[repack] WIP implement extension promotion mechanism.

src/graph/graph.hh

@@ -368,6 +368,8 @@ struct graph_t
    */
   bool assign_spaces ()
   {
+    update_parents ();
+
     hb_set_t visited;
     hb_set_t roots;
     find_space_roots (visited, roots);
@@ -632,6 +634,40 @@ struct graph_t
     return true;
   }
 
+
+  /*
+   * Adds a new node to the graph, not connected to anything.
+   */
+  unsigned new_node (char* head, char* tail)
+  {
+    positions_invalid = true;
+    distance_invalid = true;
+    parents_invalid = true; // TODO: remove
+
+    auto* clone = vertices_.push ();
+    if (vertices_.in_error ()) {
+      return -1;
+    }
+
+    clone->obj.head = head;
+    clone->obj.tail = tail;
+    clone->distance = 0;
+    clone->space = 0;
+
+    unsigned clone_idx = vertices_.length - 2;
+
+    // The last object is the root of the graph, so swap back the root to the end.
+    // The root's obj idx does change, however since it's root nothing else refers to it.
+    // all other obj idx's will be unaffected.
+    hb_swap (vertices_[vertices_.length - 2], *clone);
+
+    // Since the root moved, update the parents arrays of all children on the root.
+    for (const auto& l : root ().obj.all_links ())
+      vertices_[l.objidx].remap_parent (root_idx () - 1, root_idx ());
+
+    return clone_idx;
+  }
+
   /*
    * Raises the sorting priority of all children.
    */

src/graph/gsubgpos-graph.hh

@@ -0,0 +1,174 @@
+/*
+ * Copyright © 2022  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Garret Rieger
+ */
+
+#ifndef GRAPH_GSUBGPOS_GRAPH_HH
+#define GRAPH_GSUBGPOS_GRAPH_HH
+
+#include "graph.hh"
+#include "hb-ot-layout-gsubgpos.hh"
+#include "OT/Layout/GSUB/ExtensionSubst.hh"
+
+namespace graph {
+
+struct GSTAR : public OT::GSUBGPOS
+{
+  const void* get_lookup_list_field_offset () const
+  {
+    switch (u.version.major) {
+    case 1: return &(u.version1.lookupList);
+#ifndef HB_NO_BORING_EXPANSION
+    case 2: return &(u.version2.lookupList);
+#endif
+    default: return 0;
+    }
+  }
+
+};
+
+struct Lookup : public OT::Lookup
+{
+  unsigned extension_type (hb_tag_t table_tag)
+  {
+    switch (table_tag)
+    {
+    case HB_OT_TAG_GPOS: return 9;
+    case HB_OT_TAG_GSUB: return 7;
+    default: return 0;
+    }
+  }
+
+  bool make_extension (hb_tag_t table_tag,
+                       graph_t& graph,
+                       unsigned this_index,
+                       hb_vector_t<char>& buffer)
+  {
+    // TODO: use a context_t?
+    unsigned ext_type = extension_type (table_tag);
+    unsigned type = lookupType;
+    if (!ext_type || type == ext_type)
+    {
+      // NOOP
+      printf("Already extension (obj %u).\n", this_index);
+      return true;
+    }
+
+    printf("Promoting lookup type %u (obj %u) to extension.\n",
+           type,
+           this_index);
+
+
+    for (unsigned i = 0; i < subTable.len; i++)
+    {
+      unsigned subtable_index = graph.index_for_offset (this_index, &subTable[i]);
+      if (!make_subtable_extension (graph,
+                                    this_index,
+                                    subtable_index,
+                                    buffer))
+        return false;
+    }
+
+    lookupType = ext_type;
+    return true;
+  }
+
+  bool make_subtable_extension (graph_t& graph,
+                                unsigned lookup_index,
+                                unsigned subtable_index,
+                                hb_vector_t<char>& buffer)
+  {
+    printf("  Promoting subtable %u in lookup %u to extension.\n", subtable_index, lookup_index);
+
+    unsigned type = lookupType;
+    unsigned extension_size = OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>::static_size;
+    unsigned start = buffer.length;
+    unsigned end = start + extension_size;
+    if (!buffer.resize (buffer.length + extension_size))
+      return false;
+
+    OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>* extension =
+        (OT::ExtensionFormat1<OT::Layout::GSUB_impl::ExtensionSubst>*) &buffer[start];
+    extension->format = 1;
+    extension->extensionLookupType = type;
+    extension->extensionOffset = 0;
+
+    unsigned ext_index = graph.new_node (&buffer[start], &buffer[end]);
+    if (ext_index == (unsigned) -1) return false;
+
+    auto& lookup_vertex = graph.vertices_[lookup_index];
+    for (auto& l : lookup_vertex.obj.real_links.writer ())
+    {
+      if (l.objidx == subtable_index)
+      {
+        // Change lookup to point at the extension.
+        printf("  Changing %d to %d\n", l.objidx, ext_index);
+        l.objidx = ext_index;
+      }
+    }
+
+    // Make extension point at the subtable.
+    // TODO: update extension parents array.
+    auto& ext_vertex = graph.vertices_[ext_index];
+    auto& subtable_vertex = graph.vertices_[subtable_index];
+    auto* l = ext_vertex.obj.real_links.push ();
+
+    l->width = 4;
+    l->objidx = subtable_index;
+    l->is_signed = 0;
+    l->whence = 0;
+    l->position = 4;
+    l->bias = 0;
+
+    subtable_vertex.remap_parent (lookup_index, ext_index);
+
+    return true;
+  }
+};
+
+static inline void
+find_lookups (graph_t& graph,
+              hb_hashmap_t<unsigned, Lookup*>& lookups /* OUT */)
+{
+  // TODO: move this into GSTAR?
+  // TODO: template on types, based on gstar version.
+  const GSTAR* gstar = (const GSTAR*) graph.root ().obj.head;
+
+  unsigned lookup_list_idx = graph.index_for_offset (graph.root_idx (),
+                                                     gstar->get_lookup_list_field_offset());
+
+  const OT::LookupList<SmallTypes>* lookupList =
+      (const OT::LookupList<SmallTypes>*) graph.object (lookup_list_idx).head;
+
+  for (unsigned i = 0; i < lookupList->len; i++)
+  {
+    unsigned lookup_idx = graph.index_for_offset (lookup_list_idx, &(lookupList->arrayZ[i]));
+    Lookup* lookup = (Lookup*) graph.object (lookup_idx).head;
+    lookups.set (lookup_idx, lookup);
+  }
+}
+
+}
+
+#endif  /* GRAPH_GSUBGPOS_GRAPH_HH */

src/hb-ot-layout-gsubgpos.hh

@@ -3868,7 +3868,7 @@ struct ExtensionFormat1
     return_trace (dest_offset.serialize_subset (c, src_offset, this, get_type ()));
   }
 
-  protected:
+  public: // TODO
   HBUINT16	format;			/* Format identifier. Set to 1. */
   HBUINT16	extensionLookupType;	/* Lookup type of subtable referenced
 					 * by ExtensionOffset (i.e. the

src/hb-repacker.hh

@@ -44,7 +44,7 @@ using graph::graph_t;
  */
 
 static inline
-void _make_extensions (graph_t& sorted_graph)
+void _make_extensions (hb_tag_t table_tag, graph_t& sorted_graph, hb_vector_t<char>& buffer)
 {
   // TODO: Move this into graph or gsubgpos graph?
   hb_hashmap_t<unsigned, graph::Lookup*> lookups;
@@ -52,7 +52,7 @@ void _make_extensions (graph_t& sorted_graph)
 
   for (auto p : lookups.iter ())
   {
-    p.second->make_extension (sorted_graph, p.first);
+    p.second->make_extension (table_tag, sorted_graph, p.first, buffer);
   }
 }
 
@@ -182,12 +182,13 @@ hb_resolve_overflows (const T& packed,
     return graph::serialize (sorted_graph);
   }
 
+  hb_vector_t<char> extension_buffer;
   if ((table_tag == HB_OT_TAG_GPOS
        ||  table_tag == HB_OT_TAG_GSUB)
       && will_overflow)
   {
+    _make_extensions (table_tag, sorted_graph, extension_buffer);
     DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
-    _make_extensions (sorted_graph);
     if (sorted_graph.assign_spaces ())
       sorted_graph.sort_shortest_distance ();
   }