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.. _Associative Sequence: http://www.boost.org/doc/libs/1_55_0/libs/mpl/doc/refmanual/associative-sequence.html
.. _Metafunction Class: http://www.boost.org/doc/libs/1_57_0/libs/mpl/doc/refmanual/metafunction-class.html
Document Traversal
======================
.. _document_traversal:
document_traversal Class
-----------------------------
``document_traversal`` template class is a facade that provides access to most features of SVG++ library.
``document_traversal`` contains only static methods.
Each ``document_traversal`` method receives *context* and *XML element* parameters.
*Context* is a user defined object that will receive parsed data.
*XML element* has :ref:`type <xml_policy_types>` of XML element in chosen XML parser.
:ref:`Named template parameters <named-params>` of ``document_traversal`` class allows to configure
almost each aspect of SVG processing.
::
template<class Args...>
struct document_traversal
{
template<class XMLElement, class Context>
static bool load_document(XMLElement const & xml_root_element, Context & context)
{ return load_expected_element(xml_root_element, context, tag::element::svg()); }
template<class XMLElement, class Context, class ElementTag>
static bool load_expected_element(
XMLElement const & xml_element,
Context & context,
ElementTag expected_element);
template<class RefArgs...>
struct load_referenced_element
{
template<class XMLElement, class Context>
static bool load(XMLElement const & xml_element, Context & parent_context);
};
};
Methods
""""""""""""
::
template<class XMLElement, class Context>
static bool load_document(XMLElement const & xml_root_element, Context & context);
.. _fakeRef3:
``load_document`` - is a shortcut for ``load_expected_element`` that receives root element (**svg**) of SVG document
as ``xml_root_element`` parameter.
::
template<class XMLElement, class Context, class ElementTag>
static bool load_expected_element(
XMLElement const & xml_element,
Context & context,
ElementTag expected_element);
.. _fakeRef4:
``load_expected_element`` loads ``xml_element`` and its descendands and passes parsed data
to ``context``.
``load_expected_element`` expects that XML name of ``xml_element`` corresponds to ``ElementTag``.
Otherwise exception ``unexpected_element_error`` is thrown (see :ref:`Error Policy <error-handling>`).
::
template<class RefArgs...>
template<class XMLElement, class Context>
static bool load_referenced_element<RefArgs...>::load(
XMLElement const & xml_element,
Context & parent_context);
.. _fakeRef5:
``load_referenced_element`` mainly used to load SVG elements that are referenced by other SVG element,
e.g. **use** element or *gradients*.
Unlike ``load_expected_element``, allowed XML name of ``xml_element`` isn't limited to one and is passed
as ``expected_elements`` sequence.
Named class template parameters of ``document_traversal::load_referenced_element``
``expected_elements`` *(required)*
Value is `Associative Sequence`_.
Contains list of tags of expected elements for ``xml_element``.
If XML name of ``xml_element`` doesn't correspond to any from the list, exception
``unexpected_element_error`` (see :ref:`Error Policy <error-handling>`) is thrown.
.. note::
``traits::reusable_elements`` contains list of elements, that can be referenced by **use** element.
.. _referencing_element:
``referencing_element`` *(optional)*
Value is tag of element that references ``xml_element``.
It is used only if *Viewport Policy* requires processing of viewport by SVG++
(for correct processing of **svg** and **symbol** elements, referenced by **image** or **use** elements).
``processed_elements`` or ``ignored_elements`` *(optional)*
Only one may be set.
See :ref:`description <processed_elements>` of ``document_traversal`` parameters with the same names.
Allows to override ``document_traversal`` settings ``processed_elements``/``ignored_elements``
for the passed SVG element. Child elements will be processed with ``document_traversal`` settings.
document_traversal Named Class Template Parameters
--------------------------------------------------------
.. _processed_elements:
``ignored_elements`` and ``processed_elements``
One of them must be set to limit SVG elements processed.
It must be model of `Associative Sequence`_ (e.g. ``boost::mpl::set``),
containing element tags.
If ``processed_elements`` is set, then only the listed elements are processed,
otherwise if ``ignored_elements`` is set, then only non-listed elements are processed.
.. _processed_attributes:
``ignored_attributes`` and ``processed_attributes``
One of them must be set to limit SVG attributes processed.
It must be model of `Associative Sequence`_,
containing attribute tags. Also it may contain pairs <element tag, attribute tag>
like this ``boost::mpl::pair<tag::element::g, tag::attribute::transform>``, such pair
is matched if both processed element and processed attribute matches tags.
If ``processed_attributes`` is set, then only listed attributes are processed,
otherwise if ``ignored_attributes`` is set, then only non-listed attributes are processed.
.. _passthrough_attributes:
``passthrough_attributes`` *(optional)*
Is a `Associative Sequence`_, that contains attribute tags.
Values of listed attributes aren't parsed by SVG++, and passed to the user code as :ref:`string <passing-string>`.
``context_factories`` *(optional)*
See :ref:`context_factories`.
``attribute_traversal_policy`` *(optional)*
See :ref:`attribute_traversal_policy`.
.. _context_factories:
Context Factories
--------------------------------
When ``document_traversal`` traverses SVG tree, it, for each SVG element met, chooses context
to be used to pass attribute values and character data by corresponding *event policy*.
To configure this behavior ``context_factories`` parameter is used.
``context_factories`` parameter accepts `Metafunction Class`_, that receives:
- ``ParentContext`` - parent context type (context used for parent SVG element);
- ``ElementTag`` - element tag (corresponds to the SVG element met),
and returns *Context Factory*.
::
typedef
typename context_factories::template apply<ParentContext, ElementTag>::type
selected_context_factory;
SVG++ provides several *Context Factories*::
template<class ParentContext, class ElementTag>
class factory::context::same;
.. _fakeRef1:
The new context object isn't created, parent context will be used.
``on_enter_element(ElementTag())`` and ``on_exit_element()`` methods of parent context will be called
at the start and at the end of element processing respectively.
::
template<class ChildContext>
class factory::context::on_stack;
.. _fakeRef2:
The new object of type ``ChildContext`` is created on stack.
Constructor of the object is passed with the reference to the parent context.
After element processing is finished, method ``ChildContext::on_exit_element()`` is called before destruction.
Lifetime of context object matches processing of SVG element content (element attributes, child elements and text nodes).
``factory::context::on_stack_with_xml_element`` is the same as ``factory::context::on_stack``,
but ``ChildContext`` constructor receives second parameter - XML element.
Its type depends on XML parser used.
::
template<
class ElementTag,
class ChildContextPtr,
class ChildContext = typename boost::pointee<ChildContextPtr>::type
>
class get_ptr_from_parent;
.. _fakeRef7:
Pointer ``ChildContextPtr`` to context object is requested from parent context by call to the
method ``get_child_context(ElementTag())``. Pointer can be raw pointer or some smart pointer.
``ChildContext::on_exit_element()`` is called after element processing is finished.
.. _attribute_traversal_policy:
Attribute Traversal Policy
-----------------------------------
*Attribute Traversal Policy* configures order and other aspects of SVG attributes and CSS properties processing.
::
struct attribute_traversal_policy_concept
{
static const bool parse_style = /* true or false */;
static const bool css_hides_presentation_attribute = /* true or false */;
typedef /* Metafunction class */ get_priority_attributes_by_element;
typedef /* Metafunction class */ get_deferred_attributes_by_element;
typedef /* Metafunction class */ get_required_attributes_by_element;
};
.. _parse_style:
``parse_style = true``
Contents of **style** attribute is parsed as a sequence of semicolon-separated pairs property-value.
``css_hides_presentation_attribute = true``
Is checked only if ``parse_style = true``.
If the same property is set both in **style** attribute and as a *presentation attribute*,
then only value in **style** attribute will be parsed (it has higher priority according to SVG).
If ``css_hides_presentation_attribute = false``, then memory usage is lower, but both values
(from **style** attribute and a *presentation attribute*) of the same property will be parsed and passed to the user code
in the arbitrary order.
.. _get_priority_attributes_by_element:
``get_priority_attributes_by_element``, ``get_deferred_attributes_by_element`` and ``get_required_attributes_by_element``
They are `Metafunction classes <http://www.boost.org/doc/libs/1_57_0/libs/mpl/doc/refmanual/metafunction-class.html>`_,
receiving element tag and returning
`Forward Sequence <http://www.boost.org/doc/libs/1_57_0/libs/mpl/doc/refmanual/forward-sequence.html>`_ of attribute tags.
Attributes, returned by ``get_priority_attributes_by_element`` metafunction for current element,
will be processed before all others in the same order as in sequence.
Attributes, returned by ``get_deferred_attributes_by_element`` metafunction for current element,
will be processed after all others in the same order as in sequence.
.. _notify_in_priority:
.. note::
Sequences, returned by ``get_priority_attributes_by_element`` and ``get_deferred_attributes_by_element``,
besides attribute tags may contain elements like ``notify_context<EventTag>``.
``EventTag`` is an arbitrary tag, that will be passed to ``notify`` method of the context.
``notify(EventTag())`` will be called right after all previous attributes in the sequence are processed.
If element lacks any attribute from the sequence, returned by ``get_required_attributes_by_element`` metafunction for
this element, then ``required_attribute_not_found_error`` exception will be thrown (see :ref:`Error Policy <error-handling>`).
SVG++ contains definition of ``traits::element_required_attributes`` metafunction
that returns mandatory attributes for element, according to SVG Specification. It can be used like this::
struct my_attribute_traversal_policy
{
/* ... other members ... */
typedef boost::mpl::quote1<traits::element_required_attributes>
get_required_attributes_by_element;
};
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