/src/tmux/screen-write.c

Source
/* $OpenBSD: screen-write.c,v 1.298 2026/10/02 15:20:41 nicm Exp $ */

/*
 * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

#include <stdlib.h>
#include <string.h>

#include "tmux.h"

static struct screen_write_citem *screen_write_collect_trim(
        struct screen_write_ctx *, u_int, u_int, u_int, int *);
static void screen_write_collect_insert(struct screen_write_ctx *,
        struct screen_write_citem *);
static void screen_write_collect_insert_clear(struct screen_write_ctx *,
        u_int, u_int, u_int);
static void screen_write_collect_clear(struct screen_write_ctx *, u_int,
        u_int);
static void screen_write_collect_scroll(struct screen_write_ctx *, u_int);
static void screen_write_collect_flush(struct screen_write_ctx *, int,
        const char *);
static int  screen_write_overwrite(struct screen_write_ctx *,
        struct grid_cell *, u_int);
static int  screen_write_combine(struct screen_write_ctx *,
        const struct grid_cell *);
static void screen_write_sync_flush_dirty(struct window_pane *);
static void screen_write_sync_apply_scroll(struct screen_write_ctx *,
        struct tty_ctx *);

struct screen_write_citem {
  u_int       x;
  int       wrapped;

  enum { TEXT, CLEAR }    type;
  u_int       used;
  u_int       bg;

  struct grid_cell    gc;

  TAILQ_ENTRY(screen_write_citem) entry;
};
struct screen_write_cline {
  char        *data;
  TAILQ_HEAD(, screen_write_citem) items;
};
TAILQ_HEAD(, screen_write_citem)  screen_write_citem_freelist =
    TAILQ_HEAD_INITIALIZER(screen_write_citem_freelist);

static struct screen_write_citem *
screen_write_get_citem(void)
{
    struct screen_write_citem *ci;

    ci = TAILQ_FIRST(&screen_write_citem_freelist);
    if (ci != NULL) {
      TAILQ_REMOVE(&screen_write_citem_freelist, ci, entry);
      memset(ci, 0, sizeof *ci);
      return (ci);
    }
    return (xcalloc(1, sizeof *ci));
}

static void
screen_write_free_citem(struct screen_write_citem *ci)
{
  TAILQ_INSERT_TAIL(&screen_write_citem_freelist, ci, entry);
}

static void
screen_write_offset_timer(__unused int fd, __unused short events, void *data)
{
  struct window *w = data;

  tty_update_window_offset(w);
}

/* Set cursor position. */
static void
screen_write_set_cursor(struct screen_write_ctx *ctx, int cx, int cy)
{
  struct window_pane  *wp = ctx->wp;
  struct window   *w;
  struct screen   *s = ctx->s;
  struct timeval     tv = { .tv_usec = 10000 };

  if (cx != -1 && (u_int)cx == s->cx && cy != -1 && (u_int)cy == s->cy)
    return;

  if (cx != -1) {
    if ((u_int)cx > screen_size_x(s)) /* allow last column */
      cx = screen_size_x(s) - 1;
    s->cx = cx;
  }
  if (cy != -1) {
    if ((u_int)cy > screen_size_y(s) - 1)
      cy = screen_size_y(s) - 1;
    s->cy = cy;
  }

  if (wp == NULL)
    return;
  w = wp->window;

  if (!event_initialized(&w->offset_timer))
    evtimer_set(&w->offset_timer, screen_write_offset_timer, w);
  if (!evtimer_pending(&w->offset_timer, NULL))
    evtimer_add(&w->offset_timer, &tv);
}

/* Redraw lines. */
static void
screen_write_redraw_cb(const struct tty_ctx *ttyctx, u_int py, u_int ny)
{
  struct window_pane  *wp = ttyctx->arg;
  int      x0, y0, x1, y1;

  if (wp == NULL)
    return;

  x0 = wp->xoff;
  y0 = wp->yoff + (int)py;
  x1 = x0 + (int)wp->sx;
  y1 = y0 + (int)ny;
  if (x0 < 0)
    x0 = 0;
  if (y0 < 0)
    y0 = 0;
  if (x1 > x0 && y1 > y0)
    redraw_damage_window(wp->window, x0, y0, x1 - x0, y1 - y0);
}

/* Update context for client. */
static int
screen_write_set_client_cb(struct tty_ctx *ttyctx, struct client *c)
{
  struct window_pane  *wp = ttyctx->arg;

  if (ttyctx->flags & TTY_CTX_INVISIBLE_PANES) {
    if (session_has(c->session, wp->window))
      return (1);
    return (0);
  }

  if (c->session->curw->window != wp->window)
    return (0);
  if (wp->layout_cell == NULL)
    return (0);

  if (wp->flags & (PANE_REDRAW|PANE_DROP))
    return (-1);
  if (c->flags & CLIENT_REDRAWWINDOW) {
    /*
     * Redraw is already deferred to redraw the window - redraw this
     * one also when that happens.
     */
    log_debug("%s: adding %%%u to deferred redraw", __func__,
        wp->id);
    wp->flags |= (PANE_REDRAW|PANE_REDRAWSCROLLBAR);
    return (-1);
  }

  if (tty_window_offset(&c->tty, &ttyctx->wox, &ttyctx->woy, &ttyctx->wsx,
      &ttyctx->wsy))
    ttyctx->flags |= TTY_CTX_WINDOW_BIGGER;
  else
    ttyctx->flags &= ~TTY_CTX_WINDOW_BIGGER;

  ttyctx->xoff = ttyctx->rxoff = wp->xoff;
  ttyctx->yoff = ttyctx->ryoff = wp->yoff;

  if (status_at_line(c) == 0)
    ttyctx->yoff += status_line_size(c);

  return (1);
}

/* Return 1 if a menu or floating pane overlaps this pane. */
static int
screen_write_pane_is_obscured(struct screen_write_ctx *ctx)
{
  struct window_pane  *wp = ctx->wp;
  struct menu_data  *md;

  if (ctx->wp == NULL)
    return (0);
  if (ctx->flags & SCREEN_WRITE_CHECKED_IF_OBSCURED) {
    if (ctx->flags & SCREEN_WRITE_OBSCURED)
      return (1);
    return (0);
  }
  ctx->flags |= SCREEN_WRITE_CHECKED_IF_OBSCURED;

  md = wp->window->menu;
  if (md != NULL &&
      (int)menu_x(md) < wp->xoff + (int)wp->sx &&
      (int)(menu_x(md) + menu_width(md)) > wp->xoff &&
      (int)menu_y(md) < wp->yoff + (int)wp->sy &&
      (int)(menu_y(md) + menu_height(md)) > wp->yoff) {
    ctx->flags |= SCREEN_WRITE_OBSCURED;
    return (1);
  }

  if (ctx->wp->xoff < 0 ||
      ctx->wp->yoff < 0 ||
      ctx->wp->xoff + ctx->wp->sx > ctx->wp->window->sx ||
      ctx->wp->yoff + ctx->wp->sy > ctx->wp->window->sy) {
    ctx->flags |= SCREEN_WRITE_OBSCURED;
    return (1);
  }

  while ((wp = TAILQ_PREV(wp, window_panes, zentry)) != NULL) {
    if (window_pane_floating_overlaps(wp, ctx->wp)) {
      ctx->flags |= SCREEN_WRITE_OBSCURED;
      return (1);
    }
  }
  return (0);
}

/* Allocate dirty lines for this screen size. */
static bitstr_t *
screen_write_sync_allocate_dirty(struct window_pane *wp, u_int sy)
{
  bitstr_t  *bs = wp->sync_dirty;

  if (bs != NULL && wp->sync_dirty_size == sy)
    return (bs);

  free(bs);
  bs = wp->sync_dirty = bit_alloc(sy);
  if (bs == NULL)
    fatal("bit_alloc failed");
  if (wp->sync_dirty_size != 0) {
    bit_nset(bs, 0, sy - 1);
    wp->sync_scrolled = 0;
  }
  wp->sync_dirty_size = sy;
  return (bs);
}

/* Should we draw to the TTY? */
static int
screen_write_should_draw_lines(struct screen_write_ctx *ctx, u_int y, u_int ny)
{
  struct window_pane  *wp = ctx->wp;
  struct screen   *s = ctx->s;
  u_int      sy = screen_size_y(s);
  bitstr_t    *bs;

  if (wp != NULL && (wp->flags & (PANE_REDRAW|PANE_DROP)))
    return (0);
  if (s->mode & MODE_SYNC) {
    if (wp != NULL && y < sy && ny != 0) {
      if (ny > sy - y)
        ny = sy - y;
      bs = screen_write_sync_allocate_dirty(wp, sy);
      bit_nset(bs, y, y + ny - 1);
    }
    return (0);
  }
  return (1);
}

/* Should we draw this line to the TTY? */
static int
screen_write_should_draw_line(struct screen_write_ctx *ctx, u_int y)
{
  return (screen_write_should_draw_lines(ctx, y, 1));
}

/* Set up context for TTY command. */
static void
screen_write_initctx(struct screen_write_ctx *ctx, struct tty_ctx *ttyctx,
    int is_sync, int check_obscured)
{
  struct screen   *s = ctx->s;
  struct colour_palette *palette = NULL;

  memset(ttyctx, 0, sizeof *ttyctx);

  ttyctx->s = s;
  ttyctx->sx = screen_size_x(s);
  ttyctx->sy = screen_size_y(s);

  ttyctx->ocx = s->cx;
  ttyctx->ocy = s->cy;
  ttyctx->orlower = s->rlower;
  ttyctx->orupper = s->rupper;

  if (check_obscured && screen_write_pane_is_obscured(ctx))
    ttyctx->flags |= TTY_CTX_PANE_OBSCURED;

  memcpy(&ttyctx->defaults, &grid_default_cell, sizeof ttyctx->defaults);
  ttyctx->style_ctx.defaults = &ttyctx->defaults;
  ttyctx->style_ctx.hyperlinks = ctx->s->hyperlinks;

  if (ctx->init_ctx_cb != NULL) {
    ctx->init_ctx_cb(ctx, ttyctx);
    if (ttyctx->style_ctx.palette != NULL) {
      palette = ttyctx->style_ctx.palette;
      if (ttyctx->defaults.fg == 8)
        ttyctx->defaults.fg = palette->fg;
      if (ttyctx->defaults.bg == 8)
        ttyctx->defaults.bg = palette->bg;
    }
  } else {
    ttyctx->redraw_cb = screen_write_redraw_cb;
    if (ctx->wp != NULL) {
      tty_default_colours(&ttyctx->defaults, ctx->wp,
          &ttyctx->style_ctx.dim);
      ttyctx->style_ctx.palette = &ctx->wp->palette;
      ttyctx->set_client_cb = screen_write_set_client_cb;
      ttyctx->arg = ctx->wp;
    }
  }

  if (~ctx->flags & SCREEN_WRITE_SYNC) {
    /*
     * For the active pane showing its base screen, only use
     * synchronized updates if requested (commands that move the
     * cursor); for other panes or a pane in a mode, always use it,
     * since the cursor will have to move.
     */
    if (ctx->wp != NULL && (ctx->wp != ctx->wp->window->active ||
        ctx->wp->screen != &ctx->wp->base))
      ttyctx->flags |= TTY_CTX_SYNC;
    else if (is_sync)
      ttyctx->flags |= TTY_CTX_SYNC;
    tty_write(tty_cmd_syncstart, ttyctx);
    ctx->flags |= SCREEN_WRITE_SYNC;
  }
}

/* Make write list. */
void
screen_write_make_list(struct screen *s)
{
  u_int y;

  s->write_list = xcalloc(screen_size_y(s), sizeof *s->write_list);
  for (y = 0; y < screen_size_y(s); y++)
    TAILQ_INIT(&s->write_list[y].items);
}

/* Free write list. */
void
screen_write_free_list(struct screen *s)
{
  struct screen_write_cline *cl;
  struct screen_write_citem *ci, *ci1;
  u_int        y;

  for (y = 0; y < screen_size_y(s); y++) {
    cl = &s->write_list[y];
    TAILQ_FOREACH_SAFE(ci, &cl->items, entry, ci1) {
      TAILQ_REMOVE(&cl->items, ci, entry);
      screen_write_free_citem(ci);
    }
    free(cl->data);
  }
  free(s->write_list);
}

/* Set up for writing. */
static void
screen_write_init(struct screen_write_ctx *ctx, struct screen *s)
{
  memset(ctx, 0, sizeof *ctx);

  ctx->s = s;

  if (ctx->s->write_list == NULL)
    screen_write_make_list(ctx->s);
  ctx->item = screen_write_get_citem();

  ctx->scrolled = 0;
  ctx->bg = 8;
}

/* Initialize writing with a pane. */
void
screen_write_start_pane(struct screen_write_ctx *ctx, struct window_pane *wp,
    struct screen *s)
{
  if (s == NULL)
    s = wp->screen;
  screen_write_init(ctx, s);
  ctx->wp = wp;

  if (log_get_level() != 0) {
    log_debug("%s: size %ux%u, pane %%%u (at %u,%u)",
        __func__, screen_size_x(ctx->s), screen_size_y(ctx->s),
        wp->id, wp->xoff, wp->yoff);
  }
}

/* Initialize writing with a callback. */
void
screen_write_start_callback(struct screen_write_ctx *ctx, struct screen *s,
    screen_write_init_ctx_cb cb, void *arg)
{
  screen_write_init(ctx, s);

  ctx->init_ctx_cb = cb;
  ctx->arg = arg;

  if (log_get_level() != 0) {
    log_debug("%s: size %ux%u, with callback", __func__,
        screen_size_x(ctx->s), screen_size_y(ctx->s));
  }
}

/* Initialize writing. */
void
screen_write_start(struct screen_write_ctx *ctx, struct screen *s)
{
  screen_write_init(ctx, s);

  if (log_get_level() != 0) {
    log_debug("%s: size %ux%u, no pane", __func__,
        screen_size_x(ctx->s), screen_size_y(ctx->s));
  }
}

/* Finish writing. */
void
screen_write_stop(struct screen_write_ctx *ctx)
{
  screen_write_collect_end(ctx);
  screen_write_collect_flush(ctx, 0, __func__);

  screen_write_free_citem(ctx->item);
}

/* Reset screen state. */
void
screen_write_reset(struct screen_write_ctx *ctx)
{
  struct screen *s = ctx->s;

  screen_reset_tabs(s);
  screen_write_scrollregion(ctx, 0, screen_size_y(s) - 1);

  s->mode = MODE_CURSOR|MODE_WRAP;

  if (options_get_number(global_options, "extended-keys") == 2)
    s->mode = (s->mode & ~EXTENDED_KEY_MODES)|MODE_KEYS_EXTENDED;

  screen_write_clearscreen(ctx, 8);
  screen_write_set_cursor(ctx, 0, 0);
}

/* Write character. */
void
screen_write_putc(struct screen_write_ctx *ctx, const struct grid_cell *gcp,
    u_char ch)
{
  struct grid_cell  gc;

  memcpy(&gc, gcp, sizeof gc);

  utf8_set(&gc.data, ch);
  screen_write_cell(ctx, &gc);
}

/* Calculate string length. */
size_t
screen_write_strlen(const char *fmt, ...)
{
  va_list     ap;
  char           *msg;
  struct utf8_data  ud;
  u_char           *ptr;
  size_t      left, size = 0;
  enum utf8_state   more;

  va_start(ap, fmt);
  xvasprintf(&msg, fmt, ap);
  va_end(ap);

  ptr = msg;
  while (*ptr != '\0') {
    if (*ptr > 0x7f && utf8_open(&ud, *ptr) == UTF8_MORE) {
      ptr++;

      left = strlen(ptr);
      if (left < (size_t)ud.size - 1)
        break;
      while ((more = utf8_append(&ud, *ptr)) == UTF8_MORE)
        ptr++;
      ptr++;

      if (more == UTF8_DONE)
        size += ud.width;
    } else {
      if (*ptr == '\t' || (*ptr > 0x1f && *ptr < 0x7f))
        size++;
      ptr++;
    }
  }

  free(msg);
  return (size);
}

/* Write string wrapped over lines. */
int
screen_write_text(struct screen_write_ctx *ctx, u_int cx, u_int width,
    u_int lines, int more, const struct grid_cell *gcp, const char *fmt, ...)
{
  struct screen   *s = ctx->s;
  va_list      ap;
  char      *tmp;
  u_int      cy = s->cy, i, end, next, idx = 0, at, left;
  struct utf8_data  *text;
  struct grid_cell   gc;

  memcpy(&gc, gcp, sizeof gc);

  va_start(ap, fmt);
  xvasprintf(&tmp, fmt, ap);
  va_end(ap);

  text = utf8_fromcstr(tmp);
  free(tmp);

  left = (cx + width) - s->cx;
  for (;;) {
    /* Find the end of what can fit on the line. */
    at = 0;
    for (end = idx; text[end].size != 0; end++) {
      if (text[end].size == 1 && text[end].data[0] == '\n')
        break;
      if (at + text[end].width > left)
        break;
      at += text[end].width;
    }

    /*
     * If we're on a space, that's the end. If not, walk back to
     * try and find one.
     */
    if (text[end].size == 0)
      next = end;
    else if (text[end].size == 1 && text[end].data[0] == '\n')
      next = end + 1;
    else if (text[end].size == 1 && text[end].data[0] == ' ')
      next = end + 1;
    else {
      for (i = end; i > idx; i--) {
        if (text[i].size == 1 && text[i].data[0] == ' ')
          break;
      }
      if (i != idx) {
        next = i + 1;
        end = i;
      } else
        next = end;
    }

    /* Print the line. */
    for (i = idx; i < end; i++) {
      utf8_copy(&gc.data, &text[i]);
      screen_write_cell(ctx, &gc);
    }

    /* If at the bottom, stop. */
    idx = next;
    if (s->cy == cy + lines - 1 || text[idx].size == 0)
      break;

    screen_write_cursormove(ctx, cx, s->cy + 1, 0);
    left = width;
  }

  /*
   * Fail if on the last line and there is more to come or at the end, or
   * if the text was not entirely consumed.
   */
  if ((s->cy == cy + lines - 1 && (!more || s->cx == cx + width)) ||
      text[idx].size != 0) {
    free(text);
    return (0);
  }
  free(text);

  /*
   * If no more to come, move to the next line. Otherwise, leave on
   * the same line (except if at the end).
   */
  if (!more || s->cx == cx + width)
    screen_write_cursormove(ctx, cx, s->cy + 1, 0);
  return (1);
}

/* Write simple string (no maximum length). */
void
screen_write_puts(struct screen_write_ctx *ctx, const struct grid_cell *gcp,
    const char *fmt, ...)
{
  va_list ap;

  va_start(ap, fmt);
  screen_write_vnputs(ctx, -1, gcp, fmt, ap);
  va_end(ap);
}

/* Write string with length limit (-1 for unlimited). */
void
screen_write_nputs(struct screen_write_ctx *ctx, ssize_t maxlen,
    const struct grid_cell *gcp, const char *fmt, ...)
{
  va_list ap;

  va_start(ap, fmt);
  screen_write_vnputs(ctx, maxlen, gcp, fmt, ap);
  va_end(ap);
}

void
screen_write_vnputs(struct screen_write_ctx *ctx, ssize_t maxlen,
    const struct grid_cell *gcp, const char *fmt, va_list ap)
{
  struct grid_cell  gc;
  struct utf8_data       *ud = &gc.data;
  char           *msg;
  u_char           *ptr;
  size_t      left, size = 0;
  enum utf8_state   more;

  memcpy(&gc, gcp, sizeof gc);
  xvasprintf(&msg, fmt, ap);

  ptr = msg;
  while (*ptr != '\0') {
    if (*ptr > 0x7f && utf8_open(ud, *ptr) == UTF8_MORE) {
      ptr++;

      left = strlen(ptr);
      if (left < (size_t)ud->size - 1)
        break;
      while ((more = utf8_append(ud, *ptr)) == UTF8_MORE)
        ptr++;
      ptr++;

      if (more != UTF8_DONE)
        continue;
      if (maxlen > 0 && size + ud->width > (size_t)maxlen) {
        while (size < (size_t)maxlen) {
          screen_write_putc(ctx, &gc, ' ');
          size++;
        }
        break;
      }
      size += ud->width;
      screen_write_cell(ctx, &gc);
    } else {
      if (maxlen > 0 && size + 1 > (size_t)maxlen)
        break;

      if (*ptr == '\001')
        gc.attr ^= GRID_ATTR_CHARSET;
      else if (*ptr == '\n') {
        screen_write_linefeed(ctx, 0, 8);
        screen_write_carriagereturn(ctx);
      } else if (*ptr == '\t' || (*ptr > 0x1f && *ptr < 0x7f)) {
        size++;
        screen_write_putc(ctx, &gc, *ptr);
      }
      ptr++;
    }
  }

  free(msg);
}

/*
 * Copy from another screen but without the selection stuff. Assumes the target
 * region is already big enough.
 */
void
screen_write_fast_copy(struct screen_write_ctx *ctx, struct screen *src,
    u_int px, u_int py, u_int nx, u_int ny)
{
  struct screen   *s = ctx->s;
  struct window_pane  *wp = ctx->wp;
  struct tty_ctx     ttyctx;
  struct grid   *gd = src->grid;
  struct grid_line  *gl, *sgl;
  struct grid_cell   gc;
  u_int      xx, yy, cx = s->cx, cy = s->cy;
  int      xoff = 0, yoff = 0;
  struct visible_ranges *r;

  if (nx == 0 || ny == 0)
    return;
  if (wp != NULL) {
    xoff = wp->xoff;
    yoff = wp->yoff;
  }

  for (yy = py; yy < py + ny; yy++) {
    if (yy >= gd->hsize + gd->sy)
      break;
    s->cx = cx;
    screen_write_initctx(ctx, &ttyctx, 0, 0);
    r = window_visible_ranges(wp, xoff + s->cx, s->cy + yoff, nx,
        NULL);
    for (xx = px; xx < px + nx; xx++) {
      gl = grid_get_line(gd, yy);
      sgl = grid_get_line(s->grid, s->cy);
      if (xx >= gl->cellsize && s->cx >= sgl->cellsize)
        break;

      grid_get_cell(gd, xx, yy, &gc);
      if (xx + gc.data.width > px + nx)
        break;
      grid_view_set_cell(s->grid, s->cx, s->cy, &gc);

      if (!window_position_is_visible(r, xoff + s->cx))
        break;
      ttyctx.cell = &gc;
      ttyctx.flags &= TTY_CTX_SYNC;
      tty_write(tty_cmd_cell, &ttyctx);
      ttyctx.ocx++;

      s->cx++;
    }
    s->cy++;
  }

  s->cx = cx;
  s->cy = cy;
}

/* Select character set for drawing border lines. */
static void
screen_write_box_border_set(enum box_lines lines, int cell_type,
    struct grid_cell *gc)
{
  switch (lines) {
  case BOX_LINES_NONE:
    break;
  case BOX_LINES_DOUBLE:
    gc->attr &= ~GRID_ATTR_CHARSET;
    utf8_copy(&gc->data, tty_acs_double_borders(cell_type));
    break;
  case BOX_LINES_HEAVY:
    gc->attr &= ~GRID_ATTR_CHARSET;
    utf8_copy(&gc->data, tty_acs_heavy_borders(cell_type));
    break;
  case BOX_LINES_ROUNDED:
    gc->attr &= ~GRID_ATTR_CHARSET;
    utf8_copy(&gc->data, tty_acs_rounded_borders(cell_type));
    break;
  case BOX_LINES_SIMPLE:
    gc->attr &= ~GRID_ATTR_CHARSET;
    utf8_set(&gc->data, SIMPLE_BORDERS[cell_type]);
    break;
  case BOX_LINES_PADDED:
    gc->attr &= ~GRID_ATTR_CHARSET;
    utf8_set(&gc->data, PADDED_BORDERS[cell_type]);
    break;
  case BOX_LINES_SINGLE:
  case BOX_LINES_DEFAULT:
    gc->attr |= GRID_ATTR_CHARSET;
    utf8_set(&gc->data, CELL_BORDERS[cell_type]);
    break;
  }
}

/* Draw a horizontal line on screen. */
void
screen_write_hline(struct screen_write_ctx *ctx, u_int nx, int left, int right,
   enum box_lines lines, const struct grid_cell *border_gc)
{
  struct screen   *s = ctx->s;
  struct grid_cell   gc;
  u_int      cx, cy, i;

  cx = s->cx;
  cy = s->cy;

  if (border_gc != NULL)
    memcpy(&gc, border_gc, sizeof gc);
  else
    memcpy(&gc, &grid_default_cell, sizeof gc);
  gc.attr |= GRID_ATTR_CHARSET;

  if (left)
    screen_write_box_border_set(lines, CELL_URD, &gc);
  else
    screen_write_box_border_set(lines, CELL_LR, &gc);
  screen_write_cell(ctx, &gc);

  screen_write_box_border_set(lines, CELL_LR, &gc);
  for (i = 1; i < nx - 1; i++)
    screen_write_cell(ctx, &gc);

  if (right)
    screen_write_box_border_set(lines, CELL_ULD, &gc);
  else
    screen_write_box_border_set(lines, CELL_LR, &gc);
  screen_write_cell(ctx, &gc);

  screen_write_set_cursor(ctx, cx, cy);
}

/* Draw a vertical line on screen. */
void
screen_write_vline(struct screen_write_ctx *ctx, u_int ny, int top, int bottom,
    const struct grid_cell *gcp)
{
  struct screen   *s = ctx->s;
  struct grid_cell   gc;
  u_int      cx, cy, i;

  cx = s->cx;
  cy = s->cy;

  if (gcp != NULL)
    memcpy(&gc, gcp, sizeof gc);
  else
    memcpy(&gc, &grid_default_cell, sizeof gc);
  gc.attr |= GRID_ATTR_CHARSET;

  screen_write_putc(ctx, &gc, top ? 'w' : 'x');
  for (i = 1; i < ny - 1; i++) {
    screen_write_set_cursor(ctx, cx, cy + i);
    screen_write_putc(ctx, &gc, 'x');
  }
  screen_write_set_cursor(ctx, cx, cy + ny - 1);
  screen_write_putc(ctx, &gc, bottom ? 'v' : 'x');

  screen_write_set_cursor(ctx, cx, cy);
}

/* Draw a menu on screen. */
void
screen_write_menu(struct screen_write_ctx *ctx, struct menu *menu, int choice,
    enum box_lines lines, const struct grid_cell *menu_gc,
    const struct grid_cell *border_gc, const struct grid_cell *choice_gc)
{
  struct screen   *s = ctx->s;
  struct grid_cell   default_gc;
  const struct grid_cell  *gc = &default_gc;
  u_int      border, cx = s->cx, cy = s->cy, i, j, width;
  const char    *name;

  memcpy(&default_gc, menu_gc, sizeof default_gc);

  if (lines == BOX_LINES_NONE) {
    border = 0;
    width = menu->item_width;
  } else {
    border = 1;
    width = menu->width;
    screen_write_box(ctx, width + 4, menu->count + 2, lines,
        border_gc, menu->title);
  }

  for (i = 0; i < menu->count; i++) {
    name = menu->items[i].name;
    if (name == NULL) {
      screen_write_cursormove(ctx, cx, cy + border + i, 0);
      screen_write_hline(ctx, width + 2 + (2 * border), 1, 1,
          lines, border_gc);
      continue;
    }

    if (choice >= 0 && i == (u_int)choice && *name != '-')
      gc = choice_gc;

    screen_write_cursormove(ctx, cx + border, cy + border + i, 0);
    for (j = 0; j < width + 2; j++)
      screen_write_putc(ctx, gc, ' ');

    screen_write_cursormove(ctx, cx + border + 1, cy + border + i,
        0);
    if (*name == '-') {
      default_gc.attr |= GRID_ATTR_DIM;
      format_draw(ctx, gc, width, name + 1, NULL, 0);
      default_gc.attr &= ~GRID_ATTR_DIM;
      continue;
    }

    format_draw(ctx, gc, width, name, NULL, 0);
    gc = &default_gc;
  }

  screen_write_set_cursor(ctx, cx, cy);
}

/* Draw a box on screen. */
void
screen_write_box(struct screen_write_ctx *ctx, u_int nx, u_int ny,
    enum box_lines lines, const struct grid_cell *gcp, const char *title)
{
  struct screen   *s = ctx->s;
  struct grid_cell   gc;
  u_int      cx, cy, i;

  cx = s->cx;
  cy = s->cy;

  if (gcp != NULL)
    memcpy(&gc, gcp, sizeof gc);
  else
    memcpy(&gc, &grid_default_cell, sizeof gc);

  gc.attr |= GRID_ATTR_CHARSET;
  gc.flags |= GRID_FLAG_NOPALETTE;

  /* Draw top border */
  screen_write_box_border_set(lines, CELL_RD, &gc);
  screen_write_cell(ctx, &gc);
  screen_write_box_border_set(lines, CELL_LR, &gc);
  for (i = 1; i < nx - 1; i++)
    screen_write_cell(ctx, &gc);
  screen_write_box_border_set(lines, CELL_LD, &gc);
  screen_write_cell(ctx, &gc);

  /* Draw bottom border */
  screen_write_set_cursor(ctx, cx, cy + ny - 1);
  screen_write_box_border_set(lines, CELL_RU, &gc);
  screen_write_cell(ctx, &gc);
  screen_write_box_border_set(lines, CELL_LR, &gc);
  for (i = 1; i < nx - 1; i++)
    screen_write_cell(ctx, &gc);
  screen_write_box_border_set(lines, CELL_LU, &gc);
  screen_write_cell(ctx, &gc);

  /* Draw sides */
  screen_write_box_border_set(lines, CELL_UD, &gc);
  for (i = 1; i < ny - 1; i++) {
    /* left side */
    screen_write_set_cursor(ctx, cx, cy + i);
    screen_write_cell(ctx, &gc);
    /* right side */
    screen_write_set_cursor(ctx, cx + nx - 1, cy + i);
    screen_write_cell(ctx, &gc);
  }

  if (title != NULL) {
    gc.attr &= ~GRID_ATTR_CHARSET;
    screen_write_cursormove(ctx, cx + 2, cy, 0);
    format_draw(ctx, &gc, nx - 4, title, NULL, 0);
  }

  screen_write_set_cursor(ctx, cx, cy);
}

/*
 * Write a preview version of a window. Assumes target area is big enough and
 * already cleared.
 */
void
screen_write_preview(struct screen_write_ctx *ctx, struct screen *src, u_int nx,
    u_int ny)
{
  struct screen   *s = ctx->s;
  struct grid_cell   gc;
  u_int      cx, cy, px, py;

  cx = s->cx;
  cy = s->cy;

  /*
   * If the cursor is on, pick the area around the cursor, otherwise use
   * the top left.
   */
  if (src->mode & MODE_CURSOR) {
    px = src->cx;
    if (px < nx / 3)
      px = 0;
    else
      px = px - nx / 3;
    if (px + nx > screen_size_x(src)) {
      if (nx > screen_size_x(src))
        px = 0;
      else
        px = screen_size_x(src) - nx;
    }
    py = src->cy;
    if (py < ny / 3)
      py = 0;
    else
      py = py - ny / 3;
    if (py + ny > screen_size_y(src)) {
      if (ny > screen_size_y(src))
        py = 0;
      else
        py = screen_size_y(src) - ny;
    }
  } else {
    px = 0;
    py = 0;
  }

  screen_write_fast_copy(ctx, src, px, src->grid->hsize + py, nx, ny);

  if (src->mode & MODE_CURSOR) {
    grid_view_get_cell(src->grid, src->cx, src->cy, &gc);
    gc.attr |= GRID_ATTR_REVERSE;
    screen_write_set_cursor(ctx, cx + (src->cx - px),
        cy + (src->cy - py));
    screen_write_cell(ctx, &gc);
  }
}

/* Set a mode. */
void
screen_write_mode_set(struct screen_write_ctx *ctx, int mode)
{
  struct screen *s = ctx->s;

  s->mode |= mode;

  if (log_get_level() != 0)
    log_debug("%s: %s", __func__, screen_mode_to_string(mode));
}

/* Clear a mode. */
void
screen_write_mode_clear(struct screen_write_ctx *ctx, int mode)
{
  struct screen *s = ctx->s;

  s->mode &= ~mode;

  if (log_get_level() != 0)
    log_debug("%s: %s", __func__, screen_mode_to_string(mode));
}

/* Sync timeout callback. */
static void
screen_write_sync_callback(__unused int fd, __unused short events, void *arg)
{
  struct window_pane  *wp = arg;

  log_debug("%s: %%%u sync timer expired", __func__, wp->id);
  evtimer_del(&wp->sync_timer);

  if (wp->base.mode & MODE_SYNC) {
    wp->base.mode &= ~MODE_SYNC;
    screen_write_sync_flush_dirty(wp);
  }
}

/* Start sync mode. */
void
screen_write_start_sync(struct window_pane *wp)
{
  struct timeval  tv = { .tv_sec = 1, .tv_usec = 0 };

  if (wp == NULL)
    return;

  wp->base.mode |= MODE_SYNC;
  if (!event_initialized(&wp->sync_timer))
    evtimer_set(&wp->sync_timer, screen_write_sync_callback, wp);
  evtimer_add(&wp->sync_timer, &tv);

  log_debug("%s: %%%u started sync mode", __func__, wp->id);
}

/* Stop sync mode. */
void
screen_write_stop_sync(struct window_pane *wp)
{
  if (wp == NULL || (~wp->base.mode & MODE_SYNC))
    return;

  if (event_initialized(&wp->sync_timer))
    evtimer_del(&wp->sync_timer);
  wp->base.mode &= ~MODE_SYNC;

  screen_write_sync_flush_dirty(wp);

  log_debug("%s: %%%u stopped sync mode", __func__, wp->id);
}

/* Flush pending output before clearing sync mode. */
void
screen_write_end_sync(struct screen_write_ctx *ctx)
{
  struct window_pane  *wp = ctx->wp;

  if (wp == NULL)
    return;
  if (wp->base.mode & MODE_SYNC)
    screen_write_collect_flush(ctx, 0, __func__);
  screen_write_stop_sync(wp);
}

/* Cursor up by ny. */
void
screen_write_cursorup(struct screen_write_ctx *ctx, u_int ny)
{
  struct screen *s = ctx->s;
  u_int    cx = s->cx, cy = s->cy;

  if (ny == 0)
    ny = 1;

  if (cy < s->rupper) {
    /* Above region. */
    if (ny > cy)
      ny = cy;
  } else {
    /* Below region. */
    if (ny > cy - s->rupper)
      ny = cy - s->rupper;
  }
  if (cx == screen_size_x(s))
    cx--;

  cy -= ny;

  screen_write_set_cursor(ctx, cx, cy);
}

/* Cursor down by ny. */
void
screen_write_cursordown(struct screen_write_ctx *ctx, u_int ny)
{
  struct screen *s = ctx->s;
  u_int    cx = s->cx, cy = s->cy;

  if (ny == 0)
    ny = 1;

  if (cy > s->rlower) {
    /* Below region. */
    if (ny > screen_size_y(s) - 1 - cy)
      ny = screen_size_y(s) - 1 - cy;
  } else {
    /* Above region. */
    if (ny > s->rlower - cy)
      ny = s->rlower - cy;
  }
  if (cx == screen_size_x(s))
      cx--;
  else if (ny == 0)
    return;

  cy += ny;

  screen_write_set_cursor(ctx, cx, cy);
}

/* Cursor right by nx. */
void
screen_write_cursorright(struct screen_write_ctx *ctx, u_int nx)
{
  struct screen *s = ctx->s;
  u_int    cx = s->cx, cy = s->cy;

  if (nx == 0)
    nx = 1;

  if (nx > screen_size_x(s) - 1 - cx)
    nx = screen_size_x(s) - 1 - cx;
  if (nx == 0)
    return;

  cx += nx;

  screen_write_set_cursor(ctx, cx, cy);
}

/* Cursor left by nx. */
void
screen_write_cursorleft(struct screen_write_ctx *ctx, u_int nx)
{
  struct screen *s = ctx->s;
  u_int    cx = s->cx, cy = s->cy;

  if (nx == 0)
    nx = 1;

  if (nx > cx)
    nx = cx;
  if (nx == 0)
    return;

  cx -= nx;

  screen_write_set_cursor(ctx, cx, cy);
}

/* Backspace; cursor left unless at start of wrapped line when can move up. */
void
screen_write_backspace(struct screen_write_ctx *ctx)
{
  struct screen   *s = ctx->s;
  struct grid_line  *gl;
  u_int      cx = s->cx, cy = s->cy;

  if (cx == 0) {
    if (cy == 0)
      return;
    gl = grid_get_line(s->grid, s->grid->hsize + cy - 1);
    if (gl->flags & GRID_LINE_WRAPPED) {
      cy--;
      cx = screen_size_x(s) - 1;
    }
  } else
    cx--;

  screen_write_set_cursor(ctx, cx, cy);
}

/* Is this cell a single ASCII character? */
static int
screen_write_cell_is_single(const struct grid_cell *gc)
{
  if (gc->data.width != 1)
    return (0);
  if (gc->data.size != 1)
    return (0);
  if (*gc->data.data < 0x20 || *gc->data.data == 0x7f)
    return (0);
  if (gc->flags & GRID_FLAG_CLEARED)
    return (0);
  if (gc->flags & GRID_FLAG_PADDING)
    return (0);
  if (gc->flags & GRID_FLAG_TAB)
    return (0);
  return (1);
}

/* Redraw all visible cells on a line. */
static void
screen_write_redraw_line(struct screen_write_ctx *ctx, struct tty_ctx *ttyctx,
    u_int yy)
{
  struct window_pane  *wp = ctx->wp;
  struct screen   *s = ctx->s;
  struct grid_cell   gc, ngc;
  u_int      sx = screen_size_x(s), cx, i;
  int      xoff = wp->xoff, yoff = wp->yoff;
  struct visible_ranges *r;
  struct visible_range  *ri;

  r = window_visible_ranges(wp, xoff, yoff + yy, sx, NULL);
  for (i = 0; i < r->used; i++) {
    ri = &r->ranges[i];
    if (ri->nx == 0)
      continue;

    cx = ri->px - xoff;
    if (cx >= sx)
      continue;
    if (cx + ri->nx > sx)
      ttyctx->n = sx - cx;
    else
      ttyctx->n = ri->nx;
    if (ttyctx->n == 0)
      continue;
    ttyctx->ocx = cx;
    ttyctx->ocy = yy;

    if (ttyctx->n != 1) {
      tty_write(tty_cmd_redrawline, ttyctx);
      continue;
    }

    grid_view_get_cell(s->grid, cx, yy, &gc);
    if (!screen_write_cell_is_single(&gc)) {
      tty_write(tty_cmd_redrawline, ttyctx);
      continue;
    }
    if (~gc.flags & GRID_FLAG_SELECTED)
      ttyctx->cell = &gc;
    else {
      screen_select_cell(s, &ngc, &gc);
      ttyctx->cell = &ngc;
    }
    tty_write(tty_cmd_cell, ttyctx);
  }
}

/* Redraw dirty lines. */
static void
screen_write_sync_flush_dirty(struct window_pane *wp)
{
  struct screen_write_ctx  ctx;
  struct tty_ctx     ttyctx;
  struct screen   *s = &wp->base;
  u_int      y, sy = screen_size_y(s), lines = 0;

  if (wp->sync_dirty == NULL)
    return;

  screen_write_start_pane(&ctx, wp, s);
  screen_write_initctx(&ctx, &ttyctx, 1, 1);

  if (wp->sync_scrolled != 0)
    screen_write_sync_apply_scroll(&ctx, &ttyctx);

  if (~wp->flags & PANE_REDRAW) {
    for (y = 0; y < sy; y++) {
      if (bit_test(wp->sync_dirty, y)) {
        screen_write_redraw_line(&ctx, &ttyctx, y);
        lines++;
      }
    }
  }
  log_debug("%s: %%%u had %u dirty lines", __func__, wp->id, lines);

  screen_write_stop(&ctx);
  screen_write_sync_clear_dirty(wp);
}

/* Clear pending synchronized output. */
void
screen_write_sync_clear_dirty(struct window_pane *wp)
{
  if (wp != NULL) {
    free(wp->sync_dirty);
    wp->sync_dirty = NULL;
    wp->sync_dirty_size = 0;
    wp->sync_scrolled = 0;
  }
}

/* Defer scrolling until the synchronized update ends. */
static void
screen_write_sync_scroll_dirty(struct screen_write_ctx *ctx)
{
  struct window_pane  *wp = ctx->wp;
  struct screen   *s = ctx->s;
  u_int      n = ctx->scrolled, y, sy = screen_size_y(s);
  u_int      ry = s->rlower + 1 - s->rupper;
  bitstr_t    *bs;

  if (n > ry)
    n = ry;
  if (wp == NULL ||
      n == ry ||
      s->rlower >= sy ||
      window_pane_scrollbar_overlay_visible(wp)) {
    screen_write_should_draw_lines(ctx, s->rupper, ry);
    return;
  }
  if (wp->flags & (PANE_REDRAW|PANE_DROP))
    return;
  bs = screen_write_sync_allocate_dirty(wp, sy);

  if (wp->sync_scrolled != 0 &&
      (wp->sync_rupper != s->rupper ||
      wp->sync_rlower != s->rlower ||
      wp->sync_bg != ctx->bg)) {
    log_debug("%s: %%%u region changed, redrawing all", __func__,
        wp->id);
    bit_nset(bs, 0, sy - 1);
    wp->sync_scrolled = 0;
    return;
  }

  /* Keep dirty lines aligned with the scrolled grid. */
  for (y = s->rupper; y + n <= s->rlower; y++) {
    if (bit_test(bs, y + n))
      bit_set(bs, y);
    else
      bit_clear(bs, y);
  }
  bit_nset(bs, s->rlower + 1 - n, s->rlower);

  wp->sync_rupper = s->rupper;
  wp->sync_rlower = s->rlower;
  wp->sync_bg = ctx->bg;
  wp->sync_scrolled += n;
  if (wp->sync_scrolled >= ry) {
    bit_nset(bs, s->rupper, s->rlower);
    wp->sync_scrolled = 0;
  }
  window_pane_scrollbar_redraw(wp);

  log_debug("%s: %%%u deferred scroll of %u (region %u-%u)", __func__,
      wp->id, wp->sync_scrolled, s->rupper, s->rlower);
}

/* Redraw the scrolled lines for a client which cannot scroll them. */
static void
screen_write_sync_redraw_cb(const struct tty_ctx *ttyctx, u_int py, u_int ny)
{
  struct window_pane  *wp = ttyctx->arg;

  bit_nset(wp->sync_dirty, py, py + ny - 1);
}

/* Send the deferred scroll to the client. */
static void
screen_write_sync_apply_scroll(struct screen_write_ctx *ctx,
    struct tty_ctx *ttyctx)
{
  struct window_pane  *wp = ctx->wp;
  struct screen   *s = ctx->s;
  u_int      sy = screen_size_y(s), n = wp->sync_scrolled;
  tty_ctx_redraw_cb  redraw_cb;

  wp->sync_scrolled = 0;
  if (wp->flags & PANE_REDRAW)
    return;
  if (wp->sync_rlower >= sy || wp->sync_rupper > wp->sync_rlower) {
    bit_nset(wp->sync_dirty, 0, sy - 1);
    return;
  }
  if ((ttyctx->flags & TTY_CTX_PANE_OBSCURED) ||
      window_pane_scrollbar_overlay_visible(wp)) {
    bit_nset(wp->sync_dirty, wp->sync_rupper, wp->sync_rlower);
    return;
  }

  log_debug("%s: %%%u scroll of %u (region %u-%u)", __func__, wp->id, n,
      wp->sync_rupper, wp->sync_rlower);

  ttyctx->orupper = wp->sync_rupper;
  ttyctx->orlower = wp->sync_rlower;
  if (wp->yoff + wp->sy > wp->window->sy)
    ttyctx->orlower -= (wp->yoff + wp->sy - wp->window->sy);
  ttyctx->n = n;
  ttyctx->bg = wp->sync_bg;
  redraw_cb = ttyctx->redraw_cb;
  ttyctx->redraw_cb = screen_write_sync_redraw_cb;
  tty_write(tty_cmd_scrollup, ttyctx);

  ttyctx->redraw_cb = redraw_cb;
  ttyctx->orupper = s->rupper;
  ttyctx->orlower = s->rlower;
  ttyctx->n = 0;
}

/* Redraw all visible cells in a pane. */
static void
screen_write_redraw_pane(struct screen_write_ctx *ctx, struct tty_ctx *ttyctx)
{
  struct screen *s = ctx->s;
  u_int    yy;

  for (yy = 0; yy < screen_size_y(s); yy++)
    screen_write_redraw_line(ctx, ttyctx, yy);
}

/* VT100 alignment test. */
void
screen_write_alignmenttest(struct screen_write_ctx *ctx)
{
  struct screen   *s = ctx->s;
  struct tty_ctx     ttyctx;
  struct grid_cell   gc;
  u_int      xx, yy;

  memcpy(&gc, &grid_default_cell, sizeof gc);
  utf8_set(&gc.data, 'E');

#ifdef ENABLE_SIXEL
  if (image_free_all(s) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  for (yy = 0; yy < screen_size_y(s); yy++) {
    for (xx = 0; xx < screen_size_x(s); xx++)
      grid_view_set_cell(s->grid, xx, yy, &gc);
  }

  screen_write_set_cursor(ctx, 0, 0);

  s->rupper = 0;
  s->rlower = screen_size_y(s) - 1;

  screen_write_collect_clear(ctx, 0, screen_size_y(s) - 1);

  screen_write_initctx(ctx, &ttyctx, 1, 1);

  if (!screen_write_should_draw_lines(ctx, 0, screen_size_y(s)))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_alignmenttest, &ttyctx);
    return;
  }

  screen_write_redraw_pane(ctx, &ttyctx);
}

/* Insert nx characters. */
void
screen_write_insertcharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
{
  struct screen *s = ctx->s;
  struct tty_ctx   ttyctx;

  if (nx == 0)
    nx = 1;

  if (nx > screen_size_x(s) - s->cx)
    nx = screen_size_x(s) - s->cx;
  if (nx == 0)
    return;

  if (s->cx > screen_size_x(s) - 1)
    return;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  screen_write_initctx(ctx, &ttyctx, 0, 1);
  ttyctx.bg = bg;

  grid_view_insert_cells(s->grid, s->cx, s->cy, nx, bg);

  screen_write_collect_flush(ctx, 0, __func__);
  ttyctx.n = nx;

  if (!screen_write_should_draw_line(ctx, s->cy))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_insertcharacter, &ttyctx);
    return;
  }

  screen_write_redraw_line(ctx, &ttyctx, s->cy);
}

/* Delete nx characters. */
void
screen_write_deletecharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
{
  struct screen *s = ctx->s;
  struct tty_ctx   ttyctx;

  if (nx == 0)
    nx = 1;

  if (nx > screen_size_x(s) - s->cx)
    nx = screen_size_x(s) - s->cx;
  if (nx == 0)
    return;

  if (s->cx > screen_size_x(s) - 1)
    return;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  screen_write_initctx(ctx, &ttyctx, 0, 1);
  ttyctx.bg = bg;

  grid_view_delete_cells(s->grid, s->cx, s->cy, nx, bg);

  screen_write_collect_flush(ctx, 0, __func__);
  ttyctx.n = nx;

  if (!screen_write_should_draw_line(ctx, s->cy))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_deletecharacter, &ttyctx);
    return;
  }

  screen_write_redraw_line(ctx, &ttyctx, s->cy);
}

/* Clear nx characters. */
void
screen_write_clearcharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
{
  struct screen *s = ctx->s;
  struct tty_ctx   ttyctx;

  if (nx == 0)
    nx = 1;

  if (nx > screen_size_x(s) - s->cx)
    nx = screen_size_x(s) - s->cx;
  if (nx == 0)
    return;

  if (s->cx > screen_size_x(s) - 1)
    return;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  screen_write_initctx(ctx, &ttyctx, 0, 1);
  ttyctx.bg = bg;

  grid_view_clear(s->grid, s->cx, s->cy, nx, 1, bg);

  screen_write_collect_flush(ctx, 0, __func__);
  ttyctx.n = nx;

  if (!screen_write_should_draw_line(ctx, s->cy))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_clearcharacter, &ttyctx);
    return;
  }

  screen_write_redraw_line(ctx, &ttyctx, s->cy);
}

/* Insert ny lines. */
void
screen_write_insertline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
{
  struct screen *s = ctx->s;
  struct grid *gd = s->grid;
  struct tty_ctx   ttyctx;
  u_int    sy = screen_size_y(s);

  if (ny == 0)
    ny = 1;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, sy - s->cy) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  if (s->cy < s->rupper || s->cy > s->rlower) {
    if (ny > sy - s->cy)
      ny = sy - s->cy;
    if (ny == 0)
      return;

    screen_write_initctx(ctx, &ttyctx, 1, 1);
    ttyctx.bg = bg;

    grid_view_insert_lines(gd, s->cy, ny, bg);

    screen_write_collect_flush(ctx, 0, __func__);
    ttyctx.n = ny;

    if (!screen_write_should_draw_lines(ctx, s->cy, sy - s->cy))
      return;
    if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
      tty_write(tty_cmd_insertline, &ttyctx);
      return;
    }

    screen_write_redraw_pane(ctx, &ttyctx);
    return;
  }

  if (ny > s->rlower + 1 - s->cy)
    ny = s->rlower + 1 - s->cy;
  if (ny == 0)
    return;

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  if (s->cy < s->rupper || s->cy > s->rlower)
    grid_view_insert_lines(gd, s->cy, ny, bg);
  else
    grid_view_insert_lines_region(gd, s->rlower, s->cy, ny, bg);

  screen_write_collect_flush(ctx, 0, __func__);
  ttyctx.n = ny;

  if (!screen_write_should_draw_lines(ctx, s->cy, s->rlower + 1 - s->cy))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_insertline, &ttyctx);
    return;
  }

  screen_write_redraw_pane(ctx, &ttyctx);
}

/* Delete ny lines. */
void
screen_write_deleteline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
{
  struct screen *s = ctx->s;
  struct grid *gd = s->grid;
  struct tty_ctx   ttyctx;
  u_int    sy = screen_size_y(s), ry;

  if (ny == 0)
    ny = 1;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, sy - s->cy) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  if (s->cy < s->rupper || s->cy > s->rlower) {
    if (ny > sy - s->cy)
      ny = sy - s->cy;
    if (ny == 0)
      return;

    screen_write_initctx(ctx, &ttyctx, 1, 1);
    ttyctx.bg = bg;

    grid_view_delete_lines(gd, s->cy, ny, bg);

    screen_write_collect_flush(ctx, 0, __func__);
    ttyctx.n = ny;

    ry = s->rlower + 1 - s->rupper;
    if (!screen_write_should_draw_lines(ctx, s->rupper, ry))
      return;
    if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
      tty_write(tty_cmd_deleteline, &ttyctx);
      return;
    }

    screen_write_redraw_pane(ctx, &ttyctx);
    return;
  }

  ry = s->rlower + 1 - s->cy;
  if (ny > ry)
    ny = ry;
  if (ny == 0)
    return;

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  if (s->cy < s->rupper || s->cy > s->rlower)
    grid_view_delete_lines(gd, s->cy, ny, bg);
  else
    grid_view_delete_lines_region(gd, s->rlower, s->cy, ny, bg);

  screen_write_collect_flush(ctx, 0, __func__);
  ttyctx.n = ny;

  if (!screen_write_should_draw_lines(ctx, s->cy, ry))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_deleteline, &ttyctx);
    return;
  }

  screen_write_redraw_pane(ctx, &ttyctx);
}

/* Clear line at cursor. */
void
screen_write_clearline(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen     *s = ctx->s;
  struct grid_line    *gl;
  u_int        sx = screen_size_x(s);
  struct screen_write_citem *ci = ctx->item;
  struct osc133_data     od;
  u_int        flags;

  gl = grid_get_line(s->grid, s->grid->hsize + s->cy);
  if (gl->cellsize == 0 && COLOUR_DEFAULT(bg))
    return;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  flags = gl->flags & GRID_LINE_OSC133_FLAGS;
  memcpy(&od, &gl->osc133_data, sizeof od);
  grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
  gl = grid_get_line(s->grid, s->grid->hsize + s->cy);
  gl->flags |= flags;
  memcpy(&gl->osc133_data, &od, sizeof gl->osc133_data);

  screen_write_collect_clear(ctx, s->cy, 1);
  ci->x = 0;
  ci->used = sx;
  ci->type = CLEAR;
  ci->bg = bg;
  TAILQ_INSERT_TAIL(&ctx->s->write_list[s->cy].items, ci, entry);
  ctx->item = screen_write_get_citem();
}

/* Clear to end of line from cursor. */
void
screen_write_clearendofline(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen     *s = ctx->s;
  struct grid_line    *gl;
  u_int        sx = screen_size_x(s);
  struct screen_write_citem *ci = ctx->item;

  if (s->cx == 0) {
    screen_write_clearline(ctx, bg);
    return;
  }

  gl = grid_get_line(s->grid, s->grid->hsize + s->cy);
  if (s->cx > sx - 1 || (s->cx >= gl->cellsize && COLOUR_DEFAULT(bg)))
    return;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  grid_view_clear(s->grid, s->cx, s->cy, sx - s->cx, 1, bg);

  ci->x = s->cx;
  ci->used = sx - s->cx;
  ci->type = CLEAR;
  ci->bg = bg;
  screen_write_collect_insert(ctx, ci);
}

/* Clear to start of line from cursor. */
void
screen_write_clearstartofline(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen      *s = ctx->s;
  u_int        sx = screen_size_x(s);
  struct screen_write_citem *ci = ctx->item;

  if (s->cx >= sx - 1) {
    screen_write_clearline(ctx, bg);
    return;
  }

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  if (s->cx > sx - 1)
    grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
  else
    grid_view_clear(s->grid, 0, s->cy, s->cx + 1, 1, bg);

  ci->x = 0;
  ci->used = s->cx + 1;
  ci->type = CLEAR;
  ci->bg = bg;
  screen_write_collect_insert(ctx, ci);
}

/* Move cursor to px,py. */
void
screen_write_cursormove(struct screen_write_ctx *ctx, int px, int py,
    int origin)
{
  struct screen *s = ctx->s;

  if (origin && py != -1 && (s->mode & MODE_ORIGIN)) {
    if ((u_int)py > s->rlower - s->rupper)
      py = s->rlower;
    else
      py += s->rupper;
  }

  if (px != -1 && (u_int)px > screen_size_x(s) - 1)
    px = screen_size_x(s) - 1;
  if (py != -1 && (u_int)py > screen_size_y(s) - 1)
    py = screen_size_y(s) - 1;

  log_debug("%s: from %u,%u to %u,%u", __func__, s->cx, s->cy, px, py);
  screen_write_set_cursor(ctx, px, py);
}

/* Reverse index (up with scroll). */
void
screen_write_reverseindex(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen *s = ctx->s;
  struct tty_ctx   ttyctx;
  u_int    ry;

  if (s->cy != s->rupper) {
    if (s->cy > 0)
      screen_write_set_cursor(ctx, -1, s->cy - 1);
    return;
  }

#ifdef ENABLE_SIXEL
  if (image_free_all(s) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  grid_view_scroll_region_down(s->grid, s->rupper, s->rlower, bg);
  screen_write_collect_flush(ctx, 0, __func__);

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  ry = s->rlower + 1 - s->rupper;
  if (!screen_write_should_draw_lines(ctx, s->rupper, ry))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_reverseindex, &ttyctx);
    return;
  }

  screen_write_redraw_pane(ctx, &ttyctx);
}

/* Set scroll region. */
void
screen_write_scrollregion(struct screen_write_ctx *ctx, u_int rupper,
    u_int rlower)
{
  struct screen *s = ctx->s;

  if (rupper > screen_size_y(s) - 1)
    rupper = screen_size_y(s) - 1;
  if (rlower > screen_size_y(s) - 1)
    rlower = screen_size_y(s) - 1;
  if (rupper >= rlower)  /* cannot be one line */
    return;

  screen_write_collect_flush(ctx, 0, __func__);

  /* Cursor moves to top-left. */
  screen_write_set_cursor(ctx, 0, 0);

  s->rupper = rupper;
  s->rlower = rlower;
}

/* Line feed. */
void
screen_write_linefeed(struct screen_write_ctx *ctx, int wrapped, u_int bg)
{
  struct screen   *s = ctx->s;
  struct grid   *gd = s->grid;
  struct grid_line  *gl;
#ifdef ENABLE_SIXEL
  int      redraw = 0;
#endif
  u_int      rupper = s->rupper, rlower = s->rlower;

  gl = grid_get_line(gd, gd->hsize + s->cy);
  if (wrapped)
    gl->flags |= GRID_LINE_WRAPPED;

  log_debug("%s: at %u,%u (region %u-%u)", __func__, s->cx, s->cy,
      rupper, rlower);

  if (bg != ctx->bg) {
    screen_write_collect_flush(ctx, 1, __func__);
    ctx->bg = bg;
  }

  if (s->cy != s->rlower) {
    if (s->cy < screen_size_y(s) - 1)
      screen_write_set_cursor(ctx, -1, s->cy + 1);
    return;
  }

#ifdef ENABLE_SIXEL
  if (rlower == screen_size_y(s) - 1)
    redraw = image_scroll_up(s, 1);
  else
    redraw = image_check_line(s, rupper, rlower - rupper);
  if (redraw && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  grid_view_scroll_region_up(gd, s->rupper, s->rlower, bg);
  screen_write_collect_scroll(ctx, bg);
  ctx->scrolled++;
}

/* Scroll up. */
void
screen_write_scrollup(struct screen_write_ctx *ctx, u_int lines, u_int bg)
{
  struct screen *s = ctx->s;
  struct grid *gd = s->grid;
  u_int    i;

  if (lines == 0)
    lines = 1;
  else if (lines > s->rlower - s->rupper + 1)
    lines = s->rlower - s->rupper + 1;

  if (bg != ctx->bg) {
    screen_write_collect_flush(ctx, 1, __func__);
    ctx->bg = bg;
  }

#ifdef ENABLE_SIXEL
  if (image_scroll_up(s, lines) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  for (i = 0; i < lines; i++) {
    grid_view_scroll_region_up(gd, s->rupper, s->rlower, bg);
    screen_write_collect_scroll(ctx, bg);
  }
  ctx->scrolled += lines;
}

/* Scroll down. */
void
screen_write_scrolldown(struct screen_write_ctx *ctx, u_int lines, u_int bg)
{
  struct screen *s = ctx->s;
  struct grid *gd = s->grid;
  struct tty_ctx   ttyctx;
  u_int    i, ry;

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  if (lines == 0)
    lines = 1;
  else if (lines > s->rlower - s->rupper + 1)
    lines = s->rlower - s->rupper + 1;

#ifdef ENABLE_SIXEL
  if (image_free_all(s) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  for (i = 0; i < lines; i++)
    grid_view_scroll_region_down(gd, s->rupper, s->rlower, bg);

  screen_write_collect_flush(ctx, 0, __func__);
  ttyctx.n = lines;

  ry = s->rlower + 1 - s->rupper;
  if (!screen_write_should_draw_lines(ctx, s->rupper, ry))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED || ctx->wp == NULL) {
    tty_write(tty_cmd_scrolldown, &ttyctx);
    return;
  }

  screen_write_redraw_pane(ctx, &ttyctx);
}

/* Carriage return (cursor to start of line). */
void
screen_write_carriagereturn(struct screen_write_ctx *ctx)
{
  screen_write_set_cursor(ctx, 0, -1);
}

/* Clear to end of screen from cursor. */
void
screen_write_clearendofscreen(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen   *s = ctx->s;
  struct grid   *gd = s->grid;
  struct tty_ctx     ttyctx;
  u_int      sx = screen_size_x(s), sy = screen_size_y(s);
  u_int      y, i, xoff, yoff, ocx, ocy;
  struct visible_ranges *r;
  struct visible_range  *ri;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, s->cy, sy - s->cy) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  /* Scroll into history if it is enabled and clearing entire screen. */
  if (s->cx == 0 &&
      s->cy == 0 &&
      (gd->flags & GRID_HISTORY) &&
      ctx->wp != NULL &&
      options_get_number(ctx->wp->options, "scroll-on-clear"))
    grid_view_clear_history(gd, bg);
  else {
    if (s->cx <= sx - 1)
      grid_view_clear(gd, s->cx, s->cy, sx - s->cx, 1, bg);
    grid_view_clear(gd, 0, s->cy + 1, sx, sy - (s->cy + 1), bg);
  }

  screen_write_collect_clear(ctx, s->cy + 1, sy - (s->cy + 1));
  screen_write_collect_flush(ctx, 0, __func__);

  if (!screen_write_should_draw_lines(ctx, s->cy, sy - s->cy))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED) {
    tty_write(tty_cmd_clearendofscreen, &ttyctx);
    return;
  }

  /* Can't just clear screen, must avoid floating windows. */
  ocx = s->cx;
  ocy = s->cy;
  if (ctx->wp != NULL) {
    xoff = ctx->wp->xoff;
    yoff = ctx->wp->yoff;
  } else {
    xoff = 0;
    yoff = 0;
  }

  /* First line (containing the cursor). */
  if (s->cx <= sx - 1) {
    r = window_visible_ranges(ctx->wp, xoff + s->cx, yoff + s->cy,
        sx - s->cx, NULL);
    for (i = 0; i < r->used; i++) {
      ri = &r->ranges[i];
      if (ri->nx == 0)
        continue;
      screen_write_collect_insert_clear(ctx, ri->px - xoff,
          ri->nx, bg);
    }
  }

  /* Below cursor to bottom. */
  for (y = s->cy + 1; y < sy; y++) {
    screen_write_set_cursor(ctx, 0, y);
    r = window_visible_ranges(ctx->wp, xoff, yoff + y, sx, NULL);
    for (i = 0; i < r->used; i++) {
      ri = &r->ranges[i];
      if (ri->nx == 0)
        continue;
      screen_write_collect_insert_clear(ctx, ri->px - xoff,
          ri->nx, bg);
    }
  }
  screen_write_set_cursor(ctx, ocx, ocy);
}

/* Clear to start of screen. */
void
screen_write_clearstartofscreen(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen   *s = ctx->s;
  struct tty_ctx     ttyctx;
  u_int      sx = screen_size_x(s);
  u_int      y, i, xoff, yoff, ocx, ocy;
  struct visible_ranges *r;
  struct visible_range  *ri;

#ifdef ENABLE_SIXEL
  if (image_check_line(s, 0, s->cy - 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  if (s->cy > 0)
    grid_view_clear(s->grid, 0, 0, sx, s->cy, bg);
  if (s->cx > sx - 1)
    grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
  else
    grid_view_clear(s->grid, 0, s->cy, s->cx + 1, 1, bg);

  screen_write_collect_clear(ctx, 0, s->cy);
  screen_write_collect_flush(ctx, 0, __func__);

  if (!screen_write_should_draw_lines(ctx, 0, s->cy + 1))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED) {
    tty_write(tty_cmd_clearstartofscreen, &ttyctx);
    return;
  }

  /* Can't just clear screen, must avoid floating windows. */
  ocx = s->cx;
  ocy = s->cy;
  if (ctx->wp != NULL) {
    xoff = ctx->wp->xoff;
    yoff = ctx->wp->yoff;
  } else {
    xoff = 0;
    yoff = 0;
  }

  /* Top to above the cursor. */
  for (y = 0; y < s->cy; y++) {
    screen_write_set_cursor(ctx, 0, y);
    r = window_visible_ranges(ctx->wp, xoff, yoff + y, sx, NULL);
    for (i = 0; i < r->used; i++) {
      ri = &r->ranges[i];
      if (ri->nx == 0)
        continue;
      screen_write_collect_insert_clear(ctx, ri->px - xoff,
          ri->nx, bg);
    }
  }

  /* Last line (containing the cursor). */
  screen_write_set_cursor(ctx, 0, s->cy);
  r = window_visible_ranges(ctx->wp, xoff, yoff + ocy, s->cx + 1, NULL);
  for (i = 0; i < r->used; i++) {
    ri = &r->ranges[i];
    if (ri->nx == 0)
      continue;
    screen_write_collect_insert_clear(ctx, ri->px - xoff, ri->nx,
        bg);
  }
  screen_write_set_cursor(ctx, ocx, ocy);
}

/* Clear entire screen. */
void
screen_write_clearscreen(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen   *s = ctx->s;
  struct tty_ctx     ttyctx;
  u_int      sx = screen_size_x(s), sy = screen_size_y(s);
  u_int      y, i, xoff, yoff, ocx, ocy;
  struct visible_ranges *r;
  struct visible_range  *ri;

#ifdef ENABLE_SIXEL
  if (image_free_all(s) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  ttyctx.bg = bg;

  /* Scroll into history if it is enabled. */
  if ((s->grid->flags & GRID_HISTORY) &&
      ctx->wp != NULL &&
      options_get_number(ctx->wp->options, "scroll-on-clear"))
    grid_view_clear_history(s->grid, bg);
  else
    grid_view_clear(s->grid, 0, 0, sx, sy, bg);

  screen_write_collect_clear(ctx, 0, sy);

  if (!screen_write_should_draw_lines(ctx, 0, sy))
    return;
  if (~ttyctx.flags & TTY_CTX_PANE_OBSCURED) {
    tty_write(tty_cmd_clearscreen, &ttyctx);
    return;
  }

  /* Can't just clear screen, must avoid floating windows. */
  ocx = s->cx;
  ocy = s->cy;
  if (ctx->wp != NULL) {
    xoff = ctx->wp->xoff;
    yoff = ctx->wp->yoff;
  } else {
    xoff = 0;
    yoff = 0;
  }

  /* Clear every line. */
  for (y = 0; y < sy; y++) {
    screen_write_set_cursor(ctx, 0, y);
    r = window_visible_ranges(ctx->wp, xoff, yoff + y, sx, NULL);
    for (i = 0; i < r->used; i++) {
      ri = &r->ranges[i];
      if (ri->nx == 0)
        continue;
      screen_write_collect_insert_clear(ctx, ri->px - xoff,
          ri->nx, bg);
    }
  }
  screen_write_set_cursor(ctx, ocx, ocy);
}

/* Clear entire history. */
void
screen_write_clearhistory(struct screen_write_ctx *ctx)
{
  grid_clear_history(ctx->s->grid);
}

/* Force a full redraw. */
void
screen_write_fullredraw(struct screen_write_ctx *ctx)
{
  struct tty_ctx   ttyctx;

  screen_write_collect_flush(ctx, 0, __func__);

  screen_write_initctx(ctx, &ttyctx, 1, 0);
  if (ttyctx.redraw_cb != NULL)
    ttyctx.redraw_cb(&ttyctx, 0, ttyctx.sy);
}

/* Trim collected items. */
static struct screen_write_citem *
screen_write_collect_trim(struct screen_write_ctx *ctx, u_int y, u_int x,
    u_int used, int *wrapped)
{
  struct screen_write_cline *cl = &ctx->s->write_list[y];
  struct screen_write_citem *ci, *ci2, *tmp, *before = NULL;
  u_int        sx = x, ex = x + used - 1;
  u_int        csx, cex;

  if (TAILQ_EMPTY(&cl->items))
    return (NULL);
  TAILQ_FOREACH_SAFE(ci, &cl->items, entry, tmp) {
    csx = ci->x;
    cex = ci->x + ci->used - 1;

    /* Item is entirely before. */
    if (cex < sx) {
      log_debug("%s: %p %u-%u before %u-%u", __func__, ci,
          csx, cex, sx, ex);
      continue;
    }

    /* Item is entirely after. */
    if (csx > ex) {
      log_debug("%s: %p %u-%u after %u-%u", __func__, ci,
          csx, cex, sx, ex);
      before = ci;
      break;
    }

    /* Item is entirely inside. */
    if (csx >= sx && cex <= ex) {
      log_debug("%s: %p %u-%u inside %u-%u", __func__, ci,
          csx, cex, sx, ex);
      TAILQ_REMOVE(&cl->items, ci, entry);
      screen_write_free_citem(ci);
      if (csx == 0 && ci->wrapped && wrapped != NULL)
        *wrapped = 1;
      continue;
    }

    /* Item under the start. */
    if (csx < sx && cex >= sx && cex <= ex) {
      log_debug("%s: %p %u-%u start %u-%u", __func__, ci,
          csx, cex, sx, ex);
      ci->used = sx - csx;
      log_debug("%s: %p now %u-%u", __func__, ci, ci->x,
          ci->x + ci->used + 1);
      continue;
    }

    /* Item covers the end. */
    if (cex > ex && csx >= sx && csx <= ex) {
      log_debug("%s: %p %u-%u end %u-%u", __func__, ci,
          csx, cex, sx, ex);
      ci->x = ex + 1;
      ci->used = cex - ex;
      log_debug("%s: %p now %u-%u", __func__, ci, ci->x,
          ci->x + ci->used + 1);
      before = ci;
      break;
    }

    /* Item must cover both sides. */
    log_debug("%s: %p %u-%u under %u-%u", __func__, ci,
        csx, cex, sx, ex);
    ci2 = screen_write_get_citem();
    ci2->type = ci->type;
    ci2->bg = ci->bg;
    memcpy(&ci2->gc, &ci->gc, sizeof ci2->gc);
    TAILQ_INSERT_AFTER(&cl->items, ci, ci2, entry);

    ci->used = sx - csx;
    ci2->x = ex + 1;
    ci2->used = cex - ex;

    log_debug("%s: %p now %u-%u (%p) and %u-%u (%p)", __func__, ci,
        ci->x, ci->x + ci->used - 1, ci, ci2->x,
        ci2->x + ci2->used - 1, ci2);
    before = ci2;
    break;
  }
  return (before);
}

/* Clear collected lines. */
static void
screen_write_collect_clear(struct screen_write_ctx *ctx, u_int y, u_int n)
{
  struct screen_write_cline *cl;
  u_int        i;

  for (i = y; i < y + n; i++) {
    cl = &ctx->s->write_list[i];
    TAILQ_CONCAT(&screen_write_citem_freelist, &cl->items, entry);
  }
}

/* Scroll collected lines up. */
static void
screen_write_collect_scroll(struct screen_write_ctx *ctx, u_int bg)
{
  struct screen     *s = ctx->s;
  struct screen_write_cline *cl;
  u_int        y;
  char        *saved;
  struct screen_write_citem *ci;

  log_debug("%s: at %u,%u (region %u-%u)", __func__, s->cx, s->cy,
      s->rupper, s->rlower);

  screen_write_collect_clear(ctx, s->rupper, 1);
  saved = ctx->s->write_list[s->rupper].data;
  for (y = s->rupper; y < s->rlower; y++) {
    cl = &ctx->s->write_list[y + 1];
    TAILQ_CONCAT(&ctx->s->write_list[y].items, &cl->items, entry);
    ctx->s->write_list[y].data = cl->data;
  }
  ctx->s->write_list[s->rlower].data = saved;

  ci = screen_write_get_citem();
  ci->x = 0;
  ci->used = screen_size_x(s);
  ci->type = CLEAR;
  ci->bg = bg;
  TAILQ_INSERT_TAIL(&ctx->s->write_list[s->rlower].items, ci, entry);
}

/* Flush collected scrolling. */
static int
screen_write_collect_flush_scrolled(struct screen_write_ctx *ctx)
{
  struct window_pane  *wp = ctx->wp;
  struct screen   *s = ctx->s;
  struct tty_ctx     ttyctx;

  screen_write_initctx(ctx, &ttyctx, 1, 1);
  if (ttyctx.flags & TTY_CTX_PANE_OBSCURED && wp != NULL) {
    screen_write_redraw_pane(ctx, &ttyctx);
    return 0;
  }
  if (wp != NULL && window_pane_scrollbar_overlay_visible(wp)) {
    wp->flags |= PANE_REDRAW;
    return 0;
  }

  log_debug("%s: scrolled %u (region %u-%u)", __func__, ctx->scrolled,
      s->rupper, s->rlower);
  if (ctx->scrolled > s->rlower - s->rupper + 1)
    ctx->scrolled = s->rlower - s->rupper + 1;

  if (wp != NULL && wp->yoff + wp->sy > wp->window->sy)
    ttyctx.orlower -= (wp->yoff + wp->sy - wp->window->sy);
  ttyctx.n = ctx->scrolled;
  ttyctx.bg = ctx->bg;
  tty_write(tty_cmd_scrollup, &ttyctx);

  if (wp != NULL)
    window_pane_scrollbar_redraw(wp);
  return 1;
}

/* Flush a collected line. */
static u_int
screen_write_collect_flush_line(struct screen_write_ctx *ctx, u_int y)
{
  struct window_pane    *wp = ctx->wp;
  struct screen     *s = ctx->s;
  struct screen_write_citem *ci, *tmp;
  struct screen_write_cline *cl = &s->write_list[y];
  u_int        last = UINT_MAX, items = 0, wsx, wsy;
  u_int        w_length, i;
  int        w_start, w_end, xoff, yoff, written;
  int        r_start, r_end, c_start, c_end;
  struct tty_ctx       ttyctx;
  struct visible_ranges   *r;
  struct visible_range    *ri;

  if (wp != NULL) {
    wsx = wp->window->sx;
    wsy = wp->window->sy;
    xoff = wp->xoff;
    yoff = wp->yoff;
  } else {
    wsx = screen_size_x(s);
    wsy = screen_size_y(s);
    xoff = 0;
    yoff = 0;
  }
  if (y + yoff >= wsy)
    return (0);

  r = window_visible_ranges(wp, 0, y + yoff, wsx, NULL);
  TAILQ_FOREACH_SAFE(ci, &cl->items, entry, tmp) {
    log_debug("collect list: x=%u (last %u), y=%u, used=%u", ci->x,
        last, y, ci->used);
    if (last != UINT_MAX && ci->x <= last)
      fatalx("collect list bad order: %u <= %u", ci->x, last);

    w_length = 0;
    written = 0;
    for (i = 0; i < r->used; i++) {
      ri = &r->ranges[i];
      if (ri->nx == 0)
        continue;

      r_start = ri->px;
      r_end = ri->px + ri->nx;
      c_start = ci->x;
      c_end = ci->x + ci->used;

      if (c_start + xoff >= r_end || c_end + xoff <= r_start)
        continue;
      if (r_start > c_start + xoff)
        w_start = r_start - xoff;
      else
        w_start = c_start;
      if (c_end + xoff > r_end)
        w_end = r_end - xoff;
      else
        w_end = c_end;
      if (w_end <= w_start)
        continue;
      w_length = w_end - w_start;
      if (w_length <= 0)
        continue;

      screen_write_set_cursor(ctx, w_start, y);
      if (ci->type == CLEAR) {
        screen_write_initctx(ctx, &ttyctx, 1, 0);
        ttyctx.bg = ci->bg;
        ttyctx.n = w_length;
        tty_write(tty_cmd_clearcharacter, &ttyctx);
      } else {
        screen_write_initctx(ctx, &ttyctx, 0, 1);
        if (ttyctx.flags & TTY_CTX_PANE_OBSCURED) {
          ttyctx.n = w_length;
          tty_write(tty_cmd_redrawline, &ttyctx);
        } else {
          ttyctx.cell = &ci->gc;
          if (ci->wrapped)
            ttyctx.flags |= TTY_CTX_WRAPPED;
          ttyctx.data.data = cl->data + w_start;
          ttyctx.data.size = w_length;
          tty_write(tty_cmd_cells, &ttyctx);
        }
      }
      items++;
      written = 1;
    }
    if (written) {
      last = ci->x;
      TAILQ_REMOVE(&cl->items, ci, entry);
      screen_write_free_citem(ci);
    }
  }
  return (items);
}

/* Flush collected lines. */
static void
screen_write_collect_flush(struct screen_write_ctx *ctx, int scroll_only,
    const char *from)
{
  struct screen     *s = ctx->s;
  struct window_pane    *wp = ctx->wp;
  u_int        y, cx, cy, items = 0;
  struct screen_write_citem *ci, *tmp;
  struct screen_write_cline *cl;

  if (wp != NULL && (wp->flags & (PANE_REDRAW|PANE_DROP)))
    goto discard;
  if (s->mode & MODE_SYNC) {
    if (ctx->scrolled != 0)
      screen_write_sync_scroll_dirty(ctx);
    for (y = 0; y < screen_size_y(s); y++) {
      cl = &s->write_list[y];
      if (!TAILQ_EMPTY(&cl->items))
        screen_write_should_draw_line(ctx, y);
    }
    goto discard;
  }

  if (ctx->scrolled != 0) {
    if (!screen_write_collect_flush_scrolled(ctx))
      goto discard;
    ctx->scrolled = 0;
  }
  ctx->bg = 8;

  if (scroll_only)
    return;

  cx = s->cx; cy = s->cy;
  for (y = 0; y < screen_size_y(s); y++)
    items += screen_write_collect_flush_line(ctx, y);
  s->cx = cx; s->cy = cy;

  log_debug("%s: flushed %u items (%s)", __func__, items, from);
  return;

discard:
  for (y = 0; y < screen_size_y(s); y++) {
    cl = &s->write_list[y];
    TAILQ_FOREACH_SAFE(ci, &cl->items, entry, tmp) {
      TAILQ_REMOVE(&cl->items, ci, entry);
      screen_write_free_citem(ci);
    }
  }
  ctx->scrolled = 0;
  ctx->bg = 8;
}

/* Insert an item on current line. */
static void
screen_write_collect_insert(struct screen_write_ctx *ctx,
    struct screen_write_citem *ci)
{
  struct screen     *s = ctx->s;
  struct screen_write_cline *cl = &s->write_list[s->cy];
  struct screen_write_citem *before;

  before = screen_write_collect_trim(ctx, s->cy, ci->x, ci->used,
      &ci->wrapped);
  if (before == NULL)
    TAILQ_INSERT_TAIL(&cl->items, ci, entry);
  else
    TAILQ_INSERT_BEFORE(before, ci, entry);
  ctx->item = screen_write_get_citem();
}

/* Insert a clear for part of a line. */
static void
screen_write_collect_insert_clear(struct screen_write_ctx *ctx, u_int px,
    u_int nx, u_int bg)
{
  struct screen_write_citem *ci = ctx->item;

  if (nx != 0) {
    ci->x = px;
    ci->used = nx;
    ci->type = CLEAR;
    ci->bg = bg;
    screen_write_collect_insert(ctx, ci);
  }
}

/*
 * Clear a cell that is being broken up by a write over part of it, keeping the
 * background so the columns it covered do not lose their colour.
 */
static void
screen_write_clear_cell(struct grid *gd, u_int px, u_int py)
{
  struct grid_cell   gc;
  int      bg;

  grid_view_get_cell(gd, px, py, &gc);
  bg = gc.bg;

  memcpy(&gc, &grid_default_cell, sizeof gc);
  gc.bg = bg;
  grid_view_set_cell(gd, px, py, &gc);
}

/*
 * Insert clears for a range of cells already cleared in the grid. Adjacent
 * cells may have come from different characters and so have different
 * backgrounds, so this is done in runs of the same colour.
 */
static void
screen_write_insert_clears(struct screen_write_ctx *ctx, u_int px, u_int nx)
{
  struct screen   *s = ctx->s;
  struct grid_cell   gc;
  u_int      xx, start = px, n;
  int      bg = 8;

  for (xx = px; xx < px + nx; xx++) {
    grid_view_get_cell(s->grid, xx, s->cy, &gc);
    if (xx == start)
      bg = gc.bg;
    else if (gc.bg != bg) {
      n = xx - start;
      log_debug("%s: from %u, size %u", __func__, start, n);
      screen_write_collect_insert_clear(ctx, start, n, bg);
      start = xx;
      bg = gc.bg;
    }
  }
  log_debug("%s: from %u, size %u", __func__, start, xx - start);
  screen_write_collect_insert_clear(ctx, start, xx - start, bg);
}

/* Finish and store collected cells. */
void
screen_write_collect_end(struct screen_write_ctx *ctx)
{
  struct screen     *s = ctx->s;
  struct screen_write_citem *ci = ctx->item;
  struct screen_write_cline *cl = &s->write_list[s->cy];
  struct grid_cell     gc;
  u_int        xx, bx = 0, bnx = 0;

  if (ci->used == 0)
    return;

  ci->x = s->cx;
  screen_write_collect_insert(ctx, ci);

  log_debug("%s: %u %.*s (at %u,%u)", __func__, ci->used,
      (int)ci->used, cl->data + ci->x, s->cx, s->cy);

  if (s->cx != 0) {
    for (xx = s->cx; xx > 0; xx--) {
      grid_view_get_cell(s->grid, xx, s->cy, &gc);
      if (~gc.flags & GRID_FLAG_PADDING)
        break;
      screen_write_clear_cell(s->grid, xx, s->cy);
      log_debug("%s: padding erased (before) at %u (cx %u)",
          __func__, xx, s->cx);
    }
    if (xx != s->cx) {
      if (xx == 0)
        grid_view_get_cell(s->grid, 0, s->cy, &gc);
      if (gc.data.width > 1 ||
          (gc.flags & GRID_FLAG_PADDING)) {
        screen_write_clear_cell(s->grid, xx, s->cy);
        log_debug("%s: padding erased (before) at %u "
            "(cx %u)", __func__, xx, s->cx);
      }
      bx = xx;
      bnx = s->cx - xx;
    }
  }

#ifdef ENABLE_SIXEL
  if (image_check_area(s, s->cx, s->cy, ci->used, 1) && ctx->wp != NULL)
    ctx->wp->flags |= PANE_REDRAW;
#endif

  grid_view_set_cells(s->grid, s->cx, s->cy, &ci->gc, cl->data + ci->x,
      ci->used);
  if (bnx != 0)
    screen_write_insert_clears(ctx, bx, bnx);
  screen_write_set_cursor(ctx, s->cx + ci->used, -1);

  for (xx = s->cx; xx < screen_size_x(s); xx++) {
    grid_view_get_cell(s->grid, xx, s->cy, &gc);
    if (~gc.flags & GRID_FLAG_PADDING)
      break;
    screen_write_clear_cell(s->grid, xx, s->cy);
    log_debug("%s: padding erased (after) at %u (cx %u)", __func__,
        xx, s->cx);
  }
  if (xx != s->cx)
    screen_write_insert_clears(ctx, s->cx, xx - s->cx);
}

/* Write cell data, collecting if necessary. */
void
screen_write_collect_add(struct screen_write_ctx *ctx,
    const struct grid_cell *gc)
{
  struct screen     *s = ctx->s;
  struct screen_write_citem *ci;
  u_int        sx = screen_size_x(s);
  int        collect;

  /*
   * Don't need to check that the attributes and whatnot are still the
   * same - input_parse will end the collection when anything that isn't
   * a plain character is encountered.
   *
   * Without wrapping, collect up to but not including the last column.
   * Leave that cell to screen_write_cell so repeated writes overwrite it
   * and the cursor remains at the right edge.
   */

  collect = 1;
  if (gc->data.width != 1 || gc->data.size != 1 || *gc->data.data >= 0x7f)
    collect = 0;
  else if (gc->flags & GRID_FLAG_TAB)
    collect = 0;
  else if (gc->attr & GRID_ATTR_CHARSET)
    collect = 0;
  else if ((~s->mode & MODE_WRAP) &&
      s->cx + ctx->item->used >= sx - 1)
    collect = 0;
  else if (s->mode & MODE_INSERT)
    collect = 0;
  else if (s->sel != NULL)
    collect = 0;
  if (!collect) {
    screen_write_collect_end(ctx);
    screen_write_collect_flush(ctx, 0, __func__);
    screen_write_cell(ctx, gc);
    return;
  }

  if (s->cx > sx - 1 || ctx->item->used > sx - 1 - s->cx)
    screen_write_collect_end(ctx);
  ci = ctx->item; /* may have changed */

  if (s->cx > sx - 1) {
    log_debug("%s: wrapped at %u,%u", __func__, s->cx, s->cy);
    ci->wrapped = 1;
    screen_write_linefeed(ctx, 1, 8);
    screen_write_set_cursor(ctx, 0, -1);
  }

  if (ci->used == 0)
    memcpy(&ci->gc, gc, sizeof ci->gc);
  if (ctx->s->write_list[s->cy].data == NULL)
    ctx->s->write_list[s->cy].data = xmalloc(screen_size_x(ctx->s));
  ctx->s->write_list[s->cy].data[s->cx + ci->used++] = gc->data.data[0];
}

/* Write cell data. */
void
screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
{
  struct screen   *s = ctx->s;
  struct window_pane  *wp = ctx->wp;
  struct grid   *gd = s->grid;
  const struct utf8_data  *ud = &gc->data;
  struct grid_line  *gl;
  struct grid_cell_entry  *gce;
  struct grid_cell   tmp_gc, now_gc;
  struct tty_ctx     ttyctx;
  u_int      sx = screen_size_x(s), sy = screen_size_y(s);
  u_int      width = ud->width, xx, not_wrap, i, n, vis;
  int      selected, skip = 1, redraw = 0;
  int      yoff = 0, xoff = 0;
  struct visible_ranges *r;
  struct visible_range  *ri;

  /* Ignore padding cells. */
  if (gc->flags & GRID_FLAG_PADDING)
    return;

  /* Get the previous cell to check for combining. */
  if (screen_write_combine(ctx, gc) != 0)
    return;

  /* Flush any existing scrolling. */
  screen_write_collect_flush(ctx, 1, __func__);

  /* If this character doesn't fit, ignore it. */
  if ((~s->mode & MODE_WRAP) &&
      width > 1 &&
      (width > sx || (s->cx != sx && s->cx > sx - width)))
    return;

  /* If in insert mode, make space for the cells. */
  if (s->mode & MODE_INSERT) {
    grid_view_insert_cells(s->grid, s->cx, s->cy, width, 8);
    skip = 0;
  }

  /* Check this will fit on the current line and wrap if not. */
  if ((s->mode & MODE_WRAP) && s->cx > sx - width) {
    log_debug("%s: wrapped at %u,%u", __func__, s->cx, s->cy);
    screen_write_linefeed(ctx, 1, 8);
    screen_write_set_cursor(ctx, 0, -1);
    screen_write_collect_flush(ctx, 0, __func__);
  }

  /* Sanity check cursor position. */
  if (s->cx > sx - width || s->cy > sy - 1)
    return;
  screen_write_initctx(ctx, &ttyctx, 0, 0);

  /* Handle overwriting of UTF-8 characters. */
  gl = grid_get_line(s->grid, s->grid->hsize + s->cy);
  if (gl->flags & GRID_LINE_EXTENDED) {
    grid_view_get_cell(gd, s->cx, s->cy, &now_gc);
    if (screen_write_overwrite(ctx, &now_gc, width)) {
      redraw = 1;
      skip = 0;
    }
  }

  /*
   * If the new character is UTF-8 wide, fill in padding cells. Have
   * already ensured there is enough room.
   */
  for (xx = s->cx + 1; xx < s->cx + width; xx++) {
    log_debug("%s: new padding at %u,%u", __func__, xx, s->cy);
    grid_view_set_padding(gd, xx, s->cy, gc->bg);
    skip = 0;
  }

  /* If no change, do not draw. */
  if (skip) {
    if (s->cx >= gl->cellsize)
      skip = grid_cells_equal(gc, &grid_default_cell);
    else {
      gce = &gl->celldata[s->cx];
      if (gce->flags & GRID_FLAG_EXTENDED)
        skip = 0;
      else if (gc->flags != gce->flags)
        skip = 0;
      else if (gc->attr != gce->data.attr)
        skip = 0;
      else if (gc->fg != gce->data.fg)
        skip = 0;
      else if (gc->bg != gce->data.bg)
        skip = 0;
      else if (gc->data.width != 1)
        skip = 0;
      else if (gc->data.size != 1)
        skip = 0;
      else if (gce->data.data != gc->data.data[0])
        skip = 0;
    }
  }

  /* Update the selected flag and set the cell. */
  selected = screen_check_selection(s, s->cx, s->cy);
  if (selected && (~gc->flags & GRID_FLAG_SELECTED)) {
    memcpy(&tmp_gc, gc, sizeof tmp_gc);
    tmp_gc.flags |= GRID_FLAG_SELECTED;
    grid_view_set_cell(gd, s->cx, s->cy, &tmp_gc);
  } else if (!selected && (gc->flags & GRID_FLAG_SELECTED)) {
    memcpy(&tmp_gc, gc, sizeof tmp_gc);
    tmp_gc.flags &= ~GRID_FLAG_SELECTED;
    grid_view_set_cell(gd, s->cx, s->cy, &tmp_gc);
  } else if (!skip)
    grid_view_set_cell(gd, s->cx, s->cy, gc);
  if (selected)
    skip = 0;

  /* Get visible ranges for the character before moving the cursor. */
  if (wp != NULL) {
    xoff = wp->xoff;
    yoff = wp->yoff;
  }
  r = window_visible_ranges(wp, xoff + s->cx, s->cy + yoff, width, NULL);

  /*
   * Move the cursor. If not wrapping, stick at the last character and
   * replace it.
   */
  not_wrap = !(s->mode & MODE_WRAP);
  if (s->cx <= sx - not_wrap - width)
    screen_write_set_cursor(ctx, s->cx + width, -1);
  else
    screen_write_set_cursor(ctx, sx - not_wrap, -1);

  /* Create space for character in insert mode. */
  if (s->mode & MODE_INSERT) {
    screen_write_collect_flush(ctx, 0, __func__);
    if (wp != NULL && screen_write_pane_is_obscured(ctx)) {
      if (screen_write_should_draw_line(ctx, s->cy))
        screen_write_redraw_line(ctx, &ttyctx, s->cy);
      return;
    }
    ttyctx.n = width;
    if (screen_write_should_draw_line(ctx, s->cy))
      tty_write(tty_cmd_insertcharacter, &ttyctx);
  }

  /* If not writing, done now. */
  if (skip || !screen_write_should_draw_line(ctx, s->cy))
    return;

  /* Do a full line redraw if needed. */
  if (redraw && wp != NULL) {
    screen_write_redraw_line(ctx, &ttyctx, s->cy);
    return;
  }

  /* Work out the cell attributes. */
  if (selected)
    screen_select_cell(s, &tmp_gc, gc);
  else
    memcpy(&tmp_gc, gc, sizeof tmp_gc);
  ttyctx.cell = &tmp_gc;

  /* If the cell is fully visible, it can be written entirely. */
  for (i = 0, vis = 0; i < r->used; i++)
    vis += r->ranges[i].nx;
  if (vis >= width) {
    if (screen_write_should_draw_line(ctx, s->cy))
      tty_write(tty_cmd_cell, &ttyctx);
    return;
  }

  /*
   * Otherwise this is a wide character or tab partly obscured. Write
   * spaces in the visible regions.
   */
  utf8_set(&tmp_gc.data, ' ');
  if (!screen_write_should_draw_line(ctx, s->cy))
    return;
  for (i = 0; i < r->used; i++) {
    ri = &r->ranges[i];
    if (ri->nx == 0)
      continue;
    for (n = 0; n < ri->nx; n++) {
      ttyctx.ocx = (int)ri->px - xoff + (int)n;
      tty_write(tty_cmd_cell, &ttyctx);
    }
  }
}

/* Combine a UTF-8 zero-width character onto the previous if necessary. */
static int
screen_write_combine(struct screen_write_ctx *ctx, const struct grid_cell *gc)
{
  struct screen   *s = ctx->s;
  struct window_pane  *wp = ctx->wp;
  struct grid   *gd = s->grid;
  const struct utf8_data  *ud = &gc->data;
  struct options    *oo = global_options;
  u_int      i, n, cx = s->cx, cy = s->cy, vis;
  struct grid_cell   last;
  struct tty_ctx     ttyctx;
  int      force_wide = 0, zero_width = 0;
  int      xoff = 0, yoff = 0;
  struct visible_ranges *r;

  /* Ignore U+3164 HANGUL_FILLER entirely. */
  if (utf8_is_hangul_filler(ud))
    return (1);

  /*
   * Is this character which makes no sense without being combined? If
   * this is true then flag it here and discard the character (return 1)
   * if we cannot combine it.
   */
  if (utf8_is_zwj(ud))
    zero_width = 1;
  else if (utf8_is_vs(ud)) {
    zero_width = 1;
    if (options_get_number(oo, "variation-selector-always-wide"))
      force_wide = 1;
  } else if (ud->width == 0)
    zero_width = 1;

  /* Cannot combine empty character or at left. */
  if (ud->size < 2 || cx == 0)
    return (zero_width);
  log_debug("%s: character %.*s at %u,%u (width %u)", __func__,
      (int)ud->size, ud->data, cx, cy, ud->width);

  /* Find the cell to combine with. */
  n = 1;
  grid_view_get_cell(gd, cx - n, cy, &last);
  if (cx != 1 && (last.flags & GRID_FLAG_PADDING)) {
    n = 2;
    grid_view_get_cell(gd, cx - n, cy, &last);
  }
  if (n != last.data.width || (last.flags & GRID_FLAG_PADDING))
    return (zero_width);

  /*
   * Check if we need to combine characters. This could be a Korean
   * Hangul Jamo character, zero width (set above), a modifier character
   * (with an existing Unicode character) or a previous ZWJ.
   */
  if (!zero_width) {
    switch (hanguljamo_check_state(&last.data, ud)) {
    case HANGULJAMO_STATE_NOT_COMPOSABLE:
      return (1);
    case HANGULJAMO_STATE_CHOSEONG:
      return (0);
    case HANGULJAMO_STATE_COMPOSABLE:
      break;
    case HANGULJAMO_STATE_NOT_HANGULJAMO:
      if (utf8_should_combine(&last.data, ud))
        force_wide = 1;
      else if (utf8_should_combine(ud, &last.data))
        force_wide = 1;
      else if (!utf8_has_zwj(&last.data))
        return (0);
      break;
    }
  }

  /* Check if this combined character would be too long. */
  if (last.data.size + ud->size > sizeof last.data.data)
    return (zero_width);

  /* Combining; flush any pending output. */
  screen_write_collect_flush(ctx, 0, __func__);

  log_debug("%s: %.*s -> %.*s at %u,%u (offset %u, width %u)", __func__,
      (int)ud->size, ud->data, (int)last.data.size, last.data.data,
      cx - n, cy, n, last.data.width);

  /* Append the data. */
  memcpy(last.data.data + last.data.size, ud->data, ud->size);
  last.data.size += ud->size;

  /* Force the width to 2 for modifiers and variation selector. */
  if (last.data.width == 1 && force_wide) {
    last.data.width = 2;
    n = 2;
    cx++;
  } else
    force_wide = 0;

  /* Set the new cell. */
  grid_view_set_cell(gd, cx - n, cy, &last);
  if (force_wide)
    grid_view_set_padding(gd, cx - 1, cy, last.bg);

  /*
   * Check if all of this character is visible. No character will be
   * obscured in the middle, only on left or right, but there could be an
   * empty range in the visible ranges so we add them all up.
   */
  if (wp != NULL) {
    xoff = wp->xoff;
    yoff = wp->yoff;
  }
  r = window_visible_ranges(wp, xoff + cx - n, cy + yoff, n, NULL);
  for (i = 0, vis = 0; i < r->used; i++)
    vis += r->ranges[i].nx;
  if (vis < n) {
    /*
     * Part of this character is obscured. Return 1 and let
     * screen_write_cell write a space.
     */
    return (1);
  }

  /*
   * Redraw the combined cell. If forcing the cell to width 2, reset the
   * cached cursor position in the tty, since we don't really know
   * whether the terminal thought the character was width 1 or width 2
   * and what it is going to do now.
   */
  screen_write_set_cursor(ctx, cx - n, cy);
  screen_write_initctx(ctx, &ttyctx, 0, 0);
  ttyctx.cell = &last;
  if (force_wide)
    ttyctx.flags |= TTY_CTX_CELL_INVALIDATE;
  if (screen_write_should_draw_line(ctx, cy))
    tty_write(tty_cmd_cell, &ttyctx);
  screen_write_set_cursor(ctx, cx, cy);

  return (1);
}

/*
 * UTF-8 wide characters are a bit of an annoyance. They take up more than one
 * cell on the screen, so following cells must not be drawn by marking them as
 * padding.
 *
 * So far, so good. The problem is, when overwriting a padding cell, or a UTF-8
 * character, it is necessary to also overwrite any other cells which covered
 * by the same character.
 */
static int
screen_write_overwrite(struct screen_write_ctx *ctx, struct grid_cell *gc,
    u_int width)
{
  struct screen   *s = ctx->s;
  struct grid   *gd = s->grid;
  struct grid_cell   tmp_gc;
  u_int      xx;
  int      done = 0;

  if (gc->flags & GRID_FLAG_PADDING) {
    /*
     * A padding cell, so clear any following and leading padding
     * cells back to the character. Don't overwrite the current
     * cell as that happens later anyway.
     */
    xx = s->cx + 1;
    while (--xx > 0) {
      grid_view_get_cell(gd, xx, s->cy, &tmp_gc);
      if (~tmp_gc.flags & GRID_FLAG_PADDING)
        break;
      log_debug("%s: padding at %u,%u", __func__, xx, s->cy);
      screen_write_clear_cell(gd, xx, s->cy);
    }

    /* Overwrite the character at the start of this padding. */
    log_debug("%s: character at %u,%u", __func__, xx, s->cy);
    screen_write_clear_cell(gd, xx, s->cy);
    done = 1;
  }

  /*
   * Overwrite any padding cells that belong to any UTF-8 characters
   * we'll be overwriting with the current character.
   */
  if (width != 1 ||
      gc->data.width != 1 ||
      gc->flags & GRID_FLAG_PADDING) {
    xx = s->cx + width - 1;
    while (++xx < screen_size_x(s)) {
      grid_view_get_cell(gd, xx, s->cy, &tmp_gc);
      if (~tmp_gc.flags & GRID_FLAG_PADDING)
        break;
      log_debug("%s: overwrite at %u,%u", __func__, xx,
          s->cy);
      screen_write_clear_cell(gd, xx, s->cy);
      done = 1;
    }
  }

  return (done);
}

/* Set external clipboard. */
void
screen_write_setselection(struct screen_write_ctx *ctx, const char *clip,
    u_char *str, u_int len)
{
  struct tty_ctx  ttyctx;

  screen_write_initctx(ctx, &ttyctx, 0, 0);
  ttyctx.sel.clip = clip;
  ttyctx.sel.data = str;
  ttyctx.sel.size = len;

  tty_write(tty_cmd_setselection, &ttyctx);
}

/* Write unmodified string. */
void
screen_write_rawstring(struct screen_write_ctx *ctx, u_char *str, u_int len,
    int allow_invisible_panes)
{
  struct tty_ctx  ttyctx;

  screen_write_initctx(ctx, &ttyctx, 0, 0);
  if (allow_invisible_panes)
    ttyctx.flags |= TTY_CTX_INVISIBLE_PANES;
  ttyctx.data.data = str;
  ttyctx.data.size = len;

  tty_write(tty_cmd_rawstring, &ttyctx);
}

#ifdef ENABLE_SIXEL
/* Write a SIXEL image. */
void
screen_write_sixelimage(struct screen_write_ctx *ctx, struct sixel_image *si,
    u_int bg)
{
  struct screen   *s = ctx->s;
  struct grid   *gd = s->grid;
  struct tty_ctx     ttyctx;
  u_int      x, y, sx, sy, cx = s->cx, cy = s->cy, i, lines;
  struct sixel_image  *new;

  if (screen_size_y(s) == 1)
    return;

  sixel_size_in_cells(si, &x, &y);
  if (x > screen_size_x(s) || y > screen_size_y(s) - 1) {
    if (x > screen_size_x(s) - cx)
      sx = screen_size_x(s) - cx;
    else
      sx = x;
    if (y > screen_size_y(s) - 1)
      sy = screen_size_y(s) - 1;
    else
      sy = y;
    new = sixel_scale(si, 0, 0, 0, y - sy, sx, sy, 1);
    sixel_free(si);
    if (new == NULL)
      return;
    sixel_size_in_cells(new, &x, &y);
    si = new;
  }

  sy = screen_size_y(s) - cy;
  if (sy <= y) {
    lines = y - sy + 1;
    if (image_scroll_up(s, lines) && ctx->wp != NULL)
      ctx->wp->flags |= PANE_REDRAW;
    for (i = 0; i < lines; i++) {
      grid_view_scroll_region_up(gd, 0, screen_size_y(s) - 1,
          bg);
      screen_write_collect_scroll(ctx, bg);
    }
    ctx->scrolled += lines;
    if (lines > cy)
      screen_write_cursormove(ctx, -1, 0, 0);
    else
      screen_write_cursormove(ctx, -1, cy - lines, 0);
  }
  screen_write_collect_flush(ctx, 0, __func__);

  screen_write_initctx(ctx, &ttyctx, 0, 0);
  ttyctx.image = image_store(s, si);

  tty_write(tty_cmd_sixelimage, &ttyctx);

  screen_write_cursormove(ctx, 0, cy + y, 0);
}
#endif

/* Turn alternate screen on. */
void
screen_write_alternateon(struct screen_write_ctx *ctx, struct grid_cell *gc,
    int cursor)
{
  struct tty_ctx       ttyctx;
  struct window_pane    *wp = ctx->wp;

  if (wp != NULL && !options_get_number(wp->options, "alternate-screen"))
    return;

  screen_write_collect_flush(ctx, 0, __func__);
  if (!screen_alternate_on(ctx->s, gc, cursor))
    return;

  if (wp != NULL) {
    window_pane_clear_resizes(wp, NULL);
    if (event_initialized(&wp->resize_timer))
      evtimer_del(&wp->resize_timer);
    layout_fix_panes(wp->window, NULL);
    if (!TAILQ_EMPTY(&wp->resize_queue)) {
      window_pane_send_resize(wp, wp->sx, wp->sy);
      window_pane_clear_resizes(wp, NULL);
    }
    server_redraw_window_borders(wp->window);
  }

  screen_write_initctx(ctx, &ttyctx, 1, 0);
  if (ttyctx.redraw_cb != NULL)
    ttyctx.redraw_cb(&ttyctx, 0, ttyctx.sy);
}

/* Turn alternate screen off. */
void
screen_write_alternateoff(struct screen_write_ctx *ctx, struct grid_cell *gc,
    int cursor)
{
  struct tty_ctx     ttyctx;
  struct window_pane  *wp = ctx->wp;

  if (wp != NULL && !options_get_number(wp->options, "alternate-screen"))
    return;

  screen_write_collect_flush(ctx, 0, __func__);
  if (!screen_alternate_off(ctx->s, gc, cursor))
    return;

  if (wp != NULL) {
    layout_fix_panes(wp->window, NULL);
    server_redraw_window_borders(wp->window);
  }

  screen_write_initctx(ctx, &ttyctx, 1, 0);
  if (ttyctx.redraw_cb != NULL)
    ttyctx.redraw_cb(&ttyctx, 0, ttyctx.sy);
}

Coverage Report

Created: 2026-10-05 06:03