path: root/doc/reference/text.rst

.. _text:

****
Text
****

.. currentmodule:: cairo

Cairo has two sets of text rendering capabilities:

* The functions with text in their name form cairo's toy text API. The toy API
  takes UTF-8 encoded text and is limited in its functionality to rendering
  simple left-to-right text with no advanced features. That means for example
  that most complex scripts like Hebrew, Arabic, and Indic scripts are out of
  question. No kerning or correct positioning of diacritical marks either. The
  font selection is pretty limited too and doesn't handle the case that the
  selected font does not cover the characters in the text. This set of
  functions are really that, a toy text API, for testing and demonstration
  purposes. Any serious application should avoid them.

* The functions with glyphs in their name form cairo's low-level text API. The
  low-level API relies on the user to convert text to a set of glyph indexes
  and positions. This is a very hard problem and is best handled by external
  libraries, like the pangocairo that is part of the Pango text layout and
  rendering library. Pango is available from http://www.pango.org/.



class FontFace()
================

A *cairo.FontFace* specifies all aspects of a font other than the size or font
matrix (a font matrix is used to distort a font by sheering it or scaling it
unequally in the two directions). A *FontFace* can be set on a
:class:`Context` by using :meth:`Context.set_font_face` the size and font
matrix are set with :meth:`Context.set_font_size` and
:meth:`Context.set_font_matrix`.

There are various types of *FontFace*, depending on the font backend they
use.

.. class:: FontFace()

   .. note:: This class cannot be instantiated directly, it is returned by
     :meth:`Context.get_font_face`.



class ToyFontFace(:class:`FontFace`)
====================================

The *cairo.ToyFontFace* class can be used instead of :meth:`Context.select_font_face` to create a toy font independently of a context.

.. class:: ToyFontFace(family[, slant[, weight]])

   :param family: a font family name
   :type family: str or unicode
   :param slant: the :ref:`FONT_SLANT <constants_FONT_SLANT>` of the font,
     defaults to :data:`cairo.FONT_SLANT_NORMAL`.
   :param weight: the :ref:`FONT_WEIGHT <constants_FONT_WEIGHT>` of the font,
     defaults to :data:`cairo.FONT_WEIGHT_NORMAL`.
   :returns: a new *ToyFontFace*

   Creates a *ToyFontFace* from a triplet of family, slant, and weight. These
   font faces are used in implementation of the the "toy" font API.

   If family is the zero-length string "", the platform-specific default
   family is assumed. The default family then can be queried using
   :meth:`.get_family`.

   The :meth:`Context.select_font_face` method uses this to create font
   faces. See that function for limitations of toy font faces.

   .. versionadded:: 1.8.4

   .. method:: get_family()

      :returns: the family name of a toy font
      :rtype: str

      .. versionadded:: 1.8.4

   .. method:: get_slant()

      :returns: the :ref:`FONT_SLANT <constants_FONT_SLANT>` value

      .. versionadded:: 1.8.4

   .. method:: get_weight()

      :returns: the :ref:`FONT_WEIGHT <constants_FONT_WEIGHT>` value

      .. versionadded:: 1.8.4


class ScaledFont()
==================

A *ScaledFont* is a font scaled to a particular size and device resolution. A
*ScaledFont* is most useful for low-level font usage where a library or
application wants to cache a reference to a scaled font to speed up the
computation of metrics.

There are various types of scaled fonts, depending on the font backend they
use.

.. class:: ScaledFont(font_face, font_matrix, ctm, options)

   :param font_face: a :class:`FontFace` instance
   :param font_matrix: font space to user space transformation :class:`Matrix`
     for the font. In the simplest case of a N point font, this matrix is just
     a scale by N, but it can also be used to shear the font or stretch it
     unequally along the two axes. See :meth:`Context.set_font_matrix`.
   :param ctm: user to device transformation :class:`Matrix` with which the
     font will be used.
   :param options: a :class:`FontOptions` instance to use when getting metrics
     for the font and rendering with it.

   Creates a *ScaledFont* object from a *FontFace* and matrices that describe
   the size of the font and the environment in which it will be used.

   .. method:: extents()

      :returns: (ascent, descent, height, max_x_advance, max_y_advance), a tuple of float values.

      Gets the metrics for a *ScaledFont*.

   .. method:: get_ctm()

      Not implemented in pycairo (yet)

   .. method:: get_font_face()

      :returns: the :class:`FontFace` that this *ScaledFont* was created for.

      .. versionadded:: 1.2

   .. method:: get_font_matrix()

      Not implemented in pycairo (yet)

   .. method:: get_font_options()

      Not implemented in pycairo (yet)

   .. method:: get_scale_matrix()

      :returns: the scale :class:`Matrix`

      The scale matrix is product of the font matrix and the ctm associated
      with the scaled font, and hence is the matrix mapping from font space to
      device space.

      .. versionadded:: 1.8


   .. method:: glyph_extents()

      Not implemented in pycairo (yet)


   .. method:: text_extents(text)

      :param text: text
      :type text: str or unicode
      :returns: (x_bearing, y_bearing, width, height, x_advance, y_advance)
      :rtype: 6-tuple of float

      Gets the extents for a string of text. The extents describe a user-space
      rectangle that encloses the "inked" portion of the text drawn at the
      origin (0,0) (as it would be drawn by :meth:`Context.show_text` if the
      cairo graphics state were set to the same font_face, font_matrix, ctm,
      and font_options as *ScaledFont*).  Additionally, the x_advance and
      y_advance values indicate the amount by which the current point would be
      advanced by :meth:`Context.show_text`.

      Note that whitespace characters do not directly contribute to the size
      of the rectangle (width and height). They do contribute indirectly by
      changing the position of non-whitespace characters. In particular,
      trailing whitespace characters are likely to not affect the size of the
      rectangle, though they will affect the x_advance and y_advance values.

      .. versionadded:: 1.2

   .. method:: text_to_glyphs()

      Not implemented in pycairo (yet)



class FontOptions()
===================

An opaque structure holding all options that are used when rendering fonts.

Individual features of a *FontOptions* can be set or accessed using functions
named *FontOptions.set_<feature_name>* and
*FontOptions.get_<feature_name>*,  like :meth:`FontOptions.set_antialias`
and :meth:`FontOptions.get_antialias`.

New features may be added to a *FontOptions* in the future. For this reason,
:meth:`FontOptions.copy()`, :meth:`FontOptions.equal()`,
:meth:`FontOptions.merge()`, and :meth:`FontOptions.hash()` should be used to
copy, check for equality, merge, or compute a hash value of FontOptions
objects.

.. class:: FontOptions()

   :returns: a newly allocated *FontOptions*.

   Allocates a new *FontOptions* object with all options initialized to default values.

   .. method:: get_antialias()

      :returns: the :ref:`ANTIALIAS <constants_ANTIALIAS>` mode for the *FontOptions* object

   .. method:: get_hint_metrics()

      :returns: the :ref:`HINT METRICS <constants_HINT_METRICS>` mode for the *FontOptions* object

   .. method:: get_hint_style()

      :returns: the :ref:`HINT STYLE <constants_HINT_STYLE>` for the *FontOptions* object

   .. method:: get_subpixel_order()

      :returns: the :ref:`SUBPIXEL_ORDER <constants_SUBPIXEL_ORDER>` for the *FontOptions* object

   .. method:: set_antialias(antialias)

      :param antialias: the :ref:`ANTIALIAS <constants_ANTIALIAS>` mode

      This specifies the type of antialiasing to do when rendering text.

   .. method:: set_hint_metrics(hint_metrics)

      :param hint_metrics: the :ref:`HINT METRICS <constants_HINT_METRICS>` mode

      This controls whether metrics are quantized to integer values in device
      units.

   .. method:: set_hint_style(hint_style)

      :param hint_style: the :ref:`HINT STYLE <constants_HINT_STYLE>`

      This controls whether to fit font outlines to the pixel grid, and if so,
      whether to optimize for fidelity or contrast.

   .. method:: set_subpixel_order(subpixel_order)

      :param subpixel_order: the :ref:`SUBPIXEL_ORDER <constants_SUBPIXEL_ORDER>`

      The subpixel order specifies the order of color elements within each
      pixel on the display device when rendering with an antialiasing mode of
      :data:`cairo.ANTIALIAS_SUBPIXEL`.