Merge SIXEL branch.

Squashed commit of the following:

commit 6ebc3feb4671d9b25b3db99d3c16b2323b8e3d02
Author: topcat001 <anindya49@hotmail.com>
Date:   Sun Aug 20 16:09:51 2023 -0700

    Remove redundant {}.

commit 6f013fce39602c259a5be2d690d548c73e51cccc
Author: topcat001 <anindya49@hotmail.com>
Date:   Sun Aug 20 16:02:15 2023 -0700

    Revert "Do not defer redraw if it is just the status line (will need to do more here I"

    This reverts commit 0a15bbf3f1.

commit e6322b4196d73c975ba2e73633e6de9c46779059
Author: topcat001 <anindya49@hotmail.com>
Date:   Sun Aug 20 15:46:59 2023 -0700

    Fix placeholder label and clean up.

commit 5896ac52a1f72056a75480b3e1ada328f239df9b
Merge: ad982330 e3a8b843
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Fri Aug 18 17:00:03 2023 +0100

    Merge branch 'master' into sixel

commit ad98233066b72547aee7fa0c87838847ee7f1ece
Author: topcat001 <anindya49@hotmail.com>
Date:   Tue Aug 15 13:57:08 2023 -0700

    Better text placeholder.

commit 312d83252c27fc4d09d09d121bf7573336e3cdca
Merge: 14b8b524 3d93b0c5
Author: topcat001 <anindya49@hotmail.com>
Date:   Tue Aug 15 13:39:22 2023 -0700

    Merge remote-tracking branch 'origin/master' into sixel

commit 14b8b524523a7d5a4e42f7dfa346905c604c91e2
Merge: 4baf7642 fda39377
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Jul 22 17:29:10 2023 -0700

    Merge branch 'master' into sixel

commit 4baf76422fadb216bf27b47645b52da3379e7dea
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Wed Jun 21 07:43:53 2023 +0100

    Both files can go on one line.

commit 4c92acf6ff
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Jun 17 17:53:01 2023 -0700

    Merge topcat001/tmux/sixel.

commit 6794facc82
Merge: 7b85f5ad f41c536f
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Jun 17 17:21:02 2023 -0700

    Merge remote-tracking branch 'origin/master' into sixel

commit 7b85f5adf9a5094db580ca98e4d2231d8d5b5a4f
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jun 8 12:55:03 2023 +0100

    Do not require passthrough for SIXEL.

commit a6ee55e0925cac35d011c188db2da0421fc09be1
Merge: 6da391f4 fe385b18
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jun 8 12:19:55 2023 +0100

    Merge branch 'master' into sixel

commit 6da391f460414ed3dde23e5ab6ca3fe8e988ce51
Merge: 0d71e585 0eb5d254
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat May 20 17:05:55 2023 -0700

    Merge branch 'master' into sixel

commit 0d71e5853ffe797f90b815ac3af25ac0ad92ab07
Merge: 64368a1a fbe6fe7f
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Apr 29 17:32:07 2023 -0700

    Merge branch 'master' into sixel

commit 64368a1a63
Merge: c630a56a 22eb0334
Author: topcat001 <anindya49@hotmail.com>
Date:   Thu Mar 30 14:21:09 2023 -0700

    Merge branch 'master' into sixel

commit c630a56a62
Merge: 34c96c4c aaa043a2
Author: topcat001 <anindya49@hotmail.com>
Date:   Thu Nov 10 18:53:01 2022 -0800

    Merge branch 'master' into sixel

commit 34c96c4c4a
Merge: 2a1e16a2 50f4e0fa
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Nov 5 18:05:36 2022 -0700

    Merge branch 'master' into sixel

commit 2a1e16a24d
Merge: a82f14c7 d001a94d
Author: topcat001 <anindya49@hotmail.com>
Date:   Thu Oct 27 16:01:35 2022 -0700

    Merge branch 'master' into sixel

commit a82f14c7b2
Merge: 742c0634 f7b30ed3
Author: topcat001 <anindya49@hotmail.com>
Date:   Sun Aug 28 13:43:07 2022 -0700

    Merge branch 'master' into sixel

commit 742c063473
Merge: 906c92a5 87b248f3
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Fri Apr 1 10:14:15 2022 +0100

    Merge branch 'master' into sixel

commit 906c92a5f4
Merge: 6680a024 138ffc7c
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Wed Dec 8 10:37:33 2021 +0000

    Merge branch 'master' into sixel

commit 6680a024be
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Oct 7 13:59:08 2021 +0100

    Fix build.

commit ebd2c58593
Merge: 90dc0519 fed7b29c
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Oct 7 13:19:48 2021 +0100

    Merge branch 'master' into sixel

commit 90dc05191c
Merge: a282439f 4694afbe
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Feb 20 20:37:32 2020 +0000

    Merge branch 'master' into sixel

commit a282439fcb
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jan 30 09:12:53 2020 +0000

    Add missing declarations.

commit 3a741aacd1
Merge: 40ad0107 339832b9
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jan 30 09:11:01 2020 +0000

    Merge branch 'sixel-passthrough' into sixel

commit 339832b92c
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jan 30 09:04:51 2020 +0000

    Bad merge.

commit 92ed9fc0b2
Merge: 5bb07548 32be954b
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jan 30 09:03:38 2020 +0000

    Merge branch 'master' into sixel-passthrough

commit 40ad01073d
Merge: dd3c72f1 61b075a2
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Sun Jan 12 20:03:41 2020 +0000

    Merge branch 'master' into sixel

commit 5bb075487f
Merge: 7c033a74 54efe337
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Wed Dec 18 20:24:42 2019 +0000

    Merge branch 'master' into sixel-passthrough

commit dd3c72f132
Merge: 1a0e5fe9 54efe337
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Wed Dec 18 20:24:26 2019 +0000

    Merge branch 'master' into sixel

commit 1a0e5fe933
Merge: cf071ffe 15d7e564
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Tue Dec 10 16:34:11 2019 +0000

    Merge branch 'master' into sixel

commit cf071ffecd
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Mon Dec 9 15:41:56 2019 +0000

    Remove images when reflow happens.

commit 2006b7a563
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 09:27:15 2019 +0000

    More invalidation of images.

commit b642eac450
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 09:11:24 2019 +0000

    Redraw and scroll images and part of invalidating them.

commit 7566e37a46
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 08:51:24 2019 +0000

    Call sixel_scale with the right number of arguments.

commit 62c0280b23
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 08:48:58 2019 +0000

    Correctly remove when not visible.

commit 86c5098a88
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 08:32:25 2019 +0000

    Add helpers to scroll image up and a flag to copy the colours.

commit 49f2f0a8f1
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 00:02:55 2019 +0000

    Store images, currently at most 10.

commit 3aebcc6709
Merge: 146ee3f6 92ecd611
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Wed Dec 4 19:27:16 2019 +0000

    Merge branch 'master' into sixel

commit 7c033a74e2
Merge: 0a15bbf3 92ecd611
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Wed Dec 4 12:41:09 2019 +0000

    Merge branch 'master' into sixel-passthrough

commit 146ee3f6f8
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Sat Nov 30 09:47:53 2019 +0000

    Don't write image as text yet.

commit 0a15bbf3f1
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Sat Nov 30 09:15:35 2019 +0000

    Do not defer redraw if it is just the status line (will need to do more here I
    think).

commit a5b1e20941
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 14:20:22 2019 +0000

    Add a flag to disable blocking while sending a SIXEL image (turned off when the
    buffer hits 0 size).

commit 968382aa6a
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 12:35:18 2019 +0000

    Pass through SIXEL DCS sequences (treat similarly to the passthrough escape
    sequence) if it appears the terminal outside supports them.

commit b1904c9b8d
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Sat Nov 30 09:17:18 2019 +0000

    Store SIXELs as a box for the moment.

commit 5d8dbcdf3d
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Sat Nov 30 09:15:35 2019 +0000

    Do not defer redraw if it is just the status line (will need to do more here I
    think).

commit 0c999a402e
Merge: 28961dd5 866b053f
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Fri Nov 29 18:54:09 2019 +0000

    Merge branch 'master' into sixel

commit 28961dd5a3
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 14:24:57 2019 +0000

    Add an image.

commit d2e3f3c1cc
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 14:20:22 2019 +0000

    Add a flag to disable blocking while sending a SIXEL image (turned off when the
    buffer hits 0 size).

commit e01df67ca1
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 13:21:40 2019 +0000

    Crop and scale images as needed when drawing them.

commit e24acc0b5c
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 12:38:02 2019 +0000

    Simple SIXEL parse and modify API.

commit b34111b3da
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 12:35:18 2019 +0000

    Pass through SIXEL DCS sequences (treat similarly to the passthrough escape
    sequence) if it appears the terminal outside supports them.

Makefile.am

@@ -218,6 +218,11 @@ if HAVE_UTF8PROC
 nodist_tmux_SOURCES += compat/utf8proc.c
 endif
 
+# Enable sixel support.
+if ENABLE_SIXEL
+dist_tmux_SOURCES += image.c image-sixel.c
+endif
+
 if NEED_FUZZING
 check_PROGRAMS = fuzz/input-fuzzer
 fuzz_input_fuzzer_LDFLAGS = $(FUZZING_LIBS)

configure.ac

@@ -449,6 +449,16 @@ if test "x$enable_cgroups" = xyes; then
 	fi
 fi
 
+# Enable sixel support.
+AC_ARG_ENABLE(
+	sixel,
+	AS_HELP_STRING(--enable-sixel, enable sixel images)
+)
+if test "x$enable_sixel" = xyes; then
+	AC_DEFINE(ENABLE_SIXEL)
+fi
+AM_CONDITIONAL(ENABLE_SIXEL, [test "x$enable_sixel" = xyes])
+
 # Check for b64_ntop. If we have b64_ntop, we assume b64_pton as well.
 AC_MSG_CHECKING(for b64_ntop)
 AC_LINK_IFELSE([AC_LANG_PROGRAM(

image-sixel.c

@@ -0,0 +1,565 @@
+/* $OpenBSD$ */
+
+/*
+ * Copyright (c) 2019 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"
+
+#define SIXEL_COLOUR_REGISTERS 1024
+#define SIXEL_WIDTH_LIMIT 2016
+#define SIXEL_HEIGHT_LIMIT 2016
+
+struct sixel_line {
+	u_int		 x;
+	uint16_t	*data;
+};
+
+struct sixel_image {
+	u_int			 x;
+	u_int			 y;
+	u_int			 xpixel;
+	u_int			 ypixel;
+
+	u_int			*colours;
+	u_int			 ncolours;
+
+	u_int			 dx;
+	u_int			 dy;
+	u_int			 dc;
+
+	struct sixel_line	*lines;
+};
+
+static int
+sixel_parse_expand_lines(struct sixel_image *si, u_int y)
+{
+	if (y <= si->y)
+		return (0);
+	if (y > SIXEL_HEIGHT_LIMIT)
+		return (1);
+	si->lines = xrecallocarray(si->lines, si->y, y, sizeof *si->lines);
+	si->y = y;
+	return (0);
+}
+
+static int
+sixel_parse_expand_line(struct sixel_image *si, struct sixel_line *sl, u_int x)
+{
+	if (x <= sl->x)
+		return (0);
+	if (x > SIXEL_WIDTH_LIMIT)
+		return (1);
+	if (x > si->x)
+		si->x = x;
+	sl->data = xrecallocarray(sl->data, sl->x, si->x, sizeof *sl->data);
+	sl->x = si->x;
+	return (0);
+}
+
+static u_int
+sixel_get_pixel(struct sixel_image *si, u_int x, u_int y)
+{
+	struct sixel_line	*sl;
+
+	if (y >= si->y)
+		return (0);
+	sl = &si->lines[y];
+	if (x >= sl->x)
+		return (0);
+	return (sl->data[x]);
+}
+
+static int
+sixel_set_pixel(struct sixel_image *si, u_int x, u_int y, u_int c)
+{
+	struct sixel_line	*sl;
+
+	if (sixel_parse_expand_lines(si, y + 1) != 0)
+		return (1);
+	sl = &si->lines[y];
+	if (sixel_parse_expand_line(si, sl, x + 1) != 0)
+		return (1);
+	sl->data[x] = c;
+	return (0);
+}
+
+static int
+sixel_parse_write(struct sixel_image *si, u_int ch)
+{
+	struct sixel_line	*sl;
+	u_int			 i;
+
+	if (sixel_parse_expand_lines(si, si->dy + 6) != 0)
+		return (1);
+	sl = &si->lines[si->dy];
+
+	for (i = 0; i < 6; i++) {
+		if (sixel_parse_expand_line(si, sl, si->dx + 1) != 0)
+			return (1);
+		if (ch & (1 << i))
+			sl->data[si->dx] = si->dc;
+		sl++;
+	}
+	return (0);
+}
+
+static const char *
+sixel_parse_attributes(struct sixel_image *si, const char *cp, const char *end)
+{
+	const char	*last;
+	char		*endptr;
+	u_int		 x, y;
+
+	last = cp;
+	while (last != end) {
+		if (*last != ';' && (*last < '0' || *last > '9'))
+			break;
+		last++;
+	}
+	strtoul(cp, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (last);
+	strtoul(endptr + 1, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (NULL);
+
+	x = strtoul(endptr + 1, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (NULL);
+	if (x > SIXEL_WIDTH_LIMIT)
+		return (NULL);
+	y = strtoul(endptr + 1, &endptr, 10);
+	if (endptr != last)
+		return (NULL);
+	if (y > SIXEL_HEIGHT_LIMIT)
+		return (NULL);
+
+	si->x = x;
+	sixel_parse_expand_lines(si, y);
+
+	return (last);
+}
+
+static const char *
+sixel_parse_colour(struct sixel_image *si, const char *cp, const char *end)
+{
+	const char	*last;
+	char		*endptr;
+	u_int		 c, type, r, g, b;
+
+	last = cp;
+	while (last != end) {
+		if (*last != ';' && (*last < '0' || *last > '9'))
+			break;
+		last++;
+	}
+
+	c = strtoul(cp, &endptr, 10);
+	if (c > SIXEL_COLOUR_REGISTERS)
+		return (NULL);
+	si->dc = c + 1;
+	if (endptr == last || *endptr != ';')
+		return (last);
+
+	type = strtoul(endptr + 1, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (NULL);
+	r = strtoul(endptr + 1, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (NULL);
+	g = strtoul(endptr + 1, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (NULL);
+	b = strtoul(endptr + 1, &endptr, 10);
+	if (endptr != last)
+		return (NULL);
+
+	if (type != 1 && type != 2)
+		return (NULL);
+	if (c + 1 > si->ncolours) {
+		si->colours = xrecallocarray(si->colours, si->ncolours, c + 1,
+		    sizeof *si->colours);
+		si->ncolours = c + 1;
+	}
+	si->colours[c] = (type << 24) | (r << 16) | (g << 8) | b;
+	return (last);
+}
+
+static const char *
+sixel_parse_repeat(struct sixel_image *si, const char *cp, const char *end)
+{
+	const char	*last;
+	char		 tmp[32], ch;
+	u_int		 n = 0, i;
+	const char	*errstr = NULL;
+
+	last = cp;
+	while (last != end) {
+		if (*last < '0' || *last > '9')
+			break;
+		tmp[n++] = *last++;
+		if (n == (sizeof tmp) - 1)
+			return (NULL);
+	}
+	if (n == 0 || last == end)
+		return (NULL);
+	tmp[n] = '\0';
+
+	n = strtonum(tmp, 1, SIXEL_WIDTH_LIMIT, &errstr);
+	if (n == 0 || errstr != NULL)
+		return (NULL);
+
+	ch = (*last++) - 0x3f;
+	for (i = 0; i < n; i++) {
+		if (sixel_parse_write(si, ch) != 0)
+			return (NULL);
+		si->dx++;
+	}
+	return (last);
+}
+
+struct sixel_image *
+sixel_parse(const char *buf, size_t len, u_int xpixel, u_int ypixel)
+{
+	struct sixel_image	*si;
+	const char		*cp = buf, *end = buf + len;
+	char			 ch;
+
+	if (len == 0 || len == 1 || *cp++ != 'q')
+		return (NULL);
+
+	si = xcalloc (1, sizeof *si);
+	si->xpixel = xpixel;
+	si->ypixel = ypixel;
+
+	while (cp != end) {
+		ch = *cp++;
+		switch (ch) {
+		case '"':
+			cp = sixel_parse_attributes(si, cp, end);
+			if (cp == NULL)
+				goto bad;
+			break;
+		case '#':
+			cp = sixel_parse_colour(si, cp, end);
+			if (cp == NULL)
+				goto bad;
+			break;
+		case '!':
+			cp = sixel_parse_repeat(si, cp, end);
+			if (cp == NULL)
+				goto bad;
+			break;
+		case '-':
+			si->dx = 0;
+			si->dy += 6;
+			break;
+		case '$':
+			si->dx = 0;
+			break;
+		default:
+			if (ch < 0x20)
+				break;
+			if (ch < 0x3f || ch > 0x7e)
+				goto bad;
+			if (sixel_parse_write(si, ch - 0x3f) != 0)
+				goto bad;
+			si->dx++;
+			break;
+		}
+	}
+
+	if (si->x == 0 || si->y == 0)
+		goto bad;
+	return (si);
+
+bad:
+	free(si);
+	return (NULL);
+}
+
+void
+sixel_free(struct sixel_image *si)
+{
+	u_int	y;
+
+	for (y = 0; y < si->y; y++)
+		free(si->lines[y].data);
+	free(si->lines);
+
+	free(si->colours);
+	free(si);
+}
+
+void
+sixel_log(struct sixel_image *si)
+{
+	struct sixel_line	*sl;
+	char			 s[SIXEL_WIDTH_LIMIT + 1];
+	u_int			 i, x, y, cx, cy;
+
+	sixel_size_in_cells(si, &cx, &cy);
+	log_debug("%s: image %ux%u (%ux%u)", __func__, si->x, si->y, cx, cy);
+	for (i = 0; i < si->ncolours; i++)
+		log_debug("%s: colour %u is %07x", __func__, i, si->colours[i]);
+	for (y = 0; y < si->y; y++) {
+		sl = &si->lines[y];
+		for (x = 0; x < si->x; x++) {
+			if (x >= sl->x)
+				s[x] = '_';
+			else if (sl->data[x] != 0)
+				s[x] = '0' + (sl->data[x] - 1) % 10;
+			else
+				s[x] = '.';
+			}
+		s[x] = '\0';
+		log_debug("%s: %4u: %s", __func__, y, s);
+	}
+}
+
+void
+sixel_size_in_cells(struct sixel_image *si, u_int *x, u_int *y)
+{
+	if ((si->x % si->xpixel) == 0)
+		*x = (si->x / si->xpixel);
+	else
+		*x = 1 + (si->x / si->xpixel);
+	if ((si->y % si->ypixel) == 0)
+		*y = (si->y / si->ypixel);
+	else
+		*y = 1 + (si->y / si->ypixel);
+}
+
+struct sixel_image *
+sixel_scale(struct sixel_image *si, u_int xpixel, u_int ypixel, u_int ox,
+    u_int oy, u_int sx, u_int sy, int colours)
+{
+	struct sixel_image	*new;
+	u_int			 cx, cy, pox, poy, psx, psy, tsx, tsy, px, py;
+	u_int			 x, y, i;
+
+	/*
+	 * We want to get the section of the image at ox,oy in image cells and
+	 * map it onto the same size in terminal cells, remembering that we
+	 * can only draw vertical sections of six pixels.
+	 */
+
+	sixel_size_in_cells(si, &cx, &cy);
+	if (ox >= cx)
+		return (NULL);
+	if (oy >= cy)
+		return (NULL);
+	if (ox + sx >= cx)
+		sx = cx - ox;
+	if (oy + sy >= cy)
+		sy = cy - oy;
+
+	if (xpixel == 0)
+		xpixel = si->xpixel;
+	if (ypixel == 0)
+		ypixel = si->ypixel;
+
+	pox = ox * si->xpixel;
+	poy = oy * si->ypixel;
+	psx = sx * si->xpixel;
+	psy = sy * si->ypixel;
+
+	tsx = sx * xpixel;
+	tsy = ((sy * ypixel) / 6) * 6;
+
+	new = xcalloc (1, sizeof *si);
+	new->xpixel = xpixel;
+	new->ypixel = ypixel;
+
+	for (y = 0; y < tsy; y++) {
+		py = poy + ((double)y * psy / tsy);
+		for (x = 0; x < tsx; x++) {
+			px = pox + ((double)x * psx / tsx);
+			sixel_set_pixel(new, x, y, sixel_get_pixel(si, px, py));
+		}
+	}
+
+	if (colours) {
+		new->colours = xmalloc(si->ncolours * sizeof *new->colours);
+		for (i = 0; i < si->ncolours; i++)
+			new->colours[i] = si->colours[i];
+		new->ncolours = si->ncolours;
+	}
+	return (new);
+}
+
+static void
+sixel_print_add(char **buf, size_t *len, size_t *used, const char *s,
+    size_t slen)
+{
+	if (*used + slen >= *len + 1) {
+		(*len) *= 2;
+		*buf = xrealloc(*buf, *len);
+	}
+	memcpy(*buf + *used, s, slen);
+	(*used) += slen;
+}
+
+static void
+sixel_print_repeat(char **buf, size_t *len, size_t *used, u_int count, char ch)
+{
+	char	tmp[16];
+	size_t	tmplen;
+
+	if (count == 1)
+		sixel_print_add(buf, len, used, &ch, 1);
+	else if (count == 2) {
+		sixel_print_add(buf, len, used, &ch, 1);
+		sixel_print_add(buf, len, used, &ch, 1);
+	} else if (count == 3) {
+		sixel_print_add(buf, len, used, &ch, 1);
+		sixel_print_add(buf, len, used, &ch, 1);
+		sixel_print_add(buf, len, used, &ch, 1);
+	} else if (count != 0) {
+		tmplen = xsnprintf(tmp, sizeof tmp, "!%u%c", count, ch);
+		sixel_print_add(buf, len, used, tmp, tmplen);
+	}
+}
+
+char *
+sixel_print(struct sixel_image *si, struct sixel_image *map, size_t *size)
+{
+	char			*buf, tmp[64], *contains, data, last = 0;
+	size_t			 len, used = 0, tmplen;
+	u_int			*colours, ncolours, i, c, x, y, count;
+	struct sixel_line	*sl;
+
+	if (map != NULL) {
+		colours = map->colours;
+		ncolours = map->ncolours;
+	} else {
+		colours = si->colours;
+		ncolours = si->ncolours;
+	}
+	contains = xcalloc(1, ncolours);
+
+	len = 8192;
+	buf = xmalloc(len);
+
+	sixel_print_add(&buf, &len, &used, "\033Pq", 3);
+
+	tmplen = xsnprintf(tmp, sizeof tmp, "\"1;1;%u;%u", si->x, si->y);
+	sixel_print_add(&buf, &len, &used, tmp, tmplen);
+
+	for (i = 0; i < ncolours; i++) {
+		c = colours[i];
+		tmplen = xsnprintf(tmp, sizeof tmp, "#%u;%u;%u;%u;%u",
+		    i, c >> 24, (c >> 16) & 0xff, (c >> 8) & 0xff, c & 0xff);
+		sixel_print_add(&buf, &len, &used, tmp, tmplen);
+	}
+
+	for (y = 0; y < si->y; y += 6) {
+		memset(contains, 0, ncolours);
+		for (x = 0; x < si->x; x++) {
+			for (i = 0; i < 6; i++) {
+				if (y + i >= si->y)
+					break;
+				sl = &si->lines[y + i];
+				if (x < sl->x && sl->data[x] != 0)
+					contains[sl->data[x] - 1] = 1;
+			}
+		}
+
+		for (c = 0; c < ncolours; c++) {
+			if (!contains[c])
+				continue;
+			tmplen = xsnprintf(tmp, sizeof tmp, "#%u", c);
+			sixel_print_add(&buf, &len, &used, tmp, tmplen);
+
+			count = 0;
+			for (x = 0; x < si->x; x++) {
+				data = 0;
+				for (i = 0; i < 6; i++) {
+					if (y + i >= si->y)
+						break;
+					sl = &si->lines[y + i];
+					if (x < sl->x && sl->data[x] == c + 1)
+						data |= (1 << i);
+				}
+				data += 0x3f;
+				if (data != last) {
+					sixel_print_repeat(&buf, &len, &used,
+					    count, last);
+					last = data;
+					count = 1;
+				} else
+					count++;
+			}
+			sixel_print_repeat(&buf, &len, &used, count, data);
+			sixel_print_add(&buf, &len, &used, "$", 1);
+		}
+
+		if (buf[used - 1] == '$')
+			used--;
+		if (buf[used - 1] != '-')
+			sixel_print_add(&buf, &len, &used, "-", 1);
+	}
+	if (buf[used - 1] == '$' || buf[used - 1] == '-')
+		used--;
+
+	sixel_print_add(&buf, &len, &used, "\033\\", 2);
+
+	buf[used] = '\0';
+	if (size != NULL)
+		*size = used;
+
+	free(contains);
+	return (buf);
+}
+
+struct screen *
+sixel_to_screen(struct sixel_image *si)
+{
+	struct screen		*s;
+	struct screen_write_ctx	 ctx;
+	struct grid_cell	 gc;
+	u_int			 x, y, sx, sy;
+
+	sixel_size_in_cells(si, &sx, &sy);
+
+	s = xmalloc(sizeof *s);
+	screen_init(s, sx, sy, 0);
+
+	memcpy(&gc, &grid_default_cell, sizeof gc);
+	gc.attr |= (GRID_ATTR_CHARSET|GRID_ATTR_DIM);
+	utf8_set(&gc.data, '~');
+
+	screen_write_start(&ctx, s);
+	if (sx == 1 || sy == 1) {
+		for (y = 0; y < sy; y++) {
+			for (x = 0; x < sx; x++)
+				grid_view_set_cell(s->grid, x, y, &gc);
+		}
+	} else {
+		screen_write_box(&ctx, sx, sy, BOX_LINES_DEFAULT, NULL, NULL);
+		for (y = 1; y < sy - 1; y++) {
+			for (x = 1; x < sx - 1; x++)
+				grid_view_set_cell(s->grid, x, y, &gc);
+		}
+	}
+	screen_write_stop(&ctx);
+	return (s);
+}

image.c

@@ -0,0 +1,186 @@
+/* $OpenBSD$ */
+
+/*
+ * 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 images	all_images = TAILQ_HEAD_INITIALIZER(all_images);
+static u_int		all_images_count;
+
+static void
+image_free(struct image *im)
+{
+	struct screen	*s = im->s;
+
+	TAILQ_REMOVE(&all_images, im, all_entry);
+	all_images_count--;
+
+	TAILQ_REMOVE(&s->images, im, entry);
+	sixel_free(im->data);
+	free(im->fallback);
+	free(im);
+}
+
+int
+image_free_all(struct screen *s)
+{
+	struct image	*im, *im1;
+	int		 redraw = !TAILQ_EMPTY(&s->images);
+
+	TAILQ_FOREACH_SAFE(im, &s->images, entry, im1)
+		image_free(im);
+	return (redraw);
+}
+
+/* Create text placeholder for an image. */
+static void
+image_fallback(char **ret, u_int sx, u_int sy)
+{
+	char	*buf, *label;
+	u_int	 py, size, lsize;
+
+	/* Allocate first line. */
+	lsize = xasprintf(&label, "SIXEL IMAGE (%ux%u)\r\n", sx, sy) + 1;
+	if (sx < lsize - 3)
+		size = lsize - 1;
+	else
+		size = sx + 2;
+
+	/* Remaining lines. Every placeholder line has \r\n at the end. */
+	size += (sx + 2) * (sy - 1) + 1;
+	*ret = buf = xmalloc(size);
+
+	/* Render first line. */
+	if (sx < lsize - 3) {
+		memcpy(buf, label, lsize);
+		buf += lsize - 1;
+	} else {
+		memcpy(buf, label, lsize - 3);
+		buf += lsize - 3;
+		memset(buf, '+', sx - lsize + 3);
+		buf += sx - lsize + 3;
+		snprintf(buf, 3, "\r\n");
+		buf += 2;
+	}
+
+	/* Remaining lines. */
+	for (py = 1; py < sy; py++) {
+		memset(buf, '+', sx);
+		buf += sx;
+		snprintf(buf, 3, "\r\n");
+		buf += 2;
+	}
+
+	free(label);
+}
+
+struct image*
+image_store(struct screen *s, struct sixel_image *si)
+{
+	struct image	*im;
+
+	im = xcalloc(1, sizeof *im);
+	im->s = s;
+	im->data = si;
+
+	im->px = s->cx;
+	im->py = s->cy;
+	sixel_size_in_cells(si, &im->sx, &im->sy);
+
+	image_fallback(&im->fallback, im->sx, im->sy);
+
+	TAILQ_INSERT_TAIL(&s->images, im, entry);
+
+	TAILQ_INSERT_TAIL(&all_images, im, all_entry);
+	if (++all_images_count == 10/*XXX*/)
+		image_free(TAILQ_FIRST(&all_images));
+
+	return (im);
+}
+
+int
+image_check_line(struct screen *s, u_int py, u_int ny)
+{
+	struct image	*im, *im1;
+	int		 redraw = 0;
+
+	TAILQ_FOREACH_SAFE(im, &s->images, entry, im1) {
+		if (py + ny > im->py && py < im->py + im->sy) {
+			image_free(im);
+			redraw = 1;
+		}
+	}
+	return (redraw);
+}
+
+int
+image_check_area(struct screen *s, u_int px, u_int py, u_int nx, u_int ny)
+{
+	struct image	*im, *im1;
+	int		 redraw = 0;
+
+	TAILQ_FOREACH_SAFE(im, &s->images, entry, im1) {
+		if (py + ny <= im->py || py >= im->py + im->sy)
+			continue;
+		if (px + nx <= im->px || px >= im->px + im->sx)
+			continue;
+		image_free(im);
+		redraw = 1;
+	}
+	return (redraw);
+}
+
+int
+image_scroll_up(struct screen *s, u_int lines)
+{
+	struct image		*im, *im1;
+	int			 redraw = 0;
+	u_int			 sx, sy;
+	struct sixel_image	*new;
+
+	TAILQ_FOREACH_SAFE(im, &s->images, entry, im1) {
+		if (im->py >= lines) {
+			im->py -= lines;
+			redraw = 1;
+			continue;
+		}
+		if (im->py + im->sy <= lines) {
+			image_free(im);
+			redraw = 1;
+			continue;
+		}
+		sx = im->sx;
+		sy = (im->py + im->sy) - lines;
+
+		new = sixel_scale(im->data, 0, 0, 0, im->sy - sy, sx, sy, 1);
+		sixel_free(im->data);
+		im->data = new;
+
+		im->py = 0;
+		sixel_size_in_cells(im->data, &im->sx, &im->sy);
+
+		free(im->fallback);
+		image_fallback(&im->fallback, im->sx, im->sy);
+		redraw = 1;
+	}
+	return (redraw);
+}

input.c

@@ -1443,7 +1443,11 @@ input_csi_dispatch(struct input_ctx *ictx)
 		case -1:
 			break;
 		case 0:
+#ifdef ENABLE_SIXEL
+			input_reply(ictx, "\033[?1;2;4c");
+#else
 			input_reply(ictx, "\033[?1;2c");
+#endif
 			break;
 		default:
 			log_debug("%s: unknown '%c'", __func__, ictx->ch);
@@ -2245,13 +2249,25 @@ input_dcs_dispatch(struct input_ctx *ictx)
 	const char		 prefix[] = "tmux;";
 	const u_int		 prefixlen = (sizeof prefix) - 1;
 	long long		 allow_passthrough = 0;
+#ifdef ENABLE_SIXEL
+	struct window		*w = wp->window;
+	struct sixel_image	*si;
+#endif
 
 	if (wp == NULL)
 		return (0);
 	if (ictx->flags & INPUT_DISCARD)
 		return (0);
-	allow_passthrough = options_get_number(wp->options,
+
-	    "allow-passthrough");
+#ifdef ENABLE_SIXEL
+	if (buf[0] == 'q') {
+		si = sixel_parse(buf, len, w->xpixel, w->ypixel);
+		if (si != NULL)
+			screen_write_sixelimage(sctx, si, ictx->cell.cell.bg);
+	}
+#endif
+
+	allow_passthrough = options_get_number(wp->options, "allow-passthrough");
 	if (!allow_passthrough)
 		return (0);
 	log_debug("%s: \"%s\"", __func__, buf);

screen-redraw.c

@@ -856,4 +856,8 @@ screen_redraw_draw_pane(struct screen_redraw_ctx *ctx, struct window_pane *wp)
 		tty_default_colours(&defaults, wp);
 		tty_draw_line(tty, s, i, j, width, x, y, &defaults, palette);
 	}
+
+#ifdef ENABLE_SIXEL
+	tty_draw_images(c, wp, s);
+#endif
 }

screen-write.c

@@ -1011,6 +1011,11 @@ screen_write_alignmenttest(struct screen_write_ctx *ctx)
 	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);
@@ -1045,6 +1050,11 @@ screen_write_insertcharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
 	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);
 	ttyctx.bg = bg;
 
@@ -1073,6 +1083,11 @@ screen_write_deletecharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
 	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);
 	ttyctx.bg = bg;
 
@@ -1101,6 +1116,11 @@ screen_write_clearcharacter(struct screen_write_ctx *ctx, u_int nx, u_int bg)
 	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);
 	ttyctx.bg = bg;
 
@@ -1119,9 +1139,18 @@ screen_write_insertline(struct screen_write_ctx *ctx, u_int ny, u_int bg)
 	struct grid	*gd = s->grid;
 	struct tty_ctx	 ttyctx;
 
+#ifdef ENABLE_SIXEL
+	u_int		 sy = screen_size_y(s);
+#endif
+
 	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 > screen_size_y(s) - s->cy)
 			ny = screen_size_y(s) - s->cy;
@@ -1165,13 +1194,19 @@ 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);
 
 	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 > screen_size_y(s) - s->cy)
+		if (ny > sy - s->cy)
-			ny = screen_size_y(s) - s->cy;
+			ny = sy - s->cy;
 		if (ny == 0)
 			return;
 
@@ -1217,6 +1252,11 @@ screen_write_clearline(struct screen_write_ctx *ctx, u_int bg)
 	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
+
 	grid_view_clear(s->grid, 0, s->cy, sx, 1, bg);
 
 	screen_write_collect_clear(ctx, s->cy, 1);
@@ -1246,6 +1286,11 @@ screen_write_clearendofline(struct screen_write_ctx *ctx, u_int bg)
 	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);
 
  	before = screen_write_collect_trim(ctx, s->cy, s->cx, sx - s->cx, NULL);
@@ -1273,6 +1318,11 @@ screen_write_clearstartofline(struct screen_write_ctx *ctx, u_int 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
@@ -1320,6 +1370,11 @@ screen_write_reverseindex(struct screen_write_ctx *ctx, u_int bg)
 	struct screen	*s = ctx->s;
 	struct tty_ctx	 ttyctx;
 
+#ifdef ENABLE_SIXEL
+	if (image_free_all(s) && ctx->wp != NULL)
+		ctx->wp->flags |= PANE_REDRAW;
+#endif
+
 	if (s->cy == s->rupper) {
 		grid_view_scroll_region_down(s->grid, s->rupper, s->rlower, bg);
 		screen_write_collect_flush(ctx, 0, __func__);
@@ -1363,13 +1418,15 @@ 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;
+	int			 redraw = 0;
+	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,
-	    s->rupper, s->rlower);
+	    rupper, rlower);
 
 	if (bg != ctx->bg) {
 		screen_write_collect_flush(ctx, 1, __func__);
@@ -1377,6 +1434,14 @@ screen_write_linefeed(struct screen_write_ctx *ctx, int wrapped, u_int bg)
 	}
 
 	if (s->cy == s->rlower) {
+#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++;
@@ -1402,6 +1467,11 @@ screen_write_scrollup(struct screen_write_ctx *ctx, u_int lines, u_int bg)
 		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);
@@ -1426,6 +1496,11 @@ screen_write_scrolldown(struct screen_write_ctx *ctx, u_int lines, u_int bg)
 	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);
 
@@ -1450,6 +1525,11 @@ screen_write_clearendofscreen(struct screen_write_ctx *ctx, u_int bg)
 	struct tty_ctx	 ttyctx;
 	u_int		 sx = screen_size_x(s), sy = screen_size_y(s);
 
+#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);
 	ttyctx.bg = bg;
 
@@ -1479,6 +1559,11 @@ screen_write_clearstartofscreen(struct screen_write_ctx *ctx, u_int bg)
 	struct tty_ctx	 ttyctx;
 	u_int		 sx = screen_size_x(s);
 
+#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);
 	ttyctx.bg = bg;
 
@@ -1502,6 +1587,11 @@ screen_write_clearscreen(struct screen_write_ctx *ctx, u_int bg)
 	struct tty_ctx	 ttyctx;
 	u_int		 sx = screen_size_x(s), sy = screen_size_y(s);
 
+#ifdef ENABLE_SIXEL
+	if (image_free_all(s) && ctx->wp != NULL)
+		ctx->wp->flags |= PANE_REDRAW;
+#endif
+
 	screen_write_initctx(ctx, &ttyctx, 1);
 	ttyctx.bg = bg;
 
@@ -1770,6 +1860,11 @@ screen_write_collect_end(struct screen_write_ctx *ctx)
 		}
 	}
 
+#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);
 	screen_write_set_cursor(ctx, s->cx + ci->used, -1);
@@ -2157,6 +2252,61 @@ screen_write_rawstring(struct screen_write_ctx *ctx, u_char *str, u_int 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;
+
+	sixel_size_in_cells(si, &x, &y);
+	if (x > screen_size_x(s) || y > screen_size_y(s)) {
+		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);
+		si = new;
+		sixel_size_in_cells(si, &x, &y);
+	}
+
+	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);
+	ttyctx.ptr = 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,

screen.c

@@ -88,6 +88,10 @@ screen_init(struct screen *s, u_int sx, u_int sy, u_int hlimit)
 	s->tabs = NULL;
 	s->sel = NULL;
 
+#ifdef ENABLE_SIXEL
+	TAILQ_INIT(&s->images);
+#endif
+
 	s->write_list = NULL;
 	s->hyperlinks = NULL;
 
@@ -119,6 +123,11 @@ screen_reinit(struct screen *s)
 
 	screen_clear_selection(s);
 	screen_free_titles(s);
+
+#ifdef ENABLE_SIXEL
+	image_free_all(s);
+#endif
+
 	screen_reset_hyperlinks(s);
 }
 
@@ -151,6 +160,10 @@ screen_free(struct screen *s)
 	if (s->hyperlinks != NULL)
 		hyperlinks_free(s->hyperlinks);
 	screen_free_titles(s);
+
+#ifdef ENABLE_SIXEL
+	image_free_all(s);
+#endif
 }
 
 /* Reset tabs to default, eight spaces apart. */
@@ -294,8 +307,12 @@ screen_resize_cursor(struct screen *s, u_int sx, u_int sy, int reflow,
 	if (sy != screen_size_y(s))
 		screen_resize_y(s, sy, eat_empty, &cy);
 
-	if (reflow)
+	if (reflow) {
+#ifdef ENABLE_SIXEL
+		image_free_all(s);
+#endif
 		screen_reflow(s, sx, &cx, &cy, cursor);
+	}
 
 	if (cy >= s->grid->hsize) {
 		s->cx = cx;

tmux.h

@@ -64,6 +64,11 @@ struct screen_write_citem;
 struct screen_write_cline;
 struct screen_write_ctx;
 struct session;
+
+#ifdef ENABLE_SIXEL
+struct sixel_image;
+#endif
+
 struct tty_ctx;
 struct tty_code;
 struct tty_key;
@@ -839,6 +844,24 @@ struct style {
 	enum style_default_type	default_type;
 };
 
+#ifdef ENABLE_SIXEL
+/* Image. */
+struct image {
+	struct screen		*s;
+	struct sixel_image	*data;
+	char			*fallback;
+
+	u_int			 px;
+	u_int			 py;
+	u_int			 sx;
+	u_int			 sy;
+
+	TAILQ_ENTRY (image)	 all_entry;
+	TAILQ_ENTRY (image)	 entry;
+};
+TAILQ_HEAD(images, image);
+#endif
+
 /* Cursor style. */
 enum screen_cursor_style {
 	SCREEN_CURSOR_DEFAULT,
@@ -880,6 +903,10 @@ struct screen {
 	bitstr_t			*tabs;
 	struct screen_sel		*sel;
 
+#ifdef ENABLE_SIXEL
+	struct images			 images;
+#endif
+
 	struct screen_write_cline	*write_list;
 
 	struct hyperlinks		*hyperlinks;
@@ -1382,6 +1409,7 @@ struct tty {
 
 	u_int		 sx;
 	u_int		 sy;
+        /* Cell size in pixels. */
 	u_int		 xpixel;
 	u_int		 ypixel;
 
@@ -1390,6 +1418,8 @@ struct tty {
 	enum screen_cursor_style cstyle;
 	int		 ccolour;
 
+        /* Properties of the area being drawn on. */
+        /* When true, the drawing area is bigger than the terminal. */
 	int		 oflag;
 	u_int		 oox;
 	u_int		 ooy;
@@ -2332,6 +2362,11 @@ void	tty_set_path(struct tty *, const char *);
 void	tty_update_mode(struct tty *, int, struct screen *);
 void	tty_draw_line(struct tty *, struct screen *, u_int, u_int, u_int,
 	    u_int, u_int, const struct grid_cell *, struct colour_palette *);
+
+#ifdef ENABLE_SIXEL
+void	tty_draw_images(struct client *, struct window_pane *, struct screen *);
+#endif
+
 void	tty_sync_start(struct tty *);
 void	tty_sync_end(struct tty *);
 int	tty_open(struct tty *, char **);
@@ -2362,6 +2397,11 @@ void	tty_cmd_scrolldown(struct tty *, const struct tty_ctx *);
 void	tty_cmd_reverseindex(struct tty *, const struct tty_ctx *);
 void	tty_cmd_setselection(struct tty *, const struct tty_ctx *);
 void	tty_cmd_rawstring(struct tty *, const struct tty_ctx *);
+
+#ifdef ENABLE_SIXEL
+void	tty_cmd_sixelimage(struct tty *, const struct tty_ctx *);
+#endif
+
 void	tty_cmd_syncstart(struct tty *, const struct tty_ctx *);
 void	tty_default_colours(struct grid_cell *, struct window_pane *);
 
@@ -2946,6 +2986,10 @@ void	 screen_write_setselection(struct screen_write_ctx *, const char *,
 	     u_char *, u_int);
 void	 screen_write_rawstring(struct screen_write_ctx *, u_char *, u_int,
 	     int);
+#ifdef ENABLE_SIXEL
+void	 screen_write_sixelimage(struct screen_write_ctx *,
+	     struct sixel_image *, u_int);
+#endif
 void	 screen_write_alternateon(struct screen_write_ctx *,
 	     struct grid_cell *, int);
 void	 screen_write_alternateoff(struct screen_write_ctx *,
@@ -3365,6 +3409,26 @@ struct window_pane *spawn_pane(struct spawn_context *, char **);
 /* regsub.c */
 char		*regsub(const char *, const char *, const char *, int);
 
+#ifdef ENABLE_SIXEL
+/* image.c */
+int		 image_free_all(struct screen *);
+struct image	*image_store(struct screen *, struct sixel_image *);
+int		 image_check_line(struct screen *, u_int, u_int);
+int		 image_check_area(struct screen *, u_int, u_int, u_int, u_int);
+int		 image_scroll_up(struct screen *, u_int);
+
+/* image-sixel.c */
+struct sixel_image *sixel_parse(const char *, size_t, u_int, u_int);
+void		 sixel_free(struct sixel_image *);
+void		 sixel_log(struct sixel_image *);
+void		 sixel_size_in_cells(struct sixel_image *, u_int *, u_int *);
+struct sixel_image *sixel_scale(struct sixel_image *, u_int, u_int, u_int,
+		     u_int, u_int, u_int, int);
+char		*sixel_print(struct sixel_image *, struct sixel_image *,
+		     size_t *);
+struct screen	*sixel_to_screen(struct sixel_image *);
+#endif
+
 /* server-acl.c */
 void			 server_acl_init(void);
 struct server_acl_user	*server_acl_user_find(uid_t);

tty.c

@@ -72,6 +72,11 @@ static int	tty_check_overlay(struct tty *, u_int, u_int);
 static void	tty_check_overlay_range(struct tty *, u_int, u_int, u_int,
 		    struct overlay_ranges *);
 
+#ifdef ENABLE_SIXEL
+static void	tty_write_one(void (*)(struct tty *, const struct tty_ctx *),
+		    struct client *, struct tty_ctx *);
+#endif
+
 #define tty_use_margin(tty) \
 	(tty->term->flags & TERM_DECSLRM)
 #define tty_full_width(tty, ctx) \
@@ -1582,6 +1587,58 @@ tty_draw_line(struct tty *tty, struct screen *s, u_int px, u_int py, u_int nx,
 	tty_update_mode(tty, tty->mode, s);
 }
 
+#ifdef ENABLE_SIXEL
+/* Update context for client. */
+static int
+tty_set_client_cb(struct tty_ctx *ttyctx, struct client *c)
+{
+	struct window_pane	*wp = ttyctx->arg;
+
+	if (c->session->curw->window != wp->window)
+		return (0);
+	if (wp->layout_cell == NULL)
+		return (0);
+
+	/* Set the properties relevant to the current client. */
+	ttyctx->bigger = tty_window_offset(&c->tty, &ttyctx->wox, &ttyctx->woy,
+	    &ttyctx->wsx, &ttyctx->wsy);
+
+	ttyctx->yoff = ttyctx->ryoff = wp->yoff;
+	if (status_at_line(c) == 0)
+		ttyctx->yoff += status_line_size(c);
+
+	return (1);
+}
+
+void
+tty_draw_images(struct client *c, struct window_pane *wp, struct screen *s)
+{
+	struct image	*im;
+	struct tty_ctx	 ttyctx;
+
+	TAILQ_FOREACH(im, &s->images, entry) {
+		memset(&ttyctx, 0, sizeof ttyctx);
+
+		/* Set the client independent properties. */
+		ttyctx.ocx = im->px;
+		ttyctx.ocy = im->py;
+
+		ttyctx.orlower = s->rlower;
+		ttyctx.orupper = s->rupper;
+
+		ttyctx.xoff = ttyctx.rxoff = wp->xoff;
+		ttyctx.sx = wp->sx;
+		ttyctx.sy = wp->sy;
+
+		ttyctx.ptr = im;
+		ttyctx.arg = wp;
+		ttyctx.set_client_cb = tty_set_client_cb;
+		ttyctx.allow_invisible_panes = 1;
+		tty_write_one(tty_cmd_sixelimage, c, &ttyctx);
+	}
+}
+#endif
+
 void
 tty_sync_start(struct tty *tty)
 {
@@ -1655,6 +1712,19 @@ tty_write(void (*cmdfn)(struct tty *, const struct tty_ctx *),
 	}
 }
 
+#ifdef ENABLE_SIXEL
+/* Only write to the incoming tty instead of every client. */
+static void
+tty_write_one(void (*cmdfn)(struct tty *, const struct tty_ctx *),
+    struct client *c, struct tty_ctx *ctx)
+{
+	if (ctx->set_client_cb == NULL)
+		return;
+	if ((ctx->set_client_cb(ctx, c)) == 1)
+		cmdfn(&c->tty, ctx);
+}
+#endif
+
 void
 tty_cmd_insertcharacter(struct tty *tty, const struct tty_ctx *ctx)
 {
@@ -2156,6 +2226,58 @@ tty_cmd_rawstring(struct tty *tty, const struct tty_ctx *ctx)
 	tty_invalidate(tty);
 }
 
+#ifdef ENABLE_SIXEL
+void
+tty_cmd_sixelimage(struct tty *tty, const struct tty_ctx *ctx)
+{
+	struct image		*im = ctx->ptr;
+	struct sixel_image	*si = im->data;
+	struct sixel_image	*new;
+	char			*data;
+	size_t			 size;
+	u_int			 cx = ctx->ocx, cy = ctx->ocy, sx, sy;
+	u_int			 i, j, x, y, rx, ry;
+	int			 fallback = 0;
+
+	if ((~tty->term->flags & TERM_SIXEL) &&
+            !tty_term_has(tty->term, TTYC_SXL))
+		fallback = 1;
+	if (tty->xpixel == 0 || tty->ypixel == 0)
+		fallback = 1;
+
+	sixel_size_in_cells(si, &sx, &sy);
+	log_debug("%s: image is %ux%u", __func__, sx, sy);
+	if (!tty_clamp_area(tty, ctx, cx, cy, sx, sy, &i, &j, &x, &y, &rx, &ry))
+		return;
+	log_debug("%s: clamping to %u,%u-%u,%u", __func__, i, j, rx, ry);
+
+	if (fallback == 1) {
+		data = xstrdup(im->fallback);
+		size = strlen(data);
+	} else {
+		new = sixel_scale(si, tty->xpixel, tty->ypixel, i, j, rx, ry, 0);
+		if (new == NULL)
+			return;
+
+		data = sixel_print(new, si, &size);
+	}
+	if (data != NULL) {
+		log_debug("%s: %zu bytes: %s", __func__, size, data);
+		tty_region_off(tty);
+		tty_margin_off(tty);
+		tty_cursor(tty, x, y);
+
+		tty->flags |= TTY_NOBLOCK;
+		tty_add(tty, data, size);
+		tty_invalidate(tty);
+		free(data);
+	}
+
+	if (fallback == 0)
+		sixel_free(new);
+}
+#endif
+
 void
 tty_cmd_syncstart(struct tty *tty, const struct tty_ctx *ctx)
 {