From e24acc0b5c3ac19dcacebdea243dcc7784215ffa Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Thu, 28 Nov 2019 12:38:02 +0000
Subject: [PATCH] Simple SIXEL parse and modify API.

---
 Makefile.am |   1 +
 sixel.c     | 516 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 tmux.h      |   9 +
 3 files changed, 526 insertions(+)
 create mode 100644 sixel.c

diff --git a/Makefile.am b/Makefile.am
index ab302637..014554d4 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -161,6 +161,7 @@ dist_tmux_SOURCES = \
 	server-fn.c \
 	server.c \
 	session.c \
+	sixel.c \
 	spawn.c \
 	status.c \
 	style.c \
diff --git a/sixel.c b/sixel.c
new file mode 100644
index 00000000..76ecf48a
--- /dev/null
+++ b/sixel.c
@@ -0,0 +1,516 @@
+/* $OpenBSD$ */
+
+/*
+ * 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		 d, x, y;
+
+	last = cp;
+	while (last != end) {
+		if (*last != ';' && (*last < '0' || *last > '9'))
+			break;
+		last++;
+	}
+	d = strtoul(cp, &endptr, 10);
+	if (endptr == last || *endptr != ';')
+		return (last);
+	d = 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)
+{
+	struct sixel_image	*new;
+	u_int			 cx, cy, pox, poy, psx, psy, tsx, tsy, px, py;
+	u_int			 x, y;
+
+	/*
+	 * 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;
+
+	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));
+		}
+	}
+	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)
+{
+	char			*buf, tmp[64], *contains, data, last;
+	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';
+
+	free(contains);
+	return (buf);
+}
diff --git a/tmux.h b/tmux.h
index 7c901b9d..a5a60214 100644
--- a/tmux.h
+++ b/tmux.h
@@ -2704,4 +2704,13 @@ struct window_pane *spawn_pane(struct spawn_context *, char **);
 /* regsub.c */
 char		*regsub(const char *, const char *, const char *, int);
 
+/* 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);
+char		*sixel_print(struct sixel_image *, struct sixel_image *);
+
 #endif /* TMUX_H */