summaryrefslogtreecommitdiff
path: root/thirdparty/harfbuzz/src/hb-repacker.hh
diff options
context:
space:
mode:
Diffstat (limited to 'thirdparty/harfbuzz/src/hb-repacker.hh')
-rw-r--r--thirdparty/harfbuzz/src/hb-repacker.hh385
1 files changed, 385 insertions, 0 deletions
diff --git a/thirdparty/harfbuzz/src/hb-repacker.hh b/thirdparty/harfbuzz/src/hb-repacker.hh
new file mode 100644
index 0000000000..40a5326118
--- /dev/null
+++ b/thirdparty/harfbuzz/src/hb-repacker.hh
@@ -0,0 +1,385 @@
+/*
+ * 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-vector.hh"
+#include "graph/graph.hh"
+#include "graph/gsubgpos-graph.hh"
+#include "graph/serialize.hh"
+
+using graph::graph_t;
+
+/*
+ * For a detailed writeup on the overflow resolution algorithm see:
+ * docs/repacker.md
+ */
+
+struct lookup_size_t
+{
+ unsigned lookup_index;
+ size_t size;
+ unsigned num_subtables;
+
+ static int cmp (const void* a, const void* b)
+ {
+ return cmp ((const lookup_size_t*) a,
+ (const lookup_size_t*) b);
+ }
+
+ static int cmp (const lookup_size_t* a, const lookup_size_t* b)
+ {
+ double subtables_per_byte_a = (double) a->num_subtables / (double) a->size;
+ double subtables_per_byte_b = (double) b->num_subtables / (double) b->size;
+ if (subtables_per_byte_a == subtables_per_byte_b) {
+ return b->lookup_index - a->lookup_index;
+ }
+
+ double cmp = subtables_per_byte_b - subtables_per_byte_a;
+ if (cmp < 0) return -1;
+ if (cmp > 0) return 1;
+ return 0;
+ }
+};
+
+static inline
+bool _presplit_subtables_if_needed (graph::gsubgpos_graph_context_t& ext_context)
+{
+ // For each lookup this will check the size of subtables and split them as needed
+ // so that no subtable is at risk of overflowing. (where we support splitting for
+ // that subtable type).
+ //
+ // TODO(grieger): de-dup newly added nodes as necessary. Probably just want a full de-dup
+ // pass after this processing is done. Not super necessary as splits are
+ // only done where overflow is likely, so de-dup probably will get undone
+ // later anyways.
+ for (unsigned lookup_index : ext_context.lookups.keys ())
+ {
+ graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
+ if (!lookup->split_subtables_if_needed (ext_context, lookup_index))
+ return false;
+ }
+
+ return true;
+}
+
+/*
+ * Analyze the lookups in a GSUB/GPOS table and decide if any should be promoted
+ * to extension lookups.
+ */
+static inline
+bool _promote_extensions_if_needed (graph::gsubgpos_graph_context_t& ext_context)
+{
+ // Simple Algorithm (v1, current):
+ // 1. Calculate how many bytes each non-extension lookup consumes.
+ // 2. Select up to 64k of those to remain as non-extension (greedy, highest subtables per byte first)
+ // 3. Promote the rest.
+ //
+ // Advanced Algorithm (v2, not implemented):
+ // 1. Perform connected component analysis using lookups as roots.
+ // 2. Compute size of each connected component.
+ // 3. Select up to 64k worth of connected components to remain as non-extensions.
+ // (greedy, highest subtables per byte first)
+ // 4. Promote the rest.
+
+ // TODO(garretrieger): support extension demotion, then consider all lookups. Requires advanced algo.
+ // TODO(garretrieger): also support extension promotion during iterative resolution phase, then
+ // we can use a less conservative threshold here.
+ // TODO(grieger): skip this for the 24 bit case.
+ if (!ext_context.lookups) return true;
+
+ hb_vector_t<lookup_size_t> lookup_sizes;
+ lookup_sizes.alloc (ext_context.lookups.get_population ());
+
+ for (unsigned lookup_index : ext_context.lookups.keys ())
+ {
+ const graph::Lookup* lookup = ext_context.lookups.get(lookup_index);
+ hb_set_t visited;
+ lookup_sizes.push (lookup_size_t {
+ lookup_index,
+ ext_context.graph.find_subgraph_size (lookup_index, visited),
+ lookup->number_of_subtables (),
+ });
+ }
+
+ lookup_sizes.qsort ();
+
+ size_t lookup_list_size = ext_context.graph.vertices_[ext_context.lookup_list_index].table_size ();
+ size_t l2_l3_size = lookup_list_size; // Lookup List + Lookups
+ size_t l3_l4_size = 0; // Lookups + SubTables
+ size_t l4_plus_size = 0; // SubTables + their descendants
+
+ // Start by assuming all lookups are using extension subtables, this size will be removed later
+ // if it's decided to not make a lookup extension.
+ for (auto p : lookup_sizes)
+ {
+ unsigned subtables_size = p.num_subtables * 8;
+ l3_l4_size += subtables_size;
+ l4_plus_size += subtables_size;
+ }
+
+ bool layers_full = false;
+ for (auto p : lookup_sizes)
+ {
+ const graph::Lookup* lookup = ext_context.lookups.get(p.lookup_index);
+ if (lookup->is_extension (ext_context.table_tag))
+ // already an extension so size is counted by the loop above.
+ continue;
+
+ if (!layers_full)
+ {
+ size_t lookup_size = ext_context.graph.vertices_[p.lookup_index].table_size ();
+ hb_set_t visited;
+ size_t subtables_size = ext_context.graph.find_subgraph_size (p.lookup_index, visited, 1) - lookup_size;
+ size_t remaining_size = p.size - subtables_size - lookup_size;
+
+ l2_l3_size += lookup_size;
+ l3_l4_size += lookup_size + subtables_size;
+ l3_l4_size -= p.num_subtables * 8;
+ l4_plus_size += subtables_size + remaining_size;
+
+ if (l2_l3_size < (1 << 16)
+ && l3_l4_size < (1 << 16)
+ && l4_plus_size < (1 << 16)) continue; // this lookup fits within all layers groups
+
+ layers_full = true;
+ }
+
+ if (!ext_context.lookups.get(p.lookup_index)->make_extension (ext_context, p.lookup_index))
+ return false;
+ }
+
+ return true;
+}
+
+static inline
+bool _try_isolating_subgraphs (const hb_vector_t<graph::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::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::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::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;
+}
+
+inline bool
+hb_resolve_graph_overflows (hb_tag_t table_tag,
+ unsigned max_rounds ,
+ bool recalculate_extensions,
+ graph_t& sorted_graph /* IN/OUT */)
+{
+ sorted_graph.sort_shortest_distance ();
+
+ bool will_overflow = graph::will_overflow (sorted_graph);
+ if (!will_overflow)
+ return true;
+
+ graph::gsubgpos_graph_context_t ext_context (table_tag, sorted_graph);
+ if ((table_tag == HB_OT_TAG_GPOS
+ || table_tag == HB_OT_TAG_GSUB)
+ && will_overflow)
+ {
+ if (recalculate_extensions)
+ {
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "Splitting subtables if needed.");
+ if (!_presplit_subtables_if_needed (ext_context)) {
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "Subtable splitting failed.");
+ return false;
+ }
+
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "Promoting lookups to extensions if needed.");
+ if (!_promote_extensions_if_needed (ext_context)) {
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "Extensions promotion failed.");
+ return false;
+ }
+ }
+
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "Assigning spaces to 32 bit subgraphs.");
+ if (sorted_graph.assign_spaces ())
+ sorted_graph.sort_shortest_distance ();
+ else
+ sorted_graph.sort_shortest_distance_if_needed ();
+ }
+
+ unsigned round = 0;
+ hb_vector_t<graph::overflow_record_t> overflows;
+ // TODO(garretrieger): select a good limit for max rounds.
+ while (!sorted_graph.in_error ()
+ && graph::will_overflow (sorted_graph, &overflows)
+ && round < max_rounds) {
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "=== Overflow resolution round %d ===", round);
+ print_overflows (sorted_graph, overflows);
+
+ hb_set_t priority_bumped_parents;
+
+ if (!_try_isolating_subgraphs (overflows, sorted_graph))
+ {
+ // Don't count space isolation towards round limit. Only increment
+ // round counter if space isolation made no changes.
+ round++;
+ 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 false;
+ }
+
+ if (graph::will_overflow (sorted_graph))
+ {
+ DEBUG_MSG (SUBSET_REPACK, nullptr, "Offset overflow resolution failed.");
+ return false;
+ }
+
+ return true;
+}
+
+/*
+ * 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,
+ bool recalculate_extensions = false) {
+ graph_t sorted_graph (packed);
+ if (!hb_resolve_graph_overflows (table_tag, max_rounds, recalculate_extensions, sorted_graph))
+ return nullptr;
+
+ return graph::serialize (sorted_graph);
+}
+
+#endif /* HB_REPACKER_HH */
generated by cgit v1.2.3 (git 2.25.1) at 2024-12-24 06:01:36 +0000