ranges = circle_ptr(u.xray_range);

		for (row = u.uy-u.xray_range; row <= u.uy+u.xray_range; row++) {
		    if (row < 0) continue;	if (row >= ROWNO) break;
		    dy = v_abs(u.uy-row);	next_row = next_array[row];

		    start = max(      0, u.ux - ranges[dy]);
		    stop  = min(COLNO-1, u.ux + ranges[dy]);

		    for (col = start; col <= stop; col++) {
			char old_row_val = next_row[col];
			next_row[col] |= IN_SIGHT;
			oldseenv = levl[col][row].seenv;
			levl[col][row].seenv = SVALL;	/* see all! */
			/* Update if previously not in sight or new angle. */
			if (!(old_row_val & IN_SIGHT) || oldseenv != SVALL)
			    newsym(col,row);
		    }

		    next_rmin[row] = min(start, next_rmin[row]);
		    next_rmax[row] = max(stop, next_rmax[row]);
		}

	    } else {	/* range is 0 */
		next_array[u.uy][u.ux] |= IN_SIGHT;
		levl[u.ux][u.uy].seenv = SVALL;
		next_rmin[u.uy] = min(u.ux, next_rmin[u.uy]);
		next_rmax[u.uy] = max(u.ux, next_rmax[u.uy]);
	    }
	}

	if (has_night_vision && u.xray_range < u.nv_range) {
	    if (!u.nv_range) {	/* range is 0 */
		next_array[u.uy][u.ux] |= IN_SIGHT;
		levl[u.ux][u.uy].seenv = SVALL;
		next_rmin[u.uy] = min(u.ux, next_rmin[u.uy]);
		next_rmax[u.uy] = max(u.ux, next_rmax[u.uy]);
	    } else if (u.nv_range > 0) {
		ranges = circle_ptr(u.nv_range);

		for (row = u.uy-u.nv_range; row <= u.uy+u.nv_range; row++) {
		    if (row < 0) continue;	if (row >= ROWNO) break;
		    dy = v_abs(u.uy-row);	next_row = next_array[row];

		    start = max(      0, u.ux - ranges[dy]);
		    stop  = min(COLNO-1, u.ux + ranges[dy]);

		    for (col = start; col <= stop; col++)
			if (next_row[col]) next_row[col] |= IN_SIGHT;

		    next_rmin[row] = min(start, next_rmin[row]);
		    next_rmax[row] = max(stop, next_rmax[row]);
		}
	    }
	}
    }

    /* Set the correct bits for all light sources. */
    do_light_sources(next_array);


    /*
     * Make the viz_array the new array so that cansee() will work correctly.
     */
    temp_array = viz_array;
    viz_array = next_array;

    /*
     * The main update loop.  Here we do two things:
     *
     *	    + Set the IN_SIGHT bit for places that we could see and are lit.
     *	    + Reset changed places.
     *
     * There is one thing that make deciding what the hero can see
     * difficult:
     *
     *  1.  Directional lighting.  Items that block light create problems.
     *      The worst offenders are doors.  Suppose a door to a lit room
     *      is closed.  It is lit on one side, but not on the other.  How
     *      do you know?  You have to check the closest adjacent position.
     *	    Even so, that is not entirely correct.  But it seems close
     *	    enough for now.
     */
    colbump[u.ux] = colbump[u.ux+1] = 1;
    for (row = 0; row < ROWNO; row++) {
	dy = u.uy - row;                dy = sign(dy);
	next_row = next_array[row];     old_row = temp_array[row];

	/* Find the min and max positions on the row. */
	start = min(viz_rmin[row], next_rmin[row]);
	stop  = max(viz_rmax[row], next_rmax[row]);
	lev = &levl[start][row];

	sv = &seenv_matrix[dy+1][start < u.ux ? 0 : (start > u.ux ? 2:1)];

	for (col = start; col <= stop;
				lev += ROWNO, sv += (int) colbump[++col]) {
	    if (next_row[col] & IN_SIGHT) {
		/*
		 * We see this position because of night- or xray-vision.
		 */
		oldseenv = lev->seenv;
		lev->seenv |= new_angle(lev,sv,row,col); /* update seen angle */

		/* Update pos if previously not in sight or new angle. */
		if ( !(old_row[col] & IN_SIGHT) || oldseenv != lev->seenv)
		    newsym(col,row);
	    }

	    else if ((next_row[col] & COULD_SEE)
				&& (lev->lit || (next_row[col] & TEMP_LIT))) {
		/*
		 * We see this position because it is lit.
		 */
		if (IS_DOOR(lev->typ) && !viz_clear[row][col]) {
		    /*
		     * Make sure doors, boulders or mimics don't show up
		     * at the end of dark hallways.  We do this by checking
		     * the adjacent position.  If it is lit, then we can see
		     * the door, otherwise we can't.
		     */
		    dx = u.ux - col;	dx = sign(dx);
		    flev = &(levl[col+dx][row+dy]);
		    if (flev->lit || next_array[row+dy][col+dx] & TEMP_LIT) {
			next_row[col] |= IN_SIGHT;	/* we see it */

			oldseenv = lev->seenv;
			lev->seenv |= new_angle(lev,sv,row,col);

			/* Update pos if previously not in sight or new angle.*/
			if (!(old_row[col] & IN_SIGHT) || oldseenv!=lev->seenv)
			    newsym(col,row);
		    } else
			goto not_in_sight;	/* we don't see it */

		} else {
		    next_row[col] |= IN_SIGHT;	/* we see it */

		    oldseenv = lev->seenv;
		    lev->seenv |= new_angle(lev,sv,row,col);

		    /* Update pos if previously not in sight or new angle. */
		    if ( !(old_row[col] & IN_SIGHT) || oldseenv != lev->seenv)
			newsym(col,row);
		}
	    } else if ((next_row[col] & COULD_SEE) && lev->waslit) {
		/*
		 * If we make it here, the hero _could see_ the location,
		 * but doesn't see it (location is not lit).
		 * However, the hero _remembers_ it as lit (waslit is true).
		 * The hero can now see that it is not lit, so change waslit
		 * and update the location.
		 */
		lev->waslit = 0; /* remember lit condition */
		newsym(col,row);
	    }
	    /*
	     * At this point we know that the row position is *not* in normal
	     * sight.  That is, the position is could be seen, but is dark
	     * or LOS is just plain blocked.
	     *
	     * Update the position if:
	     * o If the old one *was* in sight.  We may need to clean up
	     *   the glyph -- E.g. darken room spot, etc.
	     * o If we now could see the location (yet the location is not
	     *   lit), but previously we couldn't see the location, or vice
	     *   versa.  Update the spot because there there may be an infared
	     *   monster there.
	     */
	    else {
not_in_sight:
		if ((old_row[col] & IN_SIGHT)
			|| ((next_row[col] & COULD_SEE)
				^ (old_row[col] & COULD_SEE)))
		    newsym(col,row);
	    }

	} /* end for col . . */
    }	/* end for row . .  */
    colbump[u.ux] = colbump[u.ux+1] = 0;

skip:
    newsym(u.ux,u.uy);		/* Make sure the hero shows up! */

    /* Set the new min and max pointers. */
    viz_rmin  = next_rmin;
    viz_rmax = next_rmax;
}


/*
 * block_point()
 *
 * Make the location opaque to light.
 */
void
block_point(x,y)
    int x, y;
{
    fill_point(y,x);

    /* recalc light sources here? */

    /*
     * We have to do a full vision recalculation if we "could see" the
     * location.  Why? Suppose some monster opened a way so that the
     * hero could see a lit room.  However, the position of the opening
     * was out of night-vision range of the hero.  Suddenly the hero should
     * see the lit room.
     */
    if (viz_array[y][x]) vision_full_recalc = 1;
}

/*
 * unblock_point()
 *
 * Make the location transparent to light.
 */
void
unblock_point(x,y)
    int x, y;
{
    dig_point(y,x);

    /* recalc light sources here? */

    if (viz_array[y][x]) vision_full_recalc = 1;
}


/*===========================================================================*\
 |									     |
 |	Everything below this line uses (y,x) instead of (x,y) --- the	     |
 |	algorithms are faster if they are less recursive and can scan	     |
 |	on a row longer.						     |
 |									     |
\*===========================================================================*/


/* ========================================================================= *\
			Left and Right Pointer Updates
\* ========================================================================= */

/*
 *			LEFT and RIGHT pointer rules
 *
 *
 * **NOTE**  The rules changed on 4/4/90.  This comment reflects the
 * new rules.  The change was so that the stone-wall optimization
 * would work.
 *
 * OK, now the tough stuff.  We must maintain our left and right
 * row pointers.  The rules are as follows:
 *
 * Left Pointers:
 * ______________
 *
 * + If you are a clear spot, your left will point to the first
 *   stone to your left.  If there is none, then point the first
 *   legal position in the row (0).
 *
 * + If you are a blocked spot, then your left will point to the
 *   left-most blocked spot to your left that is connected to you.
 *   This means that a left-edge (a blocked spot that has an open
 *   spot on its left) will point to itself.
 *
 *
 * Right Pointers:
 * ---------------
 * + If you are a clear spot, your right will point to the first
 *   stone to your right.  If there is none, then point the last
 *   legal position in the row (COLNO-1).
 *
 * + If you are a blocked spot, then your right will point to the
 *   right-most blocked spot to your right that is connected to you.
 *   This means that a right-edge (a blocked spot that has an open
 *    spot on its right) will point to itself.
 */
STATIC_OVL void
dig_point(row,col)
    int row,col;
{
    int i;

    if (viz_clear[row][col]) return;		/* already done */

    viz_clear[row][col] = 1;

    /*
     * Boundary cases first.
     */
    if (col == 0) {				/* left edge */
	if (viz_clear[row][1]) {
	    right_ptrs[row][0] = right_ptrs[row][1];
	} else {
	    right_ptrs[row][0] = 1;
	    for (i = 1; i <= right_ptrs[row][1]; i++)
		left_ptrs[row][i] = 1;
	}
    } else if (col == (COLNO-1)) {		/* right edge */

	if (viz_clear[row][COLNO-2]) {
	    left_ptrs[row][COLNO-1] = left_ptrs[row][COLNO-2];
	} else {
	    left_ptrs[row][COLNO-1] = COLNO-2;
	    for (i = left_ptrs[row][COLNO-2]; i < COLNO-1; i++)
		right_ptrs[row][i] = COLNO-2;
	}
    }

    /*
     * At this point, we know we aren't on the boundaries.
     */
    else if (viz_clear[row][col-1] && viz_clear[row][col+1]) {
	/* Both sides clear */
	for (i = left_ptrs[row][col-1]; i <= col; i++) {
	    if (!viz_clear[row][i]) continue;	/* catch non-end case */
	    right_ptrs[row][i] = right_ptrs[row][col+1];
	}
	for (i = col; i <= right_ptrs[row][col+1]; i++) {
	    if (!viz_clear[row][i]) continue;	/* catch non-end case */
	    left_ptrs[row][i] = left_ptrs[row][col-1];
	}

    } else if (viz_clear[row][col-1]) {
	/* Left side clear, right side blocked. */
	for (i = col+1; i <= right_ptrs[row][col+1]; i++)
	    left_ptrs[row][i] = col+1;

	for (i = left_ptrs[row][col-1]; i <= col; i++) {
	    if (!viz_clear[row][i]) continue;	/* catch non-end case */
	    right_ptrs[row][i] = col+1;
	}
	left_ptrs[row][col] = left_ptrs[row][col-1];

    } else if (viz_clear[row][col+1]) {
	/* Right side clear, left side blocked. */
	for (i = left_ptrs[row][col-1]; i < col; i++)
	    right_ptrs[row][i] = col-1;

	for (i = col; i <= right_ptrs[row][col+1]; i++) {
	    if (!viz_clear[row][i]) continue;	/* catch non-end case */
	    left_ptrs[row][i] = col-1;
	}
	right_ptrs[row][col] = right_ptrs[row][col+1];

    } else {
	/* Both sides blocked */
	for (i = left_ptrs[row][col-1]; i < col; i++)
	    right_ptrs[row][i] = col-1;

	for (i = col+1; i <= right_ptrs[row][col+1]; i++)
	    left_ptrs[row][i] = col+1;

	left_ptrs[row][col]  = col-1;
	right_ptrs[row][col] = col+1;
    }
}

STATIC_OVL void
fill_point(row,col)
    int row, col;
{
    int i;

    if (!viz_clear[row][col]) return;

    viz_clear[row][col] = 0;

    if (col == 0) {
	if (viz_clear[row][1]) {			/* adjacent is clear */
	    right_ptrs[row][0] = 0;
	} else {
	    right_ptrs[row][0] = right_ptrs[row][1];
	    for (i = 1; i <= right_ptrs[row][1]; i++)
		left_ptrs[row][i] = 0;
	}
    } else if (col == COLNO-1) {
	if (viz_clear[row][COLNO-2]) {		/* adjacent is clear */
	    left_ptrs[row][COLNO-1] = COLNO-1;
	} else {
	    left_ptrs[row][COLNO-1] = left_ptrs[row][COLNO-2];
	    for (i = left_ptrs[row][COLNO-2]; i < COLNO-1; i++)
		right_ptrs[row][i] = COLNO-1;
	}
    }

    /*
     * Else we know that we are not on an edge.
     */
    else if (viz_clear[row][col-1] && viz_clear[row][col+1]) {
	/* Both sides clear */
	for (i = left_ptrs[row][col-1]+1; i <= col; i++)
	    right_ptrs[row][i] = col;

	if (!left_ptrs[row][col-1])		/* catch the end case */
	    right_ptrs[row][0] = col;

	for (i = col; i < right_ptrs[row][col+1]; i++)
	    left_ptrs[row][i] = col;

	if (right_ptrs[row][col+1] == COLNO-1)	/* catch the end case */
	    left_ptrs[row][COLNO-1] = col;

    } else if (viz_clear[row][col-1]) {
	/* Left side clear, right side blocked. */
	for (i = col; i <= right_ptrs[row][col+1]; i++)
	    left_ptrs[row][i] = col;

	for (i = left_ptrs[row][col-1]+1; i < col; i++)
	    right_ptrs[row][i] = col;

	if (!left_ptrs[row][col-1])		/* catch the end case */
	    right_ptrs[row][i] = col;

	right_ptrs[row][col] = right_ptrs[row][col+1];

    } else if (viz_clear[row][col+1]) {
	/* Right side clear, left side blocked. */
	for (i = left_ptrs[row][col-1]; i <= col; i++)
	    right_ptrs[row][i] = col;

	for (i = col+1; i < right_ptrs[row][col+1]; i++)
	    left_ptrs[row][i] = col;

	if (right_ptrs[row][col+1] == COLNO-1)	/* catch the end case */
	    left_ptrs[row][i] = col;

	left_ptrs[row][col] = left_ptrs[row][col-1];

    } else {
	/* Both sides blocked */
	for (i = left_ptrs[row][col-1]; i <= col; i++)
	    right_ptrs[row][i] = right_ptrs[row][col+1];

	for (i = col; i <= right_ptrs[row][col+1]; i++)
	    left_ptrs[row][i] = left_ptrs[row][col-1];
    }
}


/*===========================================================================*/
/*===========================================================================*/
/* Use either algorithm C or D.  See the config.h for more details. =========*/

/*
 * Variables local to both Algorithms C and D.
 */
static int  start_row;
static int  start_col;
static int  step;
static char **cs_rows;
static char *cs_left;
static char *cs_right;

static void FDECL((*vis_func), (int,int,genericptr_t));
static genericptr_t varg;

/*
 * Both Algorithms C and D use the following macros.
 *
 *      good_row(z)	  - Return TRUE if the argument is a legal row.
 *      set_cs(rowp,col)  - Set the local could see array.
 *      set_min(z)	  - Save the min value of the argument and the current
 *			      row minimum.
 *      set_max(z)	  - Save the max value of the argument and the current
 *			      row maximum.
 *
 * The last three macros depend on having local pointers row_min, row_max,
 * and rowp being set correctly.
 */
#define set_cs(rowp,col) (rowp[col] = COULD_SEE)
#define good_row(z) ((z) >= 0 && (z) < ROWNO)
#define set_min(z) if (*row_min > (z)) *row_min = (z)
#define set_max(z) if (*row_max < (z)) *row_max = (z)
#define is_clear(row,col) viz_clear_rows[row][col]

/*
 * clear_path()		expanded into 4 macros/functions:
 *
 *	q1_path()
 *	q2_path()
 *	q3_path()
 *	q4_path()
 *
 * "Draw" a line from the start to the given location.  Stop if we hit
 * something that blocks light.  The start and finish points themselves are
 * not checked, just the points between them.  These routines do _not_
 * expect to be called with the same starting and stopping point.
 *
 * These routines use the generalized integer Bresenham's algorithm (fast
 * line drawing) for all quadrants.  The algorithm was taken from _Procedural
 * Elements for Computer Graphics_, by David F. Rogers.  McGraw-Hill, 1985.
 */
#ifdef MACRO_CPATH	/* quadrant calls are macros */

/*
 * When called, the result is in "result".
 * The first two arguments (srow,scol) are one end of the path.  The next
 * two arguments (row,col) are the destination.  The last argument is
 * used as a C language label.  This means that it must be different
 * in each pair of calls.
 */

/*
 *  Quadrant I (step < 0).
 */
#define q1_path(srow,scol,y2,x2,label)			\
{							\
    int dx, dy;						\
    register int k, err, x, y, dxs, dys;		\
							\
    x  = (scol);	y  = (srow);			\
    dx = (x2) - x;	dy = y - (y2);			\
							\
    result = 0;		 /* default to a blocked path */\
							\
    dxs = dx << 1;	   /* save the shifted values */\
    dys = dy << 1;					\
    if (dy > dx) {					\
	err = dxs - dy;					\
							\
	for (k = dy-1; k; k--) {			\
	    if (err >= 0) {				\
		x++;					\
		err -= dys;				\
	    }						\
	    y--;					\
	    err += dxs;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
    } else {						\
	err = dys - dx;					\
							\
	for (k = dx-1; k; k--) {			\
	    if (err >= 0) {				\
		y--;					\
		err -= dxs;				\
	    }						\
	    x++;					\
	    err += dys;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
    }							\
							\
    result = 1;						\
}

/*
 * Quadrant IV (step > 0).
 */
#define q4_path(srow,scol,y2,x2,label)			\
{							\
    int dx, dy;						\
    register int k, err, x, y, dxs, dys;		\
							\
    x  = (scol);	y  = (srow);			\
    dx = (x2) - x;	dy = (y2) - y;			\
							\
    result = 0;		 /* default to a blocked path */\
							\
    dxs = dx << 1;	   /* save the shifted values */\
    dys = dy << 1;					\
    if (dy > dx) {					\
	err = dxs - dy;					\
							\
	for (k = dy-1; k; k--) {			\
	    if (err >= 0) {				\
		x++;					\
		err -= dys;				\
	    }						\
	    y++;					\
	    err += dxs;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
							\
    } else {						\
	err = dys - dx;					\
							\
	for (k = dx-1; k; k--) {			\
	    if (err >= 0) {				\
		y++;					\
		err -= dxs;				\
	    }						\
	    x++;					\
	    err += dys;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
    }							\
							\
    result = 1;						\
}

/*
 * Quadrant II (step < 0).
 */
#define q2_path(srow,scol,y2,x2,label)			\
{							\
    int dx, dy;						\
    register int k, err, x, y, dxs, dys;		\
							\
    x  = (scol);	y  = (srow);			\
    dx = x - (x2);	dy = y - (y2);			\
							\
    result = 0;		 /* default to a blocked path */\
							\
    dxs = dx << 1;	   /* save the shifted values */\
    dys = dy << 1;					\
    if (dy > dx) {					\
	err = dxs - dy;					\
							\
	for (k = dy-1; k; k--) {			\
	    if (err >= 0) {				\
		x--;					\
		err -= dys;				\
	    }						\
	    y--;					\
	    err += dxs;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
    } else {						\
	err = dys - dx;					\
							\
	for (k = dx-1; k; k--) {			\
	    if (err >= 0) {				\
		y--;					\
		err -= dxs;				\
	    }						\
	    x--;					\
	    err += dys;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
    }							\
							\
    result = 1;						\
}

/*
 * Quadrant III (step > 0).
 */
#define q3_path(srow,scol,y2,x2,label)			\
{							\
    int dx, dy;						\
    register int k, err, x, y, dxs, dys;		\
							\
    x  = (scol);	y  = (srow);			\
    dx = x - (x2);	dy = (y2) - y;			\
							\
    result = 0;		 /* default to a blocked path */\
							\
    dxs = dx << 1;	   /* save the shifted values */\
    dys = dy << 1;					\
    if (dy > dx) {					\
	err = dxs - dy;					\
							\
	for (k = dy-1; k; k--) {			\
	    if (err >= 0) {				\
		x--;					\
		err -= dys;				\
	    }						\
	    y++;					\
	    err += dxs;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
							\
    } else {						\
	err = dys - dx;					\
							\
	for (k = dx-1; k; k--) {			\
	    if (err >= 0) {				\
		y++;					\
		err -= dxs;				\
	    }						\
	    x--;					\
	    err += dys;					\
	    if (!is_clear(y,x)) goto label;/* blocked */\
	}						\
    }							\
							\
    result = 1;						\
}

#else   /* quadrants are really functions */

STATIC_DCL int FDECL(_q1_path, (int,int,int,int));
STATIC_DCL int FDECL(_q2_path, (int,int,int,int));
STATIC_DCL int FDECL(_q3_path, (int,int,int,int));
STATIC_DCL int FDECL(_q4_path, (int,int,int,int));

#define q1_path(sy,sx,y,x,dummy) result = _q1_path(sy,sx,y,x)
#define q2_path(sy,sx,y,x,dummy) result = _q2_path(sy,sx,y,x)
#define q3_path(sy,sx,y,x,dummy) result = _q3_path(sy,sx,y,x)
#define q4_path(sy,sx,y,x,dummy) result = _q4_path(sy,sx,y,x)

/*
 * Quadrant I (step < 0).
 */
STATIC_OVL int
_q1_path(srow,scol,y2,x2)
    int scol, srow, y2, x2;
{
    int dx, dy;
    register int k, err, x, y, dxs, dys;

    x  = scol;		y  = srow;
    dx = x2 - x;	dy = y - y2;

    dxs = dx << 1;	   /* save the shifted values */
    dys = dy << 1;
    if (dy > dx) {
	err = dxs - dy;

	for (k = dy-1; k; k--) {
	    if (err >= 0) {
		x++;
		err -= dys;
	    }
	    y--;
	    err += dxs;
	    if (!is_clear(y,x)) return 0; /* blocked */
	}
    } else {
	err = dys - dx;

	for (k = dx-1; k; k--) {
	    if (err >= 0) {
		y--;
		err -= dxs;
	    }
	    x++;
	    err += dys;
	    if (!is_clear(y,x)) return 0;/* blocked */
	}
    }

    return 1;
}

/*
 * Quadrant IV (step > 0).
 */
STATIC_OVL int
_q4_path(srow,scol,y2,x2)
    int scol, srow, y2, x2;
{
    int dx, dy;
    register int k, err, x, y, dxs, dys;

    x  = scol;		y  = srow;
    dx = x2 - x;	dy = y2 - y;

    dxs = dx << 1;	   /* save the shifted values */
    dys = dy << 1;
    if (dy > dx) {
	err = dxs - dy;

	for (k = dy-1; k; k--) {
	    if (err >= 0) {
		x++;
		err -= dys;
	    }
	    y++;
	    err += dxs;
	    if (!is_clear(y,x)) return 0; /* blocked */
	}
    } else {
	err = dys - dx;

	for (k = dx-1; k; k--) {
	    if (err >= 0) {
		y++;
		err -= dxs;
	    }
	    x++;
	    err += dys;
	    if (!is_clear(y,x)) return 0;/* blocked */
	}
    }

    return 1;
}

/*
 * Quadrant II (step < 0).
 */
STATIC_OVL int
_q2_path(srow,scol,y2,x2)
    int scol, srow, y2, x2;
{
    int dx, dy;
    register int k, err, x, y, dxs, dys;

    x  = scol;		y  = srow;
    dx = x - x2;	dy = y - y2;

    dxs = dx << 1;	   /* save the shifted values */
    dys = dy << 1;
    if (dy > dx) {
	err = dxs - dy;

	for (k = dy-1; k; k--) {
	    if (err >= 0) {
		x--;
		err -= dys;
	    }
	    y--;
	    err += dxs;
	    if (!is_clear(y,x)) return 0; /* blocked */
	}
    } else {
	err = dys - dx;

	for (k = dx-1; k; k--) {
	    if (err >= 0) {
		y--;
		err -= dxs;
	    }
	    x--;
	    err += dys;
	    if (!is_clear(y,x)) return 0;/* blocked */
	}
    }

    return 1;
}

/*
 * Quadrant III (step > 0).
 */
STATIC_OVL int
_q3_path(srow,scol,y2,x2)
    int scol, srow, y2, x2;
{
    int dx, dy;
    register int k, err, x, y, dxs, dys;

    x  = scol;		y  = srow;
    dx = x - x2;	dy = y2 - y;

    dxs = dx << 1;	   /* save the shifted values */
    dys = dy << 1;
    if (dy > dx) {
	err = dxs - dy;

	for (k = dy-1; k; k--) {
	    if (err >= 0) {
		x--;
		err -= dys;
	    }
	    y++;
	    err += dxs;
	    if (!is_clear(y,x)) return 0; /* blocked */
	}
    } else {
	err = dys - dx;

	for (k = dx-1; k; k--) {
	    if (err >= 0) {
		y++;
		err -= dxs;
	    }
	    x--;
	    err += dys;
	    if (!is_clear(y,x)) return 0;/* blocked */
	}
    }

    return 1;
}

#endif	/* quadrants are functions */

/*
 * Use vision tables to determine if there is a clear path from
 * (col1,row1) to (col2,row2).  This is used by:
 *		m_cansee()
 *		m_canseeu()
 *		do_light_sources()
 */
boolean
clear_path(col1,row1,col2,row2)
    int col1, row1, col2, row2;
{
    int result;

    if(col1 < col2) {
	if(row1 > row2) {
	    q1_path(row1,col1,row2,col2,cleardone);
	} else {
	    q4_path(row1,col1,row2,col2,cleardone);
	}
    } else {
	if(row1 > row2) {
	    q2_path(row1,col1,row2,col2,cleardone);
	} else if(row1 == row2 && col1 == col2) {
	    result = 1;
	} else {
	    q3_path(row1,col1,row2,col2,cleardone);
	}
    }
cleardone:
    return((boolean)result);
}

#ifdef VISION_TABLES
/*===========================================================================*\
			    GENERAL LINE OF SIGHT
				Algorithm D
\*===========================================================================*/


/*
 * Indicate caller for the shadow routines.
 */
#define FROM_RIGHT 0
#define FROM_LEFT  1


/*
 * Include the table definitions.
 */
#include "vis_tab.h"


/* 3D table pointers. */
static close2d *close_dy[CLOSE_MAX_BC_DY];
static far2d   *far_dy[FAR_MAX_BC_DY];

STATIC_DCL void FDECL(right_side, (int,int,int,int,int,int,int,char*));
STATIC_DCL void FDECL(left_side, (int,int,int,int,int,int,int,char*));
STATIC_DCL int FDECL(close_shadow, (int,int,int,int));
STATIC_DCL int FDECL(far_shadow, (int,int,int,int));

/*
 * Initialize algorithm D's table pointers.  If we don't have these,
 * then we do 3D table lookups.  Verrrry slow.
 */
STATIC_OVL void
view_init()
{
    int i;

    for (i = 0; i < CLOSE_MAX_BC_DY; i++)
	close_dy[i] = &close_table[i];

    for (i = 0; i < FAR_MAX_BC_DY; i++)
	far_dy[i] = &far_table[i];
}


/*
 * If the far table has an entry of OFF_TABLE, then the far block prevents
 * us from seeing the location just above/below it.  I.e. the first visible
 * location is one *before* the block.
 */
#define OFF_TABLE 0xff

STATIC_OVL int
close_shadow(side,this_row,block_row,block_col)
    int side,this_row,block_row,block_col;
{
    register int sdy, sdx, pdy, offset;

    /*
     * If on the same column (block_row = -1), then we can see it.
     */
    if (block_row < 0) return block_col;

    /* Take explicit absolute values.  Adjust. */
    if ((sdy = (start_row-block_row)) < 0) sdy = -sdy; --sdy;	/* src   dy */
    if ((sdx = (start_col-block_col)) < 0) sdx = -sdx;		/* src   dx */
    if ((pdy = (block_row-this_row))  < 0) pdy = -pdy;		/* point dy */

    if (sdy < 0 || sdy >= CLOSE_MAX_SB_DY || sdx >= CLOSE_MAX_SB_DX ||
						    pdy >= CLOSE_MAX_BC_DY) {
	impossible("close_shadow:  bad value");
	return block_col;
    }
    offset = close_dy[sdy]->close[sdx][pdy];
    if (side == FROM_RIGHT)
	return block_col + offset;

    return block_col - offset;
}


STATIC_OVL int
far_shadow(side,this_row,block_row,block_col)
    int side,this_row,block_row,block_col;
{
    register int sdy, sdx, pdy, offset;

    /*
     * Take care of a bug that shows up only on the borders.
     *
     * If the block is beyond the border, then the row is negative.  Return
     * the block's column number (should be 0 or COLNO-1).
     *
     * Could easily have the column be -1, but then wouldn't know if it was
     * the left or right border.
     */
    if (block_row < 0) return block_col;

    /* Take explicit absolute values.  Adjust. */
    if ((sdy = (start_row-block_row)) < 0) sdy = -sdy;		/* src   dy */
    if ((sdx = (start_col-block_col)) < 0) sdx = -sdx; --sdx;	/* src   dx */
    if ((pdy = (block_row-this_row))  < 0) pdy = -pdy; --pdy;	/* point dy */

    if (sdy >= FAR_MAX_SB_DY || sdx < 0 || sdx >= FAR_MAX_SB_DX ||
					    pdy < 0 || pdy >= FAR_MAX_BC_DY) {
	impossible("far_shadow:  bad value");
	return block_col;
    }
    if ((offset = far_dy[sdy]->far_q[sdx][pdy]) == OFF_TABLE) offset = -1;
    if (side == FROM_RIGHT)
	return block_col + offset;

    return block_col - offset;
}


/*
 * right_side()
 *
 * Figure out what could be seen on the right side of the source.
 */
STATIC_OVL void
right_side(row, cb_row, cb_col, fb_row, fb_col, left, right_mark, limits)
    int row;		/* current row */
    int	cb_row, cb_col;	/* close block row and col */
    int	fb_row, fb_col;	/* far block row and col */
    int left;		/* left mark of the previous row */
    int	right_mark;	/* right mark of previous row */
    char *limits;	/* points at range limit for current row, or NULL */
{
    register int  i;
    register char *rowp;
    int  hit_stone = 0;
    int  left_shadow, right_shadow, loc_right;
    int  lblock_col;		/* local block column (current row) */
    int  nrow, deeper;
    char *row_min;		/* left most */
    char *row_max;		/* right most */
    int		  lim_max;	/* right most limit of circle */

    nrow    = row + step;
    deeper  = good_row(nrow) && (!limits || (*limits >= *(limits+1)));
    if(!vis_func) {
	rowp    = cs_rows[row];
	row_min = &cs_left[row];
	row_max = &cs_right[row];
    }
    if(limits) {
	lim_max = start_col + *limits;
	if(lim_max > COLNO-1) lim_max = COLNO-1;
	if(right_mark > lim_max) right_mark = lim_max;
	limits++; /* prepare for next row */
    } else
	lim_max = COLNO-1;

    /*
     * Get the left shadow from the close block.  This value could be
     * illegal.
     */
    left_shadow = close_shadow(FROM_RIGHT,row,cb_row,cb_col);

    /*
     * Mark all stone walls as seen before the left shadow.  All this work
     * for a special case.
     *
     * NOTE.  With the addition of this code in here, it is now *required*
     * for the algorithm to work correctly.  If this is commented out,
     * change the above assignment so that left and not left_shadow is the
     * variable that gets the shadow.
     */
    while (left <= right_mark) {
	loc_right = right_ptrs[row][left];
	if(loc_right > lim_max) loc_right = lim_max;
	if (viz_clear_rows[row][left]) {
	    if (loc_right >= left_shadow) {
		left = left_shadow;	/* opening ends beyond shadow */
		break;
	    }
	    left = loc_right;
	    loc_right = right_ptrs[row][left];
	    if(loc_right > lim_max) loc_right = lim_max;
	    if (left == loc_right) return;	/* boundary */

	    /* Shadow covers opening, beyond right mark */
	    if (left == right_mark && left_shadow > right_mark) return;
	}

	if (loc_right > right_mark)	/* can't see stone beyond the mark */
	    loc_right = right_mark;

	if(vis_func) {
	    for (i = left; i <= loc_right; i++) (*vis_func)(i, row, varg);
	} else {
	    for (i = left; i <= loc_right; i++) set_cs(rowp,i);
	    set_min(left);	set_max(loc_right);
	}

	if (loc_right == right_mark) return;	/* all stone */
	if (loc_right >= left_shadow) hit_stone = 1;
	left = loc_right + 1;
    }

    /*
     * At this point we are at the first visible clear spot on or beyond
     * the left shadow, unless the left shadow is an illegal value.  If we
     * have "hit stone" then we have a stone wall just to our left.
     */

    /*
     * Get the right shadow.  Make sure that it is a legal value.
     */
    if ((right_shadow = far_shadow(FROM_RIGHT,row,fb_row,fb_col)) >= COLNO)
	right_shadow = COLNO-1;
    /*
     * Make vertical walls work the way we want them.  In this case, we
     * note when the close block blocks the column just above/beneath
     * it (right_shadow < fb_col [actually right_shadow == fb_col-1]).  If
     * the location is filled, then we want to see it, so we put the
     * right shadow back (same as fb_col).
     */
    if (right_shadow < fb_col && !viz_clear_rows[row][fb_col])
	right_shadow = fb_col;
    if(right_shadow > lim_max) right_shadow = lim_max;

    /*
     * Main loop.  Within the range of sight of the previous row, mark all
     * stone walls as seen.  Follow open areas recursively.
     */
    while (left <= right_mark) {
	/* Get the far right of the opening or wall */
	loc_right = right_ptrs[row][left];
	if(loc_right > lim_max) loc_right = lim_max;

	if (!viz_clear_rows[row][left]) {
	    hit_stone = 1;	/* use stone on this row as close block */
	    /*
	     * We can see all of the wall until the next open spot or the
	     * start of the shadow caused by the far block (right).
	     *
	     * Can't see stone beyond the right mark.
	     */
	    if (loc_right > right_mark) loc_right = right_mark;

	    if(vis_func) {
		for (i = left; i <= loc_right; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = left; i <= loc_right; i++) set_cs(rowp,i);
		set_min(left);	set_max(loc_right);
	    }

	    if (loc_right == right_mark) return;	/* hit the end */
	    left = loc_right + 1;
	    loc_right = right_ptrs[row][left];
	    if(loc_right > lim_max) loc_right = lim_max;
	    /* fall through... we know at least one position is visible */
	}

	/*
	 * We are in an opening.
	 *
	 * If this is the first open spot since the could see area  (this is
	 * true if we have hit stone), get the shadow generated by the wall
	 * just to our left.
	 */
	if (hit_stone) {
	    lblock_col = left-1;	/* local block column */
	    left = close_shadow(FROM_RIGHT,row,row,lblock_col);
	    if (left > lim_max) break;		/* off the end */
	}

	/*
	 * Check if the shadow covers the opening.  If it does, then
	 * move to end of the opening.  A shadow generated on from a
	 * wall on this row does *not* cover the wall on the right
	 * of the opening.
	 */
	if (left >= loc_right) {
	    if (loc_right == lim_max) {		/* boundary */
		if (left == lim_max) {
		    if(vis_func) (*vis_func)(lim_max, row, varg);
		    else {
			set_cs(rowp,lim_max);	/* last pos */
			set_max(lim_max);
		    }
		}
		return;					/* done */
	    }
	    left = loc_right;
	    continue;
	}

	/*
	 * If the far wall of the opening (loc_right) is closer than the
	 * shadow limit imposed by the far block (right) then use the far
	 * wall as our new far block when we recurse.
	 *
	 * If the limits are the the same, and the far block really exists
	 * (fb_row >= 0) then do the same as above.
	 *
	 * Normally, the check would be for the far wall being closer OR EQUAL
	 * to the shadow limit.  However, there is a bug that arises from the
	 * fact that the clear area pointers end in an open space (if it
	 * exists) on a boundary.  This then makes a far block exist where it
	 * shouldn't --- on a boundary.  To get around that, I had to
	 * introduce the concept of a non-existent far block (when the
	 * row < 0).  Next I have to check for it.  Here is where that check
	 * exists.
	 */
	if ((loc_right < right_shadow) ||
				(fb_row >= 0 && loc_right == right_shadow)) {
	    if(vis_func) {
		for (i = left; i <= loc_right; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = left; i <= loc_right; i++) set_cs(rowp,i);
		set_min(left);	set_max(loc_right);
	    }

	    if (deeper) {
		if (hit_stone)
		    right_side(nrow,row,lblock_col,row,loc_right,
							left,loc_right,limits);
		else
		    right_side(nrow,cb_row,cb_col,row,loc_right,
							left,loc_right,limits);
	    }

	    /*
	     * The following line, setting hit_stone, is needed for those
	     * walls that are only 1 wide.  If hit stone is *not* set and
	     * the stone is only one wide, then the close block is the old
	     * one instead one on the current row.  A way around having to
	     * set it here is to make left = loc_right (not loc_right+1) and
	     * let the outer loop take care of it.  However, if we do that
	     * then we then have to check for boundary conditions here as
	     * well.
	     */
	    hit_stone = 1;

	    left = loc_right+1;
	}
	/*
	 * The opening extends beyond the right mark.  This means that
	 * the next far block is the current far block.
	 */
	else {
	    if(vis_func) {
		for (i=left; i <= right_shadow; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = left; i <= right_shadow; i++) set_cs(rowp,i);
		set_min(left);	set_max(right_shadow);
	    }

	    if (deeper) {
		if (hit_stone)
		    right_side(nrow,   row,lblock_col,fb_row,fb_col,
						     left,right_shadow,limits);
		else
		    right_side(nrow,cb_row,    cb_col,fb_row,fb_col,
						     left,right_shadow,limits);
	    }

	    return;	/* we're outta here */
	}
    }
}


/*
 * left_side()
 *
 * This routine is the mirror image of right_side().  Please see right_side()
 * for blow by blow comments.
 */
STATIC_OVL void
left_side(row, cb_row, cb_col, fb_row, fb_col, left_mark, right, limits)
    int row;		/* the current row */
    int	cb_row, cb_col;	/* close block row and col */
    int	fb_row, fb_col;	/* far block row and col */
    int	left_mark;	/* left mark of previous row */
    int right;		/* right mark of the previous row */
    char *limits;
{
    register int  i;
    register char *rowp;
    int  hit_stone = 0;
    int  left_shadow, right_shadow, loc_left;
    int  lblock_col;		/* local block column (current row) */
    int  nrow, deeper;
    char *row_min;		/* left most */
    char *row_max;		/* right most */
    int		  lim_min;

    nrow    = row + step;
    deeper  = good_row(nrow) && (!limits || (*limits >= *(limits+1)));
    if(!vis_func) {
	rowp    = cs_rows[row];
	row_min = &cs_left[row];
	row_max = &cs_right[row];
    }
    if(limits) {
	lim_min = start_col - *limits;
	if(lim_min < 0) lim_min = 0;
	if(left_mark < lim_min) left_mark = lim_min;
	limits++; /* prepare for next row */
    } else
	lim_min = 0;

    /* This value could be illegal. */
    right_shadow = close_shadow(FROM_LEFT,row,cb_row,cb_col);

    while ( right >= left_mark ) {
	loc_left = left_ptrs[row][right];
	if(loc_left < lim_min) loc_left = lim_min;
	if (viz_clear_rows[row][right]) {
	    if (loc_left <= right_shadow) {
		right = right_shadow;	/* opening ends beyond shadow */
		break;
	    }
	    right = loc_left;
	    loc_left = left_ptrs[row][right];
	    if(loc_left < lim_min) loc_left = lim_min;
	    if (right == loc_left) return;	/* boundary */
	}

	if (loc_left < left_mark)	/* can't see beyond the left mark */
	    loc_left = left_mark;

	if(vis_func) {
	    for (i = loc_left; i <= right; i++) (*vis_func)(i, row, varg);
	} else {
	    for (i = loc_left; i <= right; i++) set_cs(rowp,i);
	    set_min(loc_left);	set_max(right);
	}

	if (loc_left == left_mark) return;	/* all stone */
	if (loc_left <= right_shadow) hit_stone = 1;
	right = loc_left - 1;
    }

    /* At first visible clear spot on or beyond the right shadow. */

    if ((left_shadow = far_shadow(FROM_LEFT,row,fb_row,fb_col)) < 0)
	left_shadow = 0;

    /* Do vertical walls as we want. */
    if (left_shadow > fb_col && !viz_clear_rows[row][fb_col])
	left_shadow = fb_col;
    if(left_shadow < lim_min) left_shadow = lim_min;

    while (right >= left_mark) {
	loc_left = left_ptrs[row][right];

	if (!viz_clear_rows[row][right]) {
	    hit_stone = 1;	/* use stone on this row as close block */

	    /* We can only see walls until the left mark */
	    if (loc_left < left_mark) loc_left = left_mark;

	    if(vis_func) {
		for (i = loc_left; i <= right; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = loc_left; i <= right; i++) set_cs(rowp,i);
		set_min(loc_left);	set_max(right);
	    }

	    if (loc_left == left_mark) return;	/* hit end */
	    right = loc_left - 1;
	    loc_left = left_ptrs[row][right];
	    if (loc_left < lim_min) loc_left = lim_min;
	    /* fall through...*/
	}

	/* We are in an opening. */
	if (hit_stone) {
	    lblock_col = right+1;	/* stone block (local) */
	    right = close_shadow(FROM_LEFT,row,row,lblock_col);
	    if (right < lim_min) return;	/* off the end */
	}

	/*  Check if the shadow covers the opening. */
	if (right <= loc_left) {
	    /*  Make a boundary condition work. */
	    if (loc_left == lim_min) {	/* at boundary */
		if (right == lim_min) {
		    if(vis_func) (*vis_func)(lim_min, row, varg);
		    else {
			set_cs(rowp,lim_min);	/* caught the last pos */
			set_min(lim_min);
		    }
		}
		return;			/* and break out the loop */
	    }

	    right = loc_left;
	    continue;
	}

	/* If the far wall of the opening is closer than the shadow limit. */
	if ((loc_left > left_shadow) ||
				    (fb_row >= 0 && loc_left == left_shadow)) {
	    if(vis_func) {
		for (i = loc_left; i <= right; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = loc_left; i <= right; i++) set_cs(rowp,i);
		set_min(loc_left);	set_max(right);
	    }

	    if (deeper) {
		if (hit_stone)
		    left_side(nrow,row,lblock_col,row,loc_left,
							loc_left,right,limits);
		else
		    left_side(nrow,cb_row,cb_col,row,loc_left,
							loc_left,right,limits);
	    }

	    hit_stone = 1;	/* needed for walls of width 1 */
	    right = loc_left-1;
	}
	/*  The opening extends beyond the left mark. */
	else {
	    if(vis_func) {
		for (i=left_shadow; i <= right; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = left_shadow; i <= right; i++) set_cs(rowp,i);
		set_min(left_shadow);	set_max(right);
	    }

	    if (deeper) {
		if (hit_stone)
		    left_side(nrow,row,lblock_col,fb_row,fb_col,
						     left_shadow,right,limits);
		else
		    left_side(nrow,cb_row,cb_col,fb_row,fb_col,
						     left_shadow,right,limits);
	    }

	    return;	/* we're outta here */
	}

    }
}

/*
 * view_from
 *
 * Calculate a view from the given location.  Initialize and fill a
 * ROWNOxCOLNO array (could_see) with all the locations that could be
 * seen from the source location.  Initialize and fill the left most
 * and right most boundaries of what could be seen.
 */
STATIC_OVL void
view_from(srow,scol,loc_cs_rows,left_most,right_most, range, func, arg)
    int  srow, scol;			/* source row and column */
    char **loc_cs_rows;			/* could_see array (row pointers) */
    char *left_most, *right_most;	/* limits of what could be seen */
    int range;		/* 0 if unlimited */
    void FDECL((*func), (int,int,genericptr_t));
    genericptr_t arg;
{
    register int i;
    char	 *rowp;
    int		 nrow, left, right, left_row, right_row;
    char	 *limits;

    /* Set globals for near_shadow(), far_shadow(), etc. to use. */
    start_col = scol;
    start_row = srow;
    cs_rows   = loc_cs_rows;
    cs_left   = left_most;
    cs_right  = right_most;
    vis_func = func;
    varg = arg;

    /*  Find the left and right limits of sight on the starting row. */
    if (viz_clear_rows[srow][scol]) {
	left  = left_ptrs[srow][scol];
	right = right_ptrs[srow][scol];
    } else {
	left  = (!scol) ? 0 :
	    (viz_clear_rows[srow][scol-1] ?  left_ptrs[srow][scol-1] : scol-1);
	right = (scol == COLNO-1) ? COLNO-1 :
	    (viz_clear_rows[srow][scol+1] ? right_ptrs[srow][scol+1] : scol+1);
    }

    if(range) {
	if(range > MAX_RADIUS || range < 1)
	    panic("view_from called with range %d", range);
	limits = circle_ptr(range) + 1; /* start at next row */
	if(left < scol - range) left = scol - range;
	if(right > scol + range) right = scol + range;
    } else
	limits = (char*) 0;

    if(func) {
	for (i = left; i <= right; i++) (*func)(i, srow, arg);
    } else {
	/* Row optimization */
	rowp = cs_rows[srow];

	/* We know that we can see our row. */
	for (i = left; i <= right; i++) set_cs(rowp,i);
	cs_left[srow]  = left;
	cs_right[srow] = right;
    }

    /* The far block has a row number of -1 if we are on an edge. */
    right_row = (right == COLNO-1) ? -1 : srow;
    left_row  = (!left)		   ? -1 : srow;

    /*
     *  Check what could be seen in quadrants.
     */
    if ( (nrow = srow+1) < ROWNO ) {
	step =  1;	/* move down */
	if (scol<COLNO-1)
	    right_side(nrow,-1,scol,right_row,right,scol,right,limits);
	if (scol)
	    left_side(nrow,-1,scol,left_row, left, left, scol,limits);
    }

    if ( (nrow = srow-1) >= 0 ) {
	step = -1;	/* move up */
	if (scol<COLNO-1)
	    right_side(nrow,-1,scol,right_row,right,scol,right,limits);
	if (scol)
	    left_side(nrow,-1,scol,left_row, left, left, scol,limits);
    }
}


#else	/*===== End of algorithm D =====*/


/*===========================================================================*\
			    GENERAL LINE OF SIGHT
				Algorithm C
\*===========================================================================*/

/*
 * Defines local to Algorithm C.
 */
STATIC_DCL void FDECL(right_side, (int,int,int,char*));
STATIC_DCL void FDECL(left_side, (int,int,int,char*));

/* Initialize algorithm C (nothing). */
STATIC_OVL void
view_init()
{
}

/*
 * Mark positions as visible on one quadrant of the right side.  The
 * quadrant is determined by the value of the global variable step.
 */
STATIC_OVL void
right_side(row, left, right_mark, limits)
    int row;		/* current row */
    int left;		/* first (left side) visible spot on prev row */
    int right_mark;	/* last (right side) visible spot on prev row */
    char *limits;	/* points at range limit for current row, or NULL */
{
    int		  right;	/* right limit of "could see" */
    int		  right_edge;	/* right edge of an opening */
    int		  nrow;		/* new row (calculate once) */
    int		  deeper;	/* if TRUE, call self as needed */
    int		  result;	/* set by q?_path() */
    register int  i;		/* loop counter */
    register char *rowp;	/* row optimization */
    char	  *row_min;	/* left most  [used by macro set_min()] */
    char	  *row_max;	/* right most [used by macro set_max()] */
    int		  lim_max;	/* right most limit of circle */

#ifdef GCC_WARN
    rowp = row_min = row_max = 0;
#endif
    nrow    = row + step;
    /*
     * Can go deeper if the row is in bounds and the next row is within
     * the circle's limit.  We tell the latter by checking to see if the next
     * limit value is the start of a new circle radius (meaning we depend
     * on the structure of circle_data[]).
     */
    deeper  = good_row(nrow) && (!limits || (*limits >= *(limits+1)));
    if(!vis_func) {
	rowp    = cs_rows[row];	/* optimization */
	row_min = &cs_left[row];
	row_max = &cs_right[row];
    }
    if(limits) {
	lim_max = start_col + *limits;
	if(lim_max > COLNO-1) lim_max = COLNO-1;
	if(right_mark > lim_max) right_mark = lim_max;
	limits++; /* prepare for next row */
    } else
	lim_max = COLNO-1;

    while (left <= right_mark) {
	right_edge = right_ptrs[row][left];
	if(right_edge > lim_max) right_edge = lim_max;

	if (!is_clear(row,left)) {
	    /*
	     * Jump to the far side of a stone wall.  We can set all
	     * the points in between as seen.
	     *
	     * If the right edge goes beyond the right mark, check to see
	     * how much we can see.
	     */
	    if (right_edge > right_mark) {
		/*
		 * If the mark on the previous row was a clear position,
		 * the odds are that we can actually see part of the wall
		 * beyond the mark on this row.  If so, then see one beyond
		 * the mark.  Otherwise don't.  This is a kludge so corners
		 * with an adjacent doorway show up in nethack.
		 */
		right_edge = is_clear(row-step,right_mark) ?
						    right_mark+1 : right_mark;
	    }
	    if(vis_func) {
		for (i = left; i <= right_edge; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = left; i <= right_edge; i++) set_cs(rowp,i);
		set_min(left);      set_max(right_edge);
	    }
	    left = right_edge + 1; /* no limit check necessary */
	    continue;
	}

	/* No checking needed if our left side is the start column. */
	if (left != start_col) {
	    /*
	     * Find the left side.  Move right until we can see it or we run
	     * into a wall.
	     */
	    for (; left <= right_edge; left++) {
		if (step < 0) {
		    q1_path(start_row,start_col,row,left,rside1);
		} else {
		    q4_path(start_row,start_col,row,left,rside1);
		}
rside1:					/* used if q?_path() is a macro */
		if (result) break;
	    }

	    /*
	     * Check for boundary conditions.  We *need* check (2) to break
	     * an infinite loop where:
	     *
	     *		left == right_edge == right_mark == lim_max.
	     *
	     */
	    if (left > lim_max) return;	/* check (1) */
	    if (left == lim_max) {	/* check (2) */
		if(vis_func) (*vis_func)(lim_max, row, varg);
		else {
		    set_cs(rowp,lim_max);
		    set_max(lim_max);
		}
		return;
	    }
	    /*
	     * Check if we can see any spots in the opening.  We might
	     * (left == right_edge) or might not (left == right_edge+1) have
	     * been able to see the far wall.  Make sure we *can* see the
	     * wall (remember, we can see the spot above/below this one)
	     * by backing up.
	     */
	    if (left >= right_edge) {
		left = right_edge;	/* for the case left == right_edge+1 */
		continue;
	    }
	}

	/*
	 * Find the right side.  If the marker from the previous row is
	 * closer than the edge on this row, then we have to check
	 * how far we can see around the corner (under the overhang).  Stop
	 * at the first non-visible spot or we actually hit the far wall.
	 *
	 * Otherwise, we know we can see the right edge of the current row.
	 *
	 * This must be a strict less than so that we can always see a
	 * horizontal wall, even if it is adjacent to us.
	 */
	if (right_mark < right_edge) {
	    for (right = right_mark; right <= right_edge; right++) {
		if (step < 0) {
		    q1_path(start_row,start_col,row,right,rside2);
		} else {
		    q4_path(start_row,start_col,row,right,rside2);
		}
rside2:					/* used if q?_path() is a macro */
		if (!result) break;
	    }
	    --right;	/* get rid of the last increment */
	}
	else
	    right = right_edge;

	/*
	 * We have the range that we want.  Set the bits.  Note that
	 * there is no else --- we no longer handle splinters.
	 */
	if (left <= right) {
	    /*
	     * An ugly special case.  If you are adjacent to a vertical wall
	     * and it has a break in it, then the right mark is set to be
	     * start_col.  We *want* to be able to see adjacent vertical
	     * walls, so we have to set it back.
	     */
	    if (left == right && left == start_col &&
			start_col < (COLNO-1) && !is_clear(row,start_col+1))
		right = start_col+1;

	    if(right > lim_max) right = lim_max;
	    /* set the bits */
	    if(vis_func)
		for (i = left; i <= right; i++) (*vis_func)(i, row, varg);
	    else {
		for (i = left; i <= right; i++) set_cs(rowp,i);
		set_min(left);      set_max(right);
	    }

	    /* recursive call for next finger of light */
	    if (deeper) right_side(nrow,left,right,limits);
	    left = right + 1; /* no limit check necessary */
	}
    }
}


/*
 * This routine is the mirror image of right_side().  See right_side() for
 * extensive comments.
 */
STATIC_OVL void
left_side(row, left_mark, right, limits)
    int row, left_mark, right;
    char *limits;
{
    int		  left, left_edge, nrow, deeper, result;
    register int  i;
    register char *rowp;
    char	  *row_min, *row_max;
    int		  lim_min;

#ifdef GCC_WARN
    rowp = row_min = row_max = 0;
#endif
    nrow    = row+step;
    deeper  = good_row(nrow) && (!limits || (*limits >= *(limits+1)));
    if(!vis_func) {
	rowp    = cs_rows[row];
	row_min = &cs_left[row];
	row_max = &cs_right[row];
    }
    if(limits) {
	lim_min = start_col - *limits;
	if(lim_min < 0) lim_min = 0;
	if(left_mark < lim_min) left_mark = lim_min;
	limits++; /* prepare for next row */
    } else
	lim_min = 0;

    while (right >= left_mark) {
	left_edge = left_ptrs[row][right];
	if(left_edge < lim_min) left_edge = lim_min;

	if (!is_clear(row,right)) {
	    /* Jump to the far side of a stone wall. */
	    if (left_edge < left_mark) {
		/* Maybe see more (kludge). */
		left_edge = is_clear(row-step,left_mark) ?
						    left_mark-1 : left_mark;
	    }
	    if(vis_func) {
		for (i = left_edge; i <= right; i++) (*vis_func)(i, row, varg);
	    } else {
		for (i = left_edge; i <= right; i++) set_cs(rowp,i);
		set_min(left_edge); set_max(right);
	    }
	    right = left_edge - 1; /* no limit check necessary */
	    continue;
	}

	if (right != start_col) {
	    /* Find the right side. */
	    for (; right >= left_edge; right--) {
		if (step < 0) {
		    q2_path(start_row,start_col,row,right,lside1);
		} else {
		    q3_path(start_row,start_col,row,right,lside1);
		}
lside1:					/* used if q?_path() is a macro */
		if (result) break;
	    }

	    /* Check for boundary conditions. */
	    if (right < lim_min) return;
	    if (right == lim_min) {
		if(vis_func) (*vis_func)(lim_min, row, varg);
		else {
		    set_cs(rowp,lim_min);
		    set_min(lim_min);
		}
		return;
	    }
	    /* Check if we can see any spots in the opening. */
	    if (right <= left_edge) {
		right = left_edge;
		continue;
	    }
	}

	/* Find the left side. */
	if (left_mark > left_edge) {
	    for (left = left_mark; left >= left_edge; --left) {
		if (step < 0) {
		    q2_path(start_row,start_col,row,left,lside2);
		} else {
		    q3_path(start_row,start_col,row,left,lside2);
		}
lside2:					/* used if q?_path() is a macro */
		if (!result) break;
	    }
	    left++;	/* get rid of the last decrement */
	}
	else
	    left = left_edge;

	if (left <= right) {
	    /* An ugly special case. */
	    if (left == right && right == start_col &&
			    start_col > 0 && !is_clear(row,start_col-1))
		left = start_col-1;

	    if(left < lim_min) left = lim_min;
	    if(vis_func)
		for (i = left; i <= right; i++) (*vis_func)(i, row, varg);
	    else {
		for (i = left; i <= right; i++) set_cs(rowp,i);
		set_min(left);      set_max(right);
	    }

	    /* Recurse */
	    if (deeper) left_side(nrow,left,right,limits);
	    right = left - 1; /* no limit check necessary */
	}
    }
}


/*
 * Calculate all possible visible locations from the given location
 * (srow,scol).  NOTE this is (y,x)!  Mark the visible locations in the
 * array provided.
 */
STATIC_OVL void
view_from(srow, scol, loc_cs_rows, left_most, right_most, range, func, arg)
    int  srow, scol;	/* starting row and column */
    char **loc_cs_rows;	/* pointers to the rows of the could_see array */
    char *left_most;	/* min mark on each row */
    char *right_most;	/* max mark on each row */
    int range;		/* 0 if unlimited */
    void FDECL((*func), (int,int,genericptr_t));
    genericptr_t arg;
{
    register int i;		/* loop counter */
    char         *rowp;		/* optimization for setting could_see */
    int		 nrow;		/* the next row */
    int		 left;		/* the left-most visible column */
    int		 right;		/* the right-most visible column */
    char	 *limits;	/* range limit for next row */

    /* Set globals for q?_path(), left_side(), and right_side() to use. */
    start_col = scol;
    start_row = srow;
    cs_rows   = loc_cs_rows;	/* 'could see' rows */
    cs_left   = left_most;
    cs_right  = right_most;
    vis_func = func;
    varg = arg;

    /*
     * Determine extent of sight on the starting row.
     */
    if (is_clear(srow,scol)) {
	left =  left_ptrs[srow][scol];
	right = right_ptrs[srow][scol];
    } else {
	/*
	 * When in stone, you can only see your adjacent squares, unless
	 * you are on an array boundary or a stone/clear boundary.
	 */
	left  = (!scol) ? 0 :
		(is_clear(srow,scol-1) ? left_ptrs[srow][scol-1] : scol-1);
	right = (scol == COLNO-1) ? COLNO-1 :
		(is_clear(srow,scol+1) ? right_ptrs[srow][scol+1] : scol+1);
    }

    if(range) {
	if(range > MAX_RADIUS || range < 1)
	    panic("view_from called with range %d", range);
	limits = circle_ptr(range) + 1; /* start at next row */
	if(left < scol - range) left = scol - range;
	if(right > scol + range) right = scol + range;
    } else
	limits = (char*) 0;

    if(func) {
	for (i = left; i <= right; i++) (*func)(i, srow, arg);
    } else {
	/* Row pointer optimization. */
	rowp = cs_rows[srow];

	/* We know that we can see our row. */
	for (i = left; i <= right; i++) set_cs(rowp,i);
	cs_left[srow]  = left;
	cs_right[srow] = right;
    }

    /*
     * Check what could be seen in quadrants.  We need to check for valid
     * rows here, since we don't do it in the routines right_side() and
     * left_side() [ugliness to remove extra routine calls].
     */
    if ( (nrow = srow+1) < ROWNO ) {	/* move down */
	step =  1;
	if (scol < COLNO-1) right_side(nrow, scol, right, limits);
	if (scol)	    left_side (nrow, left,  scol, limits);
    }

    if ( (nrow = srow-1) >= 0 ) {	/* move up */
	step = -1;
	if (scol < COLNO-1) right_side(nrow, scol, right, limits);
	if (scol)	    left_side (nrow, left,  scol, limits);
    }
}

#endif	/*===== End of algorithm C =====*/

/*
 * AREA OF EFFECT "ENGINE"
 *
 * Calculate all possible visible locations as viewed from the given location
 * (srow,scol) within the range specified. Perform "func" with (x, y) args and
 * additional argument "arg" for each square.
 *
 * If not centered on the hero, just forward arguments to view_from(); it
 * will call "func" when necessary.  If the hero is the center, use the
 * vision matrix and reduce extra work.
 */
void
do_clear_area(scol,srow,range,func,arg)
    int scol, srow, range;
    void FDECL((*func), (int,int,genericptr_t));
    genericptr_t arg;
{
	/* If not centered on hero, do the hard work of figuring the area */
	if (scol != u.ux || srow != u.uy)
	    view_from(srow, scol, (char **)0, (char *)0, (char *)0,
							range, func, arg);
	else {
	    register int x;
	    int y, min_x, max_x, max_y, offset;
	    char *limits;

	    if (range > MAX_RADIUS || range < 1)
		panic("do_clear_area:  illegal range %d", range);
	    if(vision_full_recalc)
		vision_recalc(0);	/* recalc vision if dirty */
	    limits = circle_ptr(range);
	    if ((max_y = (srow + range)) >= ROWNO) max_y = ROWNO-1;
	    if ((y = (srow - range)) < 0) y = 0;
	    for (; y <= max_y; y++) {
		offset = limits[v_abs(y-srow)];
		if((min_x = (scol - offset)) < 0) min_x = 0;
		if((max_x = (scol + offset)) >= COLNO) max_x = COLNO-1;
		for (x = min_x; x <= max_x; x++)
		    if (couldsee(x, y))
			(*func)(x, y, arg);
	    }
	}
}

/*vision.c*/
