385 lines
13 KiB
C++
385 lines
13 KiB
C++
/*
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* Copyright © 2020 Google, Inc.
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*
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* This is part of HarfBuzz, a text shaping library.
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*
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* Permission is hereby granted, without written agreement and without
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* license or royalty fees, to use, copy, modify, and distribute this
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* software and its documentation for any purpose, provided that the
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* above copyright notice and the following two paragraphs appear in
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* all copies of this software.
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*
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* IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
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* DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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* ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
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* IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
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* BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
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* FITNESS FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS
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* ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
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* PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
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*
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* Google Author(s): Garret Rieger
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*/
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#ifndef HB_REPACKER_HH
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#define HB_REPACKER_HH
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#include "hb-open-type.hh"
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#include "hb-map.hh"
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#include "hb-vector.hh"
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#include "graph/graph.hh"
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#include "graph/gsubgpos-graph.hh"
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#include "graph/serialize.hh"
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using graph::graph_t;
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/*
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* For a detailed writeup on the overflow resolution algorithm see:
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* docs/repacker.md
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*/
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struct lookup_size_t
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{
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unsigned lookup_index;
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size_t size;
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unsigned num_subtables;
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static int cmp (const void* a, const void* b)
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{
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return cmp ((const lookup_size_t*) a,
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(const lookup_size_t*) b);
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}
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static int cmp (const lookup_size_t* a, const lookup_size_t* b)
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{
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double subtables_per_byte_a = (double) a->num_subtables / (double) a->size;
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double subtables_per_byte_b = (double) b->num_subtables / (double) b->size;
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if (subtables_per_byte_a == subtables_per_byte_b) {
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return b->lookup_index - a->lookup_index;
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}
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double cmp = subtables_per_byte_b - subtables_per_byte_a;
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if (cmp < 0) return -1;
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if (cmp > 0) return 1;
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return 0;
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}
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};
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static inline
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bool _presplit_subtables_if_needed (graph::gsubgpos_graph_context_t& ext_context)
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{
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// For each lookup this will check the size of subtables and split them as needed
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// so that no subtable is at risk of overflowing. (where we support splitting for
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// that subtable type).
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//
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// TODO(grieger): de-dup newly added nodes as necessary. Probably just want a full de-dup
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// pass after this processing is done. Not super necessary as splits are
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// only done where overflow is likely, so de-dup probably will get undone
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// later anyways.
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for (unsigned lookup_index : ext_context.lookups.keys ())
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{
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graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
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if (!lookup->split_subtables_if_needed (ext_context, lookup_index))
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return false;
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}
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return true;
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}
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/*
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* Analyze the lookups in a GSUB/GPOS table and decide if any should be promoted
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* to extension lookups.
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*/
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static inline
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bool _promote_extensions_if_needed (graph::gsubgpos_graph_context_t& ext_context)
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{
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// Simple Algorithm (v1, current):
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// 1. Calculate how many bytes each non-extension lookup consumes.
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// 2. Select up to 64k of those to remain as non-extension (greedy, highest subtables per byte first)
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// 3. Promote the rest.
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//
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// Advanced Algorithm (v2, not implemented):
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// 1. Perform connected component analysis using lookups as roots.
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// 2. Compute size of each connected component.
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// 3. Select up to 64k worth of connected components to remain as non-extensions.
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// (greedy, highest subtables per byte first)
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// 4. Promote the rest.
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// TODO(garretrieger): support extension demotion, then consider all lookups. Requires advanced algo.
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// TODO(garretrieger): also support extension promotion during iterative resolution phase, then
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// we can use a less conservative threshold here.
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// TODO(grieger): skip this for the 24 bit case.
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if (!ext_context.lookups) return true;
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hb_vector_t<lookup_size_t> lookup_sizes;
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lookup_sizes.alloc (ext_context.lookups.get_population ());
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for (unsigned lookup_index : ext_context.lookups.keys ())
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{
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const graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
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hb_set_t visited;
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lookup_sizes.push (lookup_size_t {
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lookup_index,
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ext_context.graph.find_subgraph_size (lookup_index, visited),
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lookup->number_of_subtables (),
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});
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}
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lookup_sizes.qsort ();
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size_t lookup_list_size = ext_context.graph.vertices_[ext_context.lookup_list_index].table_size ();
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size_t l2_l3_size = lookup_list_size; // Lookup List + Lookups
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size_t l3_l4_size = 0; // Lookups + SubTables
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size_t l4_plus_size = 0; // SubTables + their descendants
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// Start by assuming all lookups are using extension subtables, this size will be removed later
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// if it's decided to not make a lookup extension.
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for (auto p : lookup_sizes)
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{
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unsigned subtables_size = p.num_subtables * 8;
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l3_l4_size += subtables_size;
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l4_plus_size += subtables_size;
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}
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bool layers_full = false;
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for (auto p : lookup_sizes)
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{
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const graph::Lookup* lookup = ext_context.lookups.get(p.lookup_index);
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if (lookup->is_extension (ext_context.table_tag))
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// already an extension so size is counted by the loop above.
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continue;
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if (!layers_full)
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{
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size_t lookup_size = ext_context.graph.vertices_[p.lookup_index].table_size ();
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hb_set_t visited;
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size_t subtables_size = ext_context.graph.find_subgraph_size (p.lookup_index, visited, 1) - lookup_size;
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size_t remaining_size = p.size - subtables_size - lookup_size;
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l2_l3_size += lookup_size;
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l3_l4_size += lookup_size + subtables_size;
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l3_l4_size -= p.num_subtables * 8;
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l4_plus_size += subtables_size + remaining_size;
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if (l2_l3_size < (1 << 16)
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&& l3_l4_size < (1 << 16)
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&& l4_plus_size < (1 << 16)) continue; // this lookup fits within all layers groups
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layers_full = true;
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}
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if (!ext_context.lookups.get(p.lookup_index)->make_extension (ext_context, p.lookup_index))
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return false;
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}
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return true;
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}
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static inline
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bool _try_isolating_subgraphs (const hb_vector_t<graph::overflow_record_t>& overflows,
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graph_t& sorted_graph)
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{
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unsigned space = 0;
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hb_set_t roots_to_isolate;
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for (int i = overflows.length - 1; i >= 0; i--)
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{
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const graph::overflow_record_t& r = overflows[i];
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unsigned root;
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unsigned overflow_space = sorted_graph.space_for (r.parent, &root);
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if (!overflow_space) continue;
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if (sorted_graph.num_roots_for_space (overflow_space) <= 1) continue;
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if (!space) {
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space = overflow_space;
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}
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if (space == overflow_space)
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roots_to_isolate.add(root);
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}
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if (!roots_to_isolate) return false;
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unsigned maximum_to_move = hb_max ((sorted_graph.num_roots_for_space (space) / 2u), 1u);
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if (roots_to_isolate.get_population () > maximum_to_move) {
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// Only move at most half of the roots in a space at a time.
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unsigned extra = roots_to_isolate.get_population () - maximum_to_move;
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while (extra--) {
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unsigned root = HB_SET_VALUE_INVALID;
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roots_to_isolate.previous (&root);
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roots_to_isolate.del (root);
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}
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}
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DEBUG_MSG (SUBSET_REPACK, nullptr,
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"Overflow in space %d (%d roots). Moving %d roots to space %d.",
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space,
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sorted_graph.num_roots_for_space (space),
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roots_to_isolate.get_population (),
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sorted_graph.next_space ());
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sorted_graph.isolate_subgraph (roots_to_isolate);
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sorted_graph.move_to_new_space (roots_to_isolate);
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return true;
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}
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static inline
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bool _process_overflows (const hb_vector_t<graph::overflow_record_t>& overflows,
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hb_set_t& priority_bumped_parents,
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graph_t& sorted_graph)
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{
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bool resolution_attempted = false;
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// Try resolving the furthest overflows first.
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for (int i = overflows.length - 1; i >= 0; i--)
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{
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const graph::overflow_record_t& r = overflows[i];
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const auto& child = sorted_graph.vertices_[r.child];
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if (child.is_shared ())
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{
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// The child object is shared, we may be able to eliminate the overflow
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// by duplicating it.
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if (sorted_graph.duplicate (r.parent, r.child) == (unsigned) -1) continue;
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return true;
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}
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if (child.is_leaf () && !priority_bumped_parents.has (r.parent))
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{
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// This object is too far from it's parent, attempt to move it closer.
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//
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// TODO(garretrieger): initially limiting this to leaf's since they can be
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// moved closer with fewer consequences. However, this can
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// likely can be used for non-leafs as well.
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// TODO(garretrieger): also try lowering priority of the parent. Make it
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// get placed further up in the ordering, closer to it's children.
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// this is probably preferable if the total size of the parent object
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// is < then the total size of the children (and the parent can be moved).
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// Since in that case moving the parent will cause a smaller increase in
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// the length of other offsets.
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if (sorted_graph.raise_childrens_priority (r.parent)) {
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priority_bumped_parents.add (r.parent);
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resolution_attempted = true;
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}
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continue;
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}
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// TODO(garretrieger): add additional offset resolution strategies
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// - Promotion to extension lookups.
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// - Table splitting.
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}
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return resolution_attempted;
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}
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inline bool
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hb_resolve_graph_overflows (hb_tag_t table_tag,
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unsigned max_rounds ,
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bool recalculate_extensions,
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graph_t& sorted_graph /* IN/OUT */)
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{
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sorted_graph.sort_shortest_distance ();
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bool will_overflow = graph::will_overflow (sorted_graph);
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if (!will_overflow)
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return true;
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graph::gsubgpos_graph_context_t ext_context (table_tag, sorted_graph);
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if ((table_tag == HB_OT_TAG_GPOS
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|| table_tag == HB_OT_TAG_GSUB)
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&& will_overflow)
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{
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if (recalculate_extensions)
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{
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Splitting subtables if needed.");
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if (!_presplit_subtables_if_needed (ext_context)) {
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Subtable splitting failed.");
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return false;
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}
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Promoting lookups to extensions if needed.");
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if (!_promote_extensions_if_needed (ext_context)) {
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Extensions promotion failed.");
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return false;
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}
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}
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
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if (sorted_graph.assign_spaces ())
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sorted_graph.sort_shortest_distance ();
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else
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sorted_graph.sort_shortest_distance_if_needed ();
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}
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unsigned round = 0;
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hb_vector_t<graph::overflow_record_t> overflows;
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// TODO(garretrieger): select a good limit for max rounds.
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while (!sorted_graph.in_error ()
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&& graph::will_overflow (sorted_graph, &overflows)
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&& round < max_rounds) {
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DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Overflow resolution round %d ===", round);
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print_overflows (sorted_graph, overflows);
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hb_set_t priority_bumped_parents;
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if (!_try_isolating_subgraphs (overflows, sorted_graph))
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{
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// Don't count space isolation towards round limit. Only increment
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// round counter if space isolation made no changes.
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round++;
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if (!_process_overflows (overflows, priority_bumped_parents, sorted_graph))
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{
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DEBUG_MSG (SUBSET_REPACK, nullptr, "No resolution available :(");
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break;
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}
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}
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sorted_graph.sort_shortest_distance ();
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}
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if (sorted_graph.in_error ())
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{
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Sorted graph in error state.");
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return false;
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}
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if (graph::will_overflow (sorted_graph))
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{
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DEBUG_MSG (SUBSET_REPACK, nullptr, "Offset overflow resolution failed.");
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return false;
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}
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return true;
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}
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/*
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* Attempts to modify the topological sorting of the provided object graph to
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* eliminate offset overflows in the links between objects of the graph. If a
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* non-overflowing ordering is found the updated graph is serialized it into the
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* provided serialization context.
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*
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* If necessary the structure of the graph may be modified in ways that do not
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* affect the functionality of the graph. For example shared objects may be
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* duplicated.
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*
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* For a detailed writeup describing how the algorithm operates see:
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* docs/repacker.md
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*/
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template<typename T>
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inline hb_blob_t*
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hb_resolve_overflows (const T& packed,
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hb_tag_t table_tag,
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unsigned max_rounds = 20,
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bool recalculate_extensions = false) {
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graph_t sorted_graph (packed);
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if (!hb_resolve_graph_overflows (table_tag, max_rounds, recalculate_extensions, sorted_graph))
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return nullptr;
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return graph::serialize (sorted_graph);
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}
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#endif /* HB_REPACKER_HH */
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