From fe7a871a23ada0c71fb0886ef99a356c67bf5c0d Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Sun, 4 Feb 2018 10:10:39 +0000
Subject: [PATCH] Upstream ncurses has introduced terminfo capabilities to
 specify RGB colour ("true" or "direct" colour). These consist of new entries
 (such as "xterm-direct") which have a different setaf/setab implementation,
 colors and pairs set to 0x1000000 and 0x10000, and a new RGB flag.

The setaf/setab definitions seem to be geared towards what ncurses (or
emacs maybe) needs, in that the new versions do only ANSI and RGB
colours (they can't be used for the 256 colour palette); they rely on
the silly ISO colon-separated version of SGR; and they use a weird
multiplication scheme so they still only need one argument. The higher
values of colors and pairs require a recent ncurses to parse.

tmux can use the RGB flag to detect RGB colour support (keeping the old
Tc extension for backwards compatibility for now). However, as we still
want to send 256 colour information unchanged when possible, the new
setaf/setab are awkward. So when RGB is present, reserve setaf/setab
only for ANSI colours and use the escape sequences directly for 256 and
RGB colours. (To my knowledge no recent terminal uses unusual escape
sequences for these in any case.)
---
 tmux.h     |  1 +
 tty-term.c |  8 ++++++--
 tty.c      | 13 +++++++++----
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/tmux.h b/tmux.h
index b8fc0e66..aab21fc4 100644
--- a/tmux.h
+++ b/tmux.h
@@ -399,6 +399,7 @@ enum tty_code_code {
 	TTYC_MS,
 	TTYC_OP,
 	TTYC_REV,
+	TTYC_RGB,
 	TTYC_RI,
 	TTYC_RMACS,
 	TTYC_RMCUP,
diff --git a/tty-term.c b/tty-term.c
index 0807f858..b9afd96c 100644
--- a/tty-term.c
+++ b/tty-term.c
@@ -237,6 +237,7 @@ static const struct tty_term_code_entry tty_term_codes[] = {
 	[TTYC_MS] = { TTYCODE_STRING, "Ms" },
 	[TTYC_OP] = { TTYCODE_STRING, "op" },
 	[TTYC_REV] = { TTYCODE_STRING, "rev" },
+	[TTYC_RGB] = { TTYCODE_FLAG, "RGB" },
 	[TTYC_RI] = { TTYCODE_STRING, "ri" },
 	[TTYC_RMACS] = { TTYCODE_STRING, "rmacs" },
 	[TTYC_RMCUP] = { TTYCODE_STRING, "rmcup" },
@@ -525,8 +526,11 @@ tty_term_find(char *name, int fd, char **cause)
 		code->type = TTYCODE_STRING;
 	}
 
-	/* On terminals with RGB colour (TC), fill in setrgbf and setrgbb. */
-	if (tty_term_flag(term, TTYC_TC) &&
+	/*
+	 * On terminals with RGB colour (Tc or RGB), fill in setrgbf and
+	 * setrgbb if they are missing.
+	 */
+	if ((tty_term_flag(term, TTYC_TC) || tty_term_flag(term, TTYC_RGB)) &&
 	    !tty_term_has(term, TTYC_SETRGBF) &&
 	    !tty_term_has(term, TTYC_SETRGBB)) {
 		code = &term->codes[TTYC_SETRGBF];
diff --git a/tty.c b/tty.c
index 01208a25..b293d41d 100644
--- a/tty.c
+++ b/tty.c
@@ -2051,11 +2051,15 @@ tty_try_colour(struct tty *tty, int colour, const char *type)
 
 	if (colour & COLOUR_FLAG_256) {
 		/*
-		 * If the user has specified -2 to the client, setaf and setab
-		 * may not work (or they may not want to use them), so send the
-		 * usual sequence.
+		 * If the user has specified -2 to the client (meaning
+		 * TERM_256COLOURS is set), setaf and setab may not work (or
+		 * they may not want to use them), so send the usual sequence.
+		 *
+		 * Also if RGB is set, setaf and setab do not support the 256
+		 * colour palette so use the sequences directly there too.
 		 */
-		if (tty->term_flags & TERM_256COLOURS)
+		if ((tty->term_flags & TERM_256COLOURS) ||
+		    tty_term_has(tty->term, TTYC_RGB))
 			goto fallback_256;
 
 		/*
@@ -2096,6 +2100,7 @@ tty_try_colour(struct tty *tty, int colour, const char *type)
 
 fallback_256:
 	xsnprintf(s, sizeof s, "\033[%s;5;%dm", type, colour & 0xff);
+	log_debug("%s: 256 colour fallback: %s", tty->client->name, s);
 	tty_puts(tty, s);
 	return (0);
 }