字符到字形映射表

Question

我正在关注 apple.com 上的文档。

我设法获得了“cmap”编码子表。我知道 platformID、platformSpecificID 100% 是正确的，但 offset 是可疑的。数据如下：

array(3) {
  [0]=>
  array(3) {
    ["platform_id"]=>
    int(0)
    ["specific_id"]=>
    int(3)
    ["offset"]=>
    int(532)
  }
  [1]=>
  array(3) {
    ["platform_id"]=>
    int(1)
    ["specific_id"]=>
    int(0)
    ["offset"]=>
    int(28)
  }
  [2]=>
  array(3) {
    ["platform_id"]=>
    int(3)
    ["specific_id"]=>
    int(1)
    ["offset"]=>
    int(532)
  }
}

两个表的偏移量相同，532。谁能给我解释一下吗？这是从当前位置还是从文件开头的偏移量？

第 2 部分

好的。因此，我设法使用以下命令获取 format 表：

private function parseCmapTable($table)
{
    $this->position         = $table['offset'];

    // http://developer.apple.com/fonts/ttrefman/RM06/Chap6cmap.html
    // General table information

    $data   = array
    (
        'version'           => $this->getUint16(),
        'number_subtables'  => $this->getUint16(),
    );

    $sub_tables = array();

    for($i = 0; $i < $data['number_subtables']; $i++)
    {

        // http://developer.apple.com/fonts/ttrefman/RM06/Chap6cmap.html
        // The 'cmap' encoding subtables

        $sub_tables[]   = array
        (
            'platform_id'       => $this->getUint16(),
            'specific_id'       => $this->getUint16(),
            'offset'            => $this->getUint32(),
        );

    }

    // http://developer.apple.com/fonts/ttrefman/RM06/Chap6cmap.html
    // The 'cmap' formats

    $formats                = array();

    foreach($sub_tables as $t)
    {
        // http://stackoverflow.com/questions/5322019/character-to-glyph-mapping-table/5322267#5322267

        $this->position = $table['offset'] + $t['offset'];

        $format = array
        (
            'format'                    => $this->getUint16(),
            'length'                    => $this->getUint16(),
            'language'                  => $this->getUint16(),
        );

        if($format['format'] == 4)
        {
            $format     += array
            (
                'seg_count_X2'                  => $this->getUint16(),
                'search_range'                  => $this->getUint16(),
                'entry_selector'                => $this->getUint16(),
                'range_shift'                   => $this->getUint16(),
                'end_code[segCount]'            => $this->getUint16(),
                'reserved_pad'                  => $this->getUint16(),
                'start_code[segCount]'          => $this->getUint16(),
                'id_delta[segCount]'            => $this->getUint16(),
                'id_range_offset[segCount]'     => $this->getUint16(),
                'glyph_index_array[variable]'   => $this->getUint16(),
            );

            $backup = $format;

            $format['seg_count_X2']     = $backup['seg_count_X2']*2;
            $format['search_range']     = 2 * (2 * floor(log($backup['seg_count_X2'], 2)));
            $format['entry_selector']   = log($backup['search_range']/2, 2);
            $format['range_shift']      = (2 * $backup['seg_count_X2']) - $backup['search_range'];
        }

        $formats[$t['offset']]  = $format;
    }       

    die(var_dump( $sub_tables, $formats ));

输出：

array(3) {
[0]=>
  array(3) {
    ["platform_id"]=>
    int(0)
    ["specific_id"]=>
    int(3)
    ["offset"]=>
    int(532)
  }
  [1]=>
  array(3) {
    ["platform_id"]=>
    int(1)
    ["specific_id"]=>
    int(0)
    ["offset"]=>
    int(28)
  }
  [2]=>
  array(3) {
    ["platform_id"]=>
    int(3)
    ["specific_id"]=>
    int(1)
    ["offset"]=>
    int(532)
  }
}
array(2) {
  [532]=>
  array(13) {
    ["format"]=>
    int(4)
    ["length"]=>
    int(658)
    ["language"]=>
    int(0)
    ["seg_count_X2"]=>
    int(192)
    ["search_range"]=>
    float(24)
    ["entry_selector"]=>
    float(5)
    ["range_shift"]=>
    int(128)
    ["end_code[segCount]"]=>
    int(48)
    ["reserved_pad"]=>
    int(58)
    ["start_code[segCount]"]=>
    int(64)
    ["id_delta[segCount]"]=>
    int(69)
    ["id_range_offset[segCount]"]=>
    int(70)
    ["glyph_index_array[variable]"]=>
    int(90)
  }
  [28]=>
  array(3) {
    ["format"]=>
    int(6)
    ["length"]=>
    int(504)
    ["language"]=>
    int(0)
  }
}

现在，我如何从这里获取字符 Unicode 代码？我尝试阅读文档，但对于新手来说太模糊了。

http://developer.apple.com/fonts/ttrefman/RM06/Chap6cmap.html

Answer 1

偏移量是从表的开头开始的。您的数据表明 Mac 表 (platformId 1) 从偏移量 28 开始，而 Unicode (platformId 0) 和 Windows (platformId 3) 映射共享从字节偏移量 532 开始的同一个表。