Support scripts that are written both LTR and RTL

Right now only Old Italic is marked as such.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1000

src/hb-buffer.cc

@@ -687,6 +687,8 @@ hb_buffer_t::guess_segment_properties (void)
   /* If direction is set to INVALID, guess from script */
   if (props.direction == HB_DIRECTION_INVALID) {
     props.direction = hb_script_get_horizontal_direction (props.script);
+    if (props.direction == HB_DIRECTION_INVALID)
+      props.direction = HB_DIRECTION_LTR;
   }
 
   /* If language is not set, use default language from locale */
@@ -1489,6 +1491,8 @@ hb_buffer_reverse_clusters (hb_buffer_t *buffer)
  * Next, if buffer direction is not set (ie. is %HB_DIRECTION_INVALID),
  * it will be set to the natural horizontal direction of the
  * buffer script as returned by hb_script_get_horizontal_direction().
+ * If hb_script_get_horizontal_direction() returns %HB_DIRECTION_INVALID,
+ * then %HB_DIRECTION_LTR is used.
  *
  * Finally, if buffer language is not set (ie. is %HB_LANGUAGE_INVALID),
  * it will be set to the process's default language as returned by

src/hb-common.cc

@@ -536,6 +536,12 @@ hb_script_get_horizontal_direction (hb_script_t script)
     case HB_SCRIPT_ADLAM:
 
       return HB_DIRECTION_RTL;
+
+
+    /* https://github.com/harfbuzz/harfbuzz/issues/1000 */
+    case HB_SCRIPT_OLD_ITALIC:
+
+      return HB_DIRECTION_INVALID;
   }
 
   return HB_DIRECTION_LTR;

src/hb-ot-shape.cc

@@ -306,13 +306,16 @@ static void
 hb_ensure_native_direction (hb_buffer_t *buffer)
 {
   hb_direction_t direction = buffer->props.direction;
+  hb_direction_t horiz_dir = hb_script_get_horizontal_direction (buffer->props.script);
 
   /* TODO vertical:
    * The only BTT vertical script is Ogham, but it's not clear to me whether OpenType
    * Ogham fonts are supposed to be implemented BTT or not.  Need to research that
    * first. */
-  if ((HB_DIRECTION_IS_HORIZONTAL (direction) && direction != hb_script_get_horizontal_direction (buffer->props.script)) ||
-      (HB_DIRECTION_IS_VERTICAL   (direction) && direction != HB_DIRECTION_TTB))
+  if ((HB_DIRECTION_IS_HORIZONTAL (direction) &&
+       direction != horiz_dir && horiz_dir != HB_DIRECTION_INVALID) ||
+      (HB_DIRECTION_IS_VERTICAL   (direction) &&
+       direction != HB_DIRECTION_TTB))
   {
     /* Same loop as hb_form_clusters().
      * Since form_clusters() merged clusters already, we don't merge. */

test/api/test-common.c

@@ -173,6 +173,7 @@ test_types_script (void)
 
   g_assert_cmpint (hb_script_get_horizontal_direction (HB_SCRIPT_LATIN), ==, HB_DIRECTION_LTR);
   g_assert_cmpint (hb_script_get_horizontal_direction (HB_SCRIPT_ARABIC), ==, HB_DIRECTION_RTL);
+  g_assert_cmpint (hb_script_get_horizontal_direction (HB_SCRIPT_OLD_ITALIC), ==, HB_DIRECTION_INVALID);
   g_assert_cmpint (hb_script_get_horizontal_direction (hb_script_from_iso15924_tag (wWyZ)), ==, HB_DIRECTION_LTR);
 }
 

test/shaping/data/in-house/Makefile.sources

@@ -31,6 +31,7 @@ TESTS = \
 	tests/mark-filtering-sets.tests \
 	tests/mongolian-variation-selector.tests \
 	tests/myanmar-syllable.tests \
+	tests/none-directional.tests \
 	tests/spaces.tests \
 	tests/simple.tests \
 	tests/tibetan-contractions-1.tests \

test/shaping/data/in-house/tests/none-directional.tests

@@ -0,0 +1,3 @@
+../fonts/73e84dac2fc6a2d1bc9250d1414353661088937d.ttf::U+10300,U+10301:[u10300=0+1470|u10301=1+1284]
+../fonts/73e84dac2fc6a2d1bc9250d1414353661088937d.ttf:--direction=ltr:U+10300,U+10301:[u10300=0+1470|u10301=1+1284]
+../fonts/73e84dac2fc6a2d1bc9250d1414353661088937d.ttf:--direction=rtl:U+10300,U+10301:[u10301_r=1+1284|u10300_r=0+1470]