dispnew.c

/* Updating of data structures for redisplay.

Copyright (C) 1985-1988, 1993-1995, 1997-2012 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 <http://www.gnu.org/licenses/>.  */

#include <config.h>

#define DISPEXTERN_INLINE EXTERN_INLINE

#include <signal.h>
#include <stdio.h>
#include <setjmp.h>
#include <unistd.h>

#include "lisp.h"
#include "termchar.h"
#include "termopts.h"
/* cm.h must come after dispextern.h on Windows.  */
#include "dispextern.h"
#include "cm.h"
#include "character.h"
#include "buffer.h"
#include "keyboard.h"
#include "frame.h"
#include "termhooks.h"
#include "window.h"
#include "commands.h"
#include "disptab.h"
#include "indent.h"
#include "intervals.h"
#include "blockinput.h"
#include "process.h"

#include "syssignal.h"

#ifdef HAVE_WINDOW_SYSTEM
#include TERM_HEADER
#endif /* HAVE_WINDOW_SYSTEM */

/* Include systime.h after xterm.h to avoid double inclusion of time.h.  */

#include "systime.h"
#include <errno.h>

#ifdef DISPNEW_NEEDS_STDIO_EXT
#include <stdio_ext.h>
#endif

#if defined (HAVE_TERM_H) && defined (GNU_LINUX)
#include <term.h>		/* for tgetent */
#endif

/* Structure to pass dimensions around.  Used for character bounding
   boxes, glyph matrix dimensions and alike.  */

struct dim
{
  int width;
  int height;
};


/* Function prototypes.  */

static void update_frame_line (struct frame *, int);
static int required_matrix_height (struct window *);
static int required_matrix_width (struct window *);
static void adjust_frame_glyphs (struct frame *);
static void change_frame_size_1 (struct frame *, int, int, bool, bool, bool);
static void increment_row_positions (struct glyph_row *, ptrdiff_t, ptrdiff_t);
static void fill_up_frame_row_with_spaces (struct glyph_row *, int);
static void build_frame_matrix_from_window_tree (struct glyph_matrix *,
                                                 struct window *);
static void build_frame_matrix_from_leaf_window (struct glyph_matrix *,
                                                 struct window *);
static void adjust_frame_message_buffer (struct frame *);
static void adjust_decode_mode_spec_buffer (struct frame *);
static void fill_up_glyph_row_with_spaces (struct glyph_row *);
static void clear_window_matrices (struct window *, bool);
static void fill_up_glyph_row_area_with_spaces (struct glyph_row *, int);
static int scrolling_window (struct window *, bool);
static bool update_window_line (struct window *, int, bool *);
static void mirror_make_current (struct window *, int);
#ifdef GLYPH_DEBUG
static void check_matrix_pointers (struct glyph_matrix *,
                                   struct glyph_matrix *);
#endif
static void mirror_line_dance (struct window *, int, int, int *, char *);
static bool update_window_tree (struct window *, bool);
static bool update_window (struct window *, bool);
static bool update_frame_1 (struct frame *, bool, bool);
static bool scrolling (struct frame *);
static void set_window_cursor_after_update (struct window *);
static void adjust_frame_glyphs_for_window_redisplay (struct frame *);
static void adjust_frame_glyphs_for_frame_redisplay (struct frame *);


/* Redisplay preemption timers.  */

static EMACS_TIME preemption_period;
static EMACS_TIME preemption_next_check;

/* True upon entry to redisplay means do not assume anything about
   current contents of actual terminal frame; clear and redraw it.  */

bool frame_garbaged;

/* True means last display completed.  False means it was preempted.  */

bool display_completed;

Lisp_Object Qdisplay_table, Qredisplay_dont_pause;


/* The currently selected frame.  In a single-frame version, this
   variable always equals the_only_frame.  */

Lisp_Object selected_frame;

/* A frame which is not just a mini-buffer, or 0 if there are no such
   frames.  This is usually the most recent such frame that was
   selected.  In a single-frame version, this variable always holds
   the address of the_only_frame.  */

struct frame *last_nonminibuf_frame;

/* True means SIGWINCH happened when not safe.  */

static bool delayed_size_change;

/* 1 means glyph initialization has been completed at startup.  */

static bool glyphs_initialized_initially_p;

/* Updated window if != 0.  Set by update_window.  */

struct window *updated_window;

/* Glyph row updated in update_window_line, and area that is updated.  */

struct glyph_row *updated_row;
int updated_area;

/* A glyph for a space.  */

struct glyph space_glyph;

/* Counts of allocated structures.  These counts serve to diagnose
   memory leaks and double frees.  */

static int glyph_matrix_count;
static int glyph_pool_count;

/* If non-null, the frame whose frame matrices are manipulated.  If
   null, window matrices are worked on.  */

static struct frame *frame_matrix_frame;

/* True means that fonts have been loaded since the last glyph
   matrix adjustments.  Redisplay must stop, and glyph matrices must
   be adjusted when this flag becomes true during display.  The
   reason fonts can be loaded so late is that fonts of fontsets are
   loaded on demand.  Another reason is that a line contains many
   characters displayed by zero width or very narrow glyphs of
   variable-width fonts.  */

bool fonts_changed_p;

/* Convert vpos and hpos from frame to window and vice versa.
   This may only be used for terminal frames.  */

#ifdef GLYPH_DEBUG

static int window_to_frame_vpos (struct window *, int);
static int window_to_frame_hpos (struct window *, int);
#define WINDOW_TO_FRAME_VPOS(W, VPOS) window_to_frame_vpos ((W), (VPOS))
#define WINDOW_TO_FRAME_HPOS(W, HPOS) window_to_frame_hpos ((W), (HPOS))

/* One element of the ring buffer containing redisplay history
   information.  */

struct redisplay_history
{
  char trace[512 + 100];
};

/* The size of the history buffer.  */

#define REDISPLAY_HISTORY_SIZE	30

/* The redisplay history buffer.  */

static struct redisplay_history redisplay_history[REDISPLAY_HISTORY_SIZE];

/* Next free entry in redisplay_history.  */

static int history_idx;

/* A tick that's incremented each time something is added to the
   history.  */

static uprintmax_t history_tick;

/* Add to the redisplay history how window W has been displayed.
   MSG is a trace containing the information how W's glyph matrix
   has been constructed.  PAUSED_P means that the update
   has been interrupted for pending input.  */

static void
add_window_display_history (struct window *w, const char *msg, bool paused_p)
{
  char *buf;

  if (history_idx >= REDISPLAY_HISTORY_SIZE)
    history_idx = 0;
  buf = redisplay_history[history_idx].trace;
  ++history_idx;

  snprintf (buf, sizeof redisplay_history[0].trace,
	    "%"pMu": window %p (`%s')%s\n%s",
	    history_tick++,
	    w,
	    ((BUFFERP (w->buffer)
	      && STRINGP (BVAR (XBUFFER (w->buffer), name)))
	     ? SSDATA (BVAR (XBUFFER (w->buffer), name))
	     : "???"),
	    paused_p ? " ***paused***" : "",
	    msg);
}


/* Add to the redisplay history that frame F has been displayed.
   PAUSED_P means that the update has been interrupted for
   pending input.  */

static void
add_frame_display_history (struct frame *f, bool paused_p)
{
  char *buf;

  if (history_idx >= REDISPLAY_HISTORY_SIZE)
    history_idx = 0;
  buf = redisplay_history[history_idx].trace;
  ++history_idx;

  sprintf (buf, "%"pMu": update frame %p%s",
	   history_tick++,
	   f, paused_p ? " ***paused***" : "");
}


DEFUN ("dump-redisplay-history", Fdump_redisplay_history,
       Sdump_redisplay_history, 0, 0, "",
       doc: /* Dump redisplay history to stderr.  */)
  (void)
{
  int i;

  for (i = history_idx - 1; i != history_idx; --i)
    {
      if (i < 0)
	i = REDISPLAY_HISTORY_SIZE - 1;
      fprintf (stderr, "%s\n", redisplay_history[i].trace);
    }

  return Qnil;
}


#else /* not GLYPH_DEBUG */

#define WINDOW_TO_FRAME_VPOS(W, VPOS) ((VPOS) + WINDOW_TOP_EDGE_LINE (W))
#define WINDOW_TO_FRAME_HPOS(W, HPOS) ((HPOS) + WINDOW_LEFT_EDGE_COL (W))

#endif /* GLYPH_DEBUG */


#if (defined PROFILING \
     && (defined __FreeBSD__ || defined GNU_LINUX || defined __MINGW32__) \
     && !HAVE___EXECUTABLE_START)
/* This function comes first in the Emacs executable and is used only
   to estimate the text start for profiling.  */
void
__executable_start (void)
{
  abort ();
}
#endif

/***********************************************************************
			    Glyph Matrices
 ***********************************************************************/

/* Allocate and return a glyph_matrix structure.  POOL is the glyph
   pool from which memory for the matrix should be allocated, or null
   for window-based redisplay where no glyph pools are used.  The
   member `pool' of the glyph matrix structure returned is set to
   POOL, the structure is otherwise zeroed.  */

static struct glyph_matrix *
new_glyph_matrix (struct glyph_pool *pool)
{
  struct glyph_matrix *result = xzalloc (sizeof *result);

  /* Increment number of allocated matrices.  This count is used
     to detect memory leaks.  */
  ++glyph_matrix_count;

  /* Set pool and return.  */
  result->pool = pool;
  return result;
}


/* Free glyph matrix MATRIX.  Passing in a null MATRIX is allowed.

   The global counter glyph_matrix_count is decremented when a matrix
   is freed.  If the count gets negative, more structures were freed
   than allocated, i.e. one matrix was freed more than once or a bogus
   pointer was passed to this function.

   If MATRIX->pool is null, this means that the matrix manages its own
   glyph memory---this is done for matrices on X frames.  Freeing the
   matrix also frees the glyph memory in this case.  */

static void
free_glyph_matrix (struct glyph_matrix *matrix)
{
  if (matrix)
    {
      int i;

      /* Detect the case that more matrices are freed than were
	 allocated.  */
      if (--glyph_matrix_count < 0)
	abort ();

      /* Free glyph memory if MATRIX owns it.  */
      if (matrix->pool == NULL)
	for (i = 0; i < matrix->rows_allocated; ++i)
	  xfree (matrix->rows[i].glyphs[LEFT_MARGIN_AREA]);

      /* Free row structures and the matrix itself.  */
      xfree (matrix->rows);
      xfree (matrix);
    }
}


/* Return the number of glyphs to reserve for a marginal area of
   window W.  TOTAL_GLYPHS is the number of glyphs in a complete
   display line of window W.  MARGIN gives the width of the marginal
   area in canonical character units.  MARGIN should be an integer
   or a float.  */

static int
margin_glyphs_to_reserve (struct window *w, int total_glyphs, Lisp_Object margin)
{
  int n;

  if (NUMBERP (margin))
    {
      int width = XFASTINT (w->total_cols);
      double d = max (0, XFLOATINT (margin));
      d = min (width / 2 - 1, d);
      n = (int) ((double) total_glyphs / width * d);
    }
  else
    n = 0;

  return n;
}

/* Return true if ROW's hash value is correct.
   Optimized away if ENABLE_CHECKING is not defined.  */

static bool
verify_row_hash (struct glyph_row *row)
{
  return row->hash == row_hash (row);
}

/* Adjust glyph matrix MATRIX on window W or on a frame to changed
   window sizes.

   W is null if the function is called for a frame glyph matrix.
   Otherwise it is the window MATRIX is a member of.  X and Y are the
   indices of the first column and row of MATRIX within the frame
   matrix, if such a matrix exists.  They are zero for purely
   window-based redisplay.  DIM is the needed size of the matrix.

   In window-based redisplay, where no frame matrices exist, glyph
   matrices manage their own glyph storage.  Otherwise, they allocate
   storage from a common frame glyph pool which can be found in
   MATRIX->pool.

   The reason for this memory management strategy is to avoid complete
   frame redraws if possible.  When we allocate from a common pool, a
   change of the location or size of a sub-matrix within the pool
   requires a complete redisplay of the frame because we cannot easily
   make sure that the current matrices of all windows still agree with
   what is displayed on the screen.  While this is usually fast, it
   leads to screen flickering.  */

static void
adjust_glyph_matrix (struct window *w, struct glyph_matrix *matrix, int x, int y, struct dim dim)
{
  int i;
  int new_rows;
  bool marginal_areas_changed_p = 0;
  bool header_line_changed_p = 0;
  bool header_line_p = 0;
  int left = -1, right = -1;
  int window_width = -1, window_height = -1;

  /* See if W had a header line that has disappeared now, or vice versa.
     Get W's size.  */
  if (w)
    {
      window_box (w, -1, 0, 0, &window_width, &window_height);

      header_line_p = WINDOW_WANTS_HEADER_LINE_P (w);
      header_line_changed_p = header_line_p != matrix->header_line_p;
    }
  matrix->header_line_p = header_line_p;

  /* If POOL is null, MATRIX is a window matrix for window-based redisplay.
     Do nothing if MATRIX' size, position, vscroll, and marginal areas
     haven't changed.  This optimization is important because preserving
     the matrix means preventing redisplay.  */
  if (matrix->pool == NULL)
    {
      left = margin_glyphs_to_reserve (w, dim.width, w->left_margin_cols);
      right = margin_glyphs_to_reserve (w, dim.width, w->right_margin_cols);
      eassert (left >= 0 && right >= 0);
      marginal_areas_changed_p = (left != matrix->left_margin_glyphs
				  || right != matrix->right_margin_glyphs);

      if (!marginal_areas_changed_p
	  && !fonts_changed_p
	  && !header_line_changed_p
	  && matrix->window_left_col == WINDOW_LEFT_EDGE_COL (w)
	  && matrix->window_top_line == WINDOW_TOP_EDGE_LINE (w)
	  && matrix->window_height == window_height
	  && matrix->window_vscroll == w->vscroll
	  && matrix->window_width == window_width)
	return;
    }

  /* Enlarge MATRIX->rows if necessary.  New rows are cleared.  */
  if (matrix->rows_allocated < dim.height)
    {
      int old_alloc = matrix->rows_allocated;
      new_rows = dim.height - matrix->rows_allocated;
      matrix->rows = xpalloc (matrix->rows, &matrix->rows_allocated,
			      new_rows, INT_MAX, sizeof *matrix->rows);
      memset (matrix->rows + old_alloc, 0,
	      (matrix->rows_allocated - old_alloc) * sizeof *matrix->rows);
    }
  else
    new_rows = 0;

  /* If POOL is not null, MATRIX is a frame matrix or a window matrix
     on a frame not using window-based redisplay.  Set up pointers for
     each row into the glyph pool.  */
  if (matrix->pool)
    {
      eassert (matrix->pool->glyphs);

      if (w)
	{
	  left = margin_glyphs_to_reserve (w, dim.width,
					   w->left_margin_cols);
	  right = margin_glyphs_to_reserve (w, dim.width,
					    w->right_margin_cols);
	}
      else
	left = right = 0;

      for (i = 0; i < dim.height; ++i)
	{
	  struct glyph_row *row = &matrix->rows[i];

	  row->glyphs[LEFT_MARGIN_AREA]
	    = (matrix->pool->glyphs
	       + (y + i) * matrix->pool->ncolumns
	       + x);

	  if (w == NULL
	      || row == matrix->rows + dim.height - 1
	      || (row == matrix->rows && matrix->header_line_p))
	    {
	      row->glyphs[TEXT_AREA]
		= row->glyphs[LEFT_MARGIN_AREA];
	      row->glyphs[RIGHT_MARGIN_AREA]
		= row->glyphs[TEXT_AREA] + dim.width;
	      row->glyphs[LAST_AREA]
		= row->glyphs[RIGHT_MARGIN_AREA];
	    }
	  else
	    {
	      row->glyphs[TEXT_AREA]
		= row->glyphs[LEFT_MARGIN_AREA] + left;
	      row->glyphs[RIGHT_MARGIN_AREA]
		= row->glyphs[TEXT_AREA] + dim.width - left - right;
	      row->glyphs[LAST_AREA]
		= row->glyphs[LEFT_MARGIN_AREA] + dim.width;
	    }
	}

      matrix->left_margin_glyphs = left;
      matrix->right_margin_glyphs = right;
    }
  else
    {
      /* If MATRIX->pool is null, MATRIX is responsible for managing
	 its own memory.  It is a window matrix for window-based redisplay.
	 Allocate glyph memory from the heap.  */
      if (dim.width > matrix->matrix_w
	  || new_rows
	  || header_line_changed_p
	  || marginal_areas_changed_p)
	{
	  struct glyph_row *row = matrix->rows;
	  struct glyph_row *end = row + matrix->rows_allocated;

	  while (row < end)
	    {
	      row->glyphs[LEFT_MARGIN_AREA]
		= xnrealloc (row->glyphs[LEFT_MARGIN_AREA],
			     dim.width, sizeof (struct glyph));

	      /* The mode line never has marginal areas.  */
	      if (row == matrix->rows + dim.height - 1
		  || (row == matrix->rows && matrix->header_line_p))
		{
		  row->glyphs[TEXT_AREA]
		    = row->glyphs[LEFT_MARGIN_AREA];
		  row->glyphs[RIGHT_MARGIN_AREA]
		    = row->glyphs[TEXT_AREA] + dim.width;
		  row->glyphs[LAST_AREA]
		    = row->glyphs[RIGHT_MARGIN_AREA];
		}
	      else
		{
		  row->glyphs[TEXT_AREA]
		    = row->glyphs[LEFT_MARGIN_AREA] + left;
		  row->glyphs[RIGHT_MARGIN_AREA]
		    = row->glyphs[TEXT_AREA] + dim.width - left - right;
		  row->glyphs[LAST_AREA]
		    = row->glyphs[LEFT_MARGIN_AREA] + dim.width;
		}
	      ++row;
	    }
	}

      eassert (left >= 0 && right >= 0);
      matrix->left_margin_glyphs = left;
      matrix->right_margin_glyphs = right;
    }

  /* Number of rows to be used by MATRIX.  */
  matrix->nrows = dim.height;
  eassert (matrix->nrows >= 0);

  if (w)
    {
      if (matrix == w->current_matrix)
	{
	  /* Mark rows in a current matrix of a window as not having
	     valid contents.  It's important to not do this for
	     desired matrices.  When Emacs starts, it may already be
	     building desired matrices when this function runs.  */
	  if (window_width < 0)
	    window_width = window_box_width (w, -1);

	  /* Optimize the case that only the height has changed (C-x 2,
	     upper window).  Invalidate all rows that are no longer part
	     of the window.  */
	  if (!marginal_areas_changed_p
	      && !header_line_changed_p
	      && new_rows == 0
	      && dim.width == matrix->matrix_w
	      && matrix->window_left_col == WINDOW_LEFT_EDGE_COL (w)
	      && matrix->window_top_line == WINDOW_TOP_EDGE_LINE (w)
	      && matrix->window_width == window_width)
	    {
	      /* Find the last row in the window.  */
	      for (i = 0; i < matrix->nrows && matrix->rows[i].enabled_p; ++i)
		if (MATRIX_ROW_BOTTOM_Y (matrix->rows + i) >= window_height)
		  {
		    ++i;
		    break;
		  }

	      /* Window end is invalid, if inside of the rows that
		 are invalidated below.  */
	      if (INTEGERP (w->window_end_vpos)
		  && XFASTINT (w->window_end_vpos) >= i)
		wset_window_end_valid (w, Qnil);

	      while (i < matrix->nrows)
		matrix->rows[i++].enabled_p = 0;
	    }
	  else
	    {
	      for (i = 0; i < matrix->nrows; ++i)
		matrix->rows[i].enabled_p = 0;
	    }
	}
      else if (matrix == w->desired_matrix)
	{
	  /* Rows in desired matrices always have to be cleared;
	     redisplay expects this is the case when it runs, so it
	     had better be the case when we adjust matrices between
	     redisplays.  */
	  for (i = 0; i < matrix->nrows; ++i)
	    matrix->rows[i].enabled_p = 0;
	}
    }


  /* Remember last values to be able to optimize frame redraws.  */
  matrix->matrix_x = x;
  matrix->matrix_y = y;
  matrix->matrix_w = dim.width;
  matrix->matrix_h = dim.height;

  /* Record the top y location and height of W at the time the matrix
     was last adjusted.  This is used to optimize redisplay above.  */
  if (w)
    {
      matrix->window_left_col = WINDOW_LEFT_EDGE_COL (w);
      matrix->window_top_line = WINDOW_TOP_EDGE_LINE (w);
      matrix->window_height = window_height;
      matrix->window_width = window_width;
      matrix->window_vscroll = w->vscroll;
    }
}


/* Reverse the contents of rows in MATRIX between START and END.  The
   contents of the row at END - 1 end up at START, END - 2 at START +
   1 etc.  This is part of the implementation of rotate_matrix (see
   below).  */

static void
reverse_rows (struct glyph_matrix *matrix, int start, int end)
{
  int i, j;

  for (i = start, j = end - 1; i < j; ++i, --j)
    {
      /* Non-ISO HP/UX compiler doesn't like auto struct
	 initialization.  */
      struct glyph_row temp;
      temp = matrix->rows[i];
      matrix->rows[i] = matrix->rows[j];
      matrix->rows[j] = temp;
    }
}


/* Rotate the contents of rows in MATRIX in the range FIRST .. LAST -
   1 by BY positions.  BY < 0 means rotate left, i.e. towards lower
   indices.  (Note: this does not copy glyphs, only glyph pointers in
   row structures are moved around).

   The algorithm used for rotating the vector was, I believe, first
   described by Kernighan.  See the vector R as consisting of two
   sub-vectors AB, where A has length BY for BY >= 0.  The result
   after rotating is then BA.  Reverse both sub-vectors to get ArBr
   and reverse the result to get (ArBr)r which is BA.  Similar for
   rotating right.  */

void
rotate_matrix (struct glyph_matrix *matrix, int first, int last, int by)
{
  if (by < 0)
    {
      /* Up (rotate left, i.e. towards lower indices).  */
      by = -by;
      reverse_rows (matrix, first, first + by);
      reverse_rows (matrix, first + by, last);
      reverse_rows (matrix, first, last);
    }
  else if (by > 0)
    {
      /* Down (rotate right, i.e. towards higher indices).  */
      reverse_rows (matrix, last - by, last);
      reverse_rows (matrix, first, last - by);
      reverse_rows (matrix, first, last);
    }
}


/* Increment buffer positions in glyph rows of MATRIX.  Do it for rows
   with indices START <= index < END.  Increment positions by DELTA/
   DELTA_BYTES.  */

void
increment_matrix_positions (struct glyph_matrix *matrix, int start, int end,
			    ptrdiff_t delta, ptrdiff_t delta_bytes)
{
  /* Check that START and END are reasonable values.  */
  eassert (start >= 0 && start <= matrix->nrows);
  eassert (end >= 0 && end <= matrix->nrows);
  eassert (start <= end);

  for (; start < end; ++start)
    increment_row_positions (matrix->rows + start, delta, delta_bytes);
}


/* Clear the enable_p flags in a range of rows in glyph matrix MATRIX.
   START and END are the row indices of the first and last + 1 row to clear.  */

void
clear_glyph_matrix_rows (struct glyph_matrix *matrix, int start, int end)
{
  eassert (start <= end);
  eassert (start >= 0 && start < matrix->nrows);
  eassert (end >= 0 && end <= matrix->nrows);

  for (; start < end; ++start)
    matrix->rows[start].enabled_p = 0;
}


/* Clear MATRIX.

   Empty all rows in MATRIX by clearing their enabled_p flags.
   The function prepare_desired_row will eventually really clear a row
   when it sees one with a false enabled_p flag.

   Reset update hints to default values.  The only update hint
   currently present is the flag MATRIX->no_scrolling_p.  */

void
clear_glyph_matrix (struct glyph_matrix *matrix)
{
  if (matrix)
    {
      clear_glyph_matrix_rows (matrix, 0, matrix->nrows);
      matrix->no_scrolling_p = 0;
    }
}


/* Shift part of the glyph matrix MATRIX of window W up or down.
   Increment y-positions in glyph rows between START and END by DY,
   and recompute their visible height.  */

void
shift_glyph_matrix (struct window *w, struct glyph_matrix *matrix, int start, int end, int dy)
{
  int min_y, max_y;

  eassert (start <= end);
  eassert (start >= 0 && start < matrix->nrows);
  eassert (end >= 0 && end <= matrix->nrows);

  min_y = WINDOW_HEADER_LINE_HEIGHT (w);
  max_y = WINDOW_BOX_HEIGHT_NO_MODE_LINE (w);

  for (; start < end; ++start)
    {
      struct glyph_row *row = &matrix->rows[start];

      row->y += dy;
      row->visible_height = row->height;

      if (row->y < min_y)
	row->visible_height -= min_y - row->y;
      if (row->y + row->height > max_y)
	row->visible_height -= row->y + row->height - max_y;
      if (row->fringe_bitmap_periodic_p)
	row->redraw_fringe_bitmaps_p = 1;
    }
}


/* Mark all rows in current matrices of frame F as invalid.  Marking
   invalid is done by setting enabled_p to zero for all rows in a
   current matrix.  */

void
clear_current_matrices (register struct frame *f)
{
  /* Clear frame current matrix, if we have one.  */
  if (f->current_matrix)
    clear_glyph_matrix (f->current_matrix);

  /* Clear the matrix of the menu bar window, if such a window exists.
     The menu bar window is currently used to display menus on X when
     no toolkit support is compiled in.  */
  if (WINDOWP (f->menu_bar_window))
    clear_glyph_matrix (XWINDOW (f->menu_bar_window)->current_matrix);

  /* Clear the matrix of the tool-bar window, if any.  */
  if (WINDOWP (f->tool_bar_window))
    clear_glyph_matrix (XWINDOW (f->tool_bar_window)->current_matrix);

  /* Clear current window matrices.  */
  eassert (WINDOWP (FRAME_ROOT_WINDOW (f)));
  clear_window_matrices (XWINDOW (FRAME_ROOT_WINDOW (f)), 0);
}


/* Clear out all display lines of F for a coming redisplay.  */

void
clear_desired_matrices (register struct frame *f)
{
  if (f->desired_matrix)
    clear_glyph_matrix (f->desired_matrix);

  if (WINDOWP (f->menu_bar_window))
    clear_glyph_matrix (XWINDOW (f->menu_bar_window)->desired_matrix);

  if (WINDOWP (f->tool_bar_window))
    clear_glyph_matrix (XWINDOW (f->tool_bar_window)->desired_matrix);

  /* Do it for window matrices.  */
  eassert (WINDOWP (FRAME_ROOT_WINDOW (f)));
  clear_window_matrices (XWINDOW (FRAME_ROOT_WINDOW (f)), 1);
}


/* Clear matrices in window tree rooted in W.  If DESIRED_P,
   clear desired matrices, otherwise clear current matrices.  */

static void
clear_window_matrices (struct window *w, bool desired_p)
{
  while (w)
    {
      if (!NILP (w->hchild))
	{
	  eassert (WINDOWP (w->hchild));
	  clear_window_matrices (XWINDOW (w->hchild), desired_p);
	}
      else if (!NILP (w->vchild))
	{
	  eassert (WINDOWP (w->vchild));
	  clear_window_matrices (XWINDOW (w->vchild), desired_p);
	}
      else
	{
	  if (desired_p)
	    clear_glyph_matrix (w->desired_matrix);
	  else
	    {
	      clear_glyph_matrix (w->current_matrix);
	      wset_window_end_valid (w, Qnil);
	    }
	}

      w = NILP (w->next) ? 0 : XWINDOW (w->next);
    }
}



/***********************************************************************
			      Glyph Rows

      See dispextern.h for an overall explanation of glyph rows.
 ***********************************************************************/

/* Clear glyph row ROW.  Do it in a way that makes it robust against
   changes in the glyph_row structure, i.e. addition or removal of
   structure members.  */

static struct glyph_row null_row;

void
clear_glyph_row (struct glyph_row *row)
{
  struct glyph *p[1 + LAST_AREA];

  /* Save pointers.  */
  p[LEFT_MARGIN_AREA] = row->glyphs[LEFT_MARGIN_AREA];
  p[TEXT_AREA] = row->glyphs[TEXT_AREA];
  p[RIGHT_MARGIN_AREA] = row->glyphs[RIGHT_MARGIN_AREA];
  p[LAST_AREA] = row->glyphs[LAST_AREA];

  /* Clear.  */
  *row = null_row;

  /* Restore pointers.  */
  row->glyphs[LEFT_MARGIN_AREA] = p[LEFT_MARGIN_AREA];
  row->glyphs[TEXT_AREA] = p[TEXT_AREA];
  row->glyphs[RIGHT_MARGIN_AREA] = p[RIGHT_MARGIN_AREA];
  row->glyphs[LAST_AREA] = p[LAST_AREA];

#if 0 /* At some point, some bit-fields of struct glyph were not set,
	 which made glyphs unequal when compared with GLYPH_EQUAL_P.
	 Redisplay outputs such glyphs, and flickering effects were
	 the result.  This also depended on the contents of memory
	 returned by xmalloc.  If flickering happens again, activate
	 the code below.  If the flickering is gone with that, chances
	 are that the flickering has the same reason as here.  */
  memset (p[0], 0, (char *) p[LAST_AREA] - (char *) p[0]);
#endif
}


/* Make ROW an empty, enabled row of canonical character height,
   in window W starting at y-position Y.  */

void
blank_row (struct window *w, struct glyph_row *row, int y)
{
  int min_y, max_y;