[instancer] add composite_new_gids set in subset plan

This is only used by iup delta optimization where we need to know
whether glyph is composite or not

src/OT/glyf/CompositeGlyph.hh

@@ -240,7 +240,8 @@ struct CompositeGlyphRecord
     }
     if (is_anchored ()) tx = ty = 0;
 
-    trans.init ((float) tx, (float) ty);
+    /* set is_end_point flag to true, used by IUP delta optimization */
+    trans.init ((float) tx, (float) ty, true);
 
     {
       const F2DOT14 *points = (const F2DOT14 *) p;

src/OT/glyf/Glyph.hh

@@ -103,6 +103,9 @@ struct Glyph
     }
   }
 
+  bool is_composite () const
+  { return type == COMPOSITE; }
+
   bool get_all_points_without_var (const hb_face_t *face,
                                    contour_point_vector_t &points /* OUT */) const
   {

src/hb-subset-plan-member-list.hh

@@ -140,6 +140,9 @@ HB_SUBSET_PLAN_MEMBER (mutable hb_vector_t<unsigned>, bounds_height_vec)
 //map: new_gid -> contour points vector
 HB_SUBSET_PLAN_MEMBER (mutable hb_hashmap_t E(<hb_codepoint_t, contour_point_vector_t>), new_gid_contour_points_map)
 
+//new gids set for composite glyphs
+HB_SUBSET_PLAN_MEMBER (hb_set_t, composite_new_gids)
+
 #ifdef HB_EXPERIMENTAL_API
 // name table overrides map: hb_ot_name_record_ids_t-> name string new value or
 // None to indicate should remove

src/hb-subset-plan.cc

@@ -1073,8 +1073,8 @@ _update_instance_metrics_map_from_cff2 (hb_subset_plan_t *plan)
 static bool
 _get_instance_glyphs_contour_points (hb_subset_plan_t *plan)
 {
-  /* contour_points vector only needed for updating gvar table (infer delta)
-   * during partial instancing */
+  /* contour_points vector only needed for updating gvar table (infer delta and
+   * iup delta optimization) during partial instancing */
   if (plan->user_axes_location.is_empty () || plan->all_axes_pinned)
     return true;
 
@@ -1092,10 +1092,15 @@ _get_instance_glyphs_contour_points (hb_subset_plan_t *plan)
     }
 
     hb_codepoint_t old_gid = _.second;
-    if (unlikely (!glyf.glyph_for_gid (old_gid).get_all_points_without_var (plan->source, all_points)))
+    auto glyph = glyf.glyph_for_gid (old_gid);
+    if (unlikely (!glyph.get_all_points_without_var (plan->source, all_points)))
       return false;
     if (unlikely (!plan->new_gid_contour_points_map.set (new_gid, all_points)))
       return false;
+
+    /* composite new gids are only needed by iup delta optimization */
+    if ((plan->flags & HB_SUBSET_FLAGS_IUP_DELTA_OPT) && glyph.is_composite ())
+      plan->composite_new_gids.add (new_gid);
   }
   return true;
 }