Collect sequences of printable ASCII characters and process them

together instead of handling them one by one. This is significantly
faster. Sequences are terminated when we reach the end of the line, fill
the internal buffer, or a different character is seen by the input
parser (an escape sequence, or UTF-8).

Rather than writing collected sequences out immediately, hold them until
it is necessary (another screen modification, or we consume all
available data). This means we can discard changes that would have no
effect (for example, lines that would just be scrolled off the screen or
cleared). This reduces the total amount of data we write out to the
terminal - not important for fast terminals, but a big help with slow
(like xterm).

7 files changed, 319 insertions, 187 deletions

diff --git a/grid-view.c b/grid-view.c
index da0433bf..b84ac64e 100644
--- a/grid-view.c
+++ b/grid-view.c
@@ -45,6 +45,15 @@ grid_view_set_cell(struct grid *gd, u_int px, u_int py,
 	grid_set_cell(gd, grid_view_x(gd, px), grid_view_y(gd, py), gc);
 }
 
+/* Set cells. */
+void
+grid_view_set_cells(struct grid *gd, u_int px, u_int py,
+    const struct grid_cell *gc, const char *s, size_t slen)
+{
+	grid_set_cells(gd, grid_view_x(gd, px), grid_view_y(gd, py), gc, s,
+	    slen);
+}
+
 /* Clear into history. */
 void
 grid_view_clear_history(struct grid *gd, u_int bg)
diff --git a/grid.c b/grid.c
index 741e9bf3..388a2c1b 100644
--- a/grid.c
+++ b/grid.c
@@ -407,6 +407,36 @@ grid_set_cell(struct grid *gd, u_int px, u_int py, const struct grid_cell *gc)
 		grid_store_cell(gce, gc, gc->data.data[0]);
 }
 
+/* Set cells at relative position. */
+void
+grid_set_cells(struct grid *gd, u_int px, u_int py, const struct grid_cell *gc,
+    const char *s, size_t slen)
+{
+	struct grid_line	*gl;
+	struct grid_cell_entry	*gce;
+	struct grid_cell	*gcp;
+	u_int			 i;
+
+	if (grid_check_y(gd, py) != 0)
+		return;
+
+	grid_expand_line(gd, py, px + slen, 8);
+
+	gl = &gd->linedata[py];
+	if (px + slen > gl->cellused)
+		gl->cellused = px + slen;
+
+	for (i = 0; i < slen; i++) {
+		gce = &gl->celldata[px + i];
+		if (gce->flags & GRID_FLAG_EXTENDED) {
+			gcp = &gl->extddata[gce->offset];
+			memcpy(gcp, gc, sizeof *gcp);
+			utf8_set(&gcp->data, s[i]);
+		} else
+			grid_store_cell(gce, gc, s[i]);
+	}
+}
+
 /* Clear area. */
 void
 grid_clear(struct grid *gd, u_int px, u_int py, u_int nx, u_int ny, u_int bg)
diff --git a/input.c b/input.c
index 04dc8ce1..d5b8737d 100644
--- a/input.c
+++ b/input.c
@@ -896,6 +896,16 @@ input_parse(struct window_pane *wp)
 		}
 
 		/*
+		 * Any state except print stops the current collection. This is
+		 * an optimization to avoid checking if the attributes have
+		 * changed for every character. It will stop unnecessarily for
+		 * sequences that don't make a terminal change, but they should
+		 * be the minority.
+		 */
+		if (itr->handler != input_print)
+			screen_write_collect_end(&ictx->ctx);
+
+		/*
 		 * Execute the handler, if any. Don't switch state if it
 		 * returns non-zero.
 		 */
@@ -1020,7 +1030,7 @@ input_print(struct input_ctx *ictx)
 		ictx->cell.cell.attr &= ~GRID_ATTR_CHARSET;
 
 	utf8_set(&ictx->cell.cell.data, ictx->ch);
-	screen_write_cell(&ictx->ctx, &ictx->cell.cell);
+	screen_write_collect_add(&ictx->ctx, &ictx->cell.cell);
 
 	ictx->cell.cell.attr &= ~GRID_ATTR_CHARSET;
 
diff --git a/screen-write.c b/screen-write.c
index 8072981f..761ec99f 100644
--- a/screen-write.c
+++ b/screen-write.c
@@ -25,7 +25,10 @@
 
 static void	screen_write_initctx(struct screen_write_ctx *,
 		    struct tty_ctx *);
-static void	screen_write_flush(struct screen_write_ctx *);
+static void	screen_write_collect_clear(struct screen_write_ctx *, u_int,
+		    u_int);
+static void	screen_write_collect_scroll(struct screen_write_ctx *);
+static void	screen_write_collect_flush(struct screen_write_ctx *);
 
 static int	screen_write_overwrite(struct screen_write_ctx *,
 		    struct grid_cell *, u_int);
@@ -36,23 +39,29 @@ static const struct grid_cell screen_write_pad_cell = {
 	GRID_FLAG_PADDING, 0, 8, 8, { { 0 }, 0, 0, 0 }
 };
 
-#define screen_dirty_bit(s, x, y) (((y) * screen_size_x(s)) + (x))
-#define screen_dirty_clear(s, sx, sy, ex, ey)			\
-	do {							\
-		if (s->dirty != NULL) {				\
-			bit_nclear(s->dirty,			\
-			    screen_dirty_bit(s, sx, sy),	\
-			    screen_dirty_bit(s, ex, ey));	\
-		}						\
-	} while (0)
+struct screen_write_collect_item {
+	u_int			 x;
+
+	u_int			 used;
+	char			 data[256];
+
+	struct grid_cell	 gc;
+
+	TAILQ_ENTRY (screen_write_collect_item) entry;
+};
+struct screen_write_collect_line {
+	TAILQ_HEAD(, screen_write_collect_item) items;
+};
 
 /* Initialize writing with a window. */
 void
 screen_write_start(struct screen_write_ctx *ctx, struct window_pane *wp,
     struct screen *s)
 {
-	u_int	size;
 	char	tmp[16];
+	u_int	y;
+
+	memset(ctx, 0, sizeof *ctx);
 
 	ctx->wp = wp;
 	if (wp != NULL && s == NULL)
@@ -60,15 +69,10 @@ screen_write_start(struct screen_write_ctx *ctx, struct window_pane *wp,
 	else
 		ctx->s = s;
 
-	size = screen_size_x(ctx->s) * screen_size_y(ctx->s);
-	if (ctx->s->dirtysize != size) {
-		free(ctx->s->dirty);
-		ctx->s->dirty = NULL;
-		ctx->s->dirtysize = size;
-	}
-	ctx->dirty = 0;
-
-	ctx->cells = ctx->written = ctx->skipped = 0;
+	ctx->list = xcalloc(screen_size_y(ctx->s), sizeof *ctx->list);
+	for (y = 0; y < screen_size_y(ctx->s); y++)
+		TAILQ_INIT(&ctx->list[y].items);
+	ctx->item = xcalloc(1, sizeof *ctx->item);
 
 	if (wp != NULL)
 		snprintf(tmp, sizeof tmp, "pane %%%u", wp->id);
@@ -80,55 +84,14 @@ screen_write_start(struct screen_write_ctx *ctx, struct window_pane *wp,
 void
 screen_write_stop(struct screen_write_ctx *ctx)
 {
-	screen_write_flush(ctx);
+	screen_write_collect_end(ctx);
+	screen_write_collect_flush(ctx);
 
-	log_debug("%s: %u of %u written (dirty %u, skipped %u)", __func__,
-	    ctx->written, ctx->cells, ctx->cells - ctx->written, ctx->skipped);
-}
+	log_debug("%s: %u cells (%u written, %u skipped)", __func__,
+	    ctx->cells, ctx->written, ctx->skipped);
 
-/* Flush outstanding cell writes. */
-static void
-screen_write_flush(struct screen_write_ctx *ctx)
-{
-	struct screen	*s = ctx->s;
-	struct tty_ctx	 ttyctx;
-	u_int		 x, y, offset, cx, cy, dirty;
-	struct grid_cell gc;
-
-	if (ctx->dirty == 0)
-		return;
-	dirty = 0;
-	log_debug("%s: dirty %u", __func__, ctx->dirty);
-
-	cx = s->cx;
-	cy = s->cy;
-
-	offset = 0;
-	for (y = 0; y < screen_size_y(s); y++) {
-		for (x = 0; x < screen_size_x(s); x++) {
-			offset++;
-			if (!bit_test(s->dirty, offset - 1))
-				continue;
-			bit_clear(s->dirty, offset - 1);
-
-			screen_write_cursormove(ctx, x, y);
-			grid_view_get_cell(s->grid, x, y, &gc);
-
-			screen_write_initctx(ctx, &ttyctx);
-			ttyctx.cell = &gc;
-			tty_write(tty_cmd_cell, &ttyctx);
-			ctx->written++;
-
-			if (++dirty == ctx->dirty)
-				break;
-		}
-		if (dirty == ctx->dirty)
-			break;
-	}
-	ctx->dirty = 0;
-
-	s->cx = cx;
-	s->cy = cy;
+	free(ctx->item);
+	free(ctx->list); /* flush will have emptied */
 }
 
 /* Reset screen state. */
@@ -563,12 +526,9 @@ screen_write_alignmenttest(struct screen_write_ctx *ctx)
 	struct tty_ctx	 	 ttyctx;
 	struct grid_cell       	 gc;
 	u_int			 xx, yy;
-	u_int		 	 sx = screen_size_x(s), sy = screen_size_y(s);
 
 	screen_write_initctx(ctx, &ttyctx);
 
-	screen_dirty_clear(s, 0, 0, sx - 1, sy  - 1);
-
 	memcpy(&gc, &grid_default_cell, sizeof gc);
 	utf8_set(&gc.data, 'E');
 
@@ -583,6 +543,7 @@ screen_write_alignmenttest(struct screen_write_ctx *ctx)
 	s->rupper = 0;
 	s->rlower = screen_size_y(s) - 1;
 
+	screen_write_collect_clear(ctx, 0, screen_size_y(s) - 1);
 	tty_write(tty_cmd_alignmenttest, &ttyctx);
 }
 
@@ -604,12 +565,12 @@ screen_write_insertcharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
 	if (s->cx > screen_size_x(s) - 1)
 		return;
 
-	screen_write_flush(ctx);
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
 	grid_view_insert_cells(s->grid, s->cx, s->cy, nx, bg);
 
+	screen_write_collect_flush(ctx);
 	ttyctx.num = nx;
 	tty_write(tty_cmd_insertcharacter, &ttyctx);
 }
@@ -632,12 +593,12 @@ screen_write_deletecharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
 	if (s->cx > screen_size_x(s) - 1)
 		return;
 
-	screen_write_flush(ctx);
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
 	grid_view_delete_cells(s->grid, s->cx, s->cy, nx, bg);
 
+	screen_write_collect_flush(ctx);
 	ttyctx.num = nx;
 	tty_write(tty_cmd_deletecharacter, &ttyctx);
 }
@@ -662,9 +623,9 @@ screen_write_clearcharacter(struct screen_write_ctx *ctx, u_int nx)
 
 	screen_write_initctx(ctx, &ttyctx);
 
-	screen_dirty_clear(s, s->cx, s->cy, s->cx + nx - 1, s->cy);
 	grid_view_clear(s->grid, s->cx, s->cy, nx, 1, 8);
 
+	screen_write_collect_flush(ctx);
 	ttyctx.num = nx;
 	tty_write(tty_cmd_clearcharacter, &ttyctx);
 }
@@ -686,12 +647,12 @@ screen_write_insertline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 		if (ny == 0)
 			return;
 
-		screen_write_flush(ctx);
 		screen_write_initctx(ctx, &ttyctx);
 		ttyctx.bg = bg;
 
 		grid_view_insert_lines(gd, s->cy, ny, bg);
 
+		screen_write_collect_flush(ctx);
 		ttyctx.num = ny;
 		tty_write(tty_cmd_insertline, &ttyctx);
 		return;
@@ -702,7 +663,6 @@ screen_write_insertline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 	if (ny == 0)
 		return;
 
-	screen_write_flush(ctx);
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
@@ -711,6 +671,7 @@ screen_write_insertline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 	else
 		grid_view_insert_lines_region(gd, s->rlower, s->cy, ny, bg);
 
+	screen_write_collect_flush(ctx);
 	ttyctx.num = ny;
 	tty_write(tty_cmd_insertline, &ttyctx);
 }
@@ -732,12 +693,12 @@ screen_write_deleteline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 		if (ny == 0)
 			return;
 
-		screen_write_flush(ctx);
 		screen_write_initctx(ctx, &ttyctx);
 		ttyctx.bg = bg;
 
 		grid_view_delete_lines(gd, s->cy, ny, bg);
 
+		screen_write_collect_flush(ctx);
 		ttyctx.num = ny;
 		tty_write(tty_cmd_deleteline, &ttyctx);
 		return;
@@ -748,7 +709,6 @@ screen_write_deleteline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 	if (ny == 0)
 		return;
 
-	screen_write_flush(ctx);
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
@@ -757,6 +717,7 @@ screen_write_deleteline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 	else
 		grid_view_delete_lines_region(gd, s->rlower, s->cy, ny, bg);
 
+	screen_write_collect_flush(ctx);
 	ttyctx.num = ny;
 	tty_write(tty_cmd_deleteline, &ttyctx);
 }
@@ -777,9 +738,9 @@ screen_write_clearline(struct screen_write_ctx *ctx, u_int bg)
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
-	screen_dirty_clear(s, 0, s->cy, sx - 1, s->cy);
 	grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
 
+	screen_write_collect_clear(ctx, s->cy, 1);
 	tty_write(tty_cmd_clearline, &ttyctx);
 }
 
@@ -799,9 +760,12 @@ screen_write_clearendofline(struct screen_write_ctx *ctx, u_int bg)
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
-	screen_dirty_clear(s, s->cx, s->cy, sx - 1, s->cy);
 	grid_view_clear(s->grid, s->cx, s->cy, sx - s->cx, 1, bg);
 
+	if (s->cx == 0)
+		screen_write_collect_clear(ctx, s->cy, 1);
+	else
+		screen_write_collect_flush(ctx);
 	tty_write(tty_cmd_clearendofline, &ttyctx);
 }
 
@@ -816,14 +780,15 @@ screen_write_clearstartofline(struct screen_write_ctx *ctx, u_int bg)
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
-	if (s->cx > sx - 1) {
-		screen_dirty_clear(s, 0, s->cy, sx - 1, s->cy);
+	if (s->cx > sx - 1)
 		grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
-	} else {
-		screen_dirty_clear(s, 0, s->cy, s->cx, s->cy);
+	else
 		grid_view_clear(s->grid, 0, s->cy, s->cx + 1, 1, bg);
-	}
 
+	if (s->cx > sx - 1)
+		screen_write_collect_clear(ctx, s->cy, 1);
+	else
+		screen_write_collect_flush(ctx);
 	tty_write(tty_cmd_clearstartofline, &ttyctx);
 }
 
@@ -851,12 +816,12 @@ screen_write_reverseindex(struct screen_write_ctx *ctx)
 
 	screen_write_initctx(ctx, &ttyctx);
 
-	if (s->cy == s->rupper) {
-		screen_write_flush(ctx);
+	if (s->cy == s->rupper)
 		grid_view_scroll_region_down(s->grid, s->rupper, s->rlower);
-	} else if (s->cy > 0)
+	else if (s->cy > 0)
 		s->cy--;
 
+	screen_write_collect_flush(ctx);
 	tty_write(tty_cmd_reverseindex, &ttyctx);
 }
 
@@ -887,27 +852,24 @@ void
 screen_write_linefeed(struct screen_write_ctx *ctx, int wrapped)
 {
 	struct screen		*s = ctx->s;
+	struct grid		*gd = s->grid;
 	struct grid_line	*gl;
-	struct tty_ctx	 	 ttyctx;
-	u_int			 sx = screen_size_x(s), sy = screen_size_y(s);
-
-	screen_write_initctx(ctx, &ttyctx);
+	struct tty_ctx		 ttyctx;
 
-	gl = &s->grid->linedata[s->grid->hsize + s->cy];
+	gl = &gd->linedata[gd->hsize + s->cy];
 	if (wrapped)
 		gl->flags |= GRID_LINE_WRAPPED;
 	else
 		gl->flags &= ~GRID_LINE_WRAPPED;
 
 	if (s->cy == s->rlower) {
-		screen_dirty_clear(s, 0, s->rupper, sx - 1, s->rupper);
-		screen_write_flush(ctx);
-		grid_view_scroll_region_up(s->grid, s->rupper, s->rlower);
-	} else if (s->cy < sy - 1)
-		s->cy++;
+		grid_view_scroll_region_up(gd, s->rupper, s->rlower);
 
-	ttyctx.num = wrapped;
-	tty_write(tty_cmd_linefeed, &ttyctx);
+		screen_write_collect_scroll(ctx);
+		screen_write_initctx(ctx, &ttyctx);
+		tty_write(tty_cmd_linefeed, &ttyctx);
+	} else if (s->cy < screen_size_y(s) - 1)
+		s->cy++;
 }
 
 /* Carriage return (cursor to start of line). */
@@ -932,18 +894,16 @@ screen_write_clearendofscreen(struct screen_write_ctx *ctx, u_int bg)
 	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) {
-		screen_dirty_clear(s, 0, 0, sx - 1, sy  - 1);
+	if (s->cx == 0 && s->cy == 0 && (gd->flags & GRID_HISTORY))
 		grid_view_clear_history(gd, bg);
-	} else {
-		if (s->cx <= sx - 1) {
-			screen_dirty_clear(s, s->cx, s->cy, sx - 1, s->cy);
+	else {
+		if (s->cx <= sx - 1)
 			grid_view_clear(gd, s->cx, s->cy, sx - s->cx, 1, bg);
-		}
-		screen_dirty_clear(s, 0, s->cy + 1, sx - 1, sy - 1);
 		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);
 	tty_write(tty_cmd_clearendofscreen, &ttyctx);
 }
 
@@ -958,18 +918,15 @@ screen_write_clearstartofscreen(struct screen_write_ctx *ctx, u_int bg)
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
-	if (s->cy > 0) {
-		screen_dirty_clear(s, 0, 0, sx - 1, s->cy);
+	if (s->cy > 0)
 		grid_view_clear(s->grid, 0, 0, sx, s->cy, bg);
-	}
-	if (s->cx > sx - 1) {
-		screen_dirty_clear(s, 0, s->cy, sx - 1, s->cy);
-		grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
-	} else {
-		screen_dirty_clear(s, 0, s->cy, s->cx, s->cy);
-		grid_view_clear(s->grid, 0, s->cy, s->cx + 1, 1, bg);
-	}
+	if (s->cx > sx - 1)
+		grid_view_clear(s->grid, 0, s->cy, sx, 1, 8);
+	else
+		grid_view_clear(s->grid, 0, s->cy, s->cx + 1, 1, 8);
 
+	screen_write_collect_clear(ctx, 0, s->cy);
+	screen_write_collect_flush(ctx);
 	tty_write(tty_cmd_clearstartofscreen, &ttyctx);
 }
 
@@ -984,14 +941,13 @@ screen_write_clearscreen(struct screen_write_ctx *ctx, u_int bg)
 	screen_write_initctx(ctx, &ttyctx);
 	ttyctx.bg = bg;
 
-	screen_dirty_clear(s, 0, 0, sx - 1, sy  - 1);
-
 	/* Scroll into history if it is enabled. */
 	if (s->grid->flags & GRID_HISTORY)
 		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);
 	tty_write(tty_cmd_clearscreen, &ttyctx);
 }
 
@@ -1006,39 +962,165 @@ screen_write_clearhistory(struct screen_write_ctx *ctx)
 	gd->hscrolled = gd->hsize = 0;
 }
 
+/* Clear a collected line. */
+static void
+screen_write_collect_clear(struct screen_write_ctx *ctx, u_int y, u_int n)
+{
+	struct screen_write_collect_item	*ci, *tmp;
+	u_int					 i;
+	size_t					 size;
+
+	for (i = y ; i < y + n; i++) {
+		if (TAILQ_EMPTY(&ctx->list[i].items))
+			continue;
+		size = 0;
+		TAILQ_FOREACH_SAFE(ci, &ctx->list[i].items, entry, tmp) {
+			size += ci->used;
+			TAILQ_REMOVE(&ctx->list[i].items, ci, entry);
+			free(ci);
+		}
+		ctx->skipped += size;
+		log_debug("discarding %zu bytes on line %u", size, i);
+	}
+}
+
+/* Scroll collected lines up. */
+static void
+screen_write_collect_scroll(struct screen_write_ctx *ctx)
+{
+	struct screen				*s = ctx->s;
+	struct screen_write_collect_line	*cl;
+	u_int					 y;
+
+	screen_write_collect_clear(ctx, s->rupper, 1);
+	for (y = s->rupper; y < s->rlower; y++) {
+		cl = &ctx->list[y + 1];
+		TAILQ_CONCAT(&ctx->list[y].items, &cl->items, entry);
+		TAILQ_INIT(&cl->items);
+	}
+}
+
+/* Flush collected lines. */
+static void
+screen_write_collect_flush(struct screen_write_ctx *ctx)
+{
+	struct screen				*s = ctx->s;
+	struct screen_write_collect_item	*ci, *tmp;
+	u_int					 y, cx, cy;
+	struct tty_ctx				 ttyctx;
+
+	cx = s->cx; cy = s->cy;
+	for (y = 0; y < screen_size_y(s); y++) {
+		TAILQ_FOREACH_SAFE(ci, &ctx->list[y].items, entry, tmp) {
+			screen_write_cursormove(ctx, ci->x, y);
+			screen_write_initctx(ctx, &ttyctx);
+			ttyctx.cell = &ci->gc;
+			ttyctx.ptr = ci->data;
+			ttyctx.num = ci->used;
+			tty_write(tty_cmd_cells, &ttyctx);
+			ctx->written += ci->used;
+
+			TAILQ_REMOVE(&ctx->list[y].items, ci, entry);
+			free(ci);
+		}
+	}
+	s->cx = cx; s->cy = cy;
+}
+
+/* Finish and store collected cells. */
+void
+screen_write_collect_end(struct screen_write_ctx *ctx)
+{
+	struct screen				*s = ctx->s;
+	struct screen_write_collect_item	*ci = ctx->item;
+	struct grid_cell			 gc;
+
+	if (ci->used == 0)
+		return;
+	ci->data[ci->used] = '\0';
+
+	ci->x = s->cx;
+	TAILQ_INSERT_TAIL(&ctx->list[s->cy].items, ci, entry);
+	ctx->item = xcalloc(1, sizeof *ctx->item);
+
+	log_debug("%s: %u %s (at %u,%u)", __func__, ci->used, ci->data, s->cx,
+	    s->cy);
+
+	memcpy(&gc, &ci->gc, sizeof gc);
+	grid_view_set_cells(s->grid, s->cx, s->cy, &gc, ci->data, ci->used);
+	s->cx += ci->used;
+}
+
+/* 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_collect_item	*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 do a flush when anything that isn't a plain
+	 * character is encountered. Also nothing should make it here that
+	 * isn't a single ASCII character.
+	 */
+
+	collect = 1;
+	if (gc->data.width != 1)
+		collect = 0;
+	else if (gc->attr & GRID_ATTR_CHARSET)
+		collect = 0;
+	else if (~s->mode & MODE_WRAP)
+		collect = 0;
+	else if (s->mode & MODE_INSERT)
+		collect = 0;
+	else if (s->sel.flag)
+		collect = 0;
+	if (!collect) {
+		screen_write_collect_end(ctx);
+		screen_write_cell(ctx, gc);
+		return;
+	}
+	ctx->cells++;
+
+	if (s->cx > sx - 1 || ctx->item->used > sx - 1 - s->cx)
+		screen_write_collect_end(ctx);
+	if (s->cx > sx - 1) {
+		screen_write_linefeed(ctx, 1);
+		s->cx = 0;
+	}
+
+	ci = ctx->item; /* may have changed */
+	if (ci->used == 0)
+		memcpy(&ci->gc, gc, sizeof ci->gc);
+	ci->data[ci->used++] = gc->data.data[0];
+	if (ci->used == (sizeof ci->data) - 1)
+		screen_write_collect_end(ctx);
+}
+
 /* Write cell data. */
 void
 screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 {
 	struct screen		*s = ctx->s;
 	struct grid		*gd = s->grid;
-	struct tty_ctx		 ttyctx;
-	u_int		 	 width, xx, last;
-	u_int			 sx = screen_size_x(s), sy = screen_size_y(s);
 	struct grid_line	*gl;
-	struct grid_cell 	 tmp_gc, now_gc;
 	struct grid_cell_entry	*gce;
-	int			 insert, skip, selected;
-
-	ctx->cells++;
+	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 = gc->data.width, xx, last;
+	int			 selected, skip = 1;
 
-	/* Ignore padding. */
+	/* Ignore padding cells. */
 	if (gc->flags & GRID_FLAG_PADDING)
 		return;
-	width = gc->data.width;
-
-	/*
-	 * If this is a wide character and there is no room on the screen for
-	 * the entire character, don't print it.
-	 */
-	if (!(s->mode & MODE_WRAP) && (width > 1 &&
-	    (width > sx || (s->cx != sx && s->cx > sx - width))))
-		return;
+	ctx->cells++;
 
-	/*
-	 * If the width is zero, combine onto the previous character, if
-	 * there is space.
-	 */
+	/* If the width is zero, combine onto the previous character. */
 	if (width == 0) {
 		if ((gc = screen_write_combine(ctx, &gc->data, &xx)) != 0) {
 			screen_write_cursormove(ctx, xx, s->cy);
@@ -1049,29 +1131,27 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 		return;
 	}
 
+	/* 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) {
-		if (s->cx <= sx - width) {
-			screen_write_flush(ctx);
-			xx = sx - s->cx - width;
-			grid_view_insert_cells(s->grid, s->cx, s->cy, xx, 8);
-		}
-		insert = 1;
-	} else
-		insert = 0;
-	skip = !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) {
 		screen_write_linefeed(ctx, 1);
-		s->cx = 0;	/* carriage return */
+		s->cx = 0;
 	}
 
 	/* Sanity check cursor position. */
 	if (s->cx > sx - width || s->cy > sy - 1)
 		return;
-
-	/* Initialise the redraw context. */
 	screen_write_initctx(ctx, &ttyctx);
 
 	/* Handle overwriting of UTF-8 characters. */
@@ -1109,6 +1189,8 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 				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;
 		}
@@ -1116,18 +1198,18 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 
 	/* Update the selection the flag and set the cell. */
 	selected = screen_check_selection(s, s->cx, s->cy);
-	if (selected && ~gc->flags & GRID_FLAG_SELECTED) {
-		skip = 0;
+	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) {
-		skip = 0;
+	} 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;
 
 	/*
 	 * Move the cursor. If not wrapping, stick at the last character and
@@ -1140,34 +1222,21 @@ screen_write_cell(struct screen_write_ctx *ctx, const struct grid_cell *gc)
 		s->cx = sx - last;
 
 	/* Create space for character in insert mode. */
-	if (insert) {
+	if (s->mode & MODE_INSERT) {
+		screen_write_collect_flush(ctx);
 		ttyctx.num = width;
 		tty_write(tty_cmd_insertcharacter, &ttyctx);
 	}
 
 	/* Write to the screen. */
-	if (selected) {
-		screen_write_flush(ctx);
-		screen_select_cell(s, &tmp_gc, gc);
-		ttyctx.cell = &tmp_gc;
+	if (!skip) {
+		if (selected) {
+			screen_select_cell(s, &tmp_gc, gc);
+			ttyctx.cell = &tmp_gc;
+		} else
+			ttyctx.cell = gc;
 		tty_write(tty_cmd_cell, &ttyctx);
 		ctx->written++;
-	} else if (!skip) {
-		/*
-		 * If wp is NULL, we are not updating the terminal and don't
-		 * care about actually writing the cells (tty_write will just
-		 * return). So don't even bother allocating the dirty array.
-		 */
-		if (ctx->wp != NULL && s->dirty == NULL) {
-			log_debug("%s: allocating %u bits", __func__,
-			    s->dirtysize);
-			s->dirty = bit_alloc(s->dirtysize);
-		}
-		if (s->dirty != NULL) {
-			bit_set(s->dirty, screen_dirty_bit(s,
-			    ttyctx.ocx, ttyctx.ocy));
-			ctx->dirty++;
-		}
 	} else
 		ctx->skipped++;
 }
diff --git a/screen.c b/screen.c
index d6fbfecd..087611ae 100644
--- a/screen.c
+++ b/screen.c
@@ -40,9 +40,6 @@ screen_init(struct screen *s, u_int sx, u_int sy, u_int hlimit)
 	s->ccolour = xstrdup("");
 	s->tabs = NULL;
 
-	s->dirty = NULL;
-	s->dirtysize = 0;
-
 	screen_reinit(s);
 }
 
@@ -69,7 +66,6 @@ screen_reinit(struct screen *s)
 void
 screen_free(struct screen *s)
 {
-	free(s->dirty);
 	free(s->tabs);
 	free(s->title);
 	free(s->ccolour);
@@ -358,7 +354,7 @@ screen_check_selection(struct screen *s, u_int px, u_int py)
 				xx = sel->sx - 1;
 			else
 				xx = sel->sx;
-			if (py == sel->sy && px > xx)
+			if (py == sel->sy && (sel->sx == 0 || px > xx))
 				return (0);
 		} else {
 			/* starting line == ending line. */
diff --git a/tmux.h b/tmux.h
index f9f60e6a..06142164 100644
--- a/tmux.h
+++ b/tmux.h
@@ -651,17 +651,18 @@ struct screen {
 
 	bitstr_t		*tabs;
 
-	bitstr_t		*dirty;
-	u_int			 dirtysize;
-
 	struct screen_sel	 sel;
 };
 
 /* Screen write context. */
+struct screen_write_collect_item;
+struct screen_write_collect_line;
 struct screen_write_ctx {
 	struct window_pane	*wp;
 	struct screen		*s;
-	u_int			 dirty;
+
+	struct screen_write_collect_item *item;
+	struct screen_write_collect_line *list;
 
 	u_int			 cells;
 	u_int			 written;
@@ -1042,7 +1043,7 @@ struct tty {
 
 	struct grid_cell cell;
 
-	int              last_wp;
+	int		 last_wp;
 	struct grid_cell last_cell;
 
 #define TTY_NOCURSOR 0x1
@@ -1643,6 +1644,7 @@ void	tty_write(void (*)(struct tty *, const struct tty_ctx *),
 	    struct tty_ctx *);
 void	tty_cmd_alignmenttest(struct tty *, const struct tty_ctx *);
 void	tty_cmd_cell(struct tty *, const struct tty_ctx *);
+void	tty_cmd_cells(struct tty *, const struct tty_ctx *);
 void	tty_cmd_clearendofline(struct tty *, const struct tty_ctx *);
 void	tty_cmd_clearendofscreen(struct tty *, const struct tty_ctx *);
 void	tty_cmd_clearline(struct tty *, const struct tty_ctx *);
@@ -1911,6 +1913,8 @@ void	 grid_clear_history(struct grid *);
 const struct grid_line *grid_peek_line(struct grid *, u_int);
 void	 grid_get_cell(struct grid *, u_int, u_int, struct grid_cell *);
 void	 grid_set_cell(struct grid *, u_int, u_int, const struct grid_cell *);
+void	 grid_set_cells(struct grid *, u_int, u_int, const struct grid_cell *,
+	     const char *, size_t);
 void	 grid_clear(struct grid *, u_int, u_int, u_int, u_int, u_int);
 void	 grid_clear_lines(struct grid *, u_int, u_int, u_int);
 void	 grid_move_lines(struct grid *, u_int, u_int, u_int, u_int);
@@ -1925,6 +1929,8 @@ u_int	 grid_reflow(struct grid *, struct grid *, u_int);
 void	 grid_view_get_cell(struct grid *, u_int, u_int, struct grid_cell *);
 void	 grid_view_set_cell(struct grid *, u_int, u_int,
 	     const struct grid_cell *);
+void	 grid_view_set_cells(struct grid *, u_int, u_int,
+	     const struct grid_cell *, const char *, size_t);
 void	 grid_view_clear_history(struct grid *, u_int);
 void	 grid_view_clear(struct grid *, u_int, u_int, u_int, u_int, u_int);
 void	 grid_view_scroll_region_up(struct grid *, u_int, u_int);
@@ -1983,6 +1989,9 @@ void	 screen_write_clearendofscreen(struct screen_write_ctx *, u_int);
 void	 screen_write_clearstartofscreen(struct screen_write_ctx *, u_int);
 void	 screen_write_clearscreen(struct screen_write_ctx *, u_int);
 void	 screen_write_clearhistory(struct screen_write_ctx *);
+void	 screen_write_collect_end(struct screen_write_ctx *);
+void	 screen_write_collect_add(struct screen_write_ctx *,
+	     const struct grid_cell *);
 void	 screen_write_cell(struct screen_write_ctx *, const struct grid_cell *);
 void	 screen_write_setselection(struct screen_write_ctx *, u_char *, u_int);
 void	 screen_write_rawstring(struct screen_write_ctx *, u_char *, u_int);
diff --git a/tty.c b/tty.c
index 1b7fb55f..508e4bac 100644
--- a/tty.c
+++ b/tty.c
@@ -1170,6 +1170,15 @@ tty_cmd_cell(struct tty *tty, const struct tty_ctx *ctx)
 }
 
 void
+tty_cmd_cells(struct tty *tty, const struct tty_ctx *ctx)
+{
+	tty_cursor_pane(tty, ctx, ctx->ocx, ctx->ocy);
+
+	tty_attributes(tty, ctx->cell, ctx->wp);
+	tty_putn(tty, ctx->ptr, ctx->num, ctx->num);
+}
+
+void
 tty_cmd_setselection(struct tty *tty, const struct tty_ctx *ctx)
 {
 	char	*buf;