Initial commit of font compression code into public project.

2012-03-23 11:21:16 -07:00
commit dcecdd883a
49 changed files with 8454 additions and 0 deletions
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+// Copyright 2011 Google Inc. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package com.google.typography.font.compression;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Maps;
+import com.google.typography.font.sfntly.Font;
+import com.google.typography.font.sfntly.Tag;
+import com.google.typography.font.sfntly.table.core.CMap;
+import com.google.typography.font.sfntly.table.core.CMapTable;
+import com.google.typography.font.sfntly.table.core.MaximumProfileTable;
+
+import java.io.ByteArrayOutputStream;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * @author raph@google.com (Raph Levien)
+ *
+ * Experimental CMap encoder, based primarily on writing the _inverse_ encoding.
+ */
+public class CmapEncoder {
+  public static byte[] encode(Font font) {
+    int nGlyphs = font.<MaximumProfileTable>getTable(Tag.maxp).numGlyphs();
+    CMapTable cmapTable = font.getTable(Tag.cmap);
+    CMap cmap = getBestCMap(cmapTable);
+    Map<Integer, Integer> invEncoding = Maps.newHashMap();
+    List<Integer> exceptions = Lists.newArrayList();
+    for (Integer i : cmap) {
+      int glyphId = cmap.glyphId(i);
+      if (invEncoding.containsKey(glyphId)) {
+        exceptions.add(i);
+        exceptions.add(glyphId);
+      } else {
+        invEncoding.put(glyphId, i);
+      }
+    }
+    ByteArrayOutputStream os = new ByteArrayOutputStream();
+    int last = -1;
+    for (int i = 0; i < nGlyphs; i++) {
+      if (invEncoding.containsKey(i)) {
+        int value = invEncoding.get(i);
+        int delta = value - last;
+        writeVShort(os, delta);
+        last = value;
+      } else {
+        writeVShort(os, 0);
+      }
+    }
+    for (int i : exceptions) {
+      writeVShort(os, i);
+    }
+    return os.toByteArray();
+  }
+
+  private static CMap getBestCMap(CMapTable cmapTable) {
+    for (CMap cmap : cmapTable) {
+      if (cmap.format() == CMap.CMapFormat.Format12.value()) {
+        return cmap;
+      }
+    }
+    for (CMap cmap : cmapTable) {
+      if (cmap.format() == CMap.CMapFormat.Format4.value()) {
+        return cmap;
+      }
+    }
+    return null;
+  }
+
+  // A simple signed varint encoding
+  static void writeVShort(ByteArrayOutputStream os, int value) {
+    if (value >= 0x2000 || value < -0x2000) {
+      os.write((byte)(0x80 | ((value >> 14) & 0x7f)));
+    }
+    if (value >= 0x40 || value < -0x40) {
+      os.write((byte)(0x80 | ((value >> 7) & 0x7f)));
+    }
+    os.write((byte)(value & 0x7f));
+  }
+}