Don't do fallback positioning for Indic and Thai shapers

src/hb-ot-shape-complex-arabic.cc

@@ -354,4 +354,5 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_arabic =
   NULL, /* compose */
   setup_masks_arabic,
   true, /* zero_width_attached_marks */
+  true, /* fallback_position */
 };

src/hb-ot-shape-complex-indic.cc

@@ -1360,4 +1360,5 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_indic =
   compose_indic,
   setup_masks_indic,
   false, /* zero_width_attached_marks */
+  false, /* fallback_position */
 };

src/hb-ot-shape-complex-misc.cc

@@ -221,6 +221,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_default =
   compose_default,
   NULL, /* setup_masks */
   true, /* zero_width_attached_marks */
+  true, /* fallback_position */
 };
 
 
@@ -334,4 +335,5 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_thai =
   NULL, /* compose */
   NULL, /* setup_masks */
   true, /* zero_width_attached_marks */
+  false,/* fallback_position */
 };

src/hb-ot-shape-complex-private.hh

@@ -131,6 +131,7 @@ struct hb_ot_complex_shaper_t
 		       hb_font_t                *font);
 
   bool zero_width_attached_marks;
+  bool fallback_position;
 };
 
 #define HB_COMPLEX_SHAPER_IMPLEMENT(name) extern HB_INTERNAL const hb_ot_complex_shaper_t _hb_ot_complex_shaper_##name;

src/hb-ot-shape.cc

@@ -451,12 +451,6 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
   return ret;
 }
 
-static inline void
-hb_ot_position_complex_fallback (hb_ot_shape_context_t *c)
-{
-  _hb_ot_shape_fallback_position (c->plan, c->font, c->buffer);
-}
-
 static inline void
 hb_ot_truetype_kern (hb_ot_shape_context_t *c)
 {
@@ -482,12 +476,6 @@ hb_ot_truetype_kern (hb_ot_shape_context_t *c)
   }
 }
 
-static inline void
-hb_position_complex_fallback_visual (hb_ot_shape_context_t *c)
-{
-  hb_ot_truetype_kern (c);
-}
-
 static inline void
 hb_ot_position (hb_ot_shape_context_t *c)
 {
@@ -495,14 +483,16 @@ hb_ot_position (hb_ot_shape_context_t *c)
 
   hb_bool_t fallback = !hb_ot_position_complex (c);
 
-  if (fallback)
-    hb_ot_position_complex_fallback (c);
+  if (fallback && c->plan->shaper->fallback_position)
+    _hb_ot_shape_fallback_position (c->plan, c->font, c->buffer);
 
   if (HB_DIRECTION_IS_BACKWARD (c->buffer->props.direction))
     hb_buffer_reverse (c->buffer);
 
+  /* Visual fallback goes here. */
+
   if (fallback)
-    hb_position_complex_fallback_visual (c);
+    hb_ot_truetype_kern (c);
 }