Pass through SIXEL DCS sequences (treat similarly to the passthrough escape

sequence) if it appears the terminal outside supports them.

input.c

@@ -1305,8 +1305,8 @@ input_csi_dispatch(struct input_ctx *ictx)
 	if (ictx->flags & INPUT_DISCARD)
 		return (0);
 
-	log_debug("%s: '%c' \"%s\" \"%s\"",
-	    __func__, ictx->ch, ictx->interm_buf, ictx->param_buf);
+	log_debug("%s: '%c' \"%s\" \"%s\"", __func__, ictx->ch,
+	    ictx->interm_buf, ictx->param_buf);
 
 	if (input_split(ictx) != 0)
 		return (0);
@@ -2151,19 +2151,27 @@ static int
 input_dcs_dispatch(struct input_ctx *ictx)
 {
 	struct screen_write_ctx	*sctx = &ictx->ctx;
-	u_char			*buf = ictx->input_buf;
-	size_t			 len = ictx->input_len;
+	u_char			*buf = ictx->input_buf, *pbuf = ictx->param_buf;
+	size_t			 len = ictx->input_len, plen = ictx->param_len;
 	const char		 prefix[] = "tmux;";
 	const u_int		 prefixlen = (sizeof prefix) - 1;
 
 	if (ictx->flags & INPUT_DISCARD)
 		return (0);
 
-	log_debug("%s: \"%s\"", __func__, buf);
+	log_debug("%s: \"%s\" \"%s\" \"%s\"", __func__, buf, ictx->interm_buf,
+	    ictx->param_buf);
 
 	if (len >= prefixlen && strncmp(buf, prefix, prefixlen) == 0)
 		screen_write_rawstring(sctx, buf + prefixlen, len - prefixlen);
 
+	if (buf[0] == 'q') {
+		screen_write_rawsixel(sctx, (char *)"\033P", 2, 1);
+		screen_write_rawsixel(sctx, pbuf, plen, 1);
+		screen_write_rawsixel(sctx, buf, len, 1);
+		screen_write_rawsixel(sctx, (char *)"\033\\", 2, 0);
+	}
+
 	return (0);
 }
 

screen-write.c

@@ -1671,3 +1671,18 @@ screen_write_rawstring(struct screen_write_ctx *ctx, u_char *str, u_int len)
 
 	tty_write(tty_cmd_rawstring, &ttyctx);
 }
+
+/* Write unmodified SIXEL data. */
+void
+screen_write_rawsixel(struct screen_write_ctx *ctx, u_char *str, u_int len,
+    int more)
+{
+	struct tty_ctx	ttyctx;
+
+	screen_write_initctx(ctx, &ttyctx);
+	ttyctx.ptr = str;
+	ttyctx.num = len;
+	ttyctx.more = more;
+
+	tty_write(tty_cmd_rawsixel, &ttyctx);
+}

tmux.1

@@ -5200,6 +5200,8 @@ $ printf '\e033[4 q'
 If
 .Em Se
 is not set, \&Ss with argument 0 will be used to reset the cursor style instead.
+.It Em \&Sxl
+Indicates that the terminal supports SIXEL.
 .It Em \&Tc
 Indicate that the terminal supports the
 .Ql direct colour

tmux.h

@@ -446,6 +446,7 @@ enum tty_code_code {
 	TTYC_SMULX,
 	TTYC_SMUL,
 	TTYC_SMXX,
+	TTYC_SXL,
 	TTYC_SS,
 	TTYC_TC,
 	TTYC_TSL,
@@ -1145,6 +1146,7 @@ struct tty_term {
 
 #define TERM_256COLOURS 0x1
 #define TERM_EARLYWRAP 0x2
+#define TERM_SIXEL 0x4
 	int		 flags;
 
 	LIST_ENTRY(tty_term) entry;
@@ -1248,6 +1250,7 @@ struct tty_ctx {
 
 	u_int			 num;
 	void			*ptr;
+	int			 more;
 
 	/*
 	 * Cursor and region position before the screen was updated - this is
@@ -1947,7 +1950,7 @@ void	tty_draw_line(struct tty *, struct window_pane *, struct screen *,
 int	tty_open(struct tty *, char **);
 void	tty_close(struct tty *);
 void	tty_free(struct tty *);
-void	tty_set_type(struct tty *, int);
+void	tty_set_type(struct tty *, int, int);
 void	tty_write(void (*)(struct tty *, const struct tty_ctx *),
 	    struct tty_ctx *);
 void	tty_cmd_alignmenttest(struct tty *, const struct tty_ctx *);
@@ -1971,6 +1974,7 @@ void	tty_cmd_scrolldown(struct tty *, const struct tty_ctx *);
 void	tty_cmd_reverseindex(struct tty *, const struct tty_ctx *);
 void	tty_cmd_setselection(struct tty *, const struct tty_ctx *);
 void	tty_cmd_rawstring(struct tty *, const struct tty_ctx *);
+void	tty_cmd_rawsixel(struct tty *, const struct tty_ctx *);
 
 /* tty-term.c */
 extern struct tty_terms tty_terms;
@@ -2357,6 +2361,7 @@ void	 screen_write_collect_add(struct screen_write_ctx *,
 void	 screen_write_cell(struct screen_write_ctx *, const struct grid_cell *);
 void	 screen_write_setselection(struct screen_write_ctx *, u_char *, u_int);
 void	 screen_write_rawstring(struct screen_write_ctx *, u_char *, u_int);
+void	 screen_write_rawsixel(struct screen_write_ctx *, u_char *, u_int, int);
 
 /* screen-redraw.c */
 void	 screen_redraw_screen(struct client *);

tty-keys.c

@@ -1005,7 +1005,7 @@ tty_keys_device_attributes(struct tty *tty, const char *buf, size_t len,
 	u_int			 i, n = 0;
 	char			 tmp[64], *endptr, p[32] = { 0 }, *cp, *next;
 	static const char	*types[] = TTY_TYPES;
-	int			 type;
+	int			 type, flags = 0;
 
 	*size = 0;
 
@@ -1068,9 +1068,12 @@ tty_keys_device_attributes(struct tty *tty, const char *buf, size_t len,
 		type = TTY_VT520;
 		break;
 	}
-	for (i = 2; i < n; i++)
+	for (i = 2; i < n; i++) {
 		log_debug("%s: DA feature: %d", c->name, p[i]);
-	tty_set_type(tty, type);
+		if (p[i] == 4)
+			flags |= TERM_SIXEL;
+	}
+	tty_set_type(tty, type, flags);
 
 	log_debug("%s: received DA %.*s (%s)", c->name, (int)*size, buf,
 	    types[type]);

tty-term.c

@@ -252,6 +252,7 @@ static const struct tty_term_code_entry tty_term_codes[] = {
 	[TTYC_SETRGBF] = { TTYCODE_STRING, "setrgbf" },
 	[TTYC_SETULC] = { TTYCODE_STRING, "Setulc" },
 	[TTYC_SE] = { TTYCODE_STRING, "Se" },
+	[TTYC_SXL] =  { TTYCODE_FLAG, "Sxl" },
 	[TTYC_SGR0] = { TTYCODE_STRING, "sgr0" },
 	[TTYC_SITM] = { TTYCODE_STRING, "sitm" },
 	[TTYC_SMACS] = { TTYCODE_STRING, "smacs" },

tty.c

@@ -436,9 +436,10 @@ tty_free(struct tty *tty)
 }
 
 void
-tty_set_type(struct tty *tty, int type)
+tty_set_type(struct tty *tty, int type, int flags)
 {
 	tty->term_type = type;
+	tty->term_flags |= flags;
 
 	if (tty_use_margin(tty))
 		tty_puts(tty, "\033[?69h"); /* DECLRMM */
@@ -1865,6 +1866,18 @@ tty_cmd_rawstring(struct tty *tty, const struct tty_ctx *ctx)
 	tty_invalidate(tty);
 }
 
+void
+tty_cmd_rawsixel(struct tty *tty, const struct tty_ctx *ctx)
+{
+	int	flags = (tty->term->flags|tty->term_flags);
+
+	if ((flags & TERM_SIXEL) || tty_term_has(tty->term, TTYC_SXL)) {
+		tty_add(tty, ctx->ptr, ctx->num);
+		if (!ctx->more)
+			tty_invalidate(tty);
+	}
+}
+
 static void
 tty_cell(struct tty *tty, const struct grid_cell *gc, struct window_pane *wp)
 {