/*	$OpenBSD: display.c,v 1.6 2001/05/24 03:05:22 mickey Exp $	*/

/*
 * The functions in this file handle redisplay. The
 * redisplay system knows almost nothing about the editing
 * process; the editing functions do, however, set some
 * hints to eliminate a lot of the grinding. There is more
 * that can be done; the "vtputc" interface is a real
 * pig. Two conditional compilation flags; the GOSLING
 * flag enables dynamic programming redisplay, using the
 * algorithm published by Jim Gosling in SIGOA. The MEMMAP
 * changes things around for memory mapped video. With
 * both off, the terminal is a VT52.
 */
#include	"def.h"
#include	"kbd.h"

/*
 * You can change these back to the types
 * implied by the name if you get tight for space. If you
 * make both of them "int" you get better code on the VAX.
 * They do nothing if this is not Gosling redisplay, except
 * for change the size of a structure that isn't used.
 * A bit of a cheat.
 */
/* These defines really belong in sysdef.h */
#ifndef XCHAR
#define	XCHAR	int
#define	XSHORT	int
#endif

#ifdef	STANDOUT_GLITCH
#include <term.h>
#endif

/*
 * A video structure always holds
 * an array of characters whose length is equal to
 * the longest line possible. Only some of this is
 * used if "ncol" isn't the same as "NCOL".
 */
typedef struct {
	short	v_hash;		/* Hash code, for compares.	 */
	short	v_flag;		/* Flag word.			 */
	short	v_color;	/* Color of the line.		 */
	XSHORT	v_cost;		/* Cost of display.		 */
	char	v_text[NCOL];	/* The actual characters.	 */
} VIDEO;

#define VFCHG	0x0001			/* Changed.			 */
#define VFHBAD	0x0002			/* Hash and cost are bad.	 */
#define VFEXT	0x0004			/* extended line (beond ncol)	 */

/*
 * SCORE structures hold the optimal
 * trace trajectory, and the cost of redisplay, when
 * the dynamic programming redisplay code is used.
 * If no fancy redisplay, this isn't used. The trace index
 * fields can be "char", and the score a "short", but
 * this makes the code worse on the VAX.
 */
typedef struct {
	XCHAR	s_itrace;	/* "i" index for track back.	 */
	XCHAR	s_jtrace;	/* "j" index for trace back.	 */
	XSHORT	s_cost;		/* Display cost.		 */
} SCORE;


void	vtmove __P((int, int));
void	vtputc __P((int));
void	vtpute __P((int));
int	vtputs __P((char *));
void	vteeol __P((void));
void	updext __P((int, int));
void	modeline __P((MGWIN *));
void	setscores __P((int, int));
void	traceback __P((int, int, int, int));
void	ucopy __P((VIDEO *, VIDEO *));
void	uline __P((int, VIDEO *, VIDEO *));
void	hash __P((VIDEO *));


int	sgarbf = TRUE;		/* TRUE if screen is garbage.	 */
int	vtrow = 0;		/* Virtual cursor row.		 */
int	vtcol = 0;		/* Virtual cursor column.	 */
int	tthue = CNONE;		/* Current color.		 */
int	ttrow = HUGE;		/* Physical cursor row.		 */
int	ttcol = HUGE;		/* Physical cursor column.	 */
int	tttop = HUGE;		/* Top of scroll region.	 */
int	ttbot = HUGE;		/* Bottom of scroll region.	 */
int	lbound = 0;		/* leftmost bound of the current line */
					/* being displayed		 */

VIDEO	*vscreen[NROW - 1];	/* Edge vector, virtual.	 */
VIDEO	*pscreen[NROW - 1];	/* Edge vector, physical.	 */
VIDEO	video[2 * (NROW - 1)];	/* Actual screen data.		 */
VIDEO	blanks;			/* Blank line image.		 */

#ifdef	GOSLING
/*
 * This matrix is written as an array because
 * we do funny things in the "setscores" routine, which
 * is very compute intensive, to make the subscripts go away.
 * It would be "SCORE	score[NROW][NROW]" in old speak.
 * Look at "setscores" to understand what is up.
 */
SCORE score[NROW * NROW];
#endif

/*
 * Initialize the data structures used
 * by the display code. The edge vectors used
 * to access the screens are set up. The operating
 * system's terminal I/O channel is set up. Fill the
 * "blanks" array with ASCII blanks. The rest is done
 * at compile time. The original window is marked
 * as needing full update, and the physical screen
 * is marked as garbage, so all the right stuff happens
 * on the first call to redisplay.
 */
void
vtinit()
{
	VIDEO	*vp;
	int	i;

	ttopen();
	ttinit();
	vp = &video[0];
	for (i = 0; i < NROW - 1; ++i) {
		vscreen[i] = vp;
		++vp;
		pscreen[i] = vp;
		++vp;
	}
	blanks.v_color = CTEXT;
	for (i = 0; i < NCOL; ++i)
		blanks.v_text[i] = ' ';
}

/*
 * Tidy up the virtual display system
 * in anticipation of a return back to the host
 * operating system. Right now all we do is position
 * the cursor to the last line, erase the line, and
 * close the terminal channel.
 */
void
vttidy()
{

	ttcolor(CTEXT);
	ttnowindow();		/* No scroll window.	 */
	ttmove(nrow - 1, 0);	/* Echo line.		 */
	tteeol();
	tttidy();
	ttflush();
	ttclose();
}

/*
 * Move the virtual cursor to an origin
 * 0 spot on the virtual display screen. I could
 * store the column as a character pointer to the spot
 * on the line, which would make "vtputc" a little bit
 * more efficient. No checking for errors.
 */
void
vtmove(row, col)
	int row, col;
{

	vtrow = row;
	vtcol = col;
}

/*
 * Write a character to the virtual display,
 * dealing with long lines and the display of unprintable
 * things like control characters. Also expand tabs every 8
 * columns. This code only puts printing characters into
 * the virtual display image. Special care must be taken when
 * expanding tabs. On a screen whose width is not a multiple
 * of 8, it is possible for the virtual cursor to hit the
 * right margin before the next tab stop is reached. This
 * makes the tab code loop if you are not careful.
 * Three guesses how we found this.
 */
void
vtputc(c)
	int	c;
{
	VIDEO	*vp;

	vp = vscreen[vtrow];
	if (vtcol >= ncol)
		vp->v_text[ncol - 1] = '$';
	else if (c == '\t'
#ifdef	NOTAB
		 && !(curbp->b_flag & BFNOTAB)
#endif
		) {
		do {
			vtputc(' ');
		} while (vtcol < ncol && (vtcol & 0x07) != 0);
	} else if (ISCTRL(c)) {
		vtputc('^');
		vtputc(CCHR(c));
	} else
		vp->v_text[vtcol++] = c;
}

/*
 * Put a character to the virtual screen in an extended line.  If we are not
 * yet on left edge, don't print it yet.  Check for overflow on the right
 * margin.
 */
void
vtpute(c)
	int	c;
{
	VIDEO *vp;

	vp = vscreen[vtrow];

	if (vtcol >= ncol)
		vp->v_text[ncol - 1] = '$';
	else if (c == '\t'
#ifdef	NOTAB
		 && !(curbp->b_flag & BFNOTAB)
#endif
		) {
		do {
			vtpute(' ');
		}
		while (((vtcol + lbound) & 0x07) != 0 && vtcol < ncol);
	} else if (ISCTRL(c) != FALSE) {
		vtpute('^');
		vtpute(CCHR(c));
	} else {
		if (vtcol >= 0)
			vp->v_text[vtcol] = c;
		++vtcol;
	}
}

/*
 * Erase from the end of the software cursor to the end of the line on which
 * the software cursor is located. The display routines will decide if a
 * hardware erase to end of line command should be used to display this.
 */
void
vteeol()
{
	VIDEO *vp;

	vp = vscreen[vtrow];
	while (vtcol < ncol)
		vp->v_text[vtcol++] = ' ';
}

/*
 * Make sure that the display is
 * right. This is a three part process. First,
 * scan through all of the windows looking for dirty
 * ones. Check the framing, and refresh the screen.
 * Second, make sure that "currow" and "curcol" are
 * correct for the current window. Third, make the
 * virtual and physical screens the same.
 */
void
update()
{
	LINE	*lp;
	MGWIN	*wp;
	VIDEO	*vp1;
	VIDEO	*vp2;
	int	i, j;
	int	c;
	int	hflag;
	int	currow;
	int	curcol;
	int	offs;
	int	size;

	if (typeahead())
		return;
	if (sgarbf) {		/* must update everything */
		wp = wheadp;
		while (wp != NULL) {
			wp->w_flag |= WFMODE | WFHARD;
			wp = wp->w_wndp;
		}
	}
	hflag = FALSE;			/* Not hard.		 */
	wp = wheadp;
	while (wp != NULL) {
		if (wp->w_flag != 0) {	/* Need update.		 */
			if ((wp->w_flag & WFFORCE) == 0) {
				lp = wp->w_linep;
				for (i = 0; i < wp->w_ntrows; ++i) {
					if (lp == wp->w_dotp)
						goto out;
					if (lp == wp->w_bufp->b_linep)
						break;
					lp = lforw(lp);
				}
			}
			i = wp->w_force;	/* Reframe this one.	 */
			if (i > 0) {
				--i;
				if (i >= wp->w_ntrows)
					i = wp->w_ntrows - 1;
			} else if (i < 0) {
				i += wp->w_ntrows;
				if (i < 0)
					i = 0;
			} else
				i = wp->w_ntrows / 2;
			lp = wp->w_dotp;
			while (i != 0 && lback(lp) != wp->w_bufp->b_linep) {
				--i;
				lp = lback(lp);
			}
			wp->w_linep = lp;
			wp->w_flag |= WFHARD;	/* Force full.		 */
	out:
			lp = wp->w_linep;	/* Try reduced update.	 */
			i = wp->w_toprow;
			if ((wp->w_flag & ~WFMODE) == WFEDIT) {
				while (lp != wp->w_dotp) {
					++i;
					lp = lforw(lp);
				}
				vscreen[i]->v_color = CTEXT;
				vscreen[i]->v_flag |= (VFCHG | VFHBAD);
				vtmove(i, 0);
				for (j = 0; j < llength(lp); ++j)
					vtputc(lgetc(lp, j));
				vteeol();
			} else if ((wp->w_flag & (WFEDIT | WFHARD)) != 0) {
				hflag = TRUE;
				while (i < wp->w_toprow + wp->w_ntrows) {
					vscreen[i]->v_color = CTEXT;
					vscreen[i]->v_flag |= (VFCHG | VFHBAD);
					vtmove(i, 0);
					if (lp != wp->w_bufp->b_linep) {
						for (j = 0; j < llength(lp); ++j)
							vtputc(lgetc(lp, j));
						lp = lforw(lp);
					}
					vteeol();
					++i;
				}
			}
			if ((wp->w_flag & WFMODE) != 0)
				modeline(wp);
			wp->w_flag = 0;
			wp->w_force = 0;
		}
		wp = wp->w_wndp;
	}
	lp = curwp->w_linep;	/* Cursor location.	 */
	currow = curwp->w_toprow;
	while (lp != curwp->w_dotp) {
		++currow;
		lp = lforw(lp);
	}
	curcol = 0;
	i = 0;
	while (i < curwp->w_doto) {
		c = lgetc(lp, i++);
		if (c == '\t'
#ifdef	NOTAB
		    && !(curbp->b_flag & BFNOTAB)
#endif
			)
			curcol |= 0x07;
		else if (ISCTRL(c) != FALSE)
			++curcol;
		++curcol;
	}
	if (curcol >= ncol - 1) {	/* extended line. */
		/* flag we are extended and changed */
		vscreen[currow]->v_flag |= VFEXT | VFCHG;
		updext(currow, curcol);	/* and output extended line */
	} else
		lbound = 0;	/* not extended line */

	/*
	 * make sure no lines need to be de-extended because the cursor is no
	 * longer on them
	 */
	wp = wheadp;
	while (wp != NULL) {
		lp = wp->w_linep;
		i = wp->w_toprow;
		while (i < wp->w_toprow + wp->w_ntrows) {
			if (vscreen[i]->v_flag & VFEXT) {
				/* always flag extended lines as changed */
				vscreen[i]->v_flag |= VFCHG;
				if ((wp != curwp) || (lp != wp->w_dotp) ||
				    (curcol < ncol - 1)) {
					vtmove(i, 0);
					for (j = 0; j < llength(lp); ++j)
						vtputc(lgetc(lp, j));
					vteeol();
					/* this line no longer is extended */
					vscreen[i]->v_flag &= ~VFEXT;
				}
			}
			lp = lforw(lp);
			++i;
		}
		/* if garbaged then fix up mode lines */
		if (sgarbf != FALSE)
			vscreen[i]->v_flag |= VFCHG;
		/* and onward to the next window */
		wp = wp->w_wndp;
	}

	if (sgarbf != FALSE) {	/* Screen is garbage.	 */
		sgarbf = FALSE;	/* Erase-page clears	 */
		epresf = FALSE;	/* the message area.	 */
		tttop = HUGE;	/* Forget where you set */
		ttbot = HUGE;	/* scroll region.	 */
		tthue = CNONE;	/* Color unknown.	 */
		ttmove(0, 0);
		tteeop();
		for (i = 0; i < nrow - 1; ++i) {
			uline(i, vscreen[i], &blanks);
			ucopy(vscreen[i], pscreen[i]);
		}
		ttmove(currow, curcol - lbound);
		ttflush();
		return;
	}
#ifdef	GOSLING
	if (hflag != FALSE) {			/* Hard update?		*/
		for (i = 0; i < nrow - 1; ++i) {/* Compute hash data.	*/
			hash(vscreen[i]);
			hash(pscreen[i]);
		}
		offs = 0;			/* Get top match.	*/
		while (offs != nrow - 1) {
			vp1 = vscreen[offs];
			vp2 = pscreen[offs];
			if (vp1->v_color != vp2->v_color
			    || vp1->v_hash != vp2->v_hash)
				break;
			uline(offs, vp1, vp2);
			ucopy(vp1, vp2);
			++offs;
		}
		if (offs == nrow - 1) {		/* Might get it all.	*/
			ttmove(currow, curcol - lbound);
			ttflush();
			return;
		}
		size = nrow - 1;		/* Get bottom match.	*/
		while (size != offs) {
			vp1 = vscreen[size - 1];
			vp2 = pscreen[size - 1];
			if (vp1->v_color != vp2->v_color
			    || vp1->v_hash != vp2->v_hash)
				break;
			uline(size - 1, vp1, vp2);
			ucopy(vp1, vp2);
			--size;
		}
		if ((size -= offs) == 0)	/* Get screen size.	*/
			panic("Illegal screen size in update");
		setscores(offs, size);		/* Do hard update.	*/
		traceback(offs, size, size, size);
		for (i = 0; i < size; ++i)
			ucopy(vscreen[offs + i], pscreen[offs + i]);
		ttmove(currow, curcol - lbound);
		ttflush();
		return;
	}
#endif
	for (i = 0; i < nrow - 1; ++i) {	/* Easy update.		*/
		vp1 = vscreen[i];
		vp2 = pscreen[i];
		if ((vp1->v_flag & VFCHG) != 0) {
			uline(i, vp1, vp2);
			ucopy(vp1, vp2);
		}
	}
	ttmove(currow, curcol - lbound);
	ttflush();
}

/*
 * Update a saved copy of a line,
 * kept in a VIDEO structure. The "vvp" is
 * the one in the "vscreen". The "pvp" is the one
 * in the "pscreen". This is called to make the
 * virtual and physical screens the same when
 * display has done an update.
 */
void
ucopy(vvp, pvp)
	VIDEO *vvp;
	VIDEO *pvp;
{

	vvp->v_flag &= ~VFCHG;		/* Changes done.	 */
	pvp->v_flag = vvp->v_flag;	/* Update model.	 */
	pvp->v_hash = vvp->v_hash;
	pvp->v_cost = vvp->v_cost;
	pvp->v_color = vvp->v_color;
	bcopy(vvp->v_text, pvp->v_text, ncol);
}

/*
 * updext: update the extended line which the cursor is currently on at a
 * column greater than the terminal width. The line will be scrolled right or
 * left to let the user see where the cursor is
 */
void
updext(currow, curcol)
	int	currow, curcol;
{
	LINE	*lp;			/* pointer to current line */
	int	j;			/* index into line */

	/*
	 * calculate what column the left bound should be
	 * (force cursor into middle half of screen)
	 */
	lbound = curcol - (curcol % (ncol >> 1)) - (ncol >> 2);
	/*
	 * scan through the line outputing characters to the virtual screen
	 * once we reach the left edge
	 */
	vtmove(currow, -lbound);		/* start scanning offscreen */
	lp = curwp->w_dotp;			/* line to output */
	for (j = 0; j < llength(lp); ++j)	/* until the end-of-line */
		vtpute(lgetc(lp, j));
	vteeol();		/* truncate the virtual line */
	vscreen[currow]->v_text[0] = '$';	/* and put a '$' in column 1 */
}

/*
 * Update a single line. This routine only
 * uses basic functionality (no insert and delete character,
 * but erase to end of line). The "vvp" points at the VIDEO
 * structure for the line on the virtual screen, and the "pvp"
 * is the same for the physical screen. Avoid erase to end of
 * line when updating CMODE color lines, because of the way that
 * reverse video works on most terminals.
 */
void
uline(row, vvp, pvp)
	int	row;
	VIDEO	*vvp;
	VIDEO	*pvp;
{
#ifdef	MEMMAP
	putline(row + 1, 1, &vvp->v_text[0]);
#else
	char  *cp1;
	char  *cp2;
	char  *cp3;
	char  *cp4;
	char  *cp5;
	int	nbflag;

	if (vvp->v_color != pvp->v_color) {	/* Wrong color, do a	 */
		ttmove(row, 0);			/* full redraw.		 */
#ifdef	STANDOUT_GLITCH
		if (pvp->v_color != CTEXT && magic_cookie_glitch >= 0)
			tteeol();
#endif
		ttcolor(vvp->v_color);
#ifdef	STANDOUT_GLITCH
		cp1 = &vvp->v_text[magic_cookie_glitch > 0 ? magic_cookie_glitch : 0];
		/*
		 * the odd code for magic_cookie_glitch==0 is to avoid
		 * putting the invisable glitch character on the next line.
		 * (Hazeltine executive 80 model 30)
		 */
		cp2 = &vvp->v_text[ncol - (magic_cookie_glitch >= 0 ? (magic_cookie_glitch != 0 ? magic_cookie_glitch : 1) : 0)];
#else
		cp1 = &vvp->v_text[0];
		cp2 = &vvp->v_text[ncol];
#endif
		while (cp1 != cp2) {
			ttputc(*cp1++);
			++ttcol;
		}
#ifndef MOVE_STANDOUT
		ttcolor(CTEXT);
#endif
		return;
	}
	cp1 = &vvp->v_text[0];	/* Compute left match.	 */
	cp2 = &pvp->v_text[0];
	while (cp1 != &vvp->v_text[ncol] && cp1[0] == cp2[0]) {
		++cp1;
		++cp2;
	}
	if (cp1 == &vvp->v_text[ncol])	/* All equal.		 */
		return;
	nbflag = FALSE;
	cp3 = &vvp->v_text[ncol];	/* Compute right match. */
	cp4 = &pvp->v_text[ncol];
	while (cp3[-1] == cp4[-1]) {
		--cp3;
		--cp4;
		if (cp3[0] != ' ')	/* Note non-blanks in	 */
			nbflag = TRUE;	/* the right match.	 */
	}
	cp5 = cp3;			/* Is erase good?	 */
	if (nbflag == FALSE && vvp->v_color == CTEXT) {
		while (cp5 != cp1 && cp5[-1] == ' ')
			--cp5;
		/* Alcyon hack */
		if ((int) (cp3 - cp5) <= tceeol)
			cp5 = cp3;
	}
	/* Alcyon hack */
	ttmove(row, (int) (cp1 - &vvp->v_text[0]));
#ifdef	STANDOUT_GLITCH
	if (vvp->v_color != CTEXT && magic_cookie_glitch > 0) {
		if (cp1 < &vvp->v_text[magic_cookie_glitch])
			cp1 = &vvp->v_text[magic_cookie_glitch];
		if (cp5 > &vvp->v_text[ncol - magic_cookie_glitch])
			cp5 = &vvp->v_text[ncol - magic_cookie_glitch];
	} else if (magic_cookie_glitch < 0)
#endif
		ttcolor(vvp->v_color);
	while (cp1 != cp5) {
		ttputc(*cp1++);
		++ttcol;
	}
	if (cp5 != cp3)			/* Do erase.		 */
		tteeol();
#endif
}

/*
 * Redisplay the mode line for the window pointed to by the "wp".
 * This is the only routine that has any idea of how the modeline is
 * formatted. You can change the modeline format by hacking at this
 * routine. Called by "update" any time there is a dirty window.  Note
 * that if STANDOUT_GLITCH is defined, first and last magic_cookie_glitch
 * characters may never be seen.
 */
void
modeline(wp)
	MGWIN  *wp;
{
	int	n;
	BUFFER *bp;
	int	mode;

	n = wp->w_toprow + wp->w_ntrows;	/* Location.		 */
	vscreen[n]->v_color = CMODE;		/* Mode line color.	 */
	vscreen[n]->v_flag |= (VFCHG | VFHBAD);	/* Recompute, display.	 */
	vtmove(n, 0);				/* Seek to right line.	 */
	bp = wp->w_bufp;
	vtputc('-');
	vtputc('-');
	if ((bp->b_flag & BFCHG) != 0) {	/* "*" if changed.	 */
		vtputc('*');
		vtputc('*');
	} else {
		vtputc('-');
		vtputc('-');
	}
	vtputc('-');
	n = 5;
	n += vtputs("Mg: ");
	if (bp->b_bname[0] != '\0')
		n += vtputs(&(bp->b_bname[0]));
	while (n < 42) {		/* Pad out with blanks	 */
		vtputc(' ');
		++n;
	}
	vtputc('(');
	++n;
	for (mode = 0;;) {
		n += vtputs(bp->b_modes[mode]->p_name);
		if (++mode > bp->b_nmodes)
			break;
		vtputc('-');
		++n;
	}
	vtputc(')');
	++n;
	while (n < ncol) {		/* Pad out.		 */
		vtputc('-');
		++n;
	}
}
/*
 * output a string to the mode line, report how long it was.
 */
int
vtputs(s)
	char  *s;
{
	int	n = 0;

	while (*s != '\0') {
		vtputc(*s++);
		++n;
	}
	return n;
}

#ifdef	GOSLING
/*
 * Compute the hash code for the line pointed to by the "vp".
 * Recompute it if necessary. Also set the approximate redisplay
 * cost. The validity of the hash code is marked by a flag bit.
 * The cost understand the advantages of erase to end of line.
 * Tuned for the VAX by Bob McNamara; better than it used to be on
 * just about any machine.
 */
void
hash(vp)
	VIDEO *vp;
{
	int	i;
	int	n;
	char  *s;

	if ((vp->v_flag & VFHBAD) != 0) {	/* Hash bad.		 */
		s = &vp->v_text[ncol - 1];
		for (i = ncol; i != 0; --i, --s)
			if (*s != ' ')
				break;
		n = ncol - i;			/* Erase cheaper?	 */
		if (n > tceeol)
			n = tceeol;
		vp->v_cost = i + n;		/* Bytes + blanks.	 */
		for (n = 0; i != 0; --i, --s)
			n = (n << 5) + n + *s;
		vp->v_hash = n;			/* Hash code.		 */
		vp->v_flag &= ~VFHBAD;		/* Flag as all done.	 */
	}
}

/*
 * Compute the Insert-Delete
 * cost matrix. The dynamic programming algorithm
 * described by James Gosling is used. This code assumes
 * that the line above the echo line is the last line involved
 * in the scroll region. This is easy to arrange on the VT100
 * because of the scrolling region. The "offs" is the origin 0
 * offset of the first row in the virtual/physical screen that
 * is being updated; the "size" is the length of the chunk of
 * screen being updated. For a full screen update, use offs=0
 * and size=nrow-1.
 *
 * Older versions of this code implemented the score matrix by
 * a two dimensional array of SCORE nodes. This put all kinds of
 * multiply instructions in the code! This version is written to
 * use a linear array and pointers, and contains no multiplication
 * at all. The code has been carefully looked at on the VAX, with
 * only marginal checking on other machines for efficiency. In
 * fact, this has been tuned twice! Bob McNamara tuned it even
 * more for the VAX, which is a big issue for him because of
 * the 66 line X displays.
 *
 * On some machines, replacing the "for (i=1; i<=size; ++i)" with
 * i = 1; do { } while (++i <=size)" will make the code quite a
 * bit better; but it looks ugly.
 */
void
setscores(offs, size)
	int offs;
	int size;
{
	SCORE	*sp;
	SCORE	*sp1;
	int	tempcost;
	int	bestcost;
	int	j, i;
	VIDEO	**vp, **pp;
	VIDEO	**vbase, **pbase;

	vbase = &vscreen[offs - 1];	/* By hand CSE's.	 */
	pbase = &pscreen[offs - 1];
	score[0].s_itrace = 0;		/* [0, 0]		 */
	score[0].s_jtrace = 0;
	score[0].s_cost = 0;
	sp = &score[1];			/* Row 0, inserts.	 */
	tempcost = 0;
	vp = &vbase[1];
	for (j = 1; j <= size; ++j) {
		sp->s_itrace = 0;
		sp->s_jtrace = j - 1;
		tempcost += tcinsl;
		tempcost += (*vp)->v_cost;
		sp->s_cost = tempcost;
		++vp;
		++sp;
	}
	sp = &score[NROW];		/* Column 0, deletes.	 */
	tempcost = 0;
	for (i = 1; i <= size; ++i) {
		sp->s_itrace = i - 1;
		sp->s_jtrace = 0;
		tempcost += tcdell;
		sp->s_cost = tempcost;
		sp += NROW;
	}
	sp1 = &score[NROW + 1];		/* [1, 1].		 */
	pp = &pbase[1];
	for (i = 1; i <= size; ++i) {
		sp = sp1;
		vp = &vbase[1];
		for (j = 1; j <= size; ++j) {
			sp->s_itrace = i - 1;
			sp->s_jtrace = j;
			bestcost = (sp - NROW)->s_cost;
			if (j != size)	/* Cd(A[i])=0 @ Dis.	 */
				bestcost += tcdell;
			tempcost = (sp - 1)->s_cost;
			tempcost += (*vp)->v_cost;
			if (i != size)	/* Ci(B[j])=0 @ Dsj.	 */
				tempcost += tcinsl;
			if (tempcost < bestcost) {
				sp->s_itrace = i;
				sp->s_jtrace = j - 1;
				bestcost = tempcost;
			}
			tempcost = (sp - NROW - 1)->s_cost;
			if ((*pp)->v_color != (*vp)->v_color
			    || (*pp)->v_hash != (*vp)->v_hash)
				tempcost += (*vp)->v_cost;
			if (tempcost < bestcost) {
				sp->s_itrace = i - 1;
				sp->s_jtrace = j - 1;
				bestcost = tempcost;
			}
			sp->s_cost = bestcost;
			++sp;		/* Next column.		 */
			++vp;
		}
		++pp;
		sp1 += NROW;		/* Next row.		 */
	}
}

/*
 * Trace back through the dynamic programming cost
 * matrix, and update the screen using an optimal sequence
 * of redraws, insert lines, and delete lines. The "offs" is
 * the origin 0 offset of the chunk of the screen we are about to
 * update. The "i" and "j" are always started in the lower right
 * corner of the matrix, and imply the size of the screen.
 * A full screen traceback is called with offs=0 and i=j=nrow-1.
 * There is some do-it-yourself double subscripting here,
 * which is acceptable because this routine is much less compute
 * intensive then the code that builds the score matrix!
 */
void
traceback(offs, size, i, j)
	int	offs;
	int	size;
	int	i;
	int	j;
{
	int	itrace;
	int	jtrace;
	int	k;
	int	ninsl;
	int	ndraw;
	int	ndell;

	if (i == 0 && j == 0)	/* End of update.	 */
		return;
	itrace = score[(NROW * i) + j].s_itrace;
	jtrace = score[(NROW * i) + j].s_jtrace;
	if (itrace == i) {	/* [i, j-1]		 */
		ninsl = 0;	/* Collect inserts.	 */
		if (i != size)
			ninsl = 1;
		ndraw = 1;
		while (itrace != 0 || jtrace != 0) {
			if (score[(NROW * itrace) + jtrace].s_itrace != itrace)
				break;
			jtrace = score[(NROW * itrace) + jtrace].s_jtrace;
			if (i != size)
				++ninsl;
			++ndraw;
		}
		traceback(offs, size, itrace, jtrace);
		if (ninsl != 0) {
			ttcolor(CTEXT);
			ttinsl(offs + j - ninsl, offs + size - 1, ninsl);
		}
		do {		/* B[j], A[j] blank.	 */
			k = offs + j - ndraw;
			uline(k, vscreen[k], &blanks);
		} while (--ndraw);
		return;
	}
	if (jtrace == j) {	/* [i-1, j]		 */
		ndell = 0;	/* Collect deletes.	 */
		if (j != size)
			ndell = 1;
		while (itrace != 0 || jtrace != 0) {
			if (score[(NROW * itrace) + jtrace].s_jtrace != jtrace)
				break;
			itrace = score[(NROW * itrace) + jtrace].s_itrace;
			if (j != size)
				++ndell;
		}
		if (ndell != 0) {
			ttcolor(CTEXT);
			ttdell(offs + i - ndell, offs + size - 1, ndell);
		}
		traceback(offs, size, itrace, jtrace);
		return;
	}
	traceback(offs, size, itrace, jtrace);
	k = offs + j - 1;
	uline(k, vscreen[k], pscreen[offs + i - 1]);
}
#endif