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.. _transform-section:
Transform
=================
Transformation parsing is controlled by *Transform Policy* and *Transform Events Policy*.
*Transform Policy* configures the adapter
that simplifies application handling of coordinate system transformations (e.g. adapter
may substitute simple transformation steps translate/scale/rotate/skew with corresponding
transformation matrices, more convenient in some cases).
*Transform Events Policy* defines how parsed data is passed to the user code.
Transform Events Policy Concept
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
*Transform Events Policy* depends on compile-time settings in *Transform Policy*.
If ``policy::transform::raw`` *Transform Policy* is used that preserves input data at much as possible
then *Transform Events Policy* becomes::
struct transform_events_policy
{
typedef /*...*/ context_type;
static void transform_matrix(context_type & context, const boost::array<number_type, 6> & matrix);
static void transform_translate(context_type & context, number_type tx, number_type ty);
static void transform_translate(context_type & context, number_type tx);
static void transform_scale(context_type & context, number_type sx, number_type sy);
static void transform_scale(context_type & context, number_type scale);
static void transform_rotate(context_type & context, number_type angle);
static void transform_rotate(context_type & context, number_type angle, number_type cx, number_type cy);
static void transform_skew_x(context_type & context, number_type angle);
static void transform_skew_y(context_type & context, number_type angle);
};
Depending on *Transform Policy*, some of the methods aren't called by SVG++ and therefore shouldn't be implemented.
.. note::
Transformation matrix is passed as array of size 6 ``[a b c d e f]``, corresponding to this matrix:
.. image:: http://www.w3.org/TR/SVG11/images/coords/Matrix.png
:ref:`Named class template parameter <named-params>` for *Transform Events Policy* is ``transform_events_policy``.
Default *Transform Events Policy* (``policy::transform_events::forward_to_method``) forwards calls to its
static methods to methods of ``context`` object::
struct forward_to_method
{
typedef Context context_type;
template<class Number>
static void transform_matrix(context_type & context, const boost::array<Number, 6> & matrix)
{
context.transform_matrix(matrix);
}
/*...*/
};
Example of handling transforms with default settings (``src/samples/sample_transform01.cpp``):
.. literalinclude:: ../../src/samples/sample_transform01.cpp
In this example sequential transforms are joined in user code (``src/samples/sample_transform02.cpp``):
.. literalinclude:: ../../src/samples/sample_transform02.cpp
Transform Policy Concept
^^^^^^^^^^^^^^^^^^^^^^^^^^^
::
struct transform_policy_concept
{
static const bool join_transforms = /* true or false */;
static const bool no_rotate_about_point = /* true or false */;
static const bool no_shorthands = /* true or false */;
static const bool only_matrix_transform = /* true or false */;
};
*Transform Policy* is a class with ``bool`` static member constants. If they all are ``false``
(as in ``policy::transform::raw``), then adapter isn't used and the parser passes parsed values as is.
Setting some members to ``true`` programmer may simplify the application:
``join_transforms = true``
All transformations in SVG attribute are joined in single transformation matrix.
Values of other *Transform Policy* members are ignored.
*Transform Events Policy* in this case contains only one method::
struct transform_events_policy
{
typedef /*...*/ context_type;
static void transform_matrix(context_type & context, const boost::array<number_type, 6> & matrix);
}
``no_rotate_about_point = true``
**rotate(<rotate-angle> <cx> <cy>)** substituted with **translate(<cx>, <cy>) rotate(<rotate-angle>) translate(-<cx>, -<cy>)**.
``transform_rotate`` method of *Transform Events Policy* with parameters ``cx`` and ``cy`` is not used.
``no_shorthands = true``
Calls to ``transform_translate`` and ``transform_scale`` with one number substituted with
corresponding calls with two numbers.
``only_matrix_transform = true``
Each transformation step is substituted with corresponding call to ``transform_matrix``.
Therefore only this method is used in *Transform Events Policy*.
File ``svgpp/policy/transform.hpp`` contains some predefined *Transform Policies*.
``policy::transform::matrix``, used by default, sets ``join_transforms = true``.
:ref:`Named class template parameter <named-params>` for *Transform Policy* is ``transform_policy``.
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