Add support for 'kern' OpenType table....

src/kern.cc

+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "kern.h"
+
+// kern - Kerning
+// http://www.microsoft.com/opentype/otspec/kern.htm
+
+#define DROP_THIS_TABLE \
+  do { delete file->kern; file->kern = 0; } while (0)
+
+namespace ots {
+
+bool ots_kern_parse(OpenTypeFile *file, const uint8_t *data, size_t length) {
+  Buffer table(data, length);
+
+  OpenTypeKERN *kern = new OpenTypeKERN;
+  file->kern = kern;
+
+  uint16_t num_tables = 0;
+  if (!table.ReadU16(&kern->version) ||
+      !table.ReadU16(&num_tables)) {
+    return OTS_FAILURE();
+  }
+
+  if (kern->version > 0) {
+    DROP_THIS_TABLE;
+    return true;
+  }
+
+  if (num_tables == 0) {
+    OTS_WARNING("num_tables is zero");
+    DROP_THIS_TABLE;
+    return true;
+  }
+
+  kern->subtables.reserve(num_tables);
+  for (unsigned i = 0; i < num_tables; ++i) {
+    OpenTypeKERNFormat0 subtable;
+    uint16_t sub_length = 0;
+
+    if (!table.ReadU16(&subtable.version) ||
+        !table.ReadU16(&sub_length)) {
+      return OTS_FAILURE();
+    }
+
+    if (subtable.version > 0) {
+      OTS_WARNING("Bad subtable version: %d", subtable.version);
+      continue;
+    }
+
+    const size_t current_offset = table.offset();
+    if (current_offset - 4 + sub_length > length) {
+      return OTS_FAILURE();
+    }
+
+    if (!table.ReadU16(&subtable.coverage)) {
+      return OTS_FAILURE();
+    }
+
+    if (!(subtable.coverage & 0x1)) {
+      OTS_WARNING(
+          "We don't support vertical data as the renderer doesn't support it.");
+      continue;
+    }
+    if (subtable.coverage & 0xF0) {
+      OTS_WARNING("Reserved fields should zero-filled.");
+      DROP_THIS_TABLE;
+      return true;
+    }
+    const uint32_t format = (subtable.coverage & 0xFF00) >> 8;
+    if (format != 0) {
+      OTS_WARNING("Format %d is not supported.", format);
+      continue;
+    }
+
+    // Parse the format 0 field.
+    uint16_t num_pairs = 0;
+    if (!table.ReadU16(&num_pairs) ||
+        !table.ReadU16(&subtable.search_range) ||
+        !table.ReadU16(&subtable.entry_selector) ||
+        !table.ReadU16(&subtable.range_shift)) {
+      return OTS_FAILURE();
+    }
+
+    if (!num_pairs) {
+      OTS_WARNING("Zero length subtable is found.");
+      DROP_THIS_TABLE;
+      return true;
+    }
+
+    // Sanity checks for search_range, entry_selector, and range_shift. See the
+    // comment in ots.cc for details.
+    const size_t kFormat0PairSize = 6;  // left, right, and value. 2 bytes each.
+    if (num_pairs > (65536 / kFormat0PairSize)) {
+      // Some fonts (e.g. calibri.ttf, pykes_peak_zero.ttf) have pairs >= 10923.
+      OTS_WARNING("Too large subtable.");
+      DROP_THIS_TABLE;
+      return true;
+    }
+    unsigned max_pow2 = 0;
+    while (1u << (max_pow2 + 1) <= num_pairs) {
+      ++max_pow2;
+    }
+    const uint16_t expected_search_range = (1u << max_pow2) * kFormat0PairSize;
+    if (subtable.search_range != expected_search_range) {
+      OTS_WARNING("bad search range");
+      subtable.search_range = expected_search_range;
+    }
+    if (subtable.entry_selector != max_pow2) {
+      return OTS_FAILURE();
+    }
+    const uint32_t expected_range_shift
+        = kFormat0PairSize * num_pairs - subtable.search_range;
+    if (subtable.range_shift != expected_range_shift) {
+      OTS_WARNING("bad range shift");
+      subtable.range_shift = expected_range_shift;
+    }
+
+    // Read kerning pairs.
+    subtable.pairs.reserve(num_pairs);
+    uint32_t last_pair = 0;
+    for (unsigned j = 0; j < num_pairs; ++j) {
+      OpenTypeKERNFormat0Pair kerning_pair;
+      if (!table.ReadU16(&kerning_pair.left) ||
+          !table.ReadU16(&kerning_pair.right) ||
+          !table.ReadS16(&kerning_pair.value)) {
+        return OTS_FAILURE();
+      }
+      const uint32_t current_pair
+          = (kerning_pair.left << 16) + kerning_pair.right;
+      if (j != 0 && current_pair <= last_pair) {
+        OTS_WARNING("Kerning pairs are not sorted.");
+        // Many free fonts don't follow this rule, so we don't call OTS_FAILURE
+        // in order to support these fonts.
+        DROP_THIS_TABLE;
+        return true;
+      }
+      last_pair = current_pair;
+      subtable.pairs.push_back(kerning_pair);
+    }
+
+    kern->subtables.push_back(subtable);
+  }
+
+  if (!kern->subtables.size()) {
+    OTS_WARNING("All subtables are removed.");
+    DROP_THIS_TABLE;
+    return true;
+  }
+
+  return true;
+}
+
+bool ots_kern_should_serialise(OpenTypeFile *file) {
+  if (!file->glyf) return false;  // this table is not for CFF fonts.
+  return file->kern;
+}
+
+bool ots_kern_serialise(OTSStream *out, OpenTypeFile *file) {
+  const OpenTypeKERN *kern = file->kern;
+
+  if (!out->WriteU16(kern->version) ||
+      !out->WriteU16(kern->subtables.size())) {
+    return OTS_FAILURE();
+  }
+
+  for (unsigned i = 0; i < kern->subtables.size(); ++i) {
+    const uint16_t length = 14 + (6 * kern->subtables[i].pairs.size());
+    if (!out->WriteU16(kern->subtables[i].version) ||
+        !out->WriteU16(length) ||
+        !out->WriteU16(kern->subtables[i].coverage) ||
+        !out->WriteU16(kern->subtables[i].pairs.size()) ||
+        !out->WriteU16(kern->subtables[i].search_range) ||
+        !out->WriteU16(kern->subtables[i].entry_selector) ||
+        !out->WriteU16(kern->subtables[i].range_shift)) {
+      return OTS_FAILURE();
+    }
+    for (unsigned j = 0; j < kern->subtables[i].pairs.size(); ++j) {
+      if (!out->WriteU16(kern->subtables[i].pairs[j].left) ||
+          !out->WriteU16(kern->subtables[i].pairs[j].right) ||
+          !out->WriteS16(kern->subtables[i].pairs[j].value)) {
+        return OTS_FAILURE();
+      }
+    }
+  }
+
+  return true;
+}
+
+void ots_kern_free(OpenTypeFile *file) {
+  delete file->kern;
+}
+
+}  // namespace ots