/* * Copyright © 2020 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 HB_REPACKER_HH #define HB_REPACKER_HH #include "hb-open-type.hh" #include "hb-map.hh" #include "hb-priority-queue.hh" #include "hb-serialize.hh" #include "hb-vector.hh" /* * For a detailed writeup on the overflow resolution algorithm see: * docs/repacker.md */ struct graph_t { struct vertex_t { hb_serialize_context_t::object_t obj; int64_t distance = 0 ; int64_t space = 0 ; hb_vector_t<unsigned> parents; unsigned start = 0; unsigned end = 0; unsigned priority = 0; bool is_shared () const { return parents.length > 1; } unsigned incoming_edges () const { return parents.length; } void remove_parent (unsigned parent_index) { for (unsigned i = 0; i < parents.length; i++) { if (parents[i] != parent_index) continue; parents.remove (i); break; } } void remap_parents (const hb_vector_t<unsigned>& id_map) { for (unsigned i = 0; i < parents.length; i++) parents[i] = id_map[parents[i]]; } void remap_parent (unsigned old_index, unsigned new_index) { for (unsigned i = 0; i < parents.length; i++) { if (parents[i] == old_index) parents[i] = new_index; } } bool is_leaf () const { return !obj.real_links.length && !obj.virtual_links.length; } bool raise_priority () { if (has_max_priority ()) return false; priority++; return true; } bool has_max_priority () const { return priority >= 3; } int64_t modified_distance (unsigned order) const { // TODO(garretrieger): once priority is high enough, should try // setting distance = 0 which will force to sort immediately after // it's parent where possible. int64_t modified_distance = hb_min (hb_max(distance + distance_modifier (), 0), 0x7FFFFFFFFFF); if (has_max_priority ()) { modified_distance = 0; } return (modified_distance << 18) | (0x003FFFF & order); } int64_t distance_modifier () const { if (!priority) return 0; int64_t table_size = obj.tail - obj.head; if (priority == 1) return -table_size / 2; return -table_size; } }; struct overflow_record_t { unsigned parent; unsigned child; }; /* * A topological sorting of an object graph. Ordered * in reverse serialization order (first object in the * serialization is at the end of the list). This matches * the 'packed' object stack used internally in the * serializer */ template<typename T> graph_t (const T& objects) : parents_invalid (true), distance_invalid (true), positions_invalid (true), successful (true) { num_roots_for_space_.push (1); bool removed_nil = false; for (unsigned i = 0; i < objects.length; i++) { // TODO(grieger): check all links point to valid objects. // If this graph came from a serialization buffer object 0 is the // nil object. We don't need it for our purposes here so drop it. if (i == 0 && !objects[i]) { removed_nil = true; continue; } vertex_t* v = vertices_.push (); if (check_success (!vertices_.in_error ())) v->obj = *objects[i]; if (!removed_nil) continue; // Fix indices to account for removed nil object. for (auto& l : v->obj.all_links_writer ()) { l.objidx--; } } } ~graph_t () { vertices_.fini (); } bool in_error () const { return !successful || vertices_.in_error () || num_roots_for_space_.in_error (); } const vertex_t& root () const { return vertices_[root_idx ()]; } unsigned root_idx () const { // Object graphs are in reverse order, the first object is at the end // of the vector. Since the graph is topologically sorted it's safe to // assume the first object has no incoming edges. return vertices_.length - 1; } const hb_serialize_context_t::object_t& object(unsigned i) const { return vertices_[i].obj; } /* * serialize graph into the provided serialization buffer. */ hb_blob_t* serialize () const { hb_vector_t<char> buffer; size_t size = serialized_length (); if (!buffer.alloc (size)) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Unable to allocate output buffer."); return nullptr; } hb_serialize_context_t c((void *) buffer, size); c.start_serialize<void> (); for (unsigned i = 0; i < vertices_.length; i++) { c.push (); size_t size = vertices_[i].obj.tail - vertices_[i].obj.head; char* start = c.allocate_size <char> (size); if (!start) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Buffer out of space."); return nullptr; } memcpy (start, vertices_[i].obj.head, size); // Only real links needs to be serialized. for (const auto& link : vertices_[i].obj.real_links) serialize_link (link, start, &c); // All duplications are already encoded in the graph, so don't // enable sharing during packing. c.pop_pack (false); } c.end_serialize (); if (c.in_error ()) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Error during serialization. Err flag: %d", c.errors); return nullptr; } return c.copy_blob (); } /* * Generates a new topological sorting of graph using Kahn's * algorithm: https://en.wikipedia.org/wiki/Topological_sorting#Algorithms */ void sort_kahn () { positions_invalid = true; if (vertices_.length <= 1) { // Graph of 1 or less doesn't need sorting. return; } hb_vector_t<unsigned> queue; hb_vector_t<vertex_t> sorted_graph; if (unlikely (!check_success (sorted_graph.resize (vertices_.length)))) return; hb_vector_t<unsigned> id_map; if (unlikely (!check_success (id_map.resize (vertices_.length)))) return; hb_vector_t<unsigned> removed_edges; if (unlikely (!check_success (removed_edges.resize (vertices_.length)))) return; update_parents (); queue.push (root_idx ()); int new_id = vertices_.length - 1; while (!queue.in_error () && queue.length) { unsigned next_id = queue[0]; queue.remove (0); vertex_t& next = vertices_[next_id]; sorted_graph[new_id] = next; id_map[next_id] = new_id--; for (const auto& link : next.obj.all_links ()) { removed_edges[link.objidx]++; if (!(vertices_[link.objidx].incoming_edges () - removed_edges[link.objidx])) queue.push (link.objidx); } } check_success (!queue.in_error ()); check_success (!sorted_graph.in_error ()); if (!check_success (new_id == -1)) print_orphaned_nodes (); remap_all_obj_indices (id_map, &sorted_graph); hb_swap (vertices_, sorted_graph); sorted_graph.fini (); } /* * Generates a new topological sorting of graph ordered by the shortest * distance to each node. */ void sort_shortest_distance () { positions_invalid = true; if (vertices_.length <= 1) { // Graph of 1 or less doesn't need sorting. return; } update_distances (); hb_priority_queue_t queue; hb_vector_t<vertex_t> sorted_graph; if (unlikely (!check_success (sorted_graph.resize (vertices_.length)))) return; hb_vector_t<unsigned> id_map; if (unlikely (!check_success (id_map.resize (vertices_.length)))) return; hb_vector_t<unsigned> removed_edges; if (unlikely (!check_success (removed_edges.resize (vertices_.length)))) return; update_parents (); queue.insert (root ().modified_distance (0), root_idx ()); int new_id = root_idx (); unsigned order = 1; while (!queue.in_error () && !queue.is_empty ()) { unsigned next_id = queue.pop_minimum().second; vertex_t& next = vertices_[next_id]; sorted_graph[new_id] = next; id_map[next_id] = new_id--; for (const auto& link : next.obj.all_links ()) { removed_edges[link.objidx]++; if (!(vertices_[link.objidx].incoming_edges () - removed_edges[link.objidx])) // Add the order that the links were encountered to the priority. // This ensures that ties between priorities objects are broken in a consistent // way. More specifically this is set up so that if a set of objects have the same // distance they'll be added to the topological order in the order that they are // referenced from the parent object. queue.insert (vertices_[link.objidx].modified_distance (order++), link.objidx); } } check_success (!queue.in_error ()); check_success (!sorted_graph.in_error ()); if (!check_success (new_id == -1)) print_orphaned_nodes (); remap_all_obj_indices (id_map, &sorted_graph); hb_swap (vertices_, sorted_graph); sorted_graph.fini (); } /* * Assign unique space numbers to each connected subgraph of 32 bit offset(s). */ bool assign_32bit_spaces () { unsigned root_index = root_idx (); hb_set_t visited; hb_set_t roots; for (unsigned i = 0; i <= root_index; i++) { // Only real links can form 32 bit spaces for (auto& l : vertices_[i].obj.real_links) { if (l.width == 4 && !l.is_signed) { roots.add (l.objidx); find_subgraph (l.objidx, visited); } } } // Mark everything not in the subgraphs of 32 bit roots as visited. // This prevents 32 bit subgraphs from being connected via nodes not in the 32 bit subgraphs. visited.invert (); if (!roots) return false; while (roots) { unsigned next = HB_SET_VALUE_INVALID; if (unlikely (!check_success (!roots.in_error ()))) break; if (!roots.next (&next)) break; hb_set_t connected_roots; find_connected_nodes (next, roots, visited, connected_roots); if (unlikely (!check_success (!connected_roots.in_error ()))) break; isolate_subgraph (connected_roots); if (unlikely (!check_success (!connected_roots.in_error ()))) break; unsigned next_space = this->next_space (); num_roots_for_space_.push (0); for (unsigned root : connected_roots) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Subgraph %u gets space %u", root, next_space); vertices_[root].space = next_space; num_roots_for_space_[next_space] = num_roots_for_space_[next_space] + 1; distance_invalid = true; positions_invalid = true; } // TODO(grieger): special case for GSUB/GPOS use extension promotions to move 16 bit space // into the 32 bit space as needed, instead of using isolation. } return true; } /* * Isolates the subgraph of nodes reachable from root. Any links to nodes in the subgraph * that originate from outside of the subgraph will be removed by duplicating the linked to * object. * * Indices stored in roots will be updated if any of the roots are duplicated to new indices. */ bool isolate_subgraph (hb_set_t& roots) { update_parents (); hb_hashmap_t<unsigned, unsigned> subgraph; // incoming edges to root_idx should be all 32 bit in length so we don't need to de-dup these // set the subgraph incoming edge count to match all of root_idx's incoming edges hb_set_t parents; for (unsigned root_idx : roots) { subgraph.set (root_idx, wide_parents (root_idx, parents)); find_subgraph (root_idx, subgraph); } unsigned original_root_idx = root_idx (); hb_hashmap_t<unsigned, unsigned> index_map; bool made_changes = false; for (auto entry : subgraph.iter ()) { const auto& node = vertices_[entry.first]; unsigned subgraph_incoming_edges = entry.second; if (subgraph_incoming_edges < node.incoming_edges ()) { // Only de-dup objects with incoming links from outside the subgraph. made_changes = true; duplicate_subgraph (entry.first, index_map); } } if (!made_changes) return false; if (original_root_idx != root_idx () && parents.has (original_root_idx)) { // If the root idx has changed since parents was determined, update root idx in parents parents.add (root_idx ()); parents.del (original_root_idx); } auto new_subgraph = + subgraph.keys () | hb_map([&] (unsigned node_idx) { if (index_map.has (node_idx)) return index_map[node_idx]; return node_idx; }) ; remap_obj_indices (index_map, new_subgraph); remap_obj_indices (index_map, parents.iter (), true); // Update roots set with new indices as needed. unsigned next = HB_SET_VALUE_INVALID; while (roots.next (&next)) { if (index_map.has (next)) { roots.del (next); roots.add (index_map[next]); } } return true; } void find_subgraph (unsigned node_idx, hb_hashmap_t<unsigned, unsigned>& subgraph) { for (const auto& link : vertices_[node_idx].obj.all_links ()) { if (subgraph.has (link.objidx)) { subgraph.set (link.objidx, subgraph[link.objidx] + 1); continue; } subgraph.set (link.objidx, 1); find_subgraph (link.objidx, subgraph); } } void find_subgraph (unsigned node_idx, hb_set_t& subgraph) { if (subgraph.has (node_idx)) return; subgraph.add (node_idx); for (const auto& link : vertices_[node_idx].obj.all_links ()) find_subgraph (link.objidx, subgraph); } /* * duplicates all nodes in the subgraph reachable from node_idx. Does not re-assign * links. index_map is updated with mappings from old id to new id. If a duplication has already * been performed for a given index, then it will be skipped. */ void duplicate_subgraph (unsigned node_idx, hb_hashmap_t<unsigned, unsigned>& index_map) { if (index_map.has (node_idx)) return; index_map.set (node_idx, duplicate (node_idx)); for (const auto& l : object (node_idx).all_links ()) { duplicate_subgraph (l.objidx, index_map); } } /* * Creates a copy of node_idx and returns it's new index. */ unsigned duplicate (unsigned node_idx) { positions_invalid = true; distance_invalid = true; auto* clone = vertices_.push (); auto& child = vertices_[node_idx]; if (vertices_.in_error ()) { return -1; } clone->obj.head = child.obj.head; clone->obj.tail = child.obj.tail; clone->distance = child.distance; clone->space = child.space; clone->parents.reset (); unsigned clone_idx = vertices_.length - 2; for (const auto& l : child.obj.real_links) { clone->obj.real_links.push (l); vertices_[l.objidx].parents.push (clone_idx); } for (const auto& l : child.obj.virtual_links) { clone->obj.virtual_links.push (l); vertices_[l.objidx].parents.push (clone_idx); } check_success (!clone->obj.real_links.in_error ()); check_success (!clone->obj.virtual_links.in_error ()); // 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. vertex_t root = vertices_[vertices_.length - 2]; vertices_[clone_idx] = *clone; vertices_[vertices_.length - 1] = root; // 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; } /* * Creates a copy of child and re-assigns the link from * parent to the clone. The copy is a shallow copy, objects * linked from child are not duplicated. */ bool duplicate (unsigned parent_idx, unsigned child_idx) { update_parents (); unsigned links_to_child = 0; for (const auto& l : vertices_[parent_idx].obj.all_links ()) { if (l.objidx == child_idx) links_to_child++; } if (vertices_[child_idx].incoming_edges () <= links_to_child) { // Can't duplicate this node, doing so would orphan the original one as all remaining links // to child are from parent. DEBUG_MSG (SUBSET_REPACK, nullptr, " Not duplicating %d => %d", parent_idx, child_idx); return false; } DEBUG_MSG (SUBSET_REPACK, nullptr, " Duplicating %d => %d", parent_idx, child_idx); unsigned clone_idx = duplicate (child_idx); if (clone_idx == (unsigned) -1) return false; // duplicate shifts the root node idx, so if parent_idx was root update it. if (parent_idx == clone_idx) parent_idx++; auto& parent = vertices_[parent_idx]; for (auto& l : parent.obj.all_links_writer ()) { if (l.objidx != child_idx) continue; reassign_link (l, parent_idx, clone_idx); } return true; } /* * Raises the sorting priority of all children. */ bool raise_childrens_priority (unsigned parent_idx) { DEBUG_MSG (SUBSET_REPACK, nullptr, " Raising priority of all children of %d", parent_idx); // This operation doesn't change ordering until a sort is run, so no need // to invalidate positions. It does not change graph structure so no need // to update distances or edge counts. auto& parent = vertices_[parent_idx].obj; bool made_change = false; for (auto& l : parent.all_links_writer ()) made_change |= vertices_[l.objidx].raise_priority (); return made_change; } /* * Will any offsets overflow on graph when it's serialized? */ bool will_overflow (hb_vector_t<overflow_record_t>* overflows = nullptr) { if (overflows) overflows->resize (0); update_positions (); for (int parent_idx = vertices_.length - 1; parent_idx >= 0; parent_idx--) { // Don't need to check virtual links for overflow for (const auto& link : vertices_[parent_idx].obj.real_links) { int64_t offset = compute_offset (parent_idx, link); if (is_valid_offset (offset, link)) continue; if (!overflows) return true; overflow_record_t r; r.parent = parent_idx; r.child = link.objidx; overflows->push (r); } } if (!overflows) return false; return overflows->length; } void print_orphaned_nodes () { if (!DEBUG_ENABLED(SUBSET_REPACK)) return; DEBUG_MSG (SUBSET_REPACK, nullptr, "Graph is not fully connected."); parents_invalid = true; update_parents(); for (unsigned i = 0; i < root_idx (); i++) { const auto& v = vertices_[i]; if (!v.parents) DEBUG_MSG (SUBSET_REPACK, nullptr, "Node %u is orphaned.", i); } } void print_overflows (const hb_vector_t<overflow_record_t>& overflows) { if (!DEBUG_ENABLED(SUBSET_REPACK)) return; update_parents (); int limit = 10; for (const auto& o : overflows) { if (!limit--) break; const auto& parent = vertices_[o.parent]; const auto& child = vertices_[o.child]; DEBUG_MSG (SUBSET_REPACK, nullptr, " overflow from " "%4d (%4d in, %4d out, space %2d) => " "%4d (%4d in, %4d out, space %2d)", o.parent, parent.incoming_edges (), parent.obj.real_links.length + parent.obj.virtual_links.length, space_for (o.parent), o.child, child.incoming_edges (), child.obj.real_links.length + child.obj.virtual_links.length, space_for (o.child)); } if (overflows.length > 10) { DEBUG_MSG (SUBSET_REPACK, nullptr, " ... plus %d more overflows.", overflows.length - 10); } } unsigned num_roots_for_space (unsigned space) const { return num_roots_for_space_[space]; } unsigned next_space () const { return num_roots_for_space_.length; } void move_to_new_space (const hb_set_t& indices) { num_roots_for_space_.push (0); unsigned new_space = num_roots_for_space_.length - 1; for (unsigned index : indices) { auto& node = vertices_[index]; num_roots_for_space_[node.space] = num_roots_for_space_[node.space] - 1; num_roots_for_space_[new_space] = num_roots_for_space_[new_space] + 1; node.space = new_space; distance_invalid = true; positions_invalid = true; } } unsigned space_for (unsigned index, unsigned* root = nullptr) const { const auto& node = vertices_[index]; if (node.space) { if (root != nullptr) *root = index; return node.space; } if (!node.parents) { if (root) *root = index; return 0; } return space_for (node.parents[0], root); } void err_other_error () { this->successful = false; } private: size_t serialized_length () const { size_t total_size = 0; for (unsigned i = 0; i < vertices_.length; i++) { size_t size = vertices_[i].obj.tail - vertices_[i].obj.head; total_size += size; } return total_size; } /* * Returns the numbers of incoming edges that are 32bits wide. */ unsigned wide_parents (unsigned node_idx, hb_set_t& parents) const { unsigned count = 0; hb_set_t visited; for (unsigned p : vertices_[node_idx].parents) { if (visited.has (p)) continue; visited.add (p); // Only real links can be wide for (const auto& l : vertices_[p].obj.real_links) { if (l.objidx == node_idx && l.width == 4 && !l.is_signed) { count++; parents.add (p); } } } return count; } bool check_success (bool success) { return this->successful && (success || (err_other_error (), false)); } /* * Creates a map from objid to # of incoming edges. */ void update_parents () { if (!parents_invalid) return; for (unsigned i = 0; i < vertices_.length; i++) vertices_[i].parents.reset (); for (unsigned p = 0; p < vertices_.length; p++) { for (auto& l : vertices_[p].obj.all_links ()) { vertices_[l.objidx].parents.push (p); } } parents_invalid = false; } /* * compute the serialized start and end positions for each vertex. */ void update_positions () { if (!positions_invalid) return; unsigned current_pos = 0; for (int i = root_idx (); i >= 0; i--) { auto& v = vertices_[i]; v.start = current_pos; current_pos += v.obj.tail - v.obj.head; v.end = current_pos; } positions_invalid = false; } /* * Finds the distance to each object in the graph * from the initial node. */ void update_distances () { if (!distance_invalid) return; // Uses Dijkstra's algorithm to find all of the shortest distances. // https://en.wikipedia.org/wiki/Dijkstra%27s_algorithm // // Implementation Note: // Since our priority queue doesn't support fast priority decreases // we instead just add new entries into the queue when a priority changes. // Redundant ones are filtered out later on by the visited set. // According to https://www3.cs.stonybrook.edu/~rezaul/papers/TR-07-54.pdf // for practical performance this is faster then using a more advanced queue // (such as a fibonacci queue) with a fast decrease priority. for (unsigned i = 0; i < vertices_.length; i++) { if (i == vertices_.length - 1) vertices_[i].distance = 0; else vertices_[i].distance = hb_int_max (int64_t); } hb_priority_queue_t queue; queue.insert (0, vertices_.length - 1); hb_vector_t<bool> visited; visited.resize (vertices_.length); while (!queue.in_error () && !queue.is_empty ()) { unsigned next_idx = queue.pop_minimum ().second; if (visited[next_idx]) continue; const auto& next = vertices_[next_idx]; int64_t next_distance = vertices_[next_idx].distance; visited[next_idx] = true; for (const auto& link : next.obj.all_links ()) { if (visited[link.objidx]) continue; const auto& child = vertices_[link.objidx].obj; unsigned link_width = link.width ? link.width : 4; // treat virtual offsets as 32 bits wide int64_t child_weight = (child.tail - child.head) + ((int64_t) 1 << (link_width * 8)) * (vertices_[link.objidx].space + 1); int64_t child_distance = next_distance + child_weight; if (child_distance < vertices_[link.objidx].distance) { vertices_[link.objidx].distance = child_distance; queue.insert (child_distance, link.objidx); } } } check_success (!queue.in_error ()); if (!check_success (queue.is_empty ())) { print_orphaned_nodes (); return; } distance_invalid = false; } int64_t compute_offset ( unsigned parent_idx, const hb_serialize_context_t::object_t::link_t& link) const { const auto& parent = vertices_[parent_idx]; const auto& child = vertices_[link.objidx]; int64_t offset = 0; switch ((hb_serialize_context_t::whence_t) link.whence) { case hb_serialize_context_t::whence_t::Head: offset = child.start - parent.start; break; case hb_serialize_context_t::whence_t::Tail: offset = child.start - parent.end; break; case hb_serialize_context_t::whence_t::Absolute: offset = child.start; break; } assert (offset >= link.bias); offset -= link.bias; return offset; } bool is_valid_offset (int64_t offset, const hb_serialize_context_t::object_t::link_t& link) const { if (unlikely (!link.width)) // Virtual links can't overflow. return link.is_signed || offset >= 0; if (link.is_signed) { if (link.width == 4) return offset >= -((int64_t) 1 << 31) && offset < ((int64_t) 1 << 31); else return offset >= -(1 << 15) && offset < (1 << 15); } else { if (link.width == 4) return offset >= 0 && offset < ((int64_t) 1 << 32); else if (link.width == 3) return offset >= 0 && offset < ((int32_t) 1 << 24); else return offset >= 0 && offset < (1 << 16); } } /* * Updates a link in the graph to point to a different object. Corrects the * parents vector on the previous and new child nodes. */ void reassign_link (hb_serialize_context_t::object_t::link_t& link, unsigned parent_idx, unsigned new_idx) { unsigned old_idx = link.objidx; link.objidx = new_idx; vertices_[old_idx].remove_parent (parent_idx); vertices_[new_idx].parents.push (parent_idx); } /* * Updates all objidx's in all links using the provided mapping. Corrects incoming edge counts. */ template<typename Iterator, hb_requires (hb_is_iterator (Iterator))> void remap_obj_indices (const hb_hashmap_t<unsigned, unsigned>& id_map, Iterator subgraph, bool only_wide = false) { if (!id_map) return; for (unsigned i : subgraph) { for (auto& link : vertices_[i].obj.all_links_writer ()) { if (!id_map.has (link.objidx)) continue; if (only_wide && !(link.width == 4 && !link.is_signed)) continue; reassign_link (link, i, id_map[link.objidx]); } } } /* * Updates all objidx's in all links using the provided mapping. */ void remap_all_obj_indices (const hb_vector_t<unsigned>& id_map, hb_vector_t<vertex_t>* sorted_graph) const { for (unsigned i = 0; i < sorted_graph->length; i++) { (*sorted_graph)[i].remap_parents (id_map); for (auto& link : (*sorted_graph)[i].obj.all_links_writer ()) { link.objidx = id_map[link.objidx]; } } } template <typename O> void serialize_link_of_type (const hb_serialize_context_t::object_t::link_t& link, char* head, hb_serialize_context_t* c) const { OT::Offset<O>* offset = reinterpret_cast<OT::Offset<O>*> (head + link.position); *offset = 0; c->add_link (*offset, // serializer has an extra nil object at the start of the // object array. So all id's are +1 of what our id's are. link.objidx + 1, (hb_serialize_context_t::whence_t) link.whence, link.bias); } void serialize_link (const hb_serialize_context_t::object_t::link_t& link, char* head, hb_serialize_context_t* c) const { switch (link.width) { case 0: // Virtual links aren't serialized. return; case 4: if (link.is_signed) { serialize_link_of_type<OT::HBINT32> (link, head, c); } else { serialize_link_of_type<OT::HBUINT32> (link, head, c); } return; case 2: if (link.is_signed) { serialize_link_of_type<OT::HBINT16> (link, head, c); } else { serialize_link_of_type<OT::HBUINT16> (link, head, c); } return; case 3: serialize_link_of_type<OT::HBUINT24> (link, head, c); return; default: // Unexpected link width. assert (0); } } /* * Finds all nodes in targets that are reachable from start_idx, nodes in visited will be skipped. * For this search the graph is treated as being undirected. * * Connected targets will be added to connected and removed from targets. All visited nodes * will be added to visited. */ void find_connected_nodes (unsigned start_idx, hb_set_t& targets, hb_set_t& visited, hb_set_t& connected) { if (unlikely (!check_success (!visited.in_error ()))) return; if (visited.has (start_idx)) return; visited.add (start_idx); if (targets.has (start_idx)) { targets.del (start_idx); connected.add (start_idx); } const auto& v = vertices_[start_idx]; // Graph is treated as undirected so search children and parents of start_idx for (const auto& l : v.obj.all_links ()) find_connected_nodes (l.objidx, targets, visited, connected); for (unsigned p : v.parents) find_connected_nodes (p, targets, visited, connected); } public: // TODO(garretrieger): make private, will need to move most of offset overflow code into graph. hb_vector_t<vertex_t> vertices_; private: bool parents_invalid; bool distance_invalid; bool positions_invalid; bool successful; hb_vector_t<unsigned> num_roots_for_space_; }; static inline bool _try_isolating_subgraphs (const hb_vector_t<graph_t::overflow_record_t>& overflows, graph_t& sorted_graph) { unsigned space = 0; hb_set_t roots_to_isolate; for (int i = overflows.length - 1; i >= 0; i--) { const graph_t::overflow_record_t& r = overflows[i]; unsigned root; unsigned overflow_space = sorted_graph.space_for (r.parent, &root); if (!overflow_space) continue; if (sorted_graph.num_roots_for_space (overflow_space) <= 1) continue; if (!space) { space = overflow_space; } if (space == overflow_space) roots_to_isolate.add(root); } if (!roots_to_isolate) return false; unsigned maximum_to_move = hb_max ((sorted_graph.num_roots_for_space (space) / 2u), 1u); if (roots_to_isolate.get_population () > maximum_to_move) { // Only move at most half of the roots in a space at a time. unsigned extra = roots_to_isolate.get_population () - maximum_to_move; while (extra--) { unsigned root = HB_SET_VALUE_INVALID; roots_to_isolate.previous (&root); roots_to_isolate.del (root); } } DEBUG_MSG (SUBSET_REPACK, nullptr, "Overflow in space %d (%d roots). Moving %d roots to space %d.", space, sorted_graph.num_roots_for_space (space), roots_to_isolate.get_population (), sorted_graph.next_space ()); sorted_graph.isolate_subgraph (roots_to_isolate); sorted_graph.move_to_new_space (roots_to_isolate); return true; } static inline bool _process_overflows (const hb_vector_t<graph_t::overflow_record_t>& overflows, hb_set_t& priority_bumped_parents, graph_t& sorted_graph) { bool resolution_attempted = false; // Try resolving the furthest overflows first. for (int i = overflows.length - 1; i >= 0; i--) { const graph_t::overflow_record_t& r = overflows[i]; const auto& child = sorted_graph.vertices_[r.child]; if (child.is_shared ()) { // The child object is shared, we may be able to eliminate the overflow // by duplicating it. if (!sorted_graph.duplicate (r.parent, r.child)) continue; return true; } if (child.is_leaf () && !priority_bumped_parents.has (r.parent)) { // This object is too far from it's parent, attempt to move it closer. // // TODO(garretrieger): initially limiting this to leaf's since they can be // moved closer with fewer consequences. However, this can // likely can be used for non-leafs as well. // TODO(garretrieger): also try lowering priority of the parent. Make it // get placed further up in the ordering, closer to it's children. // this is probably preferable if the total size of the parent object // is < then the total size of the children (and the parent can be moved). // Since in that case moving the parent will cause a smaller increase in // the length of other offsets. if (sorted_graph.raise_childrens_priority (r.parent)) { priority_bumped_parents.add (r.parent); resolution_attempted = true; } continue; } // TODO(garretrieger): add additional offset resolution strategies // - Promotion to extension lookups. // - Table splitting. } return resolution_attempted; } /* * Attempts to modify the topological sorting of the provided object graph to * eliminate offset overflows in the links between objects of the graph. If a * non-overflowing ordering is found the updated graph is serialized it into the * provided serialization context. * * If necessary the structure of the graph may be modified in ways that do not * affect the functionality of the graph. For example shared objects may be * duplicated. * * For a detailed writeup describing how the algorithm operates see: * docs/repacker.md */ template<typename T> inline hb_blob_t* hb_resolve_overflows (const T& packed, hb_tag_t table_tag, unsigned max_rounds = 20) { // Kahn sort is ~twice as fast as shortest distance sort and works for many fonts // so try it first to save time. graph_t sorted_graph (packed); sorted_graph.sort_kahn (); if (!sorted_graph.will_overflow ()) { return sorted_graph.serialize (); } sorted_graph.sort_shortest_distance (); if ((table_tag == HB_OT_TAG_GPOS || table_tag == HB_OT_TAG_GSUB) && sorted_graph.will_overflow ()) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs."); if (sorted_graph.assign_32bit_spaces ()) sorted_graph.sort_shortest_distance (); } unsigned round = 0; hb_vector_t<graph_t::overflow_record_t> overflows; // TODO(garretrieger): select a good limit for max rounds. while (!sorted_graph.in_error () && sorted_graph.will_overflow (&overflows) && round++ < max_rounds) { DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Overflow resolution round %d ===", round); sorted_graph.print_overflows (overflows); hb_set_t priority_bumped_parents; if (!_try_isolating_subgraphs (overflows, sorted_graph)) { if (!_process_overflows (overflows, priority_bumped_parents, sorted_graph)) { DEBUG_MSG (SUBSET_REPACK, nullptr, "No resolution available :("); break; } } sorted_graph.sort_shortest_distance (); } if (sorted_graph.in_error ()) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Sorted graph in error state."); return nullptr; } if (sorted_graph.will_overflow ()) { DEBUG_MSG (SUBSET_REPACK, nullptr, "Offset overflow resolution failed."); return nullptr; } return sorted_graph.serialize (); } #endif /* HB_REPACKER_HH */