[subset] Fix wrong offset base for subsetting LigatureArray.

Offsets from LigatureArray must be relative to the beginning of the LigatureArray table. For the serialization mechanism to use the correct beginning point the LigatureArray must be created using the push()/pop() mechanism. So convert LigatureArray subsetting to use serialize_subset() instead of a manually called serialize and subset.

src/hb-ot-layout-gpos-table.hh

@@ -548,6 +548,7 @@ struct AnchorMatrix
 		  const hb_map_t         *layout_variation_idx_map,
 		  Iterator                index_iter)
   {
+    // TODO(grieger): can serialize with an iterator of anchor's?
     TRACE_SERIALIZE (this);
     if (!index_iter) return_trace (false);
     if (unlikely (!c->extend_min ((*this))))  return_trace (false);
@@ -573,6 +574,7 @@ struct AnchorMatrix
     TRACE_SUBSET (this);
     auto *out = c->serializer->start_embed (*this);
 
+    // TODO(grieger): shouldn't need to use an allocated vector to do this.
     hb_vector_t<unsigned> indexes;
     for (unsigned row : + hb_range ((unsigned) rows))
     {
@@ -2056,25 +2058,29 @@ struct LigatureArray : OffsetListOf<LigatureAttach>
   template <typename Iterator,
 	    hb_requires (hb_is_iterator (Iterator))>
   bool subset (hb_subset_context_t *c,
-	       unsigned                cols,
-	       const hb_map_t         *klass_mapping,
-	       const LigatureArray    &src_lig_array,
-	       Iterator                ligature_iter)
+	       Iterator		    coverage,
+	       unsigned		    class_count,
+	       const hb_map_t	   *klass_mapping) const
   {
-    TRACE_SERIALIZE (this);
-
-    if (!ligature_iter.len ()) return_trace (false);
-    if (unlikely (!c->serializer->extend_min ((*this))))  return_trace (false);
+    TRACE_SUBSET (this);
+    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
 
+    auto *out = c->serializer->start_embed (this);
+    if (unlikely (!c->serializer->extend_min (out)))  return_trace (false);
 
-    for (unsigned i : ligature_iter)
+    unsigned ligature_count = 0;
+    for (hb_codepoint_t gid : coverage)
     {
-      auto *out = serialize_append (c->serializer);
-      if (unlikely (!out)) break;
-      out->serialize_subset (c,
-                             src_lig_array.arrayZ[i],
-                             &src_lig_array,
-                             cols,
+      ligature_count++;
+      if (!glyphset.has (gid)) continue;
+
+      auto *matrix = out->serialize_append (c->serializer);
+      if (unlikely (!matrix)) return_trace (false);
+
+      matrix->serialize_subset (c,
+				this->arrayZ[ligature_count - 1],
+				this,
+				class_count,
 				klass_mapping);
     }
     return_trace (this->len);
@@ -2181,7 +2187,7 @@ struct MarkLigPosFormat1
   bool subset (hb_subset_context_t *c) const
   {
     TRACE_SUBSET (this);
-    const hb_set_t &glyphset = *c->plan->glyphset ();
+    const hb_set_t &glyphset = *c->plan->glyphset_gsub ();
     const hb_map_t &glyph_map = *c->plan->glyph_map;
 
     auto *out = c->serializer->start_embed (*this);
@@ -2199,15 +2205,14 @@ struct MarkLigPosFormat1
     | hb_filter (glyphset, hb_first)
     ;
 
-    hb_sorted_vector_t<hb_codepoint_t> new_coverage;
+    auto new_mark_coverage =
     + mark_iter
-    | hb_map (hb_first)
-    | hb_map (glyph_map)
-    | hb_sink (new_coverage)
+    | hb_map_retains_sorting (hb_first)
+    | hb_map_retains_sorting (glyph_map)
     ;
 
     if (!out->markCoverage.serialize (c->serializer, out)
-			  .serialize (c->serializer, new_coverage.iter ()))
+			  .serialize (c->serializer, new_mark_coverage))
       return_trace (false);
 
     out->markArray.serialize (c->serializer, out)
@@ -2218,30 +2223,18 @@ struct MarkLigPosFormat1
                               + mark_iter
                               | hb_map (hb_second));
 
-    unsigned ligcount = (this+ligatureArray).len;
-    auto ligature_iter =
-    + hb_zip (this+ligatureCoverage, hb_range (ligcount))
-    | hb_filter (glyphset, hb_first)
-    ;
-
-    new_coverage.reset ();
-    + ligature_iter
-    | hb_map (hb_first)
-    | hb_map (glyph_map)
-    | hb_sink (new_coverage)
+    auto new_ligature_coverage =
+    + hb_iter (this + ligatureCoverage)
+    | hb_filter (glyphset)
+    | hb_map_retains_sorting (glyph_map)
     ;
 
     if (!out->ligatureCoverage.serialize (c->serializer, out)
-			      .serialize (c->serializer, new_coverage.iter ()))
+			      .serialize (c->serializer, new_ligature_coverage))
       return_trace (false);
 
-    out->ligatureArray.serialize (c->serializer, out)
-		      .subset (c,
-                               (unsigned) classCount,
-                               &klass_mapping,
-                               this+ligatureArray,
-                               + ligature_iter
-                               | hb_map (hb_second));
+    out->ligatureArray.serialize_subset (c, ligatureArray, this,
+                                         hb_iter (this+ligatureCoverage), classCount, &klass_mapping);
 
     return_trace (true);
   }
@@ -2276,6 +2269,7 @@ struct MarkLigPosFormat1
   DEFINE_SIZE_STATIC (12);
 };
 
+
 struct MarkLigPos
 {
   template <typename context_t, typename ...Ts>