path: root/src/scroll.c

/* Calculate what line insertion or deletion to do, and do it

Copyright (C) 1985-1986, 1990, 1993-1994, 2001-2023 Free Software
Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */


#include <config.h>

#include "lisp.h"
#include "termchar.h"
#include "dispextern.h"
#include "frame.h"
#include "termhooks.h"

struct matrix_elt
  {
    /* Cost of outputting through this line
       if no insert/delete is done just above it.  */
    int writecost;
    /* Cost of outputting through this line
       if an insert is done just above it.  */
    int insertcost;
    /* Cost of outputting through this line
       if a delete is done just above it.  */
    int deletecost;
    /* Number of inserts so far in this run of inserts,
       for the cost in insertcost.  */
    int insertcount;
    /* Number of deletes so far in this run of deletes,
       for the cost in deletecost.  */
    int deletecount;
    /* Number of writes so far since the last insert
       or delete for the cost in writecost. */
    int writecount;
  };

static void do_direct_scrolling (struct frame *,
                                 struct glyph_matrix *,
                                 struct matrix_elt *,
                                 int, int);
static void do_scrolling (struct frame *,
                          struct glyph_matrix *,
                          struct matrix_elt *,
                          int, int);


/* Determine, in matrix[i,j], the cost of updating the first j old
   lines into the first i new lines using the general scrolling method.
   This involves using insert or delete somewhere if i != j.
   For each matrix elements, three kinds of costs are recorded:
   the smallest cost that ends with an insert, the smallest
   cost that ends with a delete, and the smallest cost that
   ends with neither one.  These are kept separate because
   on some terminals the cost of doing an insert varies
   depending on whether one was just done, etc.  */

/* draw_cost[VPOS] is the cost of outputting new line at VPOS.
   old_hash[VPOS] is the hash code of the old line at VPOS.
   new_hash[VPOS] is the hash code of the new line at VPOS.
   Note that these are not true frame vpos's, but relative
   to the place at which the first mismatch between old and
   new contents appears.  */

static void
calculate_scrolling (struct frame *frame,
		     /* matrix is of size window_size + 1 on each side.  */
		     struct matrix_elt *matrix,
		     int window_size, int lines_below,
		     int *draw_cost, unsigned *old_hash, unsigned *new_hash,
		     int free_at_end)
{
  int i, j;
  int frame_total_lines = FRAME_TOTAL_LINES (frame);
  struct matrix_elt *p, *p1;
  int cost, cost1;

  int lines_moved = window_size
    + (FRAME_SCROLL_REGION_OK (frame) ? 0 : lines_below);
  /* first_insert_cost[I] is the cost of doing the first insert-line
     at the i'th line of the lines we are considering,
     where I is origin 1 (as it is below).  */
  int *first_insert_cost
    = &FRAME_INSERT_COST (frame)[frame_total_lines - 1 - lines_moved];
  int *first_delete_cost
    = &FRAME_DELETE_COST (frame)[frame_total_lines - 1 - lines_moved];
  int *next_insert_cost
    = &FRAME_INSERTN_COST (frame)[frame_total_lines - 1 - lines_moved];
  int *next_delete_cost
    = &FRAME_DELETEN_COST (frame)[frame_total_lines - 1 - lines_moved];

  /* Discourage long scrolls on fast lines.
     Don't scroll nearly a full frame height unless it saves
     at least 1/4 second.  */
  int extra_cost
    = clip_to_bounds (1, baud_rate / (10 * 4) / frame_total_lines, INT_MAX / 2);

  /* initialize the top left corner of the matrix */
  matrix->writecost = 0;
  matrix->insertcost = SCROLL_INFINITY;
  matrix->deletecost = SCROLL_INFINITY;
  matrix->insertcount = 0;
  matrix->deletecount = 0;

  /* initialize the left edge of the matrix */
  cost = first_insert_cost[1] - next_insert_cost[1];
  for (i = 1; i <= window_size; i++)
    {
      p = matrix + i * (window_size + 1);
      cost += draw_cost[i] + next_insert_cost[i] + extra_cost;
      p->insertcost = cost;
      p->writecost = SCROLL_INFINITY;
      p->deletecost = SCROLL_INFINITY;
      p->insertcount = i;
      p->deletecount = 0;
    }

  /* initialize the top edge of the matrix */
  cost = first_delete_cost[1] - next_delete_cost[1];
  for (j = 1; j <= window_size; j++)
    {
      cost += next_delete_cost[j];
      matrix[j].deletecost = cost;
      matrix[j].writecost = SCROLL_INFINITY;
      matrix[j].insertcost = SCROLL_INFINITY;
      matrix[j].deletecount = j;
      matrix[j].insertcount = 0;
    }

  /* `i' represents the vpos among new frame contents.
     `j' represents the vpos among the old frame contents.  */
  p = matrix + window_size + 2;	/* matrix [1, 1] */
  for (i = 1; i <= window_size; i++, p++)
    for (j = 1; j <= window_size; j++, p++)
      {
	/* p contains the address of matrix [i, j] */

	/* First calculate the cost assuming we do
	   not insert or delete above this line.
	   That is, if we update through line i-1
	   based on old lines through j-1,
	   and then just change old line j to new line i.  */
	p1 = p - window_size - 2; /* matrix [i-1, j-1] */
	cost = p1->writecost;
	if (cost > p1->insertcost)
	  cost = p1->insertcost;
	if (cost > p1->deletecost)
	  cost = p1->deletecost;
	if (old_hash[j] != new_hash[i])
	  cost += draw_cost[i];
	p->writecost = cost;

	/* Calculate the cost if we do an insert-line
	   before outputting this line.
	   That is, we update through line i-1
	   based on old lines through j,
	   do an insert-line on line i,
	   and then output line i from scratch,
	   leaving old lines starting from j for reuse below.  */
	p1 = p - window_size - 1; /* matrix [i-1, j] */
	/* No need to think about doing a delete followed
	   immediately by an insert.  It cannot be as good
	   as not doing either of them.  */
	if (free_at_end == i)
	  {
	    cost = p1->writecost;
	    cost1 = p1->insertcost;
	  }
	else
	  {
	    cost = p1->writecost + first_insert_cost[i];
	    if (p1->insertcount > i)
	      emacs_abort ();
	    cost1 = p1->insertcost + next_insert_cost[i - p1->insertcount];
	  }
	p->insertcost = min (cost, cost1) + draw_cost[i] + extra_cost;
	p->insertcount = (cost < cost1) ? 1 : p1->insertcount + 1;
	if (p->insertcount > i)
	  emacs_abort ();

	/* Calculate the cost if we do a delete line after
	   outputting this line.
	   That is, we update through line i
	   based on old lines through j-1,
	   and throw away old line j.  */
	p1 = p - 1;		/* matrix [i, j-1] */
	/* No need to think about doing an insert followed
	   immediately by a delete.  */
	if (free_at_end == i)
	  {
	    cost = p1->writecost;
	    cost1 = p1->deletecost;
	  }
	else
	  {
	    cost = p1->writecost + first_delete_cost[i];
	    cost1 = p1->deletecost + next_delete_cost[i];
	  }
	p->deletecost = min (cost, cost1);
	p->deletecount = (cost < cost1) ? 1 : p1->deletecount + 1;
      }
}



/* Perform insert-lines and delete-lines operations on CURRENT_MATRIX
   according to the costs in MATRIX, using the general scrolling
   method that is used if the terminal does not support the setting of
   scroll windows (scroll_region_ok == 0).

   WINDOW_SIZE is the number of lines being considered for scrolling
   and UNCHANGED_AT_TOP is the vpos of the first line being
   considered.  These two arguments can specify any contiguous range
   of lines.  */

static void
do_scrolling (struct frame *frame, struct glyph_matrix *current_matrix,
              struct matrix_elt *matrix, int window_size,
              int unchanged_at_top)
{
  struct matrix_elt *p;
  int i, j, k;
  USE_SAFE_ALLOCA;

  /* True if we have set a terminal window with set_terminal_window.  */
  bool terminal_window_p = 0;

  /* A queue for line insertions to be done.  */
  struct queue { int count, pos; };
  struct queue *queue_start;
  SAFE_NALLOCA (queue_start, 1, current_matrix->nrows);
  struct queue *queue = queue_start;

  char *retained_p = SAFE_ALLOCA (window_size);
  int *copy_from;
  SAFE_NALLOCA (copy_from, 1, window_size);

  /* Zero means line is empty.  */
  memset (retained_p, 0, window_size * sizeof (char));
  for (k = 0; k < window_size; ++k)
    copy_from[k] = -1;

#ifdef GLYPH_DEBUG
# define CHECK_BOUNDS							\
  do									\
    {									\
      int ck;								\
      for (ck = 0; ck < window_size; ++ck)				\
	eassert (copy_from[ck] == -1					\
		 || (copy_from[ck] >= 0 && copy_from[ck] < window_size)); \
    }									\
  while (0);
#endif

  /* When j is advanced, this corresponds to deleted lines.
     When i is advanced, this corresponds to inserted lines.  */
  i = j = window_size;
  while (i > 0 || j > 0)
    {
      p = matrix + i * (window_size + 1) + j;

      if (p->insertcost < p->writecost && p->insertcost < p->deletecost)
	{
	  /* Insert should be done at vpos i-1, plus maybe some before.
	     Queue the screen operation to be performed.  */
	  queue->count = p->insertcount;
	  queue->pos = i + unchanged_at_top - p->insertcount;
	  ++queue;

	  /* By incrementing I, we leave room in the result rows
	     for the empty rows opened up.  */
	  i -= p->insertcount;
	}
      else if (p->deletecost < p->writecost)
	{
	  /* Old line at vpos j-1, and maybe some before it, should be
	     deleted.  By decrementing J, we skip some lines in the
	     temp_rows which is equivalent to omitting these lines in
	     the result rows, thus deleting them.  */
	  j -= p->deletecount;

	  /* Set the terminal window, if not done already.  */
 	  if (! terminal_window_p)
	    {
	      set_terminal_window (frame, window_size + unchanged_at_top);
	      terminal_window_p = 1;
	    }

	  /* Delete lines on the terminal.  */
	  ins_del_lines (frame, j + unchanged_at_top, - p->deletecount);
	}
      else
	{
	  /* Best thing done here is no insert or delete, i.e. a write.  */
	  --i, --j;
	  eassert (i >= 0 && i < window_size);
	  eassert (j >= 0 && j < window_size);
	  copy_from[i] = j;
	  retained_p[j] = 1;

#ifdef GLYPH_DEBUG
	  CHECK_BOUNDS;
#endif
	}
    }

  /* Now do all insertions queued above.  */
  if (queue > queue_start)
    {
      int next = -1;

      /* Set the terminal window if not yet done.  */
      if (!terminal_window_p)
	{
	  set_terminal_window (frame, window_size + unchanged_at_top);
	  terminal_window_p = 1;
	}

      do
	{
	  --queue;

	  /* Do the deletion on the terminal.  */
	  ins_del_lines (frame, queue->pos, queue->count);

	  /* All lines in the range deleted become empty in the glyph
	     matrix.  Assign to them glyph rows that are not retained.
	     K is the starting position of the deleted range relative
	     to the window we are working in.  */
	  k = queue->pos - unchanged_at_top;
	  for (j = 0; j < queue->count; ++j)
	    {
	      /* Find the next row not retained.  */
	      while (retained_p[++next])
		;

	      /* Record that this row is to be used for the empty
		 glyph row j.  */
	      copy_from[k + j] = next;
	    }
	}
      while (queue > queue_start);

    }

  for (k = 0; k < window_size; ++k)
    eassert (copy_from[k] >= 0 && copy_from[k] < window_size);

  /* Perform the row swizzling.  */
  mirrored_line_dance (current_matrix, unchanged_at_top, window_size,
		       copy_from, retained_p);

  /* Some sanity checks if GLYPH_DEBUG is defined.  */
  CHECK_MATRIX (current_matrix);

  if (terminal_window_p)
    set_terminal_window (frame, 0);
  SAFE_FREE ();
}


/* Determine, in matrix[i,j], the cost of updating the first j
   old lines into the first i new lines using the direct
   scrolling method.  When the old line and the new line have
   different hash codes, the calculated cost of updating old
   line j into new line i includes the cost of outputting new
   line i, and if i != j, the cost of outputting the old line j
   is also included, as a penalty for moving the line and then
   erasing it.  In addition, the cost of updating a sequence of
   lines with constant i - j includes the cost of scrolling the
   old lines into their new positions, unless i == j.  Scrolling
   is achieved by setting the screen window to avoid affecting
   other lines below, and inserting or deleting lines at the top
   of the scrolled region.  The cost of scrolling a sequence of
   lines includes the fixed cost of specifying a scroll region,
   plus a variable cost which can depend upon the number of lines
   involved and the distance by which they are scrolled, and an
   extra cost to discourage long scrolls.

   As reflected in the matrix, an insert or delete does not
   correspond directly to the insertion or deletion which is
   used in scrolling lines.  An insert means that the value of i
   has increased without a corresponding increase in the value
   of j.  A delete means that the value of j has increased
   without a corresponding increase in the value of i.  A write
   means that i and j are both increased by the same amount, and
   that the old lines will be moved to their new positions.

   An insert following a delete is allowed only if i > j.
   A delete following an insert is allowed only if i < j.
   These restrictions ensure that the new lines in an insert
   will always be blank as an effect of the neighboring writes.
   Thus the calculated cost of an insert is simply the cost of
   outputting the new line contents.  The direct cost of a
   delete is zero.  Inserts and deletes indirectly affect the
   total cost through their influence on subsequent writes. */

/* The vectors draw_cost, old_hash, and new_hash have the same
   meanings here as in calculate_scrolling, and old_draw_cost
   is the equivalent of draw_cost for the old line contents */

static void
calculate_direct_scrolling (struct frame *frame,
			    /* matrix is of size window_size + 1 on each side.  */
			    struct matrix_elt *matrix,
			    int window_size, int lines_below,
			    int *draw_cost, int *old_draw_cost,
			    unsigned *old_hash, unsigned *new_hash,
			    int free_at_end)
{
  int i, j;
  int frame_total_lines = FRAME_TOTAL_LINES (frame);
  struct matrix_elt *p, *p1;
  int cost, cost1, delta;

  /* first_insert_cost[-I] is the cost of doing the first insert-line
     at a position I lines above the bottom line in the scroll window. */
  int *first_insert_cost
    = &FRAME_INSERT_COST (frame)[frame_total_lines - 1];
  int *first_delete_cost
    = &FRAME_DELETE_COST (frame)[frame_total_lines - 1];
  int *next_insert_cost
    = &FRAME_INSERTN_COST (frame)[frame_total_lines - 1];
  int *next_delete_cost
    = &FRAME_DELETEN_COST (frame)[frame_total_lines - 1];

  int scroll_overhead;

  /* Discourage long scrolls on fast lines.
     Don't scroll nearly a full frame height unless it saves
     at least 1/4 second.  */
  int extra_cost
    = clip_to_bounds (1, baud_rate / (10 * 4) / frame_total_lines, INT_MAX / 2);

  /* Overhead of setting the scroll window, plus the extra
     cost of scrolling by a distance of one.  The extra cost is
     added once for consistency with the cost vectors */
  scroll_overhead
    = FRAME_SCROLL_REGION_COST (frame) + extra_cost;

  /* initialize the top left corner of the matrix */
  matrix->writecost = 0;
  matrix->insertcost = SCROLL_INFINITY;
  matrix->deletecost = SCROLL_INFINITY;
  matrix->writecount = 0;
  matrix->insertcount = 0;
  matrix->deletecount = 0;

  /* initialize the left edge of the matrix */
  cost = 0;
  for (i = 1; i <= window_size; i++)
    {
      p = matrix + i * (window_size + 1);
      cost += draw_cost[i];
      p->insertcost = cost;
      p->writecost = SCROLL_INFINITY;
      p->deletecost = SCROLL_INFINITY;
      p->insertcount = i;
      p->writecount = 0;
      p->deletecount = 0;
    }

  /* initialize the top edge of the matrix */
  for (j = 1; j <= window_size; j++)
    {
      matrix[j].deletecost = 0;
      matrix[j].writecost = SCROLL_INFINITY;
      matrix[j].insertcost = SCROLL_INFINITY;
      matrix[j].deletecount = j;
      matrix[j].writecount = 0;
      matrix[j].insertcount = 0;
    }

  /* `i' represents the vpos among new frame contents.
     `j' represents the vpos among the old frame contents.  */
  p = matrix + window_size + 2;	/* matrix [1, 1] */

  for (i = 1; i <= window_size; i++, p++)
    for (j = 1; j <= window_size; j++, p++)
      {
	/* p contains the address of matrix [i, j] */

	/* First calculate the cost assuming we do
	   not insert or delete above this line.
	   That is, if we update through line i-1
	   based on old lines through j-1,
	   and then just change old line j to new line i.

	   Depending on which choice gives the lower cost,
	   this usually involves either scrolling a single line
	   or extending a sequence of scrolled lines, but
	   when i == j, no scrolling is required. */
	p1 = p - window_size - 2; /* matrix [i-1, j-1] */
	cost = p1->insertcost;
	if (cost > p1->deletecost)
	  cost = p1->deletecost;
	cost1 = p1->writecost;
	if (i == j)
	  {
	    if (cost > cost1)
	      {
		cost = cost1;
		p->writecount = p1->writecount + 1;
	      }
	    else
	      p->writecount = 1;
	    if (old_hash[j] != new_hash[i])
	      {
		cost += draw_cost[i];
	      }
	  }
	else
	  {
	    if (i > j)
	      {
		delta = i - j;

		/* The cost added here for scrolling the first line by
		   a distance N includes the overhead of setting the
		   scroll window, the cost of inserting N lines at a
		   position N lines above the bottom line of the window,
		   and an extra cost which is proportional to N. */
		cost += scroll_overhead + first_insert_cost[-delta] +
		  (delta-1) * (next_insert_cost[-delta] + extra_cost);

		/* In the most general case, the insertion overhead and
		   the multiply factor can grow linearly as the distance
		   from the bottom of the window increases.  The incremental
		   cost of scrolling an additional line depends upon the
		   rate of change of these two parameters.  Each of these
		   growth rates can be determined by a simple difference.
		   To reduce the cumulative effects of rounding error, we
		   vary the position at which the difference is computed. */
		cost1 += first_insert_cost[-j] - first_insert_cost[1-j] +
		  (delta-1) * (next_insert_cost[-j] - next_insert_cost[1-j]);
	      }
	    else
	      {
		delta = j - i;
		cost += scroll_overhead + first_delete_cost[-delta] +
		  (delta-1) * (next_delete_cost[-delta] + extra_cost);
		cost1 += first_delete_cost[-i] - first_delete_cost[1-i] +
		  (delta-1) * ( next_delete_cost[-i] - next_delete_cost[1-i]);
	      }
	    if (cost1 < cost)
	      {
		cost = cost1;
		p->writecount = p1->writecount + 1;
	      }
	    else
	      p->writecount = 1;
	    if (old_hash[j] != new_hash[i])
	      {
		cost += draw_cost[i] + old_draw_cost[j];
	      }
	  }
	p->writecost = cost;

	/* Calculate the cost if we do an insert-line
	   before outputting this line.
	   That is, we update through line i-1
	   based on old lines through j,
	   do an insert-line on line i,
	   and then output line i from scratch,
	   leaving old lines starting from j for reuse below.  */
	p1 = p - window_size - 1; /* matrix [i-1, j] */
	cost = p1->writecost;
	/* If i > j, an insert is allowed after a delete. */
	if (i > j && p1->deletecost < cost)
	  cost = p1->deletecost;
	if (p1->insertcost <= cost)
	  {
	    cost = p1->insertcost;
	    p->insertcount = p1->insertcount + 1;
	  }
	else
	  p->insertcount = 1;
	cost += draw_cost[i];
	p->insertcost = cost;

	/* Calculate the cost if we do a delete line after
	   outputting this line.
	   That is, we update through line i
	   based on old lines through j-1,
	   and throw away old line j.  */
	p1 = p - 1;		/* matrix [i, j-1] */
	cost = p1->writecost;
	/* If i < j, a delete is allowed after an insert. */
	if (i < j && p1->insertcost < cost)
	  cost = p1->insertcost;
	cost1 = p1->deletecost;
	if (p1->deletecost <= cost)
	  {
	    cost = p1->deletecost;
	    p->deletecount = p1->deletecount + 1;
	  }
	else
	  p->deletecount = 1;
	p->deletecost = cost;
      }
}



/* Perform insert-lines and delete-lines operations on CURRENT_MATRIX
   according to the costs in MATRIX, using the direct scrolling method
   which is used when the terminal supports setting a scroll window
   (scroll_region_ok).

   WINDOW_SIZE is the number of lines being considered for scrolling
   and UNCHANGED_AT_TOP is the vpos of the first line being
   considered.  These two arguments can specify any contiguous range
   of lines.

   In the direct scrolling method, a new scroll window is selected
   before each insertion or deletion, so that groups of lines can be
   scrolled directly to their final vertical positions.  This method
   is described in more detail in calculate_direct_scrolling, where
   the cost matrix for this approach is constructed. */

static void
do_direct_scrolling (struct frame *frame, struct glyph_matrix *current_matrix,
		     struct matrix_elt *cost_matrix, int window_size,
		     int unchanged_at_top)
{
  struct matrix_elt *p;
  int i, j;
  USE_SAFE_ALLOCA;

  /* A queue of deletions and insertions to be performed.  */
  struct alt_queue { int count, pos, window; };
  struct alt_queue *queue_start;
  SAFE_NALLOCA (queue_start, 1, window_size);
  struct alt_queue *queue = queue_start;

  /* True if a terminal window has been set with set_terminal_window.  */
  bool terminal_window_p = 0;

  /* If true, a write has been selected, allowing either an insert or a
     delete to be selected next.  If false, a delete cannot be selected
     unless j < i, and an insert cannot be selected unless i < j.
     This corresponds to a similar restriction (with the ordering
     reversed) in calculate_direct_scrolling, which is intended to
     ensure that lines marked as inserted will be blank. */
  bool write_follows_p = 1;

  /* For each row in the new matrix what row of the old matrix it is.  */
  int *copy_from;
  SAFE_NALLOCA (copy_from, 1, window_size);

  /* Non-zero for each row in the new matrix that is retained from the
     old matrix.  Lines not retained are empty.  */
  char *retained_p = SAFE_ALLOCA (window_size);

  memset (retained_p, 0, window_size * sizeof (char));

  /* Perform some sanity checks when GLYPH_DEBUG is on.  */
  CHECK_MATRIX (current_matrix);

  /* We are working on the line range UNCHANGED_AT_TOP ...
     UNCHANGED_AT_TOP + WINDOW_SIZE (not including) in CURRENT_MATRIX.
     We step through lines in this range from the end to the start.  I
     is an index into new lines, j an index into old lines.  The cost
     matrix determines what to do for ranges of indices.

     If i is decremented without also decrementing j, this corresponds
     to inserting empty lines in the result.  If j is decremented
     without also decrementing i, this corresponds to omitting these
     lines in the new rows, i.e. rows are deleted.  */
  i = j = window_size;

  while (i > 0 || j > 0)
    {
      p = cost_matrix + i * (window_size + 1) + j;

      if (p->insertcost < p->writecost
	  && p->insertcost < p->deletecost
	  && (write_follows_p || i < j))
	{
	  /* Insert is cheaper than deleting or writing lines.  Leave
	     a hole in the result display that will be filled with
	     empty lines when the queue is emptied.  */
	  queue->count = 0;
	  queue->window = i;
	  queue->pos = i - p->insertcount;
	  ++queue;

	  i -= p->insertcount;
	  write_follows_p = 0;
	}
      else if (p->deletecost < p->writecost
	       && (write_follows_p || i > j))
	{
	  /* Deleting lines is cheaper.  By decrementing J, omit
	     deletecount lines from the original.  */
	  write_follows_p = 0;
	  j -= p->deletecount;
	}
      else
	{
	  /* One or more lines should be written.  In the direct
	     scrolling method we do this by scrolling the lines to the
	     place they belong.  */
	  int n_to_write = p->writecount;
	  write_follows_p = 1;
	  eassert (n_to_write > 0);

	  if (i > j)
	    {
	      /* Immediately insert lines */
	      set_terminal_window (frame, i + unchanged_at_top);
	      terminal_window_p = 1;
	      ins_del_lines (frame, j - n_to_write + unchanged_at_top, i - j);
	    }
	  else if (i < j)
	    {
	      /* Queue the deletion of a group of lines */
	      queue->pos = i - n_to_write + unchanged_at_top;
	      queue->window = j + unchanged_at_top;
	      queue->count = i - j;
	      ++queue;
	    }

	  while (n_to_write > 0)
	    {
	      --i, --j, --n_to_write;
	      copy_from[i] = j;
	      retained_p[j] = 1;
	    }
	}
    }

  /* Do queued operations.  */
  if (queue > queue_start)
    {
      int next = -1;

      do
	{
	  --queue;
	  if (queue->count)
	    {
	      set_terminal_window (frame, queue->window);
	      terminal_window_p = 1;
	      ins_del_lines (frame, queue->pos, queue->count);
	    }
	  else
	    {
	      for (j = queue->window - 1; j >= queue->pos; --j)
		{
		  while (retained_p[++next])
		    ;
		  copy_from[j] = next;
		}
	    }
	}
      while (queue > queue_start);
    }

  /* Now, for each row I in the range of rows we are working on,
     copy_from[i] gives the original line to copy to I, and
     retained_p[copy_from[i]] is zero if line I in the new display is
     empty.  */
  mirrored_line_dance (current_matrix, unchanged_at_top, window_size,
		       copy_from, retained_p);

  if (terminal_window_p)
    set_terminal_window (frame, 0);
  SAFE_FREE ();
}



void
scrolling_1 (struct frame *frame, int window_size, int unchanged_at_top,
	     int unchanged_at_bottom, int *draw_cost, int *old_draw_cost,
	     unsigned *old_hash, unsigned *new_hash, int free_at_end)
{
  USE_SAFE_ALLOCA;
  struct matrix_elt *matrix;
  SAFE_NALLOCA (matrix, window_size + 1, window_size + 1);

  if (FRAME_SCROLL_REGION_OK (frame))
    {
      calculate_direct_scrolling (frame, matrix, window_size,
				  unchanged_at_bottom,
				  draw_cost, old_draw_cost,
				  old_hash, new_hash, free_at_end);
      do_direct_scrolling (frame, frame->current_matrix,
			   matrix, window_size, unchanged_at_top);
    }
  else
    {
      calculate_scrolling (frame, matrix, window_size, unchanged_at_bottom,
			   draw_cost, old_hash, new_hash,
			   free_at_end);
      do_scrolling (frame,
                    frame->current_matrix, matrix, window_size,
		    unchanged_at_top);
    }

  SAFE_FREE ();
}



/* Return number of lines in common between current and desired frame
   contents described to us only as vectors of hash codes OLDHASH and
   NEWHASH.  Consider only vpos range START to END (not including
   END).  Ignore short lines on the assumption that avoiding redrawing
   such a line will have little weight.  */

int
scrolling_max_lines_saved (int start, int end,
                           unsigned *oldhash, unsigned *newhash,
                           int *cost)
{
  enum { LOG2_NLINES = 9 };
  enum { NLINES = 1 << LOG2_NLINES };
  struct { unsigned hash; int count; } lines[NLINES];
  int i, h;
  int matchcount = 0;
  int avg_length = 0;
  int threshold;

  /* Compute a threshold which is 1/4 of average length of these lines.  */

  for (i = start; i < end; i++)
    avg_length += cost[i];

  avg_length /= end - start;
  threshold = avg_length / 4;

  memset (lines, 0, sizeof lines);

  /* Put new lines' hash codes in hash table.  Ignore lines shorter
     than the threshold.  Thus, if the lines that are in common are
     mainly the ones that are short, they won't count.  */
  for (i = start; i < end; i++)
    {
      if (cost[i] > threshold)
	{
	  h = newhash[i] & (NLINES - 1);
	  lines[h].hash = newhash[i];
	  lines[h].count++;
	}
    }

  /* Look up old line hash codes in the hash table.  Count number of
     matches between old lines and new.  */
  for (i = start; i < end; i++)
    {
      h = oldhash[i] & (NLINES - 1);
      if (oldhash[i] == lines[h].hash)
	{
	  matchcount++;
	  if (--lines[h].count == 0)
	    lines[h].hash = 0;
	}
    }

  return matchcount;
}

/* Calculate the line insertion/deletion
   overhead and multiply factor values */

static void
line_ins_del (struct frame *frame, int ov1, int pf1, int ovn, int pfn,
              int *ov, int *mf)
{
  int i;
  int frame_total_lines = FRAME_TOTAL_LINES (frame);
  int insert_overhead = ov1 * 10;
  int next_insert_cost = ovn * 10;

  for (i = frame_total_lines - 1; i >= 0; i--)
    {
      mf[i] = next_insert_cost / 10;
      next_insert_cost += pfn;
      ov[i] = (insert_overhead + next_insert_cost) / 10;
      insert_overhead += pf1;
    }
}

static void
ins_del_costs (struct frame *frame,
	       const char *one_line_string, const char *multi_string,
	       const char *setup_string, const char *cleanup_string,
	       int *costvec, int *ncostvec,
	       int coefficient)
{
  if (multi_string)
    line_ins_del (frame,
		  string_cost (multi_string) * coefficient,
		  per_line_cost (multi_string) * coefficient,
		  0, 0, costvec, ncostvec);
  else if (one_line_string)
    line_ins_del (frame,
		  string_cost (setup_string) + string_cost (cleanup_string), 0,
		  string_cost (one_line_string),
		  per_line_cost (one_line_string),
		  costvec, ncostvec);
  else
    line_ins_del (frame,
		  9999, 0, 9999, 0,
		  costvec, ncostvec);
}

/* Calculate the insert and delete line costs.
   Note that this is done even when running with a window system
   because we want to know how long scrolling takes (and avoid it).
   This must be redone whenever the frame height changes.

   We keep the ID costs in a precomputed array based on the position
   at which the I or D is performed.  Also, there are two kinds of ID
   costs: the "once-only" and the "repeated".  This is to handle both
   those terminals that are able to insert N lines at a time (once-
   only) and those that must repeatedly insert one line.

   The cost to insert N lines at line L is
	    [tt.t_ILov  + (frame_total_lines + 1 - L) * tt.t_ILpf] +
	N * [tt.t_ILnov + (frame_total_lines + 1 - L) * tt.t_ILnpf]

   ILov represents the basic insert line overhead.  ILpf is the padding
   required to allow the terminal time to move a line: insertion at line
   L changes (frame_total_lines + 1 - L) lines.

   The first bracketed expression above is the overhead; the second is
   the multiply factor.  Both are dependent only on the position at
   which the insert is performed.  We store the overhead in
   FRAME_INSERT_COST (frame) and the multiply factor in
   FRAME_INSERTN_COST (frame).  Note however that any insertion
   must include at least one multiply factor.  Rather than compute this
   as FRAME_INSERT_COST (frame)[line]+FRAME_INSERTN_COST (frame)[line],
   we add FRAME_INSERTN_COST (frame) into FRAME_INSERT_COST (frame).
   This is reasonable because of the particular algorithm used in calcM.

   Deletion is essentially the same as insertion.
 */

void
do_line_insertion_deletion_costs (struct frame *frame,
				  const char *ins_line_string,
				  const char *multi_ins_string,
				  const char *del_line_string,
				  const char *multi_del_string,
				  const char *setup_string,
				  const char *cleanup_string,
				  int coefficient)
{
  int frame_total_lines = FRAME_TOTAL_LINES (frame);
  FRAME_INSERT_COST (frame) =
    xnrealloc (FRAME_INSERT_COST (frame), frame_total_lines, sizeof (int));
  FRAME_DELETEN_COST (frame) =
    xnrealloc (FRAME_DELETEN_COST (frame), frame_total_lines, sizeof (int));
  FRAME_INSERTN_COST (frame) =
    xnrealloc (FRAME_INSERTN_COST (frame), frame_total_lines, sizeof (int));
  FRAME_DELETE_COST (frame) =
    xnrealloc (FRAME_DELETE_COST (frame), frame_total_lines, sizeof (int));

  ins_del_costs (frame,
		 ins_line_string, multi_ins_string,
		 setup_string, cleanup_string,
		 FRAME_INSERT_COST (frame), FRAME_INSERTN_COST (frame),
		 coefficient);
  ins_del_costs (frame,
		 del_line_string, multi_del_string,
		 setup_string, cleanup_string,
		 FRAME_DELETE_COST (frame), FRAME_DELETEN_COST (frame),
		 coefficient);
}