如何检查 TrueType 字体中的 cmap table 和 subtable？

Question

A TrueType font program’s built-in encoding maps directly from character codes to glyph descriptions, using an internal data structure called a “cmap”

它继续解释 PDF 处理器的行为取决于字体文件中存在哪些 cmap 子表。

我正在尝试分析使用 fontforge 从 LibreOffice 生成的 PDF 中提取的 .ttf 字体文件。 PDF 使用单字节代码将此字体文件作为简单字体嵌入。当我查看 fontdrop.info 中的 .ttf 文件时，它告诉我“glyphIndexMap”如下：

{"0":0,"2":0,"3":0,"4":0,"5":0,"6":0,"7":0,"8":0,"9":0,"10":0,"11":0,"12":0,"13":0,"14":0,"15":0,"16":0,"17":0,"18":0,"19":0,"20":0,"21":0,"22":0,"23":0,"24":0,"25":0,"26":0,"27":0,"28":0,"29":0,"30":0,"31":0,"32":0,"33":0,"34":0,"35":0,"36":0,"37":0,"38":0,"39":0,"40":0,"41":0,"42":0,"43":0,"44":0,"45":0,"46":0,"47":0,"48":0,"49":0,"50":0,"51":0,"52":0,"53":0,"54":0,"55":0,"56":0,"57":0,"58":0,"59":0,"60":0,"61":0,"62":0,"63":0,"64":0,"65":0,"66":0,"67":0,"68":0,"69":0,"70":0,"71":0,"72":0,"73":0,"74":0,"75":0,"76":0,"77":0,"78":0,"79":0,"80":0,"81":0,"82":0,"83":0,"84":0,"85":0,"86":0,"87":0,"88":0,"89":0,"90":0,"91":0,"92":0,"93":0,"94":0,"95":0,"96":0,"97":0,"98":0,"99":0,"100":0,"101":0,"102":0,"103":0,"104":0,"105":0,"106":0,"107":0,"108":0,"109":0,"110":0,"111":0,"112":0,"113":0,"114":0,"115":0,"116":0,"117":0,"118":0,"119":0,"120":0,"121":0,"122":0,"123":0,"124":0,"125":0,"126":0,"127":0,"160":0,"161":0,"162":0,"163":0,"165":0,"167":0,"168":0,"169":0,"170":0,"171":0,"172":0,"174":0,"175":0,"176":0,"177":0,"180":0,"181":0,"182":0,"183":0,"184":0,"186":0,"187":0,"191":0,"192":0,"193":0,"194":0,"195":0,"196":0,"197":0,"198":0,"199":0,"200":0,"201":0,"202":0,"203":0,"204":0,"205":0,"206":0,"207":0,"209":0,"210":0,"211":0,"212":0,"213":0,"214":0,"216":0,"217":0,"218":0,"219":0,"220":0,"223":0,"224":0,"225":0,"226":0,"227":0,"228":0,"229":0,"230":0,"231":0,"232":0,"233":0,"234":0,"235":0,"236":0,"237":0,"238":0,"239":0,"241":0,"242":0,"243":0,"244":0,"245":0,"246":0,"247":0,"248":0,"249":0,"250":0,"251":0,"252":0,"255":0,"305":0,"338":0,"339":0,"376":0,"402":0,"675":3,"710":0,"711":0,"728":0,"729":0,"730":0,"731":0,"732":0,"733":0,"916":0,"937":0,"960":0,"8211":0,"8212":0,"8216":0,"8217":0,"8218":0,"8220":0,"8221":0,"8222":0,"8224":0,"8225":0,"8226":0,"8230":0,"8240":0,"8249":0,"8250":0,"8260":0,"8364":0,"8482":0,"8706":0,"8719":0,"8721":0,"8730":0,"8734":0,"8747":0,"8776":0,"8800":0,"8804":0,"8805":0,"9674":0,"57374":0,"64257":0,"64258":0}

（有趣的部分是"675":3）

我能理解这个字体包含 4 个字形，索引 3 处的字形是 ʣ 字符（十进制 Unicode 点 675 / U+02A3）。

但在 PDF 中，此字符在文本字符串中用作 <01>，并且没有给出其他编码 - 因此根据 PDF 参考，从 <01> 到字形的映射位于索引 3 必须根据 .ttf 文件中的映射完成：

If no Encoding entry is specified in the font dictionary, the “cmap” subtable with platform ID 1 and encoding 0 will be used to map directly from character codes to glyph descriptions, without any consideration of character names. This is the normal convention for symbolic fonts.

我已确认 PDF 中未指定任何编码条目。以下是使用 qpdf 提取的 /Font 和 /FontDescriptor 对象：

18 0 obj
<<
  /BaseFont /BAAAAA+LiberationSerif
  /FirstChar 0
  /FontDescriptor 20 0 R
  /LastChar 1
  /Subtype /TrueType
  /ToUnicode 21 0 R
  /Type /Font
  /Widths [
    777
    802
  ]
>>
endobj

20 0 obj
<<
  /Ascent 891
  /CapHeight 981
  /Descent -216
  /Flags 4
  /FontBBox [
    -543
    -303
    1277
    981
  ]
  /FontFile2 23 0 R
  /FontName /BAAAAA+LiberationSerif
  /ItalicAngle 0
  /StemV 80
  /Type /FontDescriptor
>>
endobj

那么我如何调查 .ttf 文件以确认“平台 ID 为 1 且编码为 0 的“cmap”子表”已就位并且包含我认为确实存在的映射?

编辑：the PDF in question

Answer 1

How do I inspect the cmap table and subtables in a TrueType font?

OT Master Light，来自 Dutch Type Library，是一个免费工具，对于检查内部字体表非常方便。

Answer 2

使用 OT Master Light 可以看出，cmap 1:0 将字符代码 0x01 映射到字形索引 1（第一个图像，列表中的第二个条目），即 'dz' 符号（第二个图片）。

如何检查 TrueType 字体中的 cmap table 和 subtable？

How do I inspect the cmap table and subtables in a TrueType font?

pdf

fonts

truetype