[fvar] Add named-instance API

Fixes https://github.com/harfbuzz/harfbuzz/issues/1241

docs/harfbuzz-sections.txt

@@ -589,6 +589,10 @@ hb_ot_var_get_axis_count
 hb_ot_var_get_axes
 hb_ot_var_axis_flags_t
 hb_ot_var_axis_get_flags
+hb_ot_var_get_named_instance_count
+hb_ot_var_named_instance_get_subfamily_name_id
+hb_ot_var_named_instance_get_postscript_name_id
+hb_ot_var_named_instance_get_design_coords
 hb_ot_var_normalize_variations
 hb_ot_var_normalize_coords
 </SECTION>

src/hb-ot-var-fvar-table.hh

@@ -42,6 +42,11 @@ namespace OT {
 
 struct InstanceRecord
 {
+  friend struct fvar;
+
+  inline hb_array_t<const Fixed> get_coordinates (unsigned int axis_count) const
+  { return coordinatesZ.as_array (axis_count); }
+
   inline bool sanitize (hb_sanitize_context_t *c, unsigned int axis_count) const
   {
     TRACE_SANITIZE (this);
@@ -104,7 +109,7 @@ struct fvar
 		  axisSize == 20 && /* Assumed in our code. */
 		  instanceSize >= axisCount * 4 + 4 &&
 		  get_axes ().sanitize (c) &&
-		  c->check_range (get_first_instance (), instanceCount, instanceSize));
+		  c->check_range (&get_instance (0), instanceCount, instanceSize));
   }
 
   inline unsigned int get_axis_count (void) const
@@ -186,12 +191,56 @@ struct fvar
     return (int) (v * 16384.f + (v >= 0.f ? .5f : -.5f));
   }
 
+  inline unsigned int get_instance_count (void) const
+  { return instanceCount; }
+
+  inline hb_ot_name_id_t get_instance_subfamily_name_id (unsigned int index) const
+  {
+    const InstanceRecord &instance = get_instance (index);
+    return instance.subfamilyNameID;
+  }
+
+  inline hb_ot_name_id_t get_instance_postscript_name_id (unsigned int index) const
+  {
+    const InstanceRecord &instance = get_instance (index);
+    if (instanceSize >= axisCount * 4 + 6)
+      return StructAfter<NameID> (instance.get_coordinates (axisCount));
+    return HB_OT_NAME_ID_INVALID;
+  }
+
+  inline unsigned int get_instance_coords (unsigned int  index,
+					   unsigned int *coords_length, /* IN/OUT */
+					   int          *coords         /* OUT */) const
+  {
+    if (unlikely (index >= instanceCount))
+    {
+      if (coords_length)
+        *coords_length = 0;
+      return 0;
+    }
+
+    if (coords_length && *coords_length)
+    {
+      const InstanceRecord &instance = get_instance (index);
+      hb_array_t<const Fixed> instanceCoords = instance.get_coordinates (axisCount)
+						       .sub_array (0, *coords_length);
+      for (unsigned int i = 0; i < instanceCoords.len; i++)
+        coords[i] = instanceCoords.arrayZ[i].to_float ();
+    }
+    return axisCount;
+  }
+
   protected:
   inline hb_array_t<const AxisRecord> get_axes (void) const
   { return hb_array (&(this+firstAxis), axisCount); }
 
-  inline const InstanceRecord * get_first_instance (void) const
-  { return &StructAfter<InstanceRecord> (get_axes ()); }
+  inline const InstanceRecord &get_instance (unsigned int i) const
+  {
+    if (unlikely (i >= instanceCount)) return Null (InstanceRecord);
+
+   return StructAtOffset<InstanceRecord> (&StructAfter<InstanceRecord> (get_axes ()),
+					  i * instanceSize);
+  }
 
   protected:
   FixedVersion<>version;	/* Version of the fvar table

src/hb-ot-var.cc

@@ -116,6 +116,39 @@ hb_ot_var_axis_get_flags (hb_face_t    *face,
   return face->table.fvar->get_axis_flags (axis_index);
 }
 
+/*
+ * Named instances.
+ */
+
+unsigned int
+hb_ot_var_get_named_instance_count (hb_face_t *face)
+{
+  return face->table.fvar->get_instance_count ();
+}
+
+hb_ot_name_id_t
+hb_ot_var_named_instance_get_subfamily_name_id (hb_face_t   *face,
+						unsigned int instance_index)
+{
+  return face->table.fvar->get_instance_subfamily_name_id (instance_index);
+}
+
+hb_ot_name_id_t
+hb_ot_var_named_instance_get_postscript_name_id (hb_face_t  *face,
+						unsigned int instance_index)
+{
+  return face->table.fvar->get_instance_postscript_name_id (instance_index);
+}
+
+unsigned int
+hb_ot_var_named_instance_get_design_coords (hb_face_t    *face,
+					    unsigned int  instance_index,
+					    unsigned int *coords_length, /* IN/OUT */
+					    int          *coords         /* OUT */)
+{
+  return face->table.fvar->get_instance_coords (instance_index, coords_length, coords);
+}
+
 
 /**
  * hb_ot_var_normalize_variations:

src/hb-ot-var.h

@@ -63,6 +63,11 @@ typedef struct hb_ot_var_axis_t {
 HB_EXTERN hb_bool_t
 hb_ot_var_has_data (hb_face_t *face);
 
+
+/*
+ * Variation axes.
+ */
+
 /**
  * HB_OT_VAR_NO_AXIS_INDEX:
  *
@@ -99,6 +104,33 @@ HB_EXTERN hb_ot_var_axis_flags_t
 hb_ot_var_axis_get_flags (hb_face_t    *face,
 			  unsigned int  axis_index);
 
+
+/*
+ * Named instances.
+ */
+
+HB_EXTERN unsigned int
+hb_ot_var_get_named_instance_count (hb_face_t *face);
+
+HB_EXTERN hb_ot_name_id_t
+hb_ot_var_named_instance_get_subfamily_name_id (hb_face_t   *face,
+						unsigned int instance_index);
+
+HB_EXTERN hb_ot_name_id_t
+hb_ot_var_named_instance_get_postscript_name_id (hb_face_t  *face,
+						unsigned int instance_index);
+
+HB_EXTERN unsigned int
+hb_ot_var_named_instance_get_design_coords (hb_face_t    *face,
+					    unsigned int  instance_index,
+					    unsigned int *coords_length, /* IN/OUT */
+					    int          *coords         /* OUT */);
+
+
+/*
+ * Conversions.
+ */
+
 HB_EXTERN void
 hb_ot_var_normalize_variations (hb_face_t            *face,
 				const hb_variation_t *variations, /* IN */