.. _plotting-guide-annotation:

****************
Annotating Axes
****************

Do not proceed unless you already have read :ref:`annotations-tutorial`,
:func:`~matplotlib.pyplot.text` and
:func:`~matplotlib.pyplot.annotate`!




Annotating with Text with Box
=============================

Let's start with a simple example.

.. plot:: users/plotting/examples/annotate_text_arrow.py


The :func:`~matplotlib.pyplot.text` function in the pyplot module (or
text method of the Axes class) takes bbox keyword argument, and when
given, a box around the text is drawn. ::

    bbox_props = dict(boxstyle="rarrow,pad=0.3", fc="cyan", ec="b", lw=2)
    t = ax.text(0, 0, "Direction", ha="center", va="center", rotation=45,
                size=15,
                bbox=bbox_props)


The patch object associated with the text can be accessed by::

    bb = t.get_bbox_patch()

The return value is an instance of FancyBboxPatch and the patch
properties like facecolor, edgewidth, etc. can be accessed and
modified as usual. To change the shape of the box, use *set_boxstyle*
method. ::

  bb.set_boxstyle("rarrow", pad=0.6)

The arguments are the name of the box style with its attributes as
keyword arguments. Currently, following box styles are implemented.

  ==========   ==============   ==========================
  Class        Name             Attrs
  ==========   ==============   ==========================
  LArrow       ``larrow``       pad=0.3
  RArrow       ``rarrow``       pad=0.3
  Round        ``round``        pad=0.3,rounding_size=None
  Round4       ``round4``       pad=0.3,rounding_size=None
  Roundtooth   ``roundtooth``   pad=0.3,tooth_size=None
  Sawtooth     ``sawtooth``     pad=0.3,tooth_size=None
  Square       ``square``       pad=0.3
  ==========   ==============   ==========================

.. plot:: mpl_examples/pylab_examples/fancybox_demo2.py


Note that the attributes arguments can be specified within the style
name with separating comma (this form can be used as "boxstyle" value
of bbox argument when initializing the text instance) ::

   bb.set_boxstyle("rarrow,pad=0.6")




Annotating with Arrow
=====================

The :func:`~matplotlib.pyplot.annotate` function in the pyplot module
(or annotate method of the Axes class) is used to draw an arrow
connecting two points on the plot. ::

    ax.annotate("Annotation",
                xy=(x1, y1), xycoords='data',
                xytext=(x2, y2), textcoords='offset points',
                )

This annotates a point at ``xy`` in the given coordinate (``xycoords``)
with the text at ``xytext`` given in ``textcoords``. Often, the
annotated point is specified in the *data* coordinate and the annotating
text in *offset points*.
See :func:`~matplotlib.pyplot.annotate` for available coordinate systems.

An arrow connecting two point (xy & xytext) can be optionally drawn by
specifying the ``arrowprops`` argument. To draw only an arrow, use
empty string as the first argument. ::

    ax.annotate("",
                xy=(0.2, 0.2), xycoords='data',
                xytext=(0.8, 0.8), textcoords='data',
                arrowprops=dict(arrowstyle="->",
                                connectionstyle="arc3"),
                )

.. plot:: users/plotting/examples/annotate_simple01.py

The arrow drawing takes a few steps.

1. a connecting path between two points are created. This is
   controlled by ``connectionstyle`` key value.

2. If patch object is given (*patchA* & *patchB*), the path is clipped to
   avoid the patch.

3. The path is further shrunk by given amount of pixels (*shirnkA*
   & *shrinkB*)

4. The path is transmuted to arrow patch, which is controlled by the
   ``arrowstyle`` key value.


.. plot:: users/plotting/examples/annotate_explain.py


The creation of the connecting path between two points is controlled by
``connectionstyle`` key and following styles are available.

   ==========   =============================================
   Name         Attrs
   ==========   =============================================
   ``angle``    angleA=90,angleB=0,rad=0.0
   ``angle3``   angleA=90,angleB=0
   ``arc``      angleA=0,angleB=0,armA=None,armB=None,rad=0.0
   ``arc3``     rad=0.0
   ``bar``      armA=0.0,armB=0.0,fraction=0.3,angle=None
   ==========   =============================================

Note that "3" in ``angle3`` and ``arc3`` is meant to indicate that the
resulting path is a quadratic spline segment (three control
points). As will be discussed below, some arrow style option only can
be used when the connecting path is a quadratic spline.

The behavior of each connection style is (limitedly) demonstrated in the
example below. (Warning : The behavior of the ``bar`` style is currently not
well defined, it may be changed in the future).

.. plot:: users/plotting/examples/connectionstyle_demo.py


The connecting path (after clipping and shrinking) is then mutated to
an arrow patch, according to the given ``arrowstyle``.

    ==========   =============================================
    Name         Attrs
    ==========   =============================================
    ``-``        None
    ``->``       head_length=0.4,head_width=0.2
    ``-[``       widthB=1.0,lengthB=0.2,angleB=None
    ``|-|``      widthA=1.0,widthB=1.0
    ``-|>``      head_length=0.4,head_width=0.2
    ``<-``       head_length=0.4,head_width=0.2
    ``<->``      head_length=0.4,head_width=0.2
    ``<|-``      head_length=0.4,head_width=0.2
    ``<|-|>``    head_length=0.4,head_width=0.2
    ``fancy``    head_length=0.4,head_width=0.4,tail_width=0.4
    ``simple``   head_length=0.5,head_width=0.5,tail_width=0.2
    ``wedge``    tail_width=0.3,shrink_factor=0.5
    ==========   =============================================

.. plot:: mpl_examples/pylab_examples/fancyarrow_demo.py

Some arrowstyles only work with connection style that generates a
quadratic-spline segment. They are ``fancy``, ``simple``, and ``wedge``.
For these arrow styles, you must use "angle3" or "arc3" connection
style.

If the annotation string is given, the patchA is set to the bbox patch
of the text by default.

.. plot:: users/plotting/examples/annotate_simple02.py

As in the text command, a box around the text can be drawn using
the ``bbox`` argument.

.. plot:: users/plotting/examples/annotate_simple03.py

By default, the starting point is set to the center of the text
extent.  This can be adjusted with ``relpos`` key value. The values
are normalized to the extent of the text. For example, (0,0) means
lower-left corner and (1,1) means top-right.

.. plot:: users/plotting/examples/annotate_simple04.py


Placing Artist at the anchored location of the Axes
===================================================

There are class of artist that can be placed at the anchored location
of the Axes. A common example is the legend.  This type of artists can
be created by using the OffsetBox class. A few predefined classes are
available in ``mpl_toolkits.axes_grid.anchored_artists``. ::

    from mpl_toolkits.axes_grid.anchored_artists import AnchoredText
    at = AnchoredText("Figure 1a",
                      prop=dict(size=8), frameon=True,
                      loc=2,
                      )
    at.patch.set_boxstyle("round,pad=0.,rounding_size=0.2")
    ax.add_artist(at)


.. plot:: users/plotting/examples/anchored_box01.py


The *loc* keyword has same meaning as in the legend command.

A simple application is when the size of the artist (or collection of
artists) is known in pixel size during the time of creation. For
example, If you want to draw a circle with fixed size of 20 pixel x 20
pixel (radius = 10 pixel), you can utilize
``AnchoredDrawingArea``. The instance is created with a size of the
drawing area (in pixel). And user can add arbitrary artist to the
drawing area. Note that the extents of the artists that are added to
the drawing area has nothing to do with the placement of the drawing
area itself. The initial size only matters. ::

    from mpl_toolkits.axes_grid.anchored_artists import AnchoredDrawingArea

    ada = AnchoredDrawingArea(20, 20, 0, 0,
                              loc=1, pad=0., frameon=False)
    p1 = Circle((10, 10), 10)
    ada.drawing_area.add_artist(p1)
    p2 = Circle((30, 10), 5, fc="r")
    ada.drawing_area.add_artist(p2)

The artists that are added to the drawing area should not have
transform set (they will be overridden) and the dimension of those
artists are interpreted as a pixel coordinate, i.e., the radius of the
circles in above example are 10 pixel and 5 pixel, respectively.

.. plot:: users/plotting/examples/anchored_box02.py

Sometimes, you want to your artists scale with data coordinate (or
other coordinate than canvas pixel). You can use
``AnchoredAuxTransformBox`` class. This is similar to
``AnchoredDrawingArea`` except that the extent of the artist is
determined during the drawing time respecting the specified transform. ::

  from mpl_toolkits.axes_grid.anchored_artists import AnchoredAuxTransformBox

  box = AnchoredAuxTransformBox(ax.transData, loc=2)
  el = Ellipse((0,0), width=0.1, height=0.4, angle=30) # in data coordinates!
  box.drawing_area.add_artist(el)

The ellipse in the above example will have width and height
corresponds to 0.1 and 0.4 in data coordinate and will be
automatically scaled when the view limits of the axes change.

.. plot:: users/plotting/examples/anchored_box03.py

As in the legend, the bbox_to_anchor argument can be set.  Using the
HPacker and VPacker, you can have an arrangement(?) of artist as in the
legend (as a matter of fact, this is how the legend is created).

.. plot:: users/plotting/examples/anchored_box04.py

Note that unlike the legend, the ``bbox_transform`` is set
to IdentityTransform by default.

Using Complex Coordinate with Annotation
========================================

The Annotation in matplotlib support several types of coordinate as
described in :ref:`annotations-tutorial`. For an advanced user who wants
more control, it supports a few other options.

 1. :class:`~matplotlib.transforms.Transform` instance. For example, ::

      ax.annotate("Test", xy=(0.5, 0.5), xycoords=ax.transAxes)

    is identical to ::

      ax.annotate("Test", xy=(0.5, 0.5), xycoords="axes fraction")

    With this, you can annotate a point in other axes. ::

      ax1, ax2 = subplot(121), subplot(122)
      ax2.annotate("Test", xy=(0.5, 0.5), xycoords=ax1.transData,
                   xytext=(0.5, 0.5), textcoords=ax2.transData,
                   arrowprops=dict(arrowstyle="->"))

 2. :class:`~matplotlib.artist.Artist` instance. The xy value (or
    xytext) is interpreted as a fractional coordinate of the bbox
    (return value of *get_window_extent*) of the artist. ::

      an1 = ax.annotate("Test 1", xy=(0.5, 0.5), xycoords="data",
                        va="center", ha="center",
                        bbox=dict(boxstyle="round", fc="w"))
      an2 = ax.annotate("Test 2", xy=(1, 0.5), xycoords=an1, # (1,0.5) of the an1's bbox
                        xytext=(30,0), textcoords="offset points",
                        va="center", ha="left",
                        bbox=dict(boxstyle="round", fc="w"),
                        arrowprops=dict(arrowstyle="->"))

    .. plot:: users/plotting/examples/annotate_simple_coord01.py

    Note that it is your responsibility that the extent of the
    coordinate artist (*an1* in above example) is determined before *an2*
    gets drawn. In most cases, it means that an2 needs to be drawn
    later than *an1*.


 3. A callable object that returns an instance of either
    :class:`~matplotlib.transforms.BboxBase` or
    :class:`~matplotlib.transforms.Transform`. If a transform is
    returned, it is same as 1 and if bbox is returned, it is same
    as 2.  The callable object should take a single argument of
    renderer instance. For example, following two commands give
    identical results ::

      an2 = ax.annotate("Test 2", xy=(1, 0.5), xycoords=an1,
                        xytext=(30,0), textcoords="offset points")
      an2 = ax.annotate("Test 2", xy=(1, 0.5), xycoords=an1.get_window_extent,
                        xytext=(30,0), textcoords="offset points")


 4. A tuple of two coordinate specification. The first item is for
    x-coordinate and the second is for y-coordinate. For example, ::

      annotate("Test", xy=(0.5, 1), xycoords=("data", "axes fraction"))

    0.5 is in data coordinate, and 1 is in normalized axes coordinate.
    You may use an artist or transform as with a tuple. For example,

    .. plot:: users/plotting/examples/annotate_simple_coord02.py
       :include-source:


 5. Sometimes, you want your annotation with some "offset points", but
    not from the annotated point but from other
    point. :class:`~matplotlib.text.OffsetFrom` is a helper class for such
    case.

    .. plot:: users/plotting/examples/annotate_simple_coord03.py
      :include-source:

    You may take a look at this example :ref:`pylab_examples-annotation_demo3`.

Using ConnectorPatch
====================

The ConnectorPatch is like an annotation without a text.  While the
annotate function is recommended in most of situation, the
ConnectorPatch is useful when you want to connect points in different
axes. ::

  from matplotlib.patches import ConnectionPatch
  xy = (0.2, 0.2)
  con = ConnectionPatch(xyA=xy, xyB=xy, coordsA="data", coordsB="data",
                        axesA=ax1, axesB=ax2)
  ax2.add_artist(con)

The above code connects point xy in data coordinate of ``ax1`` to
point xy int data coordinate of ``ax2``. Here is a simple example.

.. plot:: users/plotting/examples/connect_simple01.py


While the ConnectorPatch instance can be added to any axes, but you
may want it to be added to the axes in the latter (?) of the axes
drawing order to prevent overlap (?) by other axes.




Advanced Topics
***************

Zoom effect between Axes
========================

mpl_toolkits.axes_grid.inset_locator defines some patch classes useful
for interconnect two axes. Understanding the code requires some
knowledge of how mpl's transform works. But, utilizing it will be
straight forward.


.. plot:: mpl_examples/pylab_examples/axes_zoom_effect.py


Define Custom BoxStyle
======================

You can use a custom box style. The value for the ``boxstyle`` can be a
callable object in following forms.::

        def __call__(self, x0, y0, width, height, mutation_size,
                     aspect_ratio=1.):
            """
            Given the location and size of the box, return the path of
            the box around it.

              - *x0*, *y0*, *width*, *height* : location and size of the box
              - *mutation_size* : a reference scale for the mutation.
              - *aspect_ratio* : aspect-ration for the mutation.
            """
            path = ...
	    return path

Here is a complete example.

.. plot:: users/plotting/examples/custom_boxstyle01.py

However, it is recommended that you derive from the
matplotlib.patches.BoxStyle._Base as demonstrated below.

.. plot:: users/plotting/examples/custom_boxstyle02.py
   :include-source:


Similarly, you can define custom ConnectionStyle and custom ArrowStyle.
See the source code of ``lib/matplotlib/patches.py`` and check
how each style class is defined.
