Add 256 color support.

It is quite inconvenient that if an application for xterm uses 256 color
mode, text suddenly starts to blink (because of ;5; in the middle).
We'd better just implement 256 color mode and add a conversion routine
from 256 to 8 color mode, which doesn't seem to be too bad in practice.

Remapping colors is done quite simple. If one of the channels is most
actively represented, primary colors are used. If two channels are most
actively represented, secondary colors are used. If all three channels
are equal (gray), it picks between black and white.

Reported by:	Paul B. Mahol <onemda gmail com>

sys/dev/syscons/scterm-teken.c

@@ -313,11 +313,11 @@ scteken_attr(const teken_attr_t *a)
 	teken_color_t fg, bg;
 
 	if (a->ta_format & TF_REVERSE) {
-		fg = a->ta_bgcolor;
-		bg = a->ta_fgcolor;
+		fg = teken_256to8(a->ta_bgcolor);
+		bg = teken_256to8(a->ta_fgcolor);
 	} else {
-		fg = a->ta_fgcolor;
-		bg = a->ta_bgcolor;
+		fg = teken_256to8(a->ta_fgcolor);
+		bg = teken_256to8(a->ta_bgcolor);
 	}
 	if (a->ta_format & TF_BOLD)
 		attr |= fgcolors_bold[fg];

sys/teken/teken.c

@@ -409,4 +409,55 @@ teken_state_numbers(teken_t *t, teken_char_t c)
 	return (0);
 }
 
+teken_color_t
+teken_256to8(teken_color_t c)
+{
+	unsigned int r, g, b;
+
+	if (c < 16) {
+		/* Traditional color indices. */
+		return (c % 8);
+	} else if (c >= 244) {
+		/* Upper grayscale colors. */
+		return (TC_WHITE);
+	} else if (c >= 232) {
+		/* Lower grayscale colors. */
+		return (TC_BLACK);
+	}
+
+	/* Convert to RGB. */
+	c -= 16;
+	b = c % 6;
+	g = (c / 6) % 6;
+	r = c / 36;
+
+	if (r < g) {
+		/* Possibly green. */
+		if (g < b)
+			return (TC_BLUE);
+		else if (g > b)
+			return (TC_GREEN);
+		else
+			return (TC_CYAN);
+	} else if (r > g) {
+		/* Possibly red. */
+		if (r < b)
+			return (TC_BLUE);
+		else if (r > b)
+			return (TC_RED);
+		else
+			return (TC_MAGENTA);
+	} else {
+		/* Possibly brown. */
+		if (g < b)
+			return (TC_BLUE);
+		else if (g > b)
+			return (TC_BROWN);
+		else if (r < 3)
+			return (TC_BLACK);
+		else
+			return (TC_WHITE);
+	}
+}
+
 #include "teken_state.h"

sys/teken/teken.h

@@ -171,4 +171,7 @@ void	teken_set_winsize(teken_t *, const teken_pos_t *);
 void	teken_set_8bit(teken_t *);
 void	teken_set_cons25(teken_t *);
 
+/* Color conversion. */
+teken_color_t teken_256to8(teken_color_t);
+
 #endif /* !_TEKEN_H_ */

sys/teken/teken_demo.c

@@ -116,7 +116,8 @@ printchar(const teken_pos_t *p)
 	if (px->a.ta_format & TF_REVERSE)
 		attr |= A_REVERSE;
 
-	bkgdset(attr | COLOR_PAIR(px->a.ta_fgcolor + 8 * px->a.ta_bgcolor));
+	bkgdset(attr | COLOR_PAIR(teken_256to8(px->a.ta_fgcolor) +
+	      8 * teken_256to8(px->a.ta_bgcolor)));
 	mvaddstr(p->tp_row, p->tp_col, str);
 
 	move(y, x);

sys/teken/teken_subr.h

@@ -1150,6 +1150,12 @@ teken_subr_set_graphic_rendition(teken_t *t, unsigned int ncmds,
 		case 37: /* Set foreground color: white */
 			t->t_curattr.ta_fgcolor = n - 30;
 			break;
+		case 38: /* Set foreground color: 256 color mode */
+			if (i + 2 >= ncmds || cmds[i + 1] != 5)
+				continue;
+			t->t_curattr.ta_fgcolor = cmds[i + 2];
+			i += 2;
+			break;
 		case 39: /* Set default foreground color. */
 			t->t_curattr.ta_fgcolor = t->t_defattr.ta_fgcolor;
 			break;
@@ -1163,9 +1169,35 @@ teken_subr_set_graphic_rendition(teken_t *t, unsigned int ncmds,
 		case 47: /* Set background color: white */
 			t->t_curattr.ta_bgcolor = n - 40;
 			break;
+		case 48: /* Set background color: 256 color mode */
+			if (i + 2 >= ncmds || cmds[i + 1] != 5)
+				continue;
+			t->t_curattr.ta_bgcolor = cmds[i + 2];
+			i += 2;
+			break;
 		case 49: /* Set default background color. */
 			t->t_curattr.ta_bgcolor = t->t_defattr.ta_bgcolor;
 			break;
+		case 90: /* Set bright foreground color: black */
+		case 91: /* Set bright foreground color: red */
+		case 92: /* Set bright foreground color: green */
+		case 93: /* Set bright foreground color: brown */
+		case 94: /* Set bright foreground color: blue */
+		case 95: /* Set bright foreground color: magenta */
+		case 96: /* Set bright foreground color: cyan */
+		case 97: /* Set bright foreground color: white */
+			t->t_curattr.ta_fgcolor = n - 90 + 8;
+			break;
+		case 100: /* Set bright background color: black */
+		case 101: /* Set bright background color: red */
+		case 102: /* Set bright background color: green */
+		case 103: /* Set bright background color: brown */
+		case 104: /* Set bright background color: blue */
+		case 105: /* Set bright background color: magenta */
+		case 106: /* Set bright background color: cyan */
+		case 107: /* Set bright background color: white */
+			t->t_curattr.ta_bgcolor = n - 100 + 8;
+			break;
 		default:
 			teken_printf("unsupported attribute %u\n", n);
 		}

sys/teken/teken_subr_compat.h

@@ -65,10 +65,10 @@ void
 teken_get_defattr_cons25(teken_t *t, int *fg, int *bg)
 {
 
-	*fg = cons25_revcolors[t->t_defattr.ta_fgcolor];
+	*fg = cons25_revcolors[teken_256to8(t->t_defattr.ta_fgcolor)];
 	if (t->t_defattr.ta_format & TF_BOLD)
 		*fg += 8;
-	*bg = cons25_revcolors[t->t_defattr.ta_bgcolor];
+	*bg = cons25_revcolors[teken_256to8(t->t_defattr.ta_bgcolor)];
 }
 
 static void