c++ - 使用 PoDoFo 访问/差异数组

Question

这个问题是关于PoDoFo的具体问题图书馆。

如何访问字体资源的编码字典中的 /Differences 数组条目？

从Tf操作符读取字体名称后，我可以通过PoDoFo::PdfPage::GetFromResources获取字体。然而，虽然 PdfFont 类有 PoDoFo::PdfFont::GetEncoding，但我看不出你如何从那里到达 /Differences 数组.

来自 PDFSpec(我只担心 Type 1 字体):

Encoding

(Optional) A specification of the font’s character encoding if different from its built-in encoding. The value of Encoding shall be either the name of a predefined encoding (MacRomanEncoding, MacExpertEncoding, or WinAnsiEncoding, as described in Annex D) or an encoding dictionary that shall specify differences from the font’s built-in encoding or from a specified predefined encoding (see 9.6.6, "Character Encoding").

这是否意味着从 PoDoFo::PdfFont::GetEncoding 返回的 PdfEncoding 对象包含差异数组(如果有的话)？

(我刚才在 PoDoFo 邮件列表上询问过，但在这里发帖是为了看看是否有了解 PoDoFo 和 pdf 的人可以提供帮助)。

Answer 1

PoDoFo 知道许多不同种类的编码类，参见。编码对象工厂:

if (pObject->IsName ())
{
    const PdfName & rName = pObject->GetName ();
    if (rName == PdfName ("WinAnsiEncoding"))
        return PdfEncodingFactory::GlobalWinAnsiEncodingInstance ();
    else if (rName == PdfName ("MacRomanEncoding"))
        return PdfEncodingFactory::GlobalMacRomanEncodingInstance ();
    else if (rName == PdfName ("StandardEncoding"))      // OC 13.08.2010
        return PdfEncodingFactory::GlobalStandardEncodingInstance ();
    else if (rName == PdfName ("MacExpertEncoding"))     // OC 13.08.2010 TODO solved
        return PdfEncodingFactory::GlobalMacExpertEncodingInstance ();
    else if (rName == PdfName ("SymbolEncoding"))        // OC 13.08.2010
        return PdfEncodingFactory::GlobalSymbolEncodingInstance ();
    else if (rName == PdfName ("ZapfDingbatsEncoding"))  // OC 13.08.2010
        return PdfEncodingFactory::GlobalZapfDingbatsEncodingInstance ();
    else if (rName == PdfName ("Identity-H"))
        return new PdfIdentityEncoding ();
}
else if (pObject->HasStream ())     // Code for /ToUnicode object 
{
    return new PdfCMapEncoding(pObject);
}
else if (pObject->IsDictionary ())
{
    return new PdfDifferenceEncoding (pObject);
}

(PoDoFo/src/doc/PdfEncodingObjectFactory.cpp)

您对最后一个案例感兴趣。因此，如果您手头的编码对象是 PdfDifferenceEncoding 的一个实例，您可以使用:

/** PdfDifferenceEncoding is an encoding, which is based
 *  on either the fonts encoding or a predefined encoding
 *  and defines differences to this base encoding.
 */
class PODOFO_DOC_API PdfDifferenceEncoding : public PdfEncoding, private PdfElement {
 public:
[...]
    /** 
     * Get read-only access to the object containing the actual
     * differences.
     *
     * \returns the container with the actual differences
     */
    inline const PdfEncodingDifference & GetDifferences() const;
[...]
};

(PoDoFo/src/doc/PdfDifferenceEncoding.h)

PdfDifferenceEncoding 在同一个头类中声明并提供了一些有趣的方法:

/** A helper class for PdfDifferenceEncoding that
 *  can be used to create a differences array.
 */
class PODOFO_DOC_API PdfEncodingDifference {
    struct TDifference {
        int         nCode;
        PdfName     name;
        pdf_utf16be unicodeValue;
    };

    typedef std::vector<TDifference>                 TVecDifferences;
    typedef std::vector<TDifference>::iterator       TIVecDifferences;
    typedef std::vector<TDifference>::const_iterator TCIVecDifferences;

 public: 
    /** Create a PdfEncodingDifference object.
     */
    PdfEncodingDifference();

    /** Copy a PdfEncodingDifference object.
     */
    PdfEncodingDifference( const PdfEncodingDifference & rhs );

    /** Copy a PdfEncodingDifference object.
     */
    const PdfEncodingDifference & operator=( const PdfEncodingDifference & rhs );

    /** Add a difference to the object.
     * 
     *  \param nCode unicode code point of the difference (0 to 255 are legal values)
     *
     *  \see AddDifference if you know the name of the code point
     *       use the overload below which is faster
     */
    void AddDifference( int nCode );

    /** Add a difference to the object.
     * 
     *  \param nCode unicode code point of the difference (0 to 255 are legal values)
     *  \param rName name of the different code point or .notdef if none
     */
    void AddDifference( int nCode, const PdfName & rName );

    /** Tests if the specified code is part of the 
     *  differences.
     *
     *  \param nCode test if the given code is part of the differences
     *  \param rName write the associated name into this object if the 
     *               code is part of the difference
     *  \param rValue write the associated unicode value of the name to this value 
     *
     *  \returns true if the code is part of the difference
     */
    bool Contains( int nCode, PdfName & rName, pdf_utf16be & rValue ) const;

    /** Convert the PdfEncodingDifference to an array
     *
     *  \param rArray write to this array
     */
    void ToArray( PdfArray & rArray );

    /** Get the number of differences in this object.
     *  If the user added .notdef as a difference it is 
     *  counted, even it is no real difference in the final encoding.
     *  
     *  \returns the number of differences in this object
     */
    inline size_t GetCount() const;

 private:
    struct DifferenceComparatorPredicate {
        public:
          inline bool operator()( const TDifference & rDif1, 
                                  const TDifference & rDif2 ) const { 
              return rDif1.nCode < rDif2.nCode;
          }
    };

    TVecDifferences m_vecDifferences;
};

(PoDoFo/src/doc/PdfDifferenceEncoding.h)