[PATCH] rcfile: support "#rgb" format for specifying colors in 256-color terminals

[Brad Town]

This fulfills https://savannah.gnu.org/bugs/?56445.

Signed-off-by: Brad Town <brad@bradtown.com>
---
 src/rcfile.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/src/rcfile.c b/src/rcfile.c
index 174716bf..0d967155 100644
--- a/src/rcfile.c
+++ b/src/rcfile.c
@@ -990,6 +990,19 @@ void parse_includes(char *ptr)
  free(expanded);
 }

+/* Return the index of the color that is closest to the given RGB levels,
+ * assuming that the terminal uses the 6x6x6 color cube of xterm-256color. */
+short closest_index_color(short r, short g, short b)
+{
+ if (COLORS != 256)
+ return THE_DEFAULT;
+
+ /* Translation table, from 16 intended levels to 6 available levels. */
+ static const short level[] = { 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 3, 3,
4, 4, 5, 5 };
+
+ return (36 * level[r] + 6 * level[g] + level[b] + 16);
+}
+
 #define COLORCOUNT  20

 const char hues[COLORCOUNT][8] = { "red", "green", "blue",
@@ -1024,6 +1037,18 @@ short color_to_short(const char *colorname,
bool *vivid, bool *thick)
  *thick = FALSE;
  }

+ if (colorname[0] == '#' && strlen(colorname) == 4) {
+ unsigned short r, g, b;
+
+ if (*vivid) {
+ jot_error(N_("Color '%s' takes no prefix"), colorname);
+ return BAD_COLOR;
+ }
+
+ if (sscanf(colorname, "#%1hX%1hX%1hX", &r, &g, &b) == 3)
+ return closest_index_color(r, g, b);
+ }
+
  for (int index = 0; index < COLORCOUNT; index++)
  if (strcmp(colorname, hues[index]) == 0) {
  if (index > 7 && *vivid) {
-- 
2.34.0.rc1.387.gb447b232ab-goog