From 0c9165fc713d9297e59c210659e61ab6993b1b3e Mon Sep 17 00:00:00 2001
From: Nicholas Marriott <nicholas.marriott@gmail.com>
Date: Mon, 1 Sep 2025 08:31:57 +0100
Subject: [PATCH] Give another bit to the first component of SIXEL colours to
 fix the HLS color space which uses 360 degrees in its first component. From
 nincsnevem662 at gmail dot com in GitHub issue 4616.

---
 image-sixel.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/image-sixel.c b/image-sixel.c
index a03c8619..bd5e3077 100644
--- a/image-sixel.c
+++ b/image-sixel.c
@@ -196,7 +196,7 @@ 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;
+	u_int		 c, type, c1, c2, c3;
 
 	last = cp;
 	while (last != end) {
@@ -219,32 +219,36 @@ sixel_parse_colour(struct sixel_image *si, const char *cp, const char *end)
 		log_debug("%s: missing ;", __func__);
 		return (NULL);
 	}
-	r = strtoul(endptr + 1, &endptr, 10);
+	c1 = strtoul(endptr + 1, &endptr, 10);
 	if (endptr == last || *endptr != ';') {
 		log_debug("%s: missing ;", __func__);
 		return (NULL);
 	}
-	g = strtoul(endptr + 1, &endptr, 10);
+	c2 = strtoul(endptr + 1, &endptr, 10);
 	if (endptr == last || *endptr != ';') {
 		log_debug("%s: missing ;", __func__);
 		return (NULL);
 	}
-	b = strtoul(endptr + 1, &endptr, 10);
+	c3 = strtoul(endptr + 1, &endptr, 10);
 	if (endptr != last) {
 		log_debug("%s: missing ;", __func__);
 		return (NULL);
 	}
 
-	if (type != 1 && type != 2) {
-		log_debug("%s: invalid type %d", __func__, type);
+	if ((type != 1 && type != 2) ||
+	    (type == 1 && (c1 > 360 || c2 > 100 || c3 > 100)) ||
+	    (type == 2 && (c1 > 100 || c2 > 100 || c3 > 100))) {
+		log_debug("%s: invalid color %u;%u;%u;%u", __func__, type,
+		    c1, c2, c3);
 		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;
+	si->colours[c] = (type << 25) | (c1 << 16) | (c2 << 8) | c3;
 	return (last);
 }
 
@@ -598,7 +602,7 @@ sixel_print(struct sixel_image *si, struct sixel_image *map, size_t *size)
 	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);
+		    i, c >> 25, (c >> 16) & 0x1ff, (c >> 8) & 0xff, c & 0xff);
 		sixel_print_add(&buf, &len, &used, tmp, tmplen);
 
 		chunk = &chunks[i];