Re: [Audacity-devel] XML code checked in

[Brian G. <bm...@ya...>]

Ok, I will make a project file.

Brian G.

--- Dominic Mazzoni <do...@mi...> wrote:
> Audacity now stores its project files in XML.
> 
> To use the new code, be sure to run "cvs update -d"
> so that you get new directories (lib-src/expat, to
> be specific).  You will need to run configure again,
> as well.
> 
> I'd appreciate it if someone could create a Windows
> project file for expat.  It should be extremely
> simple: the only C files to include are:
> 
>    xmlparse/xmlparse.c
>    xmltok/xmlrole.c
>    xmltok/xmltok.c
> 
> Do not include any of the other ".c" files in the
> project - they're actually included by the other
> C files.
> 
> You'll also have to add one source file from the
> "xml/" directory to audacity.dsp, and hopefully
> everything else will just work.
> 
> On to the implementation details:
> 
> I made some decisions to keep the code as simple as
> possible for now, while allowing for the possibility
> of expanding its functionality later.
> 
> * I'm only using XML tags, no characters.  In other
>    words, all markup, no text.  For example, instead
>    of marking up a label track like this:
> 
>    <labeltrack>
>      <label>
>        <time>0.5</time>
>        <title>red</title>
>      </label>
>      <label>
>        <time>2.3</time>
>        <title>green</title>
>      </label>
>    </labeltrack>
> 
>    ...instead I mark it up like this:
> 
>    <labeltrack>
>      <label time=0.5 title="red" />
>      <label time=2.3 title="green" />
>    </labeltrack>
> 
>    I find that the latter form is not only shorter,
>    but also much simpler to parse.  Thus many tags
>    have required attributes.
> 
>    Audacity will not break if it is given character
>    data (i.e. text outside of tags) - it will just skip
>    over it for now.  If we choose to use character
>    data later, we'll still be able to read old-format
>    files, too.
> 
> * I'm using expat 1.2 as the XML parser.  It's good,
>    clean, cross-platform C code.  There are newer
>    versions of expat under development, but version 1.2
>    is supposed to be stable, and I didn't see any
>    reason not to use it.
> 
>    expat is an event-based parser.  In other words, it
>    uses very few of its own data structures, and we can
>    load very large XML files as they're parsed, rather
>    than having to wait for the whole file to be read in
>    first.
> 
> * There's no XML generator.  I'm just passing a FILE *
>    down the tree, and each class writes valid XML tags
>    to the file, complete with indentation.
> 
>    Later on, we may wish to use an XML generator class.
>    It may make it a lot easier to support Unicode
>    strings, for example.
> 
> * The bridge between Audacity and expat is the class
>    XMLFileReader, in src/xml/XMLFileReader.{cpp,h}.
> 
>    When a project wants to read itself from an XML file,
>    it constructs an XMLFileReader and passes itself as
>    the tag handler.  The XMLFileReader then parses the
>    file, calling the project back when it gets the
>    outermost tag.  When the XMLFileReader gets a child
>    tag, it asks the project to give it a class which can
>    parse the child tag, and it keeps a stack of the
>    handlers as it goes.
> 
>    If that wasn't clear, try looking at the code - it's
>    not that long.
> 
> * Basically, if a class wants to be able to load/save
>    from an XML file, it just needs to inherit from
>    XMLTagHandler (also in src/xml) and implement the
>    following three methods:
> 
>    virtual bool HandleXMLTag(const char *tag, const char **attrs);
>    virtual XMLTagHandler *HandleXMLChild(const char *tag);
>    virtual void WriteXML(int depth, FILE *fp);
> 
>    The methods are commented in src/xml/XMLTagHandler.h,
>    so read that header file for details.
> 
>    Note that a class can return itself in HandleXMLChild.
>    This makes the code cleaner sometimes, by letting a
>    class handle parsing its children.
> 
> The only thing left to do is load/save Envelopes, I
> left that out for now.  Be sure to let me know if you
> find any problems.
> 
> Importing the old project format will be a future
> task, as well.
> 
> - Dominic
> 
> 
> _______________________________________________
> Audacity-devel mailing list
> Aud...@li...
> https://lists.sourceforge.net/lists/listinfo/audacity-devel


__________________________________________________
Do You Yahoo!?
Yahoo! Tax Center - online filing with TurboTax
http://taxes.yahoo.com/