[subset] fix collect_variation_idx in PairPosFormat2

src/hb-ot-layout-common.hh

@@ -1894,6 +1894,7 @@ struct ClassDefFormat1
 
     if (unlikely (!it))
     {
+      classFormat = 1;
       startGlyph = 0;
       classValue.len = 0;
       return_trace (true);
@@ -1917,6 +1918,7 @@ struct ClassDefFormat1
 
   bool subset (hb_subset_context_t *c,
 	       hb_map_t *klass_map = nullptr /*OUT*/,
+               bool keep_empty_table = true,
                bool use_class_zero = true,
                const Coverage* glyph_filter = nullptr) const
   {
@@ -1950,7 +1952,7 @@ struct ClassDefFormat1
     use_class_zero = use_class_zero && glyph_count <= gid_org_klass_map.get_population ();
     ClassDef_remap_and_serialize (c->serializer, gid_org_klass_map,
 				  glyphs, orig_klasses, use_class_zero, klass_map);
-    return_trace ((bool) glyphs);
+    return_trace (keep_empty_table || (bool) glyphs);
   }
 
   bool sanitize (hb_sanitize_context_t *c) const
@@ -2071,6 +2073,7 @@ struct ClassDefFormat2
 
     if (unlikely (!it))
     {
+      classFormat = 2;
       rangeRecord.len = 0;
       return_trace (true);
     }
@@ -2117,6 +2120,7 @@ struct ClassDefFormat2
 
   bool subset (hb_subset_context_t *c,
 	       hb_map_t *klass_map = nullptr /*OUT*/,
+               bool keep_empty_table = true,
                bool use_class_zero = true,
                const Coverage* glyph_filter = nullptr) const
   {
@@ -2151,7 +2155,7 @@ struct ClassDefFormat2
     use_class_zero = use_class_zero && glyph_count <= gid_org_klass_map.get_population ();
     ClassDef_remap_and_serialize (c->serializer, gid_org_klass_map,
 				  glyphs, orig_klasses, use_class_zero, klass_map);
-    return_trace ((bool) glyphs);
+    return_trace (keep_empty_table || (bool) glyphs);
   }
 
   bool sanitize (hb_sanitize_context_t *c) const
@@ -2350,13 +2354,14 @@ struct ClassDef
 
   bool subset (hb_subset_context_t *c,
 	       hb_map_t *klass_map = nullptr /*OUT*/,
+               bool keep_empty_table = true,
                bool use_class_zero = true,
                const Coverage* glyph_filter = nullptr) const
   {
     TRACE_SUBSET (this);
     switch (u.format) {
-    case 1: return_trace (u.format1.subset (c, klass_map, use_class_zero, glyph_filter));
+    case 1: return_trace (u.format1.subset (c, klass_map, keep_empty_table, use_class_zero, glyph_filter));
-    case 2: return_trace (u.format2.subset (c, klass_map, use_class_zero, glyph_filter));
+    case 2: return_trace (u.format2.subset (c, klass_map, keep_empty_table, use_class_zero, glyph_filter));
     default:return_trace (false);
     }
   }

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

@@ -643,10 +643,10 @@ struct GDEF
     auto *out = c->serializer->embed (*this);
     if (unlikely (!out)) return_trace (false);
 
-    bool subset_glyphclassdef = out->glyphClassDef.serialize_subset (c, glyphClassDef, this);
+    bool subset_glyphclassdef = out->glyphClassDef.serialize_subset (c, glyphClassDef, this, nullptr, false, true);
     bool subset_attachlist = out->attachList.serialize_subset (c, attachList, this);
     bool subset_ligcaretlist = out->ligCaretList.serialize_subset (c, ligCaretList, this);
-    bool subset_markattachclassdef = out->markAttachClassDef.serialize_subset (c, markAttachClassDef, this);
+    bool subset_markattachclassdef = out->markAttachClassDef.serialize_subset (c, markAttachClassDef, this, nullptr, false, true);
 
     bool subset_markglyphsetsdef = true;
     if (version.to_int () >= 0x00010002u)

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

@@ -1488,14 +1488,28 @@ struct PairPosFormat2
   void closure_lookups (hb_closure_lookups_context_t *c) const {}
   void collect_variation_indices (hb_collect_variation_indices_context_t *c) const
   {
+    if (!intersects (c->glyph_set)) return;
     if ((!valueFormat1.has_device ()) && (!valueFormat2.has_device ())) return;
 
+    hb_set_t klass1_glyphs, klass2_glyphs;
+    if (!(this+classDef1).collect_coverage (&klass1_glyphs)) return;
+    if (!(this+classDef2).collect_coverage (&klass2_glyphs)) return;
+
     hb_set_t class1_set, class2_set;
     for (const unsigned cp : + c->glyph_set->iter () | hb_filter (this + coverage))
+    {
+      if (!klass1_glyphs.has (cp)) class1_set.add (0);
+      else
       {
         unsigned klass1 = (this+classDef1).get (cp);
-      unsigned klass2 = (this+classDef2).get (cp);
         class1_set.add (klass1);
+      }
+    }
+
+    class2_set.add (0);
+    for (const unsigned cp : + c->glyph_set->iter () | hb_filter (klass2_glyphs))
+    {
+      unsigned klass2 = (this+classDef2).get (cp);
       class2_set.add (klass2);
     }
 
@@ -1569,11 +1583,11 @@ struct PairPosFormat2
     out->format = format;
 
     hb_map_t klass1_map;
-    out->classDef1.serialize_subset (c, classDef1, this, &klass1_map, true, &(this + coverage));
+    out->classDef1.serialize_subset (c, classDef1, this, &klass1_map, true, true, &(this + coverage));
     out->class1Count = klass1_map.get_population ();
 
     hb_map_t klass2_map;
-    out->classDef2.serialize_subset (c, classDef2, this, &klass2_map, false);
+    out->classDef2.serialize_subset (c, classDef2, this, &klass2_map, true, false);
     out->class2Count = klass2_map.get_population ();
 
     unsigned len1 = valueFormat1.get_len ();