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