Curses: fixed colors on emulators with less than 256 color pairs

* For instance on TERM=rxvt.
  Generally 8-color emulators will usually support only 65 color pairs.
* On emulators that support more than 256 pairs, we must still limit them
  to 256 (or 128 for Scinterm and SciTECO) since we still use a single
  attribute for colors and misc. attributes (see COLOR_PAIR()).

1 files changed, 17 insertions, 9 deletions

diff --git a/src/interface-curses/interface.c b/src/interface-curses/interface.c
index d07ff21..6c8b231 100644
--- a/src/interface-curses/interface.c
+++ b/src/interface-curses/interface.c
@@ -232,12 +232,12 @@ static struct {
  *
  * Scinterm no longer initializes all color pairs for all combinations of
  * the builtin foreground and background colors.
- * Since curses guarantees only 256 color pairs, we cannot do that either.
- * Instead we allocate color pairs beginnig at 128 on demand
- * (similar to what Scinterm does).
+ * Since curses does not guarantee any number of color pairs, we cannot do that either.
+ * Instead we allocate color pairs beginnig at the second half of
+ * color pair space on demand (similar to what Scinterm does).
  *
  * @note Scinterm now also has scintilla_set_color_offsets(),
- * so we could use the lower 127 color pairs as well.
+ * so we could use the color pairs beginning with 1 as well.
  *
  * @param fg curses foreground color
  * @param bg curses background color
@@ -246,16 +246,24 @@ static struct {
 static gshort
 teco_color_pair(gshort fg, gshort bg)
 {
-	static gshort last_pair = 127;
+	static gshort allocated_pairs = 0;
 
 	G_STATIC_ASSERT(sizeof(gshort)*2 <= sizeof(guint));
-	gpointer key = GUINT_TO_POINTER(((guint)fg << 16) | bg);
+	gpointer key = GUINT_TO_POINTER(((guint)fg << 8*sizeof(bg)) | bg);
 	gpointer value = g_hash_table_lookup(teco_interface.pair_table, key);
 	if (G_LIKELY(value != NULL))
 		return GPOINTER_TO_UINT(value);
-	init_pair(++last_pair, fg, bg);
-	g_hash_table_insert(teco_interface.pair_table, key, GUINT_TO_POINTER(last_pair));
-	return last_pair;
+	/*
+	 * We are still adding colors with COLOR_PAIR(), which allows
+	 * at most 256 color pairs (1-255).
+	 */
+	gshort new_pair = MIN(COLOR_PAIRS, 256)/2 + allocated_pairs;
+	if (G_UNLIKELY(new_pair >= 256))
+		return 0;
+	allocated_pairs++;
+	init_pair(new_pair, fg, bg);
+	g_hash_table_insert(teco_interface.pair_table, key, GUINT_TO_POINTER(new_pair));
+	return new_pair;
 }
 
 /**