Merge pull request #42 from google/hmtx

hmtx optimization decoding. never encodes hmtx optimized as yet

src/font.cc

@@ -79,6 +79,7 @@ bool ReadTrueTypeFont(Buffer* file, const uint8_t* data, size_t len,
   std::map<uint32_t, uint32_t> intervals;
   for (uint16_t i = 0; i < font->num_tables; ++i) {
     Font::Table table;
+    table.flag_byte = 0;
     table.reuse_of = NULL;
     if (!file->ReadU32(&table.tag) ||
         !file->ReadU32(&table.checksum) ||

src/font.h

@@ -47,6 +47,8 @@ struct Font {
     // Intended use is to bypass re-processing tables
     Font::Table* reuse_of;
 
+    uint8_t flag_byte;
+
     // Is this table reused by a TTC
     bool IsReused() const;
   };

src/glyph.cc

@@ -78,11 +78,6 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
     return FONT_COMPRESSION_FAILURE();
   }
 
-  if (num_contours == 0) {
-    // Empty glyph.
-    return true;
-  }
-
   // Read the bounding box.
   if (!buffer.ReadS16(&glyph->x_min) ||
       !buffer.ReadS16(&glyph->y_min) ||
@@ -91,6 +86,11 @@ bool ReadGlyph(const uint8_t* data, size_t len, Glyph* glyph) {
     return FONT_COMPRESSION_FAILURE();
   }
 
+  if (num_contours == 0) {
+    // Empty glyph.
+    return true;
+  }
+
   if (num_contours > 0) {
     // Simple glyph.
     glyph->contours.resize(num_contours);

src/table_tags.h

@@ -27,6 +27,9 @@ static const uint32_t kHeadTableTag = 0x68656164;
 static const uint32_t kLocaTableTag = 0x6c6f6361;
 static const uint32_t kDsigTableTag = 0x44534947;
 static const uint32_t kCffTableTag = 0x43464620;
+static const uint32_t kHmtxTableTag = 0x686d7478;
+static const uint32_t kHheaTableTag = 0x68686561;
+static const uint32_t kMaxpTableTag = 0x6d617870;
 
 extern const uint32_t kKnownTags[];
 

src/transform.cc

@@ -290,4 +290,131 @@ bool TransformGlyfAndLocaTables(Font* font) {
   return true;
 }
 
+// See https://www.microsoft.com/typography/otspec/hmtx.htm
+// See WOFF2 spec, 5.4. Transformed hmtx table format
+bool TransformHmtxTable(Font* font) {
+  const Font::Table* glyf_table = font->FindTable(kGlyfTableTag);
+  const Font::Table* hmtx_table = font->FindTable(kHmtxTableTag);
+  const Font::Table* hhea_table = font->FindTable(kHheaTableTag);
+
+  // If you don't have hmtx or a glyf not much is going to happen here
+  if (hmtx_table == NULL || glyf_table == NULL) {
+    return true;
+  }
+
+  // hmtx without hhea doesn't make sense
+  if (hhea_table == NULL) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  // Skip 34 to reach 'hhea' numberOfHMetrics
+  Buffer hhea_buf(hhea_table->data, hhea_table->length);
+  uint16_t num_hmetrics;
+  if (!hhea_buf.Skip(34) || !hhea_buf.ReadU16(&num_hmetrics)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  // Must have at least one hMetric
+  if (num_hmetrics < 1) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  int num_glyphs = NumGlyphs(*font);
+
+  // Most fonts can be transformed; assume it's a go until proven otherwise
+  std::vector<uint16_t> advance_widths;
+  std::vector<int16_t> proportional_lsbs;
+  std::vector<int16_t> monospace_lsbs;
+
+  bool remove_proportional_lsb = true;
+  bool remove_monospace_lsb = (num_glyphs - num_hmetrics) > 0;
+
+  Buffer hmtx_buf(hmtx_table->data, hmtx_table->length);
+  for (int i = 0; i < num_glyphs; i++) {
+    Glyph glyph;
+    const uint8_t* glyph_data;
+    size_t glyph_size;
+    if (!GetGlyphData(*font, i, &glyph_data, &glyph_size) ||
+        (glyph_size > 0 && !ReadGlyph(glyph_data, glyph_size, &glyph))) {
+      return FONT_COMPRESSION_FAILURE();
+    }
+
+    uint16_t advance_width = 0;
+    int16_t lsb = 0;
+
+    if (i < num_hmetrics) {
+      // [0, num_hmetrics) are proportional hMetrics
+      if (!hmtx_buf.ReadU16(&advance_width)) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+
+      if (!hmtx_buf.ReadS16(&lsb)) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+
+      if (glyph_size > 0 && glyph.x_min != lsb) {
+        remove_proportional_lsb = false;
+      }
+
+      advance_widths.push_back(advance_width);
+      proportional_lsbs.push_back(lsb);
+    } else {
+      // [num_hmetrics, num_glyphs) are monospace leftSideBearing's
+      if (!hmtx_buf.ReadS16(&lsb)) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+      if (glyph_size > 0 && glyph.x_min != lsb) {
+        remove_monospace_lsb = false;
+      }
+      monospace_lsbs.push_back(lsb);
+    }
+
+    // If we know we can't optimize, bail out completely
+    if (!remove_proportional_lsb && !remove_monospace_lsb) {
+      return true;
+    }
+  }
+
+  Font::Table* transformed_hmtx = &font->tables[kHmtxTableTag ^ 0x80808080];
+
+  uint8_t flags = 0;
+  size_t transformed_size = 1 + 2 * advance_widths.size();
+  if (remove_proportional_lsb) {
+    flags |= 1;
+  } else {
+    transformed_size += 2 * proportional_lsbs.size();
+  }
+  if (remove_monospace_lsb) {
+    flags |= 1 << 1;
+  } else {
+    transformed_size += 2 * monospace_lsbs.size();
+  }
+
+  transformed_hmtx->buffer.reserve(transformed_size);
+  std::vector<uint8_t>* out = &transformed_hmtx->buffer;
+  WriteBytes(out, &flags, 1);
+  for (uint16_t advance_width : advance_widths) {
+    WriteUShort(out, advance_width);
+  }
+
+  if (!remove_proportional_lsb) {
+    for (int16_t lsb : proportional_lsbs) {
+      WriteUShort(out, lsb);
+    }
+  }
+  if (!remove_monospace_lsb) {
+    for (int16_t lsb : monospace_lsbs) {
+      WriteUShort(out, lsb);
+    }
+  }
+
+  transformed_hmtx->tag = kHmtxTableTag ^ 0x80808080;
+  transformed_hmtx->flag_byte = 1 << 6;
+  transformed_hmtx->length = transformed_hmtx->buffer.size();
+  transformed_hmtx->data = transformed_hmtx->buffer.data();
+
+
+  return true;
+}
+
 } // namespace woff2

src/transform.h

@@ -26,6 +26,9 @@ namespace woff2 {
 // derived from the original tag by flipping the MSBs of every byte.
 bool TransformGlyfAndLocaTables(Font* font);
 
+// Apply transformation to hmtx table if applicable for this font.
+bool TransformHmtxTable(Font* font);
+
 } // namespace woff2
 
 #endif  // WOFF2_TRANSFORM_H_

src/woff2_common.h

@@ -26,7 +26,8 @@ namespace woff2 {
 
 static const uint32_t kWoff2Signature = 0x774f4632;  // "wOF2"
 
-const unsigned int kWoff2FlagsTransform = 1 << 5;
+// Leave the first byte open to store flag_byte
+const unsigned int kWoff2FlagsTransform = 1 << 8;
 
 // TrueType Collection ID string: 'ttcf'
 static const uint32_t kTtcFontFlavor = 0x74746366;

src/woff2_dec.cc

@@ -24,6 +24,7 @@
 #include <string>
 #include <vector>
 #include <map>
+#include <unordered_set>
 #include <memory>
 
 #include "./buffer.h"
@@ -401,6 +402,7 @@ bool ReconstructGlyf(const uint8_t* data, size_t data_size,
     }
     uint8_t* glyf_dst = dst + loca_offset;
     size_t glyf_dst_size = dst_size - loca_offset;
+
     if (n_contours == 0xffff) {
       // composite glyph
       bool have_instructions = false;
@@ -542,6 +544,200 @@ const Table* FindTable(const std::vector<Table>& tables, uint32_t tag) {
   return NULL;
 }
 
+// https://www.microsoft.com/typography/otspec/maxp.htm
+bool ReadNumGlyphs(const Table* maxp_table,
+                   uint8_t* dst, size_t dst_length, uint16_t* num_glyphs) {
+  if (PREDICT_FALSE(static_cast<uint64_t>(maxp_table->dst_offset +
+      maxp_table->dst_length) > dst_length)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  Buffer buffer(dst + maxp_table->dst_offset, maxp_table->dst_length);
+  // Skip 4 to reach 'maxp' numGlyphs
+  if (PREDICT_FALSE(!buffer.Skip(4) || !buffer.ReadU16(num_glyphs))) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  return true;
+}
+
+// Get numberOfHMetrics, https://www.microsoft.com/typography/otspec/hhea.htm
+bool ReadNumHMetrics(const Table* hhea_table,
+                     uint8_t* dst, size_t dst_length, uint16_t* num_hmetrics) {
+  if (PREDICT_FALSE(static_cast<uint64_t>(hhea_table->dst_offset +
+      hhea_table->dst_length) > dst_length)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  // Skip 34 to reach 'hhea' numberOfHMetrics
+  Buffer buffer(dst + hhea_table->dst_offset, hhea_table->dst_length);
+  if (PREDICT_FALSE(!buffer.Skip(34) || !buffer.ReadU16(num_hmetrics))) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  return true;
+}
+
+// x_min for glyph; https://www.microsoft.com/typography/otspec/glyf.htm
+bool ReadGlyphXMin(Buffer* glyf_buff, Buffer* loca_buff, int16_t loca_format,
+                   uint16_t index, int16_t* x_min) {
+  uint32_t offset1, offset2;
+  loca_buff->set_offset((loca_format == 0 ? 2 : 4) * index);
+  if (loca_format == 0) {
+    uint16_t tmp1, tmp2;
+    if (PREDICT_FALSE(!loca_buff->ReadU16(&tmp1) ||
+                      !loca_buff->ReadU16(&tmp2))) {
+      return FONT_COMPRESSION_FAILURE();
+    }
+    // https://www.microsoft.com/typography/otspec/loca.htm
+    // "The actual local offset divided by 2 is stored."
+    offset1 = tmp1 * 2;
+    offset2 = tmp2 * 2;
+  } else if (PREDICT_FALSE(!loca_buff->ReadU32(&offset1) ||
+                           !loca_buff->ReadU32(&offset2))) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  if (offset1 != offset2) {
+    glyf_buff->set_offset(offset1 + 2);
+    if (!glyf_buff->ReadS16(x_min)) {
+      return FONT_COMPRESSION_FAILURE();
+    }
+  } else {
+    *x_min = 0;
+  }
+  return true;
+}
+
+// http://dev.w3.org/webfonts/WOFF2/spec/Overview.html#hmtx_table_format
+bool ReconstructTransformedHmtx(const uint8_t* transformed_buf,
+                                size_t transformed_size,
+                                const Table* glyf_table,
+                                const Table* hhea_table,
+                                const Table* hmtx_table,
+                                const Table* loca_table,
+                                const Table* maxp_table,
+                                uint8_t* dst, size_t dst_length) {
+  if (PREDICT_FALSE(!glyf_table)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (PREDICT_FALSE(!hhea_table)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (PREDICT_FALSE(!hmtx_table)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (PREDICT_FALSE(!loca_table)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (PREDICT_FALSE(!maxp_table)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  uint16_t num_glyphs, num_hmetrics;
+  if (!ReadNumGlyphs(maxp_table, dst, dst_length, &num_glyphs)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (!ReadNumHMetrics(hhea_table, dst, dst_length, &num_hmetrics)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  if (PREDICT_FALSE(static_cast<uint64_t>(hmtx_table->dst_offset +
+      hmtx_table->dst_length) > dst_length)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  Buffer hmtx_buff_in(transformed_buf, transformed_size);
+
+  uint8_t hmtx_flags;
+  if (PREDICT_FALSE(!hmtx_buff_in.ReadU8(&hmtx_flags))) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  std::vector<uint16_t> advance_widths;
+  std::vector<int16_t> lsbs;
+  bool has_proportional_lsbs = (hmtx_flags & 1) == 0;
+  bool has_monospace_lsbs = (hmtx_flags & 2) == 0;
+
+  // you say you transformed but there is little evidence of it
+  if (has_proportional_lsbs && has_monospace_lsbs) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  // glyf/loca are done already so we can use them to recover x_min's
+  if (PREDICT_FALSE(static_cast<uint64_t>(glyf_table->dst_offset +
+      glyf_table->dst_length) > dst_length)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (PREDICT_FALSE(static_cast<uint64_t>(loca_table->dst_offset +
+      loca_table->dst_length) > dst_length)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  Buffer glyf_buff(dst + glyf_table->dst_offset, glyf_table->dst_length);
+  Buffer loca_buff(dst + loca_table->dst_offset, loca_table->dst_length);
+  int16_t loca_format;
+  if (loca_table->dst_length == 2 * (num_glyphs + 1)) {
+    loca_format = 0;
+  } else if (loca_table->dst_length == 4 * (num_glyphs + 1)) {
+    loca_format = 1;
+  } else {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  for (uint16_t i = 0; i < num_hmetrics; i++) {
+    uint16_t advance_width;
+    if (PREDICT_FALSE(!hmtx_buff_in.ReadU16(&advance_width))) {
+      return FONT_COMPRESSION_FAILURE();
+    }
+    advance_widths.push_back(advance_width);
+  }
+
+  for (uint16_t i = 0; i < num_hmetrics; i++) {
+    int16_t lsb;
+    if (has_proportional_lsbs) {
+      if (PREDICT_FALSE(!hmtx_buff_in.ReadS16(&lsb))) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+    } else {
+      if (PREDICT_FALSE(!ReadGlyphXMin(&glyf_buff, &loca_buff, loca_format, i,
+          &lsb))) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+    }
+    lsbs.push_back(lsb);
+  }
+
+  for (uint16_t i = num_hmetrics; i < num_glyphs; i++) {
+    int16_t lsb;
+    if (has_monospace_lsbs) {
+      if (PREDICT_FALSE(!hmtx_buff_in.ReadS16(&lsb))) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+    } else {
+      if (PREDICT_FALSE(!ReadGlyphXMin(&glyf_buff, &loca_buff, loca_format, i,
+          &lsb))) {
+        return FONT_COMPRESSION_FAILURE();
+      }
+    }
+    lsbs.push_back(lsb);
+  }
+
+  // bake me a shiny new hmtx table
+  uint32_t hmtx_output_size = 2 * num_glyphs + 2 * num_hmetrics;
+  if (hmtx_output_size > hmtx_table->dst_length) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+  if (PREDICT_FALSE(static_cast<uint64_t>(hmtx_table->dst_offset +
+      hmtx_table->dst_length) > dst_length)) {
+    return FONT_COMPRESSION_FAILURE();
+  }
+
+  size_t dst_offset = hmtx_table->dst_offset;
+  for (uint32_t i = 0; i < num_glyphs; i++) {
+    if (i < num_hmetrics) {
+      Store16(advance_widths[i], &dst_offset, dst);
+    }
+    Store16(lsbs[i], &dst_offset, dst);
+  }
+
+  return true;
+}
+
 bool ReconstructTransformedGlyf(const uint8_t* transformed_buf,
     size_t transformed_size, const Table* glyf_table, const Table* loca_table,
     uint8_t* dst, size_t dst_length) {
@@ -561,9 +757,11 @@ bool ReconstructTransformedGlyf(const uint8_t* transformed_buf,
                          dst + loca_table->dst_offset, loca_table->dst_length);
 }
 
+// Reconstructs a single font. tables must not contain duplicates.
 bool ReconstructTransformed(const std::vector<Table>& tables, uint32_t tag,
     const uint8_t* transformed_buf, size_t transformed_size,
     uint8_t* dst, size_t dst_length) {
+
   if (tag == kGlyfTableTag) {
     const Table* glyf_table = FindTable(tables, tag);
     const Table* loca_table = FindTable(tables, kLocaTableTag);
@@ -574,6 +772,20 @@ bool ReconstructTransformed(const std::vector<Table>& tables, uint32_t tag,
     if (PREDICT_FALSE(!FindTable(tables, kGlyfTableTag))) {
       return FONT_COMPRESSION_FAILURE();
     }
+  } else if (tag == kHmtxTableTag) {
+    // Tables are sorted for a non-collection.
+    // glyf is before hmtx and includes loca so all our accesses are safe.
+    const Table* glyf_table = FindTable(tables, kGlyfTableTag);
+    const Table* hhea_table = FindTable(tables, kHheaTableTag);
+    const Table* hmtx_table = FindTable(tables, kHmtxTableTag);
+    const Table* loca_table = FindTable(tables, kLocaTableTag);
+    const Table* maxp_table = FindTable(tables, kMaxpTableTag);
+
+    if (PREDICT_FALSE(!ReconstructTransformedHmtx(
+        transformed_buf, transformed_size, glyf_table, hhea_table,
+        hmtx_table, loca_table, maxp_table, dst, dst_length))) {
+      return FONT_COMPRESSION_FAILURE();
+    }
   } else {
     // transform for the tag is not known
     return FONT_COMPRESSION_FAILURE();
@@ -696,15 +908,19 @@ bool ReadTableDirectory(Buffer* file, std::vector<Table>* tables,
     } else {
       tag = kKnownTags[flag_byte & 0x3f];
     }
-    // Bits 6 and 7 are reserved and must be 0.
-    if (PREDICT_FALSE((flag_byte & 0xC0)) != 0) {
-      return FONT_COMPRESSION_FAILURE();
-    }
     uint32_t flags = 0;
-    // Always transform the glyf and loca tables
+    uint8_t xform_version = (flag_byte >> 6) & 0x03;
+
+    // 0 means xform for glyph/loca, non-0 for others
     if (tag == kGlyfTableTag || tag == kLocaTableTag) {
+      if (xform_version == 0) {
         flags |= kWoff2FlagsTransform;
       }
+    } else if (xform_version != 0) {
+      flags |= kWoff2FlagsTransform;
+    }
+    flags |= xform_version;
+
     uint32_t dst_length;
     if (PREDICT_FALSE(!ReadBase128(file, &dst_length))) {
       return FONT_COMPRESSION_FAILURE();
@@ -781,6 +997,29 @@ uint64_t ComputeOffsetToFirstTable(const uint32_t header_version,
   return offset;
 }
 
+bool ReconstructTransformedFont(const std::vector<Table>& tables,
+                                std::map<uint32_t, const uint8_t*>* src_by_dest,
+                                uint8_t* result, size_t result_length) {
+  for (const auto& table : tables) {
+    if ((table.flags & kWoff2FlagsTransform) != kWoff2FlagsTransform) {
+      continue;
+    }
+    const auto it = src_by_dest->find(table.dst_offset);
+    if (it == src_by_dest->end()) {
+      continue;
+    }
+    const uint8_t* transform_buf = (*it).second;
+    src_by_dest->erase(table.dst_offset);
+
+    size_t transform_length = table.transform_length;
+    if (PREDICT_FALSE(!ReconstructTransformed(tables, table.tag,
+            transform_buf, transform_length, result, result_length))) {
+      return FONT_COMPRESSION_FAILURE();
+    }
+  }
+  return true;
+}
+
 bool ConvertWOFF2ToTTF(uint8_t* result, size_t result_length,
                        const uint8_t* data, size_t length) {
   Buffer file(data, length);
@@ -1046,14 +1285,31 @@ bool ConvertWOFF2ToTTF(uint8_t* result, size_t result_length,
                        src_buf, compressed_length))) {
     return FONT_COMPRESSION_FAILURE();
   }
+
+  // round 1, copy across all the unmodified tables
   transform_buf = &uncompressed_buf[0];
+  const uint8_t* const transform_buf_end = &uncompressed_buf[0]
+                                           + uncompressed_buf.size();
+
+  // We wipe out the values as they get written into the final result to dedup
+  std::map<uint32_t, const uint8_t*> src_by_dest;
+  for (uint16_t i = 0; i < num_tables; ++i) {
+    const Table* table = &tables[i];
+    size_t transform_length = table->transform_length;
+
+    src_by_dest[table->dst_offset] = transform_buf;
+
+    if (PREDICT_FALSE(transform_buf + transform_length > transform_buf_end)) {
+      return FONT_COMPRESSION_FAILURE();
+    }
+    transform_buf += transform_length;
+  }
 
   for (uint16_t i = 0; i < num_tables; ++i) {
     const Table* table = &tables[i];
-    uint32_t flags = table->flags;
-    size_t transform_length = table->transform_length;
+    const size_t transform_length = table->transform_length;
 
-    if ((flags & kWoff2FlagsTransform) == 0) {
+    if ((table->flags & kWoff2FlagsTransform) != kWoff2FlagsTransform) {
       if (PREDICT_FALSE(transform_length != table->dst_length)) {
         return FONT_COMPRESSION_FAILURE();
       }
@@ -1061,31 +1317,29 @@ bool ConvertWOFF2ToTTF(uint8_t* result, size_t result_length,
           transform_length) > result_length)) {
         return FONT_COMPRESSION_FAILURE();
       }
+      transform_buf = src_by_dest.at(table->dst_offset);
+      src_by_dest.erase(table->dst_offset);
+      std::memcpy(result + table->dst_offset, transform_buf, transform_length);
+    }
+  }
 
-      std::memcpy(result + table->dst_offset, transform_buf,
-          transform_length);
-    } else {
-      if (header_version) {
-        if (table->tag == kGlyfTableTag) {
-          const Table* loca_table = loca_by_glyf[table];
-          if (PREDICT_FALSE(!ReconstructTransformedGlyf(transform_buf,
-              transform_length, table, loca_table, result, result_length))) {
+  // round 2, reconstruct transformed tables
+  if (PREDICT_FALSE(header_version)) {
+    // Rebuild collection font by font.
+    std::vector<Table> font_tables;
+    for (const auto& ttc_font : ttc_fonts) {
+      font_tables.resize(ttc_font.table_indices.size());
+      for (auto i = 0; i < ttc_font.table_indices.size(); i++) {
+        font_tables[i] = tables[ttc_font.table_indices[i]];
+      }
+      if (PREDICT_FALSE(!ReconstructTransformedFont(font_tables, &src_by_dest,
+                                                    result, result_length))) {
         return FONT_COMPRESSION_FAILURE();
       }
-        } else if (PREDICT_FALSE(table->tag != kLocaTableTag)) {
-          // transform for this tag not known
-          return FONT_COMPRESSION_FAILURE();
     }
   } else {
-        if (PREDICT_FALSE(!ReconstructTransformed(tables, table->tag,
-                transform_buf, transform_length, result, result_length))) {
-          return FONT_COMPRESSION_FAILURE();
-        }
-      }
-    }
-    transform_buf += transform_length;
-    if (PREDICT_FALSE(
-        transform_buf > &uncompressed_buf[0] + uncompressed_buf.size())) {
+    if (PREDICT_FALSE(!ReconstructTransformedFont(tables, &src_by_dest, result,
+                                                  result_length))) {
       return FONT_COMPRESSION_FAILURE();
     }
   }

src/woff2_enc.cc

@@ -34,10 +34,12 @@
 #include "./variable_length.h"
 #include "./woff2_common.h"
 
+
 namespace woff2 {
 
 namespace {
 
+
 using std::string;
 using std::vector;
 
@@ -82,7 +84,7 @@ int KnownTableIndex(uint32_t tag) {
 }
 
 void StoreTableEntry(const Table& table, size_t* offset, uint8_t* dst) {
-  uint8_t flag_byte = KnownTableIndex(table.tag);
+  uint8_t flag_byte = (table.flags & 0xC0) | KnownTableIndex(table.tag);
   dst[(*offset)++] = flag_byte;
   // The index here is treated as a set of flag bytes because
   // bits 6 and 7 of the byte are reserved for future use as flags.
@@ -109,6 +111,7 @@ size_t TableEntrySize(const Table& table) {
 size_t ComputeWoff2Length(const FontCollection& font_collection,
                           const std::vector<Table>& tables,
                           std::map<uint32_t, uint16_t> index_by_offset,
+                          size_t compressed_data_length,
                           size_t extended_metadata_length) {
   size_t size = kWoff2HeaderSize;
 
@@ -137,10 +140,8 @@ size_t ComputeWoff2Length(const FontCollection& font_collection,
   }
 
   // compressed data
-  for (const auto& table : tables) {
-    size += table.dst_length;
+  size += compressed_data_length;
   size = Round4(size);
-  }
 
   size += extended_metadata_length;
   return size;
@@ -217,7 +218,7 @@ bool TransformFontCollection(FontCollection* font_collection) {
   for (auto& font : font_collection->fonts) {
     if (!TransformGlyfAndLocaTables(&font)) {
 #ifdef FONT_COMPRESSION_BIN
-      fprintf(stderr, "Font transformation failed.\n");
+      fprintf(stderr, "glyf/loca transformation failed.\n");
 #endif
       return FONT_COMPRESSION_FAILURE();
     }
@@ -291,6 +292,11 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
     return FONT_COMPRESSION_FAILURE();
   }
 
+#ifdef FONT_COMPRESSION_BIN
+  fprintf(stderr, "Compressed %zu to %u.\n", total_transform_length,
+          total_compressed_length);
+#endif
+
   // Compress the extended metadata
   // TODO(user): how does this apply to collections
   uint32_t compressed_metadata_buf_length =
@@ -331,30 +337,25 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
 
       Table table;
       table.tag = src_table.tag;
-      table.flags = 0;
+      table.flags = src_table.flag_byte;
       table.src_length = src_table.length;
       table.transform_length = src_table.length;
       const uint8_t* transformed_data = src_table.data;
       const Font::Table* transformed_table =
           font.FindTable(src_table.tag ^ 0x80808080);
       if (transformed_table != NULL) {
+        table.flags = transformed_table->flag_byte;
         table.flags |= kWoff2FlagsTransform;
         table.transform_length = transformed_table->length;
         transformed_data = transformed_table->data;
-      }
-      if (tables.empty()) {
-        table.dst_length = total_compressed_length;
-        table.dst_data = &compression_buf[0];
-      } else {
-        table.dst_length = 0;
-        table.dst_data = NULL;
+
       }
       tables.push_back(table);
     }
   }
 
   size_t woff2_length = ComputeWoff2Length(font_collection, tables,
-      index_by_offset, compressed_metadata_buf_length);
+      index_by_offset, total_compressed_length, compressed_metadata_buf_length);
   if (woff2_length > *result_length) {
 #ifdef FONT_COMPRESSION_BIN
     fprintf(stderr, "Result allocation was too small (%zd vs %zd bytes).\n",
@@ -444,10 +445,10 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
   }
 
   // compressed data format (http://www.w3.org/TR/WOFF2/#table_format)
-  for (const auto& table : tables) {
-    StoreBytes(table.dst_data, table.dst_length, &offset, result);
+
+  StoreBytes(&compression_buf[0], total_compressed_length, &offset, result);
   offset = Round4(offset);
-  }
+
   StoreBytes(compressed_metadata_buf.data(), compressed_metadata_buf_length,
              &offset, result);