[layout] Add hb_ot_layout_get_optical_bound()

src/OT/Layout/GPOS/SinglePosFormat1.hh

@@ -80,6 +80,17 @@ struct SinglePosFormat1
     return_trace (true);
   }
 
+  bool
+  position_single (hb_ot_apply_context_t *c,
+		   hb_codepoint_t         gid,
+		   hb_glyph_position_t   &pos) const
+  {
+    unsigned int index = (this+coverage).get_coverage  (gid);
+    if (likely (index == NOT_COVERED)) return false;
+    valueFormat.apply_value (c, this, values, pos);
+    return true;
+  }
+
   template<typename Iterator,
       typename SrcLookup,
       hb_requires (hb_is_iterator (Iterator))>

src/OT/Layout/GPOS/SinglePosFormat2.hh

@@ -68,7 +68,7 @@ struct SinglePosFormat2
     unsigned int index = (this+coverage).get_coverage  (buffer->cur().codepoint);
     if (likely (index == NOT_COVERED)) return_trace (false);
 
-    if (likely (index >= valueCount)) return_trace (false);
+    if (unlikely (index >= valueCount)) return_trace (false);
 
     if (HB_BUFFER_MESSAGE_MORE && c->buffer->messaging ())
     {
@@ -92,6 +92,21 @@ struct SinglePosFormat2
     return_trace (true);
   }
 
+  bool
+  position_single (hb_ot_apply_context_t *c,
+		   hb_codepoint_t         gid,
+		   hb_glyph_position_t   &pos) const
+  {
+    unsigned int index = (this+coverage).get_coverage  (gid);
+    if (likely (index == NOT_COVERED)) return false;
+    if (unlikely (index >= valueCount)) return false;
+    valueFormat.apply_value (c, this,
+                             &values[index * valueFormat.get_len ()],
+                             pos);
+    return true;
+  }
+
+
   template<typename Iterator,
       typename SrcLookup,
       hb_requires (hb_is_iterator (Iterator))>

src/hb-ot-layout.cc

@@ -1709,6 +1709,63 @@ hb_ot_layout_get_size_params (hb_face_t       *face,
 
   return false;
 }
+
+struct hb_position_single_dispatch_t :
+       hb_dispatch_context_t<hb_position_single_dispatch_t, bool>
+{
+  static return_t default_return_value () { return false; }
+  bool stop_sublookup_iteration (return_t r) const { return r; }
+
+  private:
+  template <typename T, typename ...Ts> auto
+  _dispatch (const T &obj, hb_priority<1>, Ts&&... ds) HB_AUTO_RETURN
+  ( obj.position_single (std::forward<Ts> (ds)...) )
+  template <typename T, typename ...Ts> auto
+  _dispatch (const T &obj, hb_priority<0>, Ts&&... ds) HB_AUTO_RETURN
+  ( default_return_value () )
+  public:
+  template <typename T, typename ...Ts> auto
+  dispatch (const T &obj, Ts&&... ds) HB_AUTO_RETURN
+  ( _dispatch (obj, hb_prioritize, std::forward<Ts> (ds)...) )
+};
+
+hb_position_t
+hb_ot_layout_get_optical_bound (hb_font_t      *font,
+				unsigned        lookup_index,
+				hb_direction_t  direction,
+				hb_codepoint_t  glyph)
+{
+  /* This is ugly... */
+  hb_buffer_t buffer;
+  buffer.props.direction = direction;
+  OT::hb_ot_apply_context_t c_apply (1, font, &buffer);
+  const OT::PosLookup &lookup = font->face->table.GPOS->table->get_lookup (lookup_index);
+  hb_glyph_position_t pos = {0};
+  hb_position_single_dispatch_t c;
+  lookup.dispatch (&c, &c_apply, glyph, pos);
+  hb_position_t ret = 0;
+  switch (direction)
+  {
+    case HB_DIRECTION_LTR:
+      ret = pos.x_offset;
+      break;
+    case HB_DIRECTION_RTL:
+      ret = pos.x_advance - pos.x_offset;
+      break;
+    case HB_DIRECTION_TTB:
+      ret = pos.y_offset;
+      break;
+    case HB_DIRECTION_BTT:
+      ret = pos.y_advance - pos.y_offset;
+      break;
+    case HB_DIRECTION_INVALID:
+    default:
+      break;
+  }
+  return ret;
+}
+
+
 /**
  * hb_ot_layout_feature_get_name_ids:
  * @face: #hb_face_t to work upon

src/hb-ot-layout.h

@@ -403,6 +403,12 @@ hb_ot_layout_get_size_params (hb_face_t       *face,
 			      unsigned int    *range_start,       /* OUT.  May be NULL */
 			      unsigned int    *range_end          /* OUT.  May be NULL */);
 
+HB_EXTERN hb_position_t
+hb_ot_layout_get_optical_bound (hb_font_t      *font,
+				unsigned        lookup_index,
+				hb_direction_t  direction,
+				hb_codepoint_t  glyph);
+
 
 HB_EXTERN hb_bool_t
 hb_ot_layout_feature_get_name_ids (hb_face_t       *face,