use expression_factory::parse_from_string not parse_expression in text formatting load_xml

[springmeyer]

No description provided.

[springmeyer]

@herm - was this in your plans? Were re-using the grammars in the fast_cast stuff but it appears we're not yet re-using grammers in the text formatting/placement from_xml parsing. Am I seeing that right?

[springmeyer]

this looks like the performance culprit: https://github.com/mapnik/mapnik/blob/master/src/formatting/text.cpp#L50

[artemp]

@herm did you have a chance to look into this ?

[springmeyer]

It looks to me that being able to pass the grammar through is going to require some serious cleanup and refactoring of the new text formatting/placement stuff. @herm - can you comment on how you see this working?

[artemp]

@herm @springmeyer

this line :

return boost::make_shared<text_node>(parse_expression(data, "utf8"));

expands to :

transcoder tr("utf8");
mapnik::expression_grammar<std::string::const_iterator> grammar(tr);
expression_ptr expr(boost::make_shared<expr_node>(false));
expression_factory::parse_from_string(expr, data, grammar);
return boost::make_shared<text_node>(expr);

which is expensive.