[subset] Hook up GSUB/GPOS, but still disabled

They are still in the drop list.

src/hb-ot-hdmx-table.hh

@@ -177,7 +177,8 @@ struct hdmx
 
     hb_serialize_context_t c (dest, dest_size);
     hdmx *hdmx_prime = c.start_serialize<hdmx> ();
-    if (!hdmx_prime || !hdmx_prime->serialize (&c, this, plan)) {
+    if (!hdmx_prime || !hdmx_prime->serialize (&c, this, plan))
+    {
       free (dest);
       return false;
     }

src/hb-subset.cc

@@ -40,8 +40,75 @@
 #include "hb-ot-maxp-table.hh"
 #include "hb-ot-os2-table.hh"
 #include "hb-ot-post-table.hh"
+#include "hb-ot-layout-gsub-table.hh"
+#include "hb-ot-layout-gpos-table.hh"
 
 
+static unsigned int
+_plan_estimate_subset_table_size (hb_subset_plan_t *plan,
+				  unsigned int table_len)
+{
+  unsigned int src_glyphs = plan->source->get_num_glyphs ();
+  unsigned int dst_glyphs = plan->glyphset->get_population ();
+
+  return 512 + (unsigned int) (table_len * sqrt ((double) dst_glyphs / src_glyphs));
+}
+
+template<typename TableType>
+static bool
+_subset2 (hb_subset_plan_t *plan)
+{
+  hb_blob_t *source_blob = hb_sanitize_context_t ().reference_table<TableType> (plan->source);
+  const TableType *table = source_blob->as<TableType> ();
+
+  hb_tag_t tag = TableType::tableTag;
+  hb_bool_t result = false;
+  if (source_blob->data)
+  {
+    hb_auto_t<hb_vector_t<char>> buf;
+    unsigned int buf_size = _plan_estimate_subset_table_size (plan, source_blob->length);
+    DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c initial estimated table size: %u bytes.", HB_UNTAG(tag), buf_size);
+    if (unlikely (!buf.alloc (buf_size)))
+    {
+      DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c failed to allocate %u bytes.", HB_UNTAG(tag), buf_size);
+      return false;
+    }
+  retry:
+    hb_serialize_context_t serializer (buf.arrayZ, buf_size);
+    hb_subset_context_t c (plan, &serializer);
+    result = table->subset (&c);
+    if (serializer.ran_out_of_room)
+    {
+      buf_size += (buf_size >> 1) + 32;
+      DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c ran out of room; reallocating to %u bytes.", HB_UNTAG(tag), buf_size);
+      if (unlikely (!buf.alloc (buf_size)))
+      {
+	DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c failed to reallocate %u bytes.", HB_UNTAG(tag), buf_size);
+	return false;
+      }
+      goto retry;
+    }
+    if (result)
+    {
+      hb_blob_t *dest_blob = serializer.copy_blob ();
+      DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c final subset table size: %u bytes.", HB_UNTAG(tag), dest_blob->length);
+      result = c.plan->add_table (tag, dest_blob);
+      hb_blob_destroy (dest_blob);
+    }
+    else
+    {
+      DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c::subset table subsetted to empty.", HB_UNTAG(tag));
+      result = true;
+    }
+  }
+  else
+    DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c::subset sanitize failed on source table.", HB_UNTAG(tag));
+
+  hb_blob_destroy (source_blob);
+  DEBUG_MSG(SUBSET, nullptr, "OT::%c%c%c%c::subset %s", HB_UNTAG(tag), result ? "success" : "FAILED!");
+  return result;
+}
+
 template<typename TableType>
 static bool
 _subset (hb_subset_plan_t *plan)
@@ -107,6 +174,14 @@ _subset_table (hb_subset_plan_t *plan,
     case HB_OT_TAG_post:
       result = _subset<const OT::post> (plan);
       break;
+
+    case HB_OT_TAG_GSUB:
+      result = _subset2<const OT::GSUB> (plan);
+      break;
+    case HB_OT_TAG_GPOS:
+      result = _subset2<const OT::GPOS> (plan);
+      break;
+
     default:
       hb_blob_t *source_table = hb_face_reference_table(plan->source, tag);
       if (likely (source_table))