testbed/matplotlib__matplotlib/galleries/users_explain/text/annotations.py

r"""
.. redirect-from:: /gallery/userdemo/annotate_simple01
.. redirect-from:: /gallery/userdemo/annotate_simple02
.. redirect-from:: /gallery/userdemo/annotate_simple03
.. redirect-from:: /gallery/userdemo/annotate_simple04
.. redirect-from:: /gallery/userdemo/anchored_box04
.. redirect-from:: /gallery/userdemo/annotate_simple_coord01
.. redirect-from:: /gallery/userdemo/annotate_simple_coord02
.. redirect-from:: /gallery/userdemo/annotate_simple_coord03
.. redirect-from:: /gallery/userdemo/connect_simple01
.. redirect-from:: /tutorials/text/annotations

.. _annotations:

Annotations
===========

Annotations are graphical elements, often pieces of text, that explain, add
context to, or otherwise highlight some portion of the visualized data.
`~.Axes.annotate` supports a number of coordinate systems for flexibly
positioning data and annotations relative to each other and a variety of
options of for styling the text. Axes.annotate also provides an optional arrow
from the text to the data and this arrow can be styled in various ways.
`~.Axes.text` can also be used for simple text annotation, but does not
provide as much flexibility in positioning and styling as `~.Axes.annotate`.

.. contents:: Table of Contents
   :depth: 3
"""
# %%
# .. _annotations-tutorial:
#
# Basic annotation
# ----------------
#
# In an annotation, there are two points to consider: the location of the data
# being annotated *xy* and the location of the annotation text *xytext*.  Both
# of these arguments are ``(x, y)`` tuples:

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots(figsize=(3, 3))

t = np.arange(0.0, 5.0, 0.01)
s = np.cos(2*np.pi*t)
line, = ax.plot(t, s, lw=2)

ax.annotate('local max', xy=(2, 1), xytext=(3, 1.5),
            arrowprops=dict(facecolor='black', shrink=0.05))
ax.set_ylim(-2, 2)

# %%
# In this example, both the *xy* (arrow tip) and *xytext* locations
# (text location) are in data coordinates.  There are a variety of other
# coordinate systems one can choose -- you can specify the coordinate
# system of *xy* and *xytext* with one of the following strings for
# *xycoords* and *textcoords* (default is 'data')
#
# ==================  ========================================================
# argument            coordinate system
# ==================  ========================================================
# 'figure points'     points from the lower left corner of the figure
# 'figure pixels'     pixels from the lower left corner of the figure
# 'figure fraction'   (0, 0) is lower left of figure and (1, 1) is upper right
# 'axes points'       points from lower left corner of axes
# 'axes pixels'       pixels from lower left corner of axes
# 'axes fraction'     (0, 0) is lower left of axes and (1, 1) is upper right
# 'data'              use the axes data coordinate system
# ==================  ========================================================
#
# The following strings are also valid arguments for *textcoords*
#
# ==================  ========================================================
# argument            coordinate system
# ==================  ========================================================
# 'offset points'     offset (in points) from the xy value
# 'offset pixels'     offset (in pixels) from the xy value
# ==================  ========================================================
#
# For physical coordinate systems (points or pixels) the origin is the
# bottom-left of the figure or axes. Points are
# `typographic points <https://en.wikipedia.org/wiki/Point_(typography)>`_
# meaning that they are a physical unit measuring 1/72 of an inch. Points and
# pixels are discussed in further detail in :ref:`transforms-fig-scale-dpi`.
#
# .. _annotation-data:
#
# Annotating data
# ^^^^^^^^^^^^^^^
#
# This example places the text coordinates in fractional axes coordinates:

fig, ax = plt.subplots(figsize=(3, 3))

t = np.arange(0.0, 5.0, 0.01)
s = np.cos(2*np.pi*t)
line, = ax.plot(t, s, lw=2)

ax.annotate('local max', xy=(2, 1), xycoords='data',
            xytext=(0.01, .99), textcoords='axes fraction',
            va='top', ha='left',
            arrowprops=dict(facecolor='black', shrink=0.05))
ax.set_ylim(-2, 2)

# %%
#
# Annotating an Artist
# ^^^^^^^^^^^^^^^^^^^^
#
# Annotations can be positioned relative to an `.Artist` instance by passing
# that Artist in as *xycoords*. Then *xy* is interpreted as a fraction of the
# Artist's bounding box.

import matplotlib.patches as mpatches

fig, ax = plt.subplots(figsize=(3, 3))
arr = mpatches.FancyArrowPatch((1.25, 1.5), (1.75, 1.5),
                               arrowstyle='->,head_width=.15', mutation_scale=20)
ax.add_patch(arr)
ax.annotate("label", (.5, .5), xycoords=arr, ha='center', va='bottom')
ax.set(xlim=(1, 2), ylim=(1, 2))

# %%
# Here the annotation is placed at position (.5,.5) relative to the arrow's
# lower left corner and is vertically and horizontally at that position.
# Vertically, the bottom aligns to that reference point so that the label
# is above the line. For an example of chaining annotation Artists, see the
# :ref:`Artist section <artist_annotation_coord>` of
# :ref:`annotating_coordinate_systems`.
#
#
# .. _annotation-with-arrow:
#
# Annotating with arrows
# ^^^^^^^^^^^^^^^^^^^^^^
#
# You can enable drawing of an arrow from the text to the annotated point
# by giving a dictionary of arrow properties in the optional keyword
# argument *arrowprops*.
#
# ==================== =====================================================
# *arrowprops* key     description
# ==================== =====================================================
# width                the width of the arrow in points
# frac                 the fraction of the arrow length occupied by the head
# headwidth            the width of the base of the arrow head in points
# shrink               move the tip and base some percent away from
#                      the annotated point and text
#
# \*\*kwargs           any key for :class:`matplotlib.patches.Polygon`,
#                      e.g., ``facecolor``
# ==================== =====================================================
#
# In the example below, the *xy* point is in the data coordinate system
# since *xycoords* defaults to 'data'. For a polar axes, this is in
# (theta, radius) space. The text in this example is placed in the
# fractional figure coordinate system. :class:`matplotlib.text.Text`
# keyword arguments like *horizontalalignment*, *verticalalignment* and
# *fontsize* are passed from `~matplotlib.axes.Axes.annotate` to the
# ``Text`` instance.

fig = plt.figure()
ax = fig.add_subplot(projection='polar')
r = np.arange(0, 1, 0.001)
theta = 2 * 2*np.pi * r
line, = ax.plot(theta, r, color='#ee8d18', lw=3)

ind = 800
thisr, thistheta = r[ind], theta[ind]
ax.plot([thistheta], [thisr], 'o')
ax.annotate('a polar annotation',
            xy=(thistheta, thisr),  # theta, radius
            xytext=(0.05, 0.05),    # fraction, fraction
            textcoords='figure fraction',
            arrowprops=dict(facecolor='black', shrink=0.05),
            horizontalalignment='left',
            verticalalignment='bottom')

# %%
# For more on plotting with arrows, see :ref:`annotation_with_custom_arrow`
#
# .. _annotations-offset-text:
#
# Placing text annotations relative to data
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# Annotations can be positioned at a relative offset to the *xy* input to
# annotation by setting the *textcoords* keyword argument to ``'offset points'``
# or ``'offset pixels'``.

fig, ax = plt.subplots(figsize=(3, 3))
x = [1, 3, 5, 7, 9]
y = [2, 4, 6, 8, 10]
annotations = ["A", "B", "C", "D", "E"]
ax.scatter(x, y, s=20)

for xi, yi, text in zip(x, y, annotations):
    ax.annotate(text,
                xy=(xi, yi), xycoords='data',
                xytext=(1.5, 1.5), textcoords='offset points')

# %%
# The annotations are offset 1.5 points (1.5*1/72 inches) from the *xy* values.
#
# .. _plotting-guide-annotation:
#
# Advanced annotation
# -------------------
#
# We recommend reading :ref:`annotations-tutorial`, :func:`~matplotlib.pyplot.text`
# and :func:`~matplotlib.pyplot.annotate` before reading this section.
#
# Annotating with boxed text
# ^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# `~.Axes.text` takes a *bbox* keyword argument, which draws a box around the
# text:

fig, ax = plt.subplots(figsize=(5, 5))
t = ax.text(0.5, 0.5, "Direction",
            ha="center", va="center", rotation=45, size=15,
            bbox=dict(boxstyle="rarrow,pad=0.3",
                      fc="lightblue", ec="steelblue", lw=2))

# %%
# The arguments are the name of the box style with its attributes as
# keyword arguments. Currently, following box styles are implemented:
#
# ==========   ==============   ==========================
# Class        Name             Attrs
# ==========   ==============   ==========================
# Circle       ``circle``       pad=0.3
# DArrow       ``darrow``       pad=0.3
# Ellipse      ``ellipse``      pad=0.3
# 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
# ==========   ==============   ==========================
#
# .. figure:: /gallery/shapes_and_collections/images/sphx_glr_fancybox_demo_001.png
#    :target: /gallery/shapes_and_collections/fancybox_demo.html
#    :align: center
#
# The patch object (box) associated with the text can be accessed using::
#
#     bb = t.get_bbox_patch()
#
# The return value is a `.FancyBboxPatch`; patch properties
# (facecolor, edgewidth, etc.) can be accessed and modified as usual.
# `.FancyBboxPatch.set_boxstyle` sets the box shape::
#
#    bb.set_boxstyle("rarrow", pad=0.6)
#
# The attribute arguments can also be specified within the style
# name with separating comma::
#
#    bb.set_boxstyle("rarrow, pad=0.6")
#
#
# Defining custom box styles
# ^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# You can use a custom box style. The value for the ``boxstyle`` can be a
# callable object in the following forms:

from matplotlib.path import Path


def custom_box_style(x0, y0, width, height, mutation_size):
    """
    Given the location and size of the box, return the path of the box around
    it. Rotation is automatically taken care of.

    Parameters
    ----------
    x0, y0, width, height : float
       Box location and size.
    mutation_size : float
    Mutation reference scale, typically the text font size.
    """
    # padding
    mypad = 0.3
    pad = mutation_size * mypad
    # width and height with padding added.
    width = width + 2 * pad
    height = height + 2 * pad
    # boundary of the padded box
    x0, y0 = x0 - pad, y0 - pad
    x1, y1 = x0 + width, y0 + height
    # return the new path
    return Path([(x0, y0), (x1, y0), (x1, y1), (x0, y1),
                 (x0-pad, (y0+y1)/2), (x0, y0), (x0, y0)],
                closed=True)

fig, ax = plt.subplots(figsize=(3, 3))
ax.text(0.5, 0.5, "Test", size=30, va="center", ha="center", rotation=30,
        bbox=dict(boxstyle=custom_box_style, alpha=0.2))

# %%
# See also :doc:`/gallery/userdemo/custom_boxstyle01`. Similarly, you can define a
# custom `.ConnectionStyle` and a custom `.ArrowStyle`. View the source code at
# `.patches` to learn how each class is defined.
#
# .. _annotation_with_custom_arrow:
#
# Customizing annotation arrows
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# An arrow connecting *xy* to *xytext* can be optionally drawn by
# specifying the *arrowprops* argument. To draw only an arrow, use
# empty string as the first argument:

fig, ax = plt.subplots(figsize=(3, 3))
ax.annotate("",
            xy=(0.2, 0.2), xycoords='data',
            xytext=(0.8, 0.8), textcoords='data',
            arrowprops=dict(arrowstyle="->", connectionstyle="arc3"))

# %%
# The arrow is drawn as follows:
#
# 1. A path connecting the two points is created, as specified by the
#    *connectionstyle* parameter.
# 2. The path is clipped to avoid patches *patchA* and *patchB*, if these are
#    set.
# 3. The path is further shrunk by *shrinkA* and *shrinkB* (in pixels).
# 4. The path is transmuted to an arrow patch, as specified by the *arrowstyle*
#    parameter.
#
# .. figure:: /gallery/userdemo/images/sphx_glr_annotate_explain_001.png
#    :target: /gallery/userdemo/annotate_explain.html
#    :align: center
#
# The creation of the connecting path between two points is controlled by
# ``connectionstyle`` key and the 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 options can only
# 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 and may be changed in the future).
#
# .. figure:: /gallery/userdemo/images/sphx_glr_connectionstyle_demo_001.png
#    :target: /gallery/userdemo/connectionstyle_demo.html
#    :align: center
#
# 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
# ==========   =============================================
#
# .. figure:: /gallery/text_labels_and_annotations/images/sphx_glr_fancyarrow_demo_001.png
#    :target: /gallery/text_labels_and_annotations/fancyarrow_demo.html
#    :align: center
#
# Some arrowstyles only work with connection styles that generate a
# quadratic-spline segment. They are ``fancy``, ``simple``, and ``wedge``.
# For these arrow styles, you must use the "angle3" or "arc3" connection
# style.
#
# If the annotation string is given, the patch is set to the bbox patch
# of the text by default.

fig, ax = plt.subplots(figsize=(3, 3))

ax.annotate("Test",
            xy=(0.2, 0.2), xycoords='data',
            xytext=(0.8, 0.8), textcoords='data',
            size=20, va="center", ha="center",
            arrowprops=dict(arrowstyle="simple",
                            connectionstyle="arc3,rad=-0.2"))

# %%
# As with `~.Axes.text`, a box around the text can be drawn using the *bbox*
# argument.

fig, ax = plt.subplots(figsize=(3, 3))

ann = ax.annotate("Test",
                  xy=(0.2, 0.2), xycoords='data',
                  xytext=(0.8, 0.8), textcoords='data',
                  size=20, va="center", ha="center",
                  bbox=dict(boxstyle="round4", fc="w"),
                  arrowprops=dict(arrowstyle="-|>",
                                  connectionstyle="arc3,rad=-0.2",
                                  fc="w"))

# %%
# 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.

fig, ax = plt.subplots(figsize=(3, 3))

ann = ax.annotate("Test",
                  xy=(0.2, 0.2), xycoords='data',
                  xytext=(0.8, 0.8), textcoords='data',
                  size=20, va="center", ha="center",
                  bbox=dict(boxstyle="round4", fc="w"),
                  arrowprops=dict(arrowstyle="-|>",
                                  connectionstyle="arc3,rad=0.2",
                                  relpos=(0., 0.),
                                  fc="w"))

ann = ax.annotate("Test",
                  xy=(0.2, 0.2), xycoords='data',
                  xytext=(0.8, 0.8), textcoords='data',
                  size=20, va="center", ha="center",
                  bbox=dict(boxstyle="round4", fc="w"),
                  arrowprops=dict(arrowstyle="-|>",
                                  connectionstyle="arc3,rad=-0.2",
                                  relpos=(1., 0.),
                                  fc="w"))

# %%
# Placing Artist at anchored Axes locations
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# There are classes of artists that can be placed at an anchored
# location in the Axes.  A common example is the legend.  This type
# of artist can be created by using the `.OffsetBox` class. A few
# predefined classes are available in :mod:`matplotlib.offsetbox` and in
# :mod:`mpl_toolkits.axes_grid1.anchored_artists`.

from matplotlib.offsetbox import AnchoredText

fig, ax = plt.subplots(figsize=(3, 3))
at = AnchoredText("Figure 1a",
                  prop=dict(size=15), frameon=True, loc='upper left')
at.patch.set_boxstyle("round,pad=0.,rounding_size=0.2")
ax.add_artist(at)

# %%
# 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
# `~mpl_toolkits.axes_grid1.anchored_artists.AnchoredDrawingArea`. The instance
# is created with a size of the drawing area (in pixels), and arbitrary artists
# can be added to the drawing area. Note that the extents of the artists that are
# added to the drawing area are not related to the placement of the drawing
# area itself. Only the initial size matters.
#
# The artists that are added to the drawing area should not have a
# transform set (it will be overridden) and the dimensions of those
# artists are interpreted as a pixel coordinate, i.e., the radius of the
# circles in above example are 10 pixels and 5 pixels, respectively.

from matplotlib.patches import Circle
from mpl_toolkits.axes_grid1.anchored_artists import AnchoredDrawingArea

fig, ax = plt.subplots(figsize=(3, 3))
ada = AnchoredDrawingArea(40, 20, 0, 0,
                          loc='upper right', 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)
ax.add_artist(ada)

# %%
# Sometimes, you want your artists to scale with the data coordinate (or
# coordinates other than canvas pixels). You can use
# `~mpl_toolkits.axes_grid1.anchored_artists.AnchoredAuxTransformBox` class.
# This is similar to
# `~mpl_toolkits.axes_grid1.anchored_artists.AnchoredDrawingArea` except that
# the extent of the artist is determined during the drawing time respecting the
# specified transform.
#
# The ellipse in the example below will have width and height
# corresponding to 0.1 and 0.4 in data coordinates and will be
# automatically scaled when the view limits of the axes change.

from matplotlib.patches import Ellipse
from mpl_toolkits.axes_grid1.anchored_artists import AnchoredAuxTransformBox

fig, ax = plt.subplots(figsize=(3, 3))
box = AnchoredAuxTransformBox(ax.transData, loc='upper left')
el = Ellipse((0, 0), width=0.1, height=0.4, angle=30)  # in data coordinates!
box.drawing_area.add_artist(el)
ax.add_artist(box)

# %%
# Another method of anchoring an artist relative to a parent axes or anchor
# point is via the *bbox_to_anchor* argument of `.AnchoredOffsetbox`. This
# artist can then be automatically positioned relative to another artist using
# `.HPacker` and `.VPacker`:

from matplotlib.offsetbox import (AnchoredOffsetbox, DrawingArea, HPacker,
                                  TextArea)

fig, ax = plt.subplots(figsize=(3, 3))

box1 = TextArea(" Test: ", textprops=dict(color="k"))
box2 = DrawingArea(60, 20, 0, 0)

el1 = Ellipse((10, 10), width=16, height=5, angle=30, fc="r")
el2 = Ellipse((30, 10), width=16, height=5, angle=170, fc="g")
el3 = Ellipse((50, 10), width=16, height=5, angle=230, fc="b")
box2.add_artist(el1)
box2.add_artist(el2)
box2.add_artist(el3)

box = HPacker(children=[box1, box2],
              align="center",
              pad=0, sep=5)

anchored_box = AnchoredOffsetbox(loc='lower left',
                                 child=box, pad=0.,
                                 frameon=True,
                                 bbox_to_anchor=(0., 1.02),
                                 bbox_transform=ax.transAxes,
                                 borderpad=0.,)

ax.add_artist(anchored_box)
fig.subplots_adjust(top=0.8)

# %%
# Note that, unlike in `.Legend`, the ``bbox_transform`` is set to
# `.IdentityTransform` by default
#
# .. _annotating_coordinate_systems:
#
# Coordinate systems for annotations
# ----------------------------------
#
# Matplotlib Annotations support several types of coordinate systems. The
# examples in :ref:`annotations-tutorial` used the ``data`` coordinate system;
# Some others more advanced options are:
#
# `.Transform` instance
# ^^^^^^^^^^^^^^^^^^^^^
#
# Transforms map coordinates into different coordinate systems, usually the
# display coordinate system. See :ref:`transforms_tutorial` for a detailed
# explanation. Here Transform objects are used to identify the coordinate
# system of the corresponding points. For example, the ``Axes.transAxes``
# transform positions the annotation relative to the Axes coordinates; therefore
# using it is identical to setting the coordinate system to "axes fraction":

fig, (ax1, ax2) = plt.subplots(nrows=1, ncols=2, figsize=(6, 3))
ax1.annotate("Test", xy=(0.2, 0.2), xycoords=ax1.transAxes)
ax2.annotate("Test", xy=(0.2, 0.2), xycoords="axes fraction")

# %%
# Another commonly used `.Transform` instance is ``Axes.transData``. This
# transform  is the coordinate system of the data plotted in the axes. In this
# example, it is used to draw an arrow between related data points in two
# Axes. We have passed an empty text because in this case, the annotation
# connects data points.

x = np.linspace(-1, 1)

fig, (ax1, ax2) = plt.subplots(nrows=1, ncols=2, figsize=(6, 3))
ax1.plot(x, -x**3)
ax2.plot(x, -3*x**2)
ax2.annotate("",
             xy=(0, 0), xycoords=ax1.transData,
             xytext=(0, 0), textcoords=ax2.transData,
             arrowprops=dict(arrowstyle="<->"))

# %%
# .. _artist_annotation_coord:
#
# `.Artist` instance
# ^^^^^^^^^^^^^^^^^^
#
# The *xy* value (or *xytext*) is interpreted as a fractional coordinate of the
# bounding box (bbox) of the artist:

fig, ax = plt.subplots(nrows=1, ncols=1, figsize=(3, 3))
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 an1's bbox
                  xytext=(30, 0), textcoords="offset points",
                  va="center", ha="left",
                  bbox=dict(boxstyle="round", fc="w"),
                  arrowprops=dict(arrowstyle="->"))

# %%
# Note that you must ensure that the extent of the coordinate artist (*an1* in
# this example) is determined before *an2* gets drawn. Usually, this means
# that *an2* needs to be drawn after *an1*. The base class for all bounding
# boxes is `.BboxBase`
#
# Callable that returns `.Transform` of `.BboxBase`
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# A callable object that takes the renderer instance as single argument, and
# returns either a `.Transform` or a `.BboxBase`. For example, the return
# value of `.Artist.get_window_extent` is a bbox, so this method is identical
# to (2) passing in the artist:

fig, ax = plt.subplots(nrows=1, ncols=1, figsize=(3, 3))
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.get_window_extent,
                  xytext=(30, 0), textcoords="offset points",
                  va="center", ha="left",
                  bbox=dict(boxstyle="round", fc="w"),
                  arrowprops=dict(arrowstyle="->"))

# %%
# `.Artist.get_window_extent` is the bounding box of the Axes object and is
# therefore identical to setting the coordinate system to axes fraction:

fig, (ax1, ax2) = plt.subplots(nrows=1, ncols=2, figsize=(6, 3))

an1 = ax1.annotate("Test1", xy=(0.5, 0.5), xycoords="axes fraction")
an2 = ax2.annotate("Test 2", xy=(0.5, 0.5), xycoords=ax2.get_window_extent)

# %%
# Blended coordinate specification
# ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
#
# A blended pair of coordinate specifications -- the first for the
# x-coordinate, and the second is for the y-coordinate. For example, x=0.5 is
# in data coordinates, and y=1 is in normalized axes coordinates:

fig, ax = plt.subplots(figsize=(3, 3))
ax.annotate("Test", xy=(0.5, 1), xycoords=("data", "axes fraction"))
ax.axvline(x=.5, color='lightgray')
ax.set(xlim=(0, 2), ylim=(1, 2))

# %%
# Any of the supported coordinate systems can be used in a blended
# specification. For example, the text "Anchored to 1 & 2" is positioned
# relative to the two `.Text` Artists:

fig, ax = plt.subplots(figsize=(3, 3))

t1 = ax.text(0.05, .05, "Text 1", va='bottom', ha='left')
t2 = ax.text(0.90, .90, "Text 2", ha='right')
t3 = ax.annotate("Anchored to 1 & 2", xy=(0, 0), xycoords=(t1, t2),
                 va='bottom', color='tab:orange',)

# %%
# `.text.OffsetFrom`
# ^^^^^^^^^^^^^^^^^^
#
# Sometimes, you want your annotation with some "offset points", not from the
# annotated point but from some other point or artist. `.text.OffsetFrom` is
# a helper for such cases.

from matplotlib.text import OffsetFrom

fig, ax = plt.subplots(figsize=(3, 3))
an1 = ax.annotate("Test 1", xy=(0.5, 0.5), xycoords="data",
                  va="center", ha="center",
                  bbox=dict(boxstyle="round", fc="w"))

offset_from = OffsetFrom(an1, (0.5, 0))
an2 = ax.annotate("Test 2", xy=(0.1, 0.1), xycoords="data",
                  xytext=(0, -10), textcoords=offset_from,
                  # xytext is offset points from "xy=(0.5, 0), xycoords=an1"
                  va="top", ha="center",
                  bbox=dict(boxstyle="round", fc="w"),
                  arrowprops=dict(arrowstyle="->"))

# %%
# Non-text annotations
# --------------------
#
# .. _using_connectionpatch:
#
# Using ConnectionPatch
# ^^^^^^^^^^^^^^^^^^^^^
#
# `.ConnectionPatch` is like an annotation without text. While `~.Axes.annotate`
# is sufficient in most situations, `.ConnectionPatch` is useful when you want
# to connect points in different axes. For example, here we connect the point
# *xy* in the data coordinates of ``ax1`` to point *xy* in the data coordinates
# of ``ax2``:

from matplotlib.patches import ConnectionPatch

fig, (ax1, ax2) = plt.subplots(nrows=1, ncols=2, figsize=(6, 3))
xy = (0.3, 0.2)
con = ConnectionPatch(xyA=xy, coordsA=ax1.transData,
                      xyB=xy, coordsB=ax2.transData)

fig.add_artist(con)

# %%
# Here, we added the `.ConnectionPatch` to the *figure*
# (with `~.Figure.add_artist`) rather than to either axes. This ensures that
# the ConnectionPatch artist is drawn on top of both axes, and is also necessary
# when using :ref:`constrained_layout <constrainedlayout_guide>`
# for positioning the axes.
#
# Zoom effect between Axes
# ^^^^^^^^^^^^^^^^^^^^^^^^
#
# `mpl_toolkits.axes_grid1.inset_locator` defines some patch classes useful for
# interconnecting two axes.
#
# .. figure:: /gallery/subplots_axes_and_figures/images/sphx_glr_axes_zoom_effect_001.png
#    :target: /gallery/subplots_axes_and_figures/axes_zoom_effect.html
#    :align: center
#
# The code for this figure is at
# :doc:`/gallery/subplots_axes_and_figures/axes_zoom_effect` and
# familiarity with :ref:`transforms_tutorial`
# is recommended.