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 0a15bbf3f1972dc84c5c84d5128024c1bc4c0074.

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 4c92acf6ff24dde37ad41cd168ea2d3bcefb8567
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Jun 17 17:53:01 2023 -0700

    Merge topcat001/tmux/sixel.

commit 6794facc82e98f8448c192913cf62fe6e10fde63
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 64368a1a63f04fb877b57e4286c9a2e1efe966c9
Merge: c630a56a 22eb0334
Author: topcat001 <anindya49@hotmail.com>
Date:   Thu Mar 30 14:21:09 2023 -0700

    Merge branch 'master' into sixel

commit c630a56a621b9761eed558cbd566a36cb09adf8f
Merge: 34c96c4c aaa043a2
Author: topcat001 <anindya49@hotmail.com>
Date:   Thu Nov 10 18:53:01 2022 -0800

    Merge branch 'master' into sixel

commit 34c96c4c4a33f86b49c8a53dc48b2b817db24e95
Merge: 2a1e16a2 50f4e0fa
Author: topcat001 <anindya49@hotmail.com>
Date:   Sat Nov 5 18:05:36 2022 -0700

    Merge branch 'master' into sixel

commit 2a1e16a24dc75741c66f5d72fa5bf26b73507993
Merge: a82f14c7 d001a94d
Author: topcat001 <anindya49@hotmail.com>
Date:   Thu Oct 27 16:01:35 2022 -0700

    Merge branch 'master' into sixel

commit a82f14c7b23a239a2114c756ef73bba8609ebe33
Merge: 742c0634 f7b30ed3
Author: topcat001 <anindya49@hotmail.com>
Date:   Sun Aug 28 13:43:07 2022 -0700

    Merge branch 'master' into sixel

commit 742c0634734e6b2840762e58b0bf27626b5ac24b
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 906c92a5f458b8843e7abd1d6f419dc091f8063c
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 6680a024be5e173a27c10e9a0be6c9072576086d
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Oct 7 13:59:08 2021 +0100

    Fix build.

commit ebd2c585937f18045d334226d4a0cc788fe14353
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 90dc05191cbba8de6d9d77ee7f9726325abe844e
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 a282439fcb2f597927a5ba33d2c378c90eec8b42
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jan 30 09:12:53 2020 +0000

    Add missing declarations.

commit 3a741aacd108538f99239c68bfa2cd416bf0eb46
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 339832b92c298538f398754f6d3fc21d15d13326
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Jan 30 09:04:51 2020 +0000

    Bad merge.

commit 92ed9fc0b20440f2bc553757e6bfe3126fe84be4
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 40ad01073d73a531b4e85b0138f78bf0b472b354
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 5bb075487f5897d7402adb880e678043c0f7f3e0
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 dd3c72f132c911b0ba61b56a56f46510704d3392
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 1a0e5fe933e89932f2f658936c52eb50644fbef4
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 cf071ffecd5a0d33008fd0a8b66a22f6855c7a8d
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Mon Dec 9 15:41:56 2019 +0000

    Remove images when reflow happens.

commit 2006b7a5631787a7086c6bae364e62d0a0b5948a
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 09:27:15 2019 +0000

    More invalidation of images.

commit b642eac4503cc89cde01103f7bacca57cc9c1a2b
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 7566e37a461bf245bd2e54e1d522e919071e9c44
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 62c0280b23cf67fc43f691392a8eca5cd7ff0727
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 08:48:58 2019 +0000

    Correctly remove when not visible.

commit 86c5098a887f2cd09b828e051ccf0fab21bf4f6a
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 49f2f0a8f1e72389f4128aa38119ed124cdc31c5
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Dec 5 00:02:55 2019 +0000

    Store images, currently at most 10.

commit 3aebcc67099ccbc5964c744fc1435931c1a78583
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 7c033a74e25957d333217cb71a7658b860583501
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 146ee3f6f8ee2629c6a88b6900a71f3e6fd14e4d
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Sat Nov 30 09:47:53 2019 +0000

    Don't write image as text yet.

commit 0a15bbf3f1972dc84c5c84d5128024c1bc4c0074
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 a5b1e209417b7d3f5b0099642dd317c312f79377
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 968382aa6a4b9c71fbc221aa4f0e899f6a83a260
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 b1904c9b8db514133d3372aac13b2ff0b2093cc3
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 5d8dbcdf3d76d0e69b8f2d21eff48f819dcec199
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 0c999a402ece7b40e6ae84547893421b52d508ff
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 28961dd5a38dd5a7b703ed0e6625fa9a65556d35
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 14:24:57 2019 +0000

    Add an image.

commit d2e3f3c1cca5410570c5392340d14e96ae7a354c
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 e01df67ca106e57f5c689e75f313f8cda6f8b805
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 e24acc0b5c3ac19dcacebdea243dcc7784215ffa
Author: Nicholas Marriott <nicholas.marriott@gmail.com>
Date:   Thu Nov 28 12:38:02 2019 +0000

    Simple SIXEL parse and modify API.

commit b34111b3da1e4b1769a976cd40486144f7b4f5a2
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.

1 files changed, 565 insertions, 0 deletions

diff --git a/image-sixel.c b/image-sixel.c
new file mode 100644
index 00000000..f4492d95
--- /dev/null
+++ b/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);
+}