python-matplotlib 1.3.1-1ubuntu5 / usr / share / pyshared / matplotlib / backend_bases.py

"""
Abstract base classes define the primitives that renderers and
graphics contexts must implement to serve as a matplotlib backend

:class:`RendererBase`
    An abstract base class to handle drawing/rendering operations.

:class:`FigureCanvasBase`
    The abstraction layer that separates the
    :class:`matplotlib.figure.Figure` from the backend specific
    details like a user interface drawing area

:class:`GraphicsContextBase`
    An abstract base class that provides color, line styles, etc...

:class:`Event`
    The base class for all of the matplotlib event
    handling.  Derived classes suh as :class:`KeyEvent` and
    :class:`MouseEvent` store the meta data like keys and buttons
    pressed, x and y locations in pixel and
    :class:`~matplotlib.axes.Axes` coordinates.

:class:`ShowBase`
    The base class for the Show class of each interactive backend;
    the 'show' callable is then set to Show.__call__, inherited from
    ShowBase.

"""

from __future__ import division, print_function
import os
import warnings
import time
import io

import numpy as np
import matplotlib.cbook as cbook
import matplotlib.colors as colors
import matplotlib.transforms as transforms
import matplotlib.widgets as widgets
#import matplotlib.path as path
from matplotlib import rcParams
from matplotlib import is_interactive
from matplotlib import get_backend
from matplotlib._pylab_helpers import Gcf

from matplotlib.transforms import Bbox, TransformedBbox, Affine2D

import matplotlib.tight_bbox as tight_bbox
import matplotlib.textpath as textpath
from matplotlib.path import Path
from matplotlib.cbook import mplDeprecation

try:
    from PIL import Image
    _has_pil = True
except ImportError:
    _has_pil = False

_backend_d = {}


def register_backend(format, backend_class):
    _backend_d[format] = backend_class


class ShowBase(object):
    """
    Simple base class to generate a show() callable in backends.

    Subclass must override mainloop() method.
    """
    def __call__(self, block=None):
        """
        Show all figures.  If *block* is not None, then
        it is a boolean that overrides all other factors
        determining whether show blocks by calling mainloop().
        The other factors are:
        it does not block if run inside "ipython --pylab";
        it does not block in interactive mode.
        """
        managers = Gcf.get_all_fig_managers()
        if not managers:
            return

        for manager in managers:
            manager.show()

        if block is not None:
            if block:
                self.mainloop()
                return
            else:
                return

        # Hack: determine at runtime whether we are
        # inside ipython in pylab mode.
        from matplotlib import pyplot
        try:
            ipython_pylab = not pyplot.show._needmain
            # IPython versions >= 0.10 tack the _needmain
            # attribute onto pyplot.show, and always set
            # it to False, when in --pylab mode.
            ipython_pylab = ipython_pylab and get_backend() != 'WebAgg'
            # TODO: The above is a hack to get the WebAgg backend
            # working with `ipython --pylab` until proper integration
            # is implemented.
        except AttributeError:
            ipython_pylab = False

        # Leave the following as a separate step in case we
        # want to control this behavior with an rcParam.
        if ipython_pylab:
            return

        if not is_interactive() or get_backend() == 'WebAgg':
            self.mainloop()

    def mainloop(self):
        pass


class RendererBase:
    """An abstract base class to handle drawing/rendering operations.

    The following methods *must* be implemented in the backend:

    * :meth:`draw_path`
    * :meth:`draw_image`
    * :meth:`draw_text`
    * :meth:`get_text_width_height_descent`

    The following methods *should* be implemented in the backend for
    optimization reasons:

    * :meth:`draw_markers`
    * :meth:`draw_path_collection`
    * :meth:`draw_quad_mesh`
    """
    def __init__(self):
        self._texmanager = None

        self._text2path = textpath.TextToPath()

    def open_group(self, s, gid=None):
        """
        Open a grouping element with label *s*. If *gid* is given, use
        *gid* as the id of the group. Is only currently used by
        :mod:`~matplotlib.backends.backend_svg`.
        """
        pass

    def close_group(self, s):
        """
        Close a grouping element with label *s*
        Is only currently used by :mod:`~matplotlib.backends.backend_svg`
        """
        pass

    def draw_path(self, gc, path, transform, rgbFace=None):
        """
        Draws a :class:`~matplotlib.path.Path` instance using the
        given affine transform.
        """
        raise NotImplementedError

    def draw_markers(self, gc, marker_path, marker_trans, path,
                     trans, rgbFace=None):
        """
        Draws a marker at each of the vertices in path.  This includes
        all vertices, including control points on curves.  To avoid
        that behavior, those vertices should be removed before calling
        this function.

        *gc*
            the :class:`GraphicsContextBase` instance

        *marker_trans*
            is an affine transform applied to the marker.

        *trans*
             is an affine transform applied to the path.

        This provides a fallback implementation of draw_markers that
        makes multiple calls to :meth:`draw_path`.  Some backends may
        want to override this method in order to draw the marker only
        once and reuse it multiple times.
        """
        for vertices, codes in path.iter_segments(trans, simplify=False):
            if len(vertices):
                x, y = vertices[-2:]
                self.draw_path(gc, marker_path,
                               marker_trans +
                               transforms.Affine2D().translate(x, y),
                               rgbFace)

    def draw_path_collection(self, gc, master_transform, paths, all_transforms,
                             offsets, offsetTrans, facecolors, edgecolors,
                             linewidths, linestyles, antialiaseds, urls,
                             offset_position):
        """
        Draws a collection of paths selecting drawing properties from
        the lists *facecolors*, *edgecolors*, *linewidths*,
        *linestyles* and *antialiaseds*. *offsets* is a list of
        offsets to apply to each of the paths.  The offsets in
        *offsets* are first transformed by *offsetTrans* before being
        applied.  *offset_position* may be either "screen" or "data"
        depending on the space that the offsets are in.

        This provides a fallback implementation of
        :meth:`draw_path_collection` that makes multiple calls to
        :meth:`draw_path`.  Some backends may want to override this in
        order to render each set of path data only once, and then
        reference that path multiple times with the different offsets,
        colors, styles etc.  The generator methods
        :meth:`_iter_collection_raw_paths` and
        :meth:`_iter_collection` are provided to help with (and
        standardize) the implementation across backends.  It is highly
        recommended to use those generators, so that changes to the
        behavior of :meth:`draw_path_collection` can be made globally.
        """
        path_ids = []
        for path, transform in self._iter_collection_raw_paths(
                master_transform, paths, all_transforms):
            path_ids.append((path, transform))

        for xo, yo, path_id, gc0, rgbFace in self._iter_collection(
            gc, master_transform, all_transforms, path_ids, offsets,
            offsetTrans, facecolors, edgecolors, linewidths, linestyles,
                antialiaseds, urls, offset_position):
            path, transform = path_id
            transform = transforms.Affine2D(
                            transform.get_matrix()).translate(xo, yo)
            self.draw_path(gc0, path, transform, rgbFace)

    def draw_quad_mesh(self, gc, master_transform, meshWidth, meshHeight,
                       coordinates, offsets, offsetTrans, facecolors,
                       antialiased, edgecolors):
        """
        This provides a fallback implementation of
        :meth:`draw_quad_mesh` that generates paths and then calls
        :meth:`draw_path_collection`.
        """

        from matplotlib.collections import QuadMesh
        paths = QuadMesh.convert_mesh_to_paths(
            meshWidth, meshHeight, coordinates)

        if edgecolors is None:
            edgecolors = facecolors
        linewidths = np.array([gc.get_linewidth()], np.float_)

        return self.draw_path_collection(
            gc, master_transform, paths, [], offsets, offsetTrans, facecolors,
            edgecolors, linewidths, [], [antialiased], [None], 'screen')

    def draw_gouraud_triangle(self, gc, points, colors, transform):
        """
        Draw a Gouraud-shaded triangle.

        *points* is a 3x2 array of (x, y) points for the triangle.

        *colors* is a 3x4 array of RGBA colors for each point of the
        triangle.

        *transform* is an affine transform to apply to the points.
        """
        raise NotImplementedError

    def draw_gouraud_triangles(self, gc, triangles_array, colors_array,
                               transform):
        """
        Draws a series of Gouraud triangles.

        *points* is a Nx3x2 array of (x, y) points for the trianglex.

        *colors* is a Nx3x4 array of RGBA colors for each point of the
        triangles.

        *transform* is an affine transform to apply to the points.
        """
        transform = transform.frozen()
        for tri, col in zip(triangles_array, colors_array):
            self.draw_gouraud_triangle(gc, tri, col, transform)

    def _iter_collection_raw_paths(self, master_transform, paths,
                                   all_transforms):
        """
        This is a helper method (along with :meth:`_iter_collection`) to make
        it easier to write a space-efficent :meth:`draw_path_collection`
        implementation in a backend.

        This method yields all of the base path/transform
        combinations, given a master transform, a list of paths and
        list of transforms.

        The arguments should be exactly what is passed in to
        :meth:`draw_path_collection`.

        The backend should take each yielded path and transform and
        create an object that can be referenced (reused) later.
        """
        Npaths = len(paths)
        Ntransforms = len(all_transforms)
        N = max(Npaths, Ntransforms)

        if Npaths == 0:
            return

        transform = transforms.IdentityTransform()
        for i in xrange(N):
            path = paths[i % Npaths]
            if Ntransforms:
                transform = all_transforms[i % Ntransforms]
            yield path, transform + master_transform

    def _iter_collection(self, gc, master_transform, all_transforms,
                         path_ids, offsets, offsetTrans, facecolors,
                         edgecolors, linewidths, linestyles,
                         antialiaseds, urls, offset_position):
        """
        This is a helper method (along with
        :meth:`_iter_collection_raw_paths`) to make it easier to write
        a space-efficent :meth:`draw_path_collection` implementation in a
        backend.

        This method yields all of the path, offset and graphics
        context combinations to draw the path collection.  The caller
        should already have looped over the results of
        :meth:`_iter_collection_raw_paths` to draw this collection.

        The arguments should be the same as that passed into
        :meth:`draw_path_collection`, with the exception of
        *path_ids*, which is a list of arbitrary objects that the
        backend will use to reference one of the paths created in the
        :meth:`_iter_collection_raw_paths` stage.

        Each yielded result is of the form::

           xo, yo, path_id, gc, rgbFace

        where *xo*, *yo* is an offset; *path_id* is one of the elements of
        *path_ids*; *gc* is a graphics context and *rgbFace* is a color to
        use for filling the path.
        """
        Ntransforms = len(all_transforms)
        Npaths = len(path_ids)
        Noffsets = len(offsets)
        N = max(Npaths, Noffsets)
        Nfacecolors = len(facecolors)
        Nedgecolors = len(edgecolors)
        Nlinewidths = len(linewidths)
        Nlinestyles = len(linestyles)
        Naa = len(antialiaseds)
        Nurls = len(urls)

        if (Nfacecolors == 0 and Nedgecolors == 0) or Npaths == 0:
            return
        if Noffsets:
            toffsets = offsetTrans.transform(offsets)

        gc0 = self.new_gc()
        gc0.copy_properties(gc)

        if Nfacecolors == 0:
            rgbFace = None

        if Nedgecolors == 0:
            gc0.set_linewidth(0.0)

        xo, yo = 0, 0
        for i in xrange(N):
            path_id = path_ids[i % Npaths]
            if Noffsets:
                xo, yo = toffsets[i % Noffsets]
                if offset_position == 'data':
                    if Ntransforms:
                        transform = (all_transforms[i % Ntransforms] +
                                     master_transform)
                    else:
                        transform = master_transform
                    xo, yo = transform.transform_point((xo, yo))
                    xp, yp = transform.transform_point((0, 0))
                    xo = -(xp - xo)
                    yo = -(yp - yo)
            if not (np.isfinite(xo) and np.isfinite(yo)):
                continue
            if Nfacecolors:
                rgbFace = facecolors[i % Nfacecolors]
            if Nedgecolors:
                if Nlinewidths:
                    gc0.set_linewidth(linewidths[i % Nlinewidths])
                if Nlinestyles:
                    gc0.set_dashes(*linestyles[i % Nlinestyles])
                fg = edgecolors[i % Nedgecolors]
                if len(fg) == 4:
                    if fg[3] == 0.0:
                        gc0.set_linewidth(0)
                    else:
                        gc0.set_foreground(fg)
                else:
                    gc0.set_foreground(fg)
            if rgbFace is not None and len(rgbFace) == 4:
                if rgbFace[3] == 0:
                    rgbFace = None
            gc0.set_antialiased(antialiaseds[i % Naa])
            if Nurls:
                gc0.set_url(urls[i % Nurls])

            yield xo, yo, path_id, gc0, rgbFace
        gc0.restore()

    def get_image_magnification(self):
        """
        Get the factor by which to magnify images passed to :meth:`draw_image`.
        Allows a backend to have images at a different resolution to other
        artists.
        """
        return 1.0

    def draw_image(self, gc, x, y, im):
        """
        Draw the image instance into the current axes;

        *gc*
            a GraphicsContext containing clipping information

        *x*
            is the distance in pixels from the left hand side of the canvas.

        *y*
            the distance from the origin.  That is, if origin is
            upper, y is the distance from top.  If origin is lower, y
            is the distance from bottom

        *im*
            the :class:`matplotlib._image.Image` instance
        """
        raise NotImplementedError

    def option_image_nocomposite(self):
        """
        override this method for renderers that do not necessarily
        want to rescale and composite raster images. (like SVG)
        """
        return False

    def option_scale_image(self):
        """
        override this method for renderers that support arbitrary
        scaling of image (most of the vector backend).
        """
        return False

    def draw_tex(self, gc, x, y, s, prop, angle, ismath='TeX!', mtext=None):
        """
        """
        self._draw_text_as_path(gc, x, y, s, prop, angle, ismath="TeX")

    def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
        """
        Draw the text instance

        *gc*
            the :class:`GraphicsContextBase` instance

        *x*
            the x location of the text in display coords

        *y*
            the y location of the text baseline in display coords

        *s*
            the text string

        *prop*
          a :class:`matplotlib.font_manager.FontProperties` instance

        *angle*
            the rotation angle in degrees

        *mtext*
            a :class:`matplotlib.text.Text` instance

        **backend implementers note**

        When you are trying to determine if you have gotten your bounding box
        right (which is what enables the text layout/alignment to work
        properly), it helps to change the line in text.py::

            if 0: bbox_artist(self, renderer)

        to if 1, and then the actual bounding box will be plotted along with
        your text.
        """

        self._draw_text_as_path(gc, x, y, s, prop, angle, ismath)

    def _get_text_path_transform(self, x, y, s, prop, angle, ismath):
        """
        return the text path and transform

        *prop*
          font property

        *s*
          text to be converted

        *usetex*
          If True, use matplotlib usetex mode.

        *ismath*
          If True, use mathtext parser. If "TeX", use *usetex* mode.
        """

        text2path = self._text2path
        fontsize = self.points_to_pixels(prop.get_size_in_points())

        if ismath == "TeX":
            verts, codes = text2path.get_text_path(prop, s, ismath=False,
                                                   usetex=True)
        else:
            verts, codes = text2path.get_text_path(prop, s, ismath=ismath,
                                                   usetex=False)

        path = Path(verts, codes)
        angle = angle / 180. * 3.141592
        if self.flipy():
            transform = Affine2D().scale(fontsize / text2path.FONT_SCALE,
                                         fontsize / text2path.FONT_SCALE)
            transform = transform.rotate(angle).translate(x, self.height - y)
        else:
            transform = Affine2D().scale(fontsize / text2path.FONT_SCALE,
                                         fontsize / text2path.FONT_SCALE)
            transform = transform.rotate(angle).translate(x, y)

        return path, transform

    def _draw_text_as_path(self, gc, x, y, s, prop, angle, ismath):
        """
        draw the text by converting them to paths using textpath module.

        *prop*
          font property

        *s*
          text to be converted

        *usetex*
          If True, use matplotlib usetex mode.

        *ismath*
          If True, use mathtext parser. If "TeX", use *usetex* mode.
        """

        path, transform = self._get_text_path_transform(
            x, y, s, prop, angle, ismath)
        color = gc.get_rgb()

        gc.set_linewidth(0.0)
        self.draw_path(gc, path, transform, rgbFace=color)

    def get_text_width_height_descent(self, s, prop, ismath):
        """
        get the width and height, and the offset from the bottom to the
        baseline (descent), in display coords of the string s with
        :class:`~matplotlib.font_manager.FontProperties` prop
        """
        if ismath == 'TeX':
            # todo: handle props
            size = prop.get_size_in_points()
            texmanager = self._text2path.get_texmanager()
            fontsize = prop.get_size_in_points()
            w, h, d = texmanager.get_text_width_height_descent(s, fontsize,
                                                               renderer=self)
            return w, h, d

        dpi = self.points_to_pixels(72)
        if ismath:
            dims = self._text2path.mathtext_parser.parse(s, dpi, prop)
            return dims[0:3]  # return width, height, descent

        flags = self._text2path._get_hinting_flag()
        font = self._text2path._get_font(prop)
        size = prop.get_size_in_points()
        font.set_size(size, dpi)
        # the width and height of unrotated string
        font.set_text(s, 0.0, flags=flags)
        w, h = font.get_width_height()
        d = font.get_descent()
        w /= 64.0  # convert from subpixels
        h /= 64.0
        d /= 64.0
        return w, h, d

    def flipy(self):
        """
        Return true if y small numbers are top for renderer Is used
        for drawing text (:mod:`matplotlib.text`) and images
        (:mod:`matplotlib.image`) only
        """
        return True

    def get_canvas_width_height(self):
        'return the canvas width and height in display coords'
        return 1, 1

    def get_texmanager(self):
        """
        return the :class:`matplotlib.texmanager.TexManager` instance
        """
        if self._texmanager is None:
            from matplotlib.texmanager import TexManager
            self._texmanager = TexManager()
        return self._texmanager

    def new_gc(self):
        """
        Return an instance of a :class:`GraphicsContextBase`
        """
        return GraphicsContextBase()

    def points_to_pixels(self, points):
        """
        Convert points to display units

        *points*
            a float or a numpy array of float

        return points converted to pixels

        You need to override this function (unless your backend
        doesn't have a dpi, eg, postscript or svg).  Some imaging
        systems assume some value for pixels per inch::

            points to pixels = points * pixels_per_inch/72.0 * dpi/72.0
        """
        return points

    def strip_math(self, s):
        return cbook.strip_math(s)

    def start_rasterizing(self):
        """
        Used in MixedModeRenderer. Switch to the raster renderer.
        """
        pass

    def stop_rasterizing(self):
        """
        Used in MixedModeRenderer. Switch back to the vector renderer
        and draw the contents of the raster renderer as an image on
        the vector renderer.
        """
        pass

    def start_filter(self):
        """
        Used in AggRenderer. Switch to a temporary renderer for image
        filtering effects.
        """
        pass

    def stop_filter(self, filter_func):
        """
        Used in AggRenderer. Switch back to the original renderer.
        The contents of the temporary renderer is processed with the
        *filter_func* and is drawn on the original renderer as an
        image.
        """
        pass


class GraphicsContextBase:
    """
    An abstract base class that provides color, line styles, etc...
    """

    # a mapping from dash styles to suggested offset, dash pairs
    dashd = {
        'solid': (None, None),
        'dashed': (0, (6.0, 6.0)),
        'dashdot': (0, (3.0, 5.0, 1.0, 5.0)),
        'dotted': (0, (1.0, 3.0)),
    }

    def __init__(self):
        self._alpha = 1.0
        self._forced_alpha = False  # if True, _alpha overrides A from RGBA
        self._antialiased = 1  # use 0,1 not True, False for extension code
        self._capstyle = 'butt'
        self._cliprect = None
        self._clippath = None
        self._dashes = None, None
        self._joinstyle = 'round'
        self._linestyle = 'solid'
        self._linewidth = 1
        self._rgb = (0.0, 0.0, 0.0, 1.0)
        self._orig_color = (0.0, 0.0, 0.0, 1.0)
        self._hatch = None
        self._url = None
        self._gid = None
        self._snap = None
        self._sketch = None

    def copy_properties(self, gc):
        'Copy properties from gc to self'
        self._alpha = gc._alpha
        self._forced_alpha = gc._forced_alpha
        self._antialiased = gc._antialiased
        self._capstyle = gc._capstyle
        self._cliprect = gc._cliprect
        self._clippath = gc._clippath
        self._dashes = gc._dashes
        self._joinstyle = gc._joinstyle
        self._linestyle = gc._linestyle
        self._linewidth = gc._linewidth
        self._rgb = gc._rgb
        self._orig_color = gc._orig_color
        self._hatch = gc._hatch
        self._url = gc._url
        self._gid = gc._gid
        self._snap = gc._snap
        self._sketch = gc._sketch

    def restore(self):
        """
        Restore the graphics context from the stack - needed only
        for backends that save graphics contexts on a stack
        """
        pass

    def get_alpha(self):
        """
        Return the alpha value used for blending - not supported on
        all backends
        """
        return self._alpha

    def get_antialiased(self):
        "Return true if the object should try to do antialiased rendering"
        return self._antialiased

    def get_capstyle(self):
        """
        Return the capstyle as a string in ('butt', 'round', 'projecting')
        """
        return self._capstyle

    def get_clip_rectangle(self):
        """
        Return the clip rectangle as a :class:`~matplotlib.transforms.Bbox`
        instance
        """
        return self._cliprect

    def get_clip_path(self):
        """
        Return the clip path in the form (path, transform), where path
        is a :class:`~matplotlib.path.Path` instance, and transform is
        an affine transform to apply to the path before clipping.
        """
        if self._clippath is not None:
            return self._clippath.get_transformed_path_and_affine()
        return None, None

    def get_dashes(self):
        """
        Return the dash information as an offset dashlist tuple.

        The dash list is a even size list that gives the ink on, ink
        off in pixels.

        See p107 of to PostScript `BLUEBOOK
        <http://www-cdf.fnal.gov/offline/PostScript/BLUEBOOK.PDF>`_
        for more info.

        Default value is None
        """
        return self._dashes

    def get_forced_alpha(self):
        """
        Return whether the value given by get_alpha() should be used to
        override any other alpha-channel values.
        """
        return self._forced_alpha

    def get_joinstyle(self):
        """
        Return the line join style as one of ('miter', 'round', 'bevel')
        """
        return self._joinstyle

    def get_linestyle(self, style):
        """
        Return the linestyle: one of ('solid', 'dashed', 'dashdot',
        'dotted').
        """
        return self._linestyle

    def get_linewidth(self):
        """
        Return the line width in points as a scalar
        """
        return self._linewidth

    def get_rgb(self):
        """
        returns a tuple of three or four floats from 0-1.
        """
        return self._rgb

    def get_url(self):
        """
        returns a url if one is set, None otherwise
        """
        return self._url

    def get_gid(self):
        """
        Return the object identifier if one is set, None otherwise.
        """
        return self._gid

    def get_snap(self):
        """
        returns the snap setting which may be:

          * True: snap vertices to the nearest pixel center

          * False: leave vertices as-is

          * None: (auto) If the path contains only rectilinear line
            segments, round to the nearest pixel center
        """
        return self._snap

    def set_alpha(self, alpha):
        """
        Set the alpha value used for blending - not supported on all backends.
        If ``alpha=None`` (the default), the alpha components of the
        foreground and fill colors will be used to set their respective
        transparencies (where applicable); otherwise, ``alpha`` will override
        them.
        """
        if alpha is not None:
            self._alpha = alpha
            self._forced_alpha = True
        else:
            self._alpha = 1.0
            self._forced_alpha = False
        self.set_foreground(self._orig_color)

    def set_antialiased(self, b):
        """
        True if object should be drawn with antialiased rendering
        """

        # use 0, 1 to make life easier on extension code trying to read the gc
        if b:
            self._antialiased = 1
        else:
            self._antialiased = 0

    def set_capstyle(self, cs):
        """
        Set the capstyle as a string in ('butt', 'round', 'projecting')
        """
        if cs in ('butt', 'round', 'projecting'):
            self._capstyle = cs
        else:
            raise ValueError('Unrecognized cap style.  Found %s' % cs)

    def set_clip_rectangle(self, rectangle):
        """
        Set the clip rectangle with sequence (left, bottom, width, height)
        """
        self._cliprect = rectangle

    def set_clip_path(self, path):
        """
        Set the clip path and transformation.  Path should be a
        :class:`~matplotlib.transforms.TransformedPath` instance.
        """
        assert path is None or isinstance(path, transforms.TransformedPath)
        self._clippath = path

    def set_dashes(self, dash_offset, dash_list):
        """
        Set the dash style for the gc.

        *dash_offset*
            is the offset (usually 0).

        *dash_list*
            specifies the on-off sequence as points.
            ``(None, None)`` specifies a solid line

        """
        if dash_list is not None:
            dl = np.asarray(dash_list)
            if np.any(dl <= 0.0):
                raise ValueError("All values in the dash list must be positive")
        self._dashes = dash_offset, dash_list

    def set_foreground(self, fg, isRGBA=False):
        """
        Set the foreground color.  fg can be a MATLAB format string, a
        html hex color string, an rgb or rgba unit tuple, or a float between 0
        and 1.  In the latter case, grayscale is used.

        If you know fg is rgba, set ``isRGBA=True`` for efficiency.
        """
        self._orig_color = fg
        if self._forced_alpha:
            self._rgb = colors.colorConverter.to_rgba(fg, self._alpha)
        elif isRGBA:
            self._rgb = fg
        else:
            self._rgb = colors.colorConverter.to_rgba(fg)

    def set_graylevel(self, frac):
        """
        Set the foreground color to be a gray level with *frac*
        """
        self._orig_color = frac
        self._rgb = (frac, frac, frac, self._alpha)

    def set_joinstyle(self, js):
        """
        Set the join style to be one of ('miter', 'round', 'bevel')
        """
        if js in ('miter', 'round', 'bevel'):
            self._joinstyle = js
        else:
            raise ValueError('Unrecognized join style.  Found %s' % js)

    def set_linewidth(self, w):
        """
        Set the linewidth in points
        """
        self._linewidth = w

    def set_linestyle(self, style):
        """
        Set the linestyle to be one of ('solid', 'dashed', 'dashdot',
        'dotted'). One may specify customized dash styles by providing
        a tuple of (offset, dash pairs). For example, the predefiend
        linestyles have following values.:

         'dashed'  : (0, (6.0, 6.0)),
         'dashdot' : (0, (3.0, 5.0, 1.0, 5.0)),
         'dotted'  : (0, (1.0, 3.0)),
        """

        if style in self.dashd:
            offset, dashes = self.dashd[style]
        elif isinstance(style, tuple):
            offset, dashes = style
        else:
            raise ValueError('Unrecognized linestyle: %s' % str(style))

        self._linestyle = style
        self.set_dashes(offset, dashes)

    def set_url(self, url):
        """
        Sets the url for links in compatible backends
        """
        self._url = url

    def set_gid(self, id):
        """
        Sets the id.
        """
        self._gid = id

    def set_snap(self, snap):
        """
        Sets the snap setting which may be:

          * True: snap vertices to the nearest pixel center

          * False: leave vertices as-is

          * None: (auto) If the path contains only rectilinear line
            segments, round to the nearest pixel center
        """
        self._snap = snap

    def set_hatch(self, hatch):
        """
        Sets the hatch style for filling
        """
        self._hatch = hatch

    def get_hatch(self):
        """
        Gets the current hatch style
        """
        return self._hatch

    def get_hatch_path(self, density=6.0):
        """
        Returns a Path for the current hatch.
        """
        if self._hatch is None:
            return None
        return Path.hatch(self._hatch, density)

    def get_sketch_params(self):
        """
        Returns the sketch parameters for the artist.

        Returns
        -------
        sketch_params : tuple or `None`

        A 3-tuple with the following elements:

          * `scale`: The amplitude of the wiggle perpendicular to the
            source line.

          * `length`: The length of the wiggle along the line.

          * `randomness`: The scale factor by which the length is
            shrunken or expanded.

        May return `None` if no sketch parameters were set.
        """
        return self._sketch

    def set_sketch_params(self, scale=None, length=None, randomness=None):
        """
        Sets the the sketch parameters.

        Parameters
        ----------

        scale : float, optional
            The amplitude of the wiggle perpendicular to the source
            line, in pixels.  If scale is `None`, or not provided, no
            sketch filter will be provided.

        length : float, optional
             The length of the wiggle along the line, in pixels
             (default 128.0)

        randomness : float, optional
            The scale factor by which the length is shrunken or
            expanded (default 16.0)
        """
        if scale is None:
            self._sketch = None
        else:
            self._sketch = (scale, length or 128.0, randomness or 16.0)


class TimerBase(object):
    '''
    A base class for providing timer events, useful for things animations.
    Backends need to implement a few specific methods in order to use their
    own timing mechanisms so that the timer events are integrated into their
    event loops.

    Mandatory functions that must be implemented:

        * `_timer_start`: Contains backend-specific code for starting
          the timer

        * `_timer_stop`: Contains backend-specific code for stopping
          the timer

    Optional overrides:

        * `_timer_set_single_shot`: Code for setting the timer to
          single shot operating mode, if supported by the timer
          object. If not, the `Timer` class itself will store the flag
          and the `_on_timer` method should be overridden to support
          such behavior.

        * `_timer_set_interval`: Code for setting the interval on the
          timer, if there is a method for doing so on the timer
          object.

        * `_on_timer`: This is the internal function that any timer
          object should call, which will handle the task of running
          all callbacks that have been set.

    Attributes:

        * `interval`: The time between timer events in
          milliseconds. Default is 1000 ms.

        * `single_shot`: Boolean flag indicating whether this timer
          should operate as single shot (run once and then
          stop). Defaults to `False`.

        * `callbacks`: Stores list of (func, args) tuples that will be
          called upon timer events. This list can be manipulated
          directly, or the functions `add_callback` and
          `remove_callback` can be used.
    '''
    def __init__(self, interval=None, callbacks=None):
        #Initialize empty callbacks list and setup default settings if necssary
        if callbacks is None:
            self.callbacks = []
        else:
            self.callbacks = callbacks[:]  # Create a copy

        if interval is None:
            self._interval = 1000
        else:
            self._interval = interval

        self._single = False

        # Default attribute for holding the GUI-specific timer object
        self._timer = None

    def __del__(self):
        'Need to stop timer and possibly disconnect timer.'
        self._timer_stop()

    def start(self, interval=None):
        '''
        Start the timer object. `interval` is optional and will be used
        to reset the timer interval first if provided.
        '''
        if interval is not None:
            self._set_interval(interval)
        self._timer_start()

    def stop(self):
        '''
        Stop the timer.
        '''
        self._timer_stop()

    def _timer_start(self):
        pass

    def _timer_stop(self):
        pass

    def _get_interval(self):
        return self._interval

    def _set_interval(self, interval):
        # Force to int since none of the backends actually support fractional
        # milliseconds, and some error or give warnings.
        interval = int(interval)
        self._interval = interval
        self._timer_set_interval()

    interval = property(_get_interval, _set_interval)

    def _get_single_shot(self):
        return self._single

    def _set_single_shot(self, ss=True):
        self._single = ss
        self._timer_set_single_shot()

    single_shot = property(_get_single_shot, _set_single_shot)

    def add_callback(self, func, *args, **kwargs):
        '''
        Register `func` to be called by timer when the event fires. Any
        additional arguments provided will be passed to `func`.
        '''
        self.callbacks.append((func, args, kwargs))

    def remove_callback(self, func, *args, **kwargs):
        '''
        Remove `func` from list of callbacks. `args` and `kwargs` are optional
        and used to distinguish between copies of the same function registered
        to be called with different arguments.
        '''
        if args or kwargs:
            self.callbacks.remove((func, args, kwargs))
        else:
            funcs = [c[0] for c in self.callbacks]
            if func in funcs:
                self.callbacks.pop(funcs.index(func))

    def _timer_set_interval(self):
        'Used to set interval on underlying timer object.'
        pass

    def _timer_set_single_shot(self):
        'Used to set single shot on underlying timer object.'
        pass

    def _on_timer(self):
        '''
        Runs all function that have been registered as callbacks. Functions
        can return False (or 0) if they should not be called any more. If there
        are no callbacks, the timer is automatically stopped.
        '''
        for func, args, kwargs in self.callbacks:
            ret = func(*args, **kwargs)
            # docstring above explains why we use `if ret == False` here,
            # instead of `if not ret`.
            if ret == False:
                self.callbacks.remove((func, args, kwargs))

        if len(self.callbacks) == 0:
            self.stop()


class Event:
    """
    A matplotlib event.  Attach additional attributes as defined in
    :meth:`FigureCanvasBase.mpl_connect`.  The following attributes
    are defined and shown with their default values

    *name*
        the event name

    *canvas*
        the FigureCanvas instance generating the event

    *guiEvent*
        the GUI event that triggered the matplotlib event


    """
    def __init__(self, name, canvas, guiEvent=None):
        self.name = name
        self.canvas = canvas
        self.guiEvent = guiEvent


class IdleEvent(Event):
    """
    An event triggered by the GUI backend when it is idle -- useful
    for passive animation
    """
    pass


class DrawEvent(Event):
    """
    An event triggered by a draw operation on the canvas

    In addition to the :class:`Event` attributes, the following event
    attributes are defined:

    *renderer*
        the :class:`RendererBase` instance for the draw event

    """
    def __init__(self, name, canvas, renderer):
        Event.__init__(self, name, canvas)
        self.renderer = renderer


class ResizeEvent(Event):
    """
    An event triggered by a canvas resize

    In addition to the :class:`Event` attributes, the following event
    attributes are defined:

    *width*
        width of the canvas in pixels

    *height*
        height of the canvas in pixels

    """
    def __init__(self, name, canvas):
        Event.__init__(self, name, canvas)
        self.width, self.height = canvas.get_width_height()


class CloseEvent(Event):
    """
    An event triggered by a figure being closed

    In addition to the :class:`Event` attributes, the following event
    attributes are defined:
    """
    def __init__(self, name, canvas, guiEvent=None):
        Event.__init__(self, name, canvas, guiEvent)


class LocationEvent(Event):
    """
    An event that has a screen location

    The following additional attributes are defined and shown with
    their default values.

    In addition to the :class:`Event` attributes, the following
    event attributes are defined:

    *x*
        x position - pixels from left of canvas

    *y*
        y position - pixels from bottom of canvas

    *inaxes*
        the :class:`~matplotlib.axes.Axes` instance if mouse is over axes

    *xdata*
        x coord of mouse in data coords

    *ydata*
        y coord of mouse in data coords

    """
    x = None       # x position - pixels from left of canvas
    y = None       # y position - pixels from right of canvas
    inaxes = None  # the Axes instance if mouse us over axes
    xdata = None   # x coord of mouse in data coords
    ydata = None   # y coord of mouse in data coords

    # the last event that was triggered before this one
    lastevent = None

    def __init__(self, name, canvas, x, y, guiEvent=None):
        """
        *x*, *y* in figure coords, 0,0 = bottom, left
        """
        Event.__init__(self, name, canvas, guiEvent=guiEvent)
        self.x = x
        self.y = y

        if x is None or y is None:
            # cannot check if event was in axes if no x,y info
            self.inaxes = None
            self._update_enter_leave()
            return

        # Find all axes containing the mouse
        if self.canvas.mouse_grabber is None:
            axes_list = [a for a in self.canvas.figure.get_axes()
                         if a.in_axes(self)]
        else:
            axes_list = [self.canvas.mouse_grabber]

        if len(axes_list) == 0:  # None found
            self.inaxes = None
            self._update_enter_leave()
            return
        elif (len(axes_list) > 1):  # Overlap, get the highest zorder
            axes_list.sort(key=lambda x: x.zorder)
            self.inaxes = axes_list[-1]  # Use the highest zorder
        else:  # Just found one hit
            self.inaxes = axes_list[0]

        try:
            trans = self.inaxes.transData.inverted()
            xdata, ydata = trans.transform_point((x, y))
        except ValueError:
            self.xdata = None
            self.ydata = None
        else:
            self.xdata = xdata
            self.ydata = ydata

        self._update_enter_leave()

    def _update_enter_leave(self):
        'process the figure/axes enter leave events'
        if LocationEvent.lastevent is not None:
            last = LocationEvent.lastevent
            if last.inaxes != self.inaxes:
                # process axes enter/leave events
                try:
                    if last.inaxes is not None:
                        last.canvas.callbacks.process('axes_leave_event', last)
                except:
                    pass
                    # See ticket 2901582.
                    # I think this is a valid exception to the rule
                    # against catching all exceptions; if anything goes
                    # wrong, we simply want to move on and process the
                    # current event.
                if self.inaxes is not None:
                    self.canvas.callbacks.process('axes_enter_event', self)

        else:
            # process a figure enter event
            if self.inaxes is not None:
                self.canvas.callbacks.process('axes_enter_event', self)

        LocationEvent.lastevent = self


class MouseEvent(LocationEvent):
    """
    A mouse event ('button_press_event',
                   'button_release_event',
                   'scroll_event',
                   'motion_notify_event').

    In addition to the :class:`Event` and :class:`LocationEvent`
    attributes, the following attributes are defined:

    *button*
        button pressed None, 1, 2, 3, 'up', 'down' (up and down are used
        for scroll events)

    *key*
        the key depressed when the mouse event triggered (see
        :class:`KeyEvent`)

    *step*
        number of scroll steps (positive for 'up', negative for 'down')


    Example usage::

        def on_press(event):
            print('you pressed', event.button, event.xdata, event.ydata)

        cid = fig.canvas.mpl_connect('button_press_event', on_press)

    """
    x = None         # x position - pixels from left of canvas
    y = None         # y position - pixels from right of canvas
    button = None    # button pressed None, 1, 2, 3
    dblclick = None  # whether or not the event is the result of a double click
    inaxes = None    # the Axes instance if mouse us over axes
    xdata = None     # x coord of mouse in data coords
    ydata = None     # y coord of mouse in data coords
    step = None      # scroll steps for scroll events

    def __init__(self, name, canvas, x, y, button=None, key=None,
                 step=0, dblclick=False, guiEvent=None):
        """
        x, y in figure coords, 0,0 = bottom, left
        button pressed None, 1, 2, 3, 'up', 'down'
        """
        LocationEvent.__init__(self, name, canvas, x, y, guiEvent=guiEvent)
        self.button = button
        self.key = key
        self.step = step
        self.dblclick = dblclick

    def __str__(self):
        return ("MPL MouseEvent: xy=(%d,%d) xydata=(%s,%s) button=%d " +
                "dblclick=%s inaxes=%s") % (self.x, self.y, self.xdata,
                                            self.ydata, self.button,
                                            self.dblclick, self.inaxes)


class PickEvent(Event):
    """
    a pick event, fired when the user picks a location on the canvas
    sufficiently close to an artist.

    Attrs: all the :class:`Event` attributes plus

    *mouseevent*
        the :class:`MouseEvent` that generated the pick

    *artist*
        the :class:`~matplotlib.artist.Artist` picked

    other
        extra class dependent attrs -- eg a
        :class:`~matplotlib.lines.Line2D` pick may define different
        extra attributes than a
        :class:`~matplotlib.collections.PatchCollection` pick event


    Example usage::

        line, = ax.plot(rand(100), 'o', picker=5)  # 5 points tolerance

        def on_pick(event):
            thisline = event.artist
            xdata, ydata = thisline.get_data()
            ind = event.ind
            print('on pick line:', zip(xdata[ind], ydata[ind]))

        cid = fig.canvas.mpl_connect('pick_event', on_pick)

    """
    def __init__(self, name, canvas, mouseevent, artist,
                 guiEvent=None, **kwargs):
        Event.__init__(self, name, canvas, guiEvent)
        self.mouseevent = mouseevent
        self.artist = artist
        self.__dict__.update(kwargs)


class KeyEvent(LocationEvent):
    """
    A key event (key press, key release).

    Attach additional attributes as defined in
    :meth:`FigureCanvasBase.mpl_connect`.

    In addition to the :class:`Event` and :class:`LocationEvent`
    attributes, the following attributes are defined:

    *key*
        the key(s) pressed. Could be **None**, a single case sensitive ascii
        character ("g", "G", "#", etc.), a special key
        ("control", "shift", "f1", "up", etc.) or a
        combination of the above (e.g., "ctrl+alt+g", "ctrl+alt+G").

    .. note::

        Modifier keys will be prefixed to the pressed key and will be in the
        order "ctrl", "alt", "super". The exception to this rule is when the
        pressed key is itself a modifier key, therefore "ctrl+alt" and
        "alt+control" can both be valid key values.


    Example usage::

        def on_key(event):
            print('you pressed', event.key, event.xdata, event.ydata)

        cid = fig.canvas.mpl_connect('key_press_event', on_key)

    """
    def __init__(self, name, canvas, key, x=0, y=0, guiEvent=None):
        LocationEvent.__init__(self, name, canvas, x, y, guiEvent=guiEvent)
        self.key = key


class FigureCanvasBase(object):
    """
    The canvas the figure renders into.

    Public attributes

        *figure*
            A :class:`matplotlib.figure.Figure` instance

      """
    events = [
        'resize_event',
        'draw_event',
        'key_press_event',
        'key_release_event',
        'button_press_event',
        'button_release_event',
        'scroll_event',
        'motion_notify_event',
        'pick_event',
        'idle_event',
        'figure_enter_event',
        'figure_leave_event',
        'axes_enter_event',
        'axes_leave_event',
        'close_event'
    ]

    supports_blit = True

    def __init__(self, figure):
        figure.set_canvas(self)
        self.figure = figure
        # a dictionary from event name to a dictionary that maps cid->func
        self.callbacks = cbook.CallbackRegistry()
        self.widgetlock = widgets.LockDraw()
        self._button = None  # the button pressed
        self._key = None  # the key pressed
        self._lastx, self._lasty = None, None
        self.button_pick_id = self.mpl_connect('button_press_event', self.pick)
        self.scroll_pick_id = self.mpl_connect('scroll_event', self.pick)
        self.mouse_grabber = None  # the axes currently grabbing mouse
        self.toolbar = None  # NavigationToolbar2 will set me
        self._is_saving = False
        if False:
            ## highlight the artists that are hit
            self.mpl_connect('motion_notify_event', self.onHilite)
            ## delete the artists that are clicked on
            #self.mpl_disconnect(self.button_pick_id)
            #self.mpl_connect('button_press_event',self.onRemove)

    def is_saving(self):
        """
        Returns `True` when the renderer is in the process of saving
        to a file, rather than rendering for an on-screen buffer.
        """
        return self._is_saving

    def onRemove(self, ev):
        """
        Mouse event processor which removes the top artist
        under the cursor.  Connect this to the 'mouse_press_event'
        using::

            canvas.mpl_connect('mouse_press_event',canvas.onRemove)
        """
        def sort_artists(artists):
            # This depends on stable sort and artists returned
            # from get_children in z order.
            L = [(h.zorder, h) for h in artists]
            L.sort()
            return [h for zorder, h in L]

        # Find the top artist under the cursor
        under = sort_artists(self.figure.hitlist(ev))
        h = None
        if under:
            h = under[-1]

        # Try deleting that artist, or its parent if you
        # can't delete the artist
        while h:
            if h.remove():
                self.draw_idle()
                break
            parent = None
            for p in under:
                if h in p.get_children():
                    parent = p
                    break
            h = parent

    def onHilite(self, ev):
        """
        Mouse event processor which highlights the artists
        under the cursor.  Connect this to the 'motion_notify_event'
        using::

            canvas.mpl_connect('motion_notify_event',canvas.onHilite)
        """
        if not hasattr(self, '_active'):
            self._active = dict()

        under = self.figure.hitlist(ev)
        enter = [a for a in under if a not in self._active]
        leave = [a for a in self._active if a not in under]
        #print "within:"," ".join([str(x) for x in under])
        #print "entering:",[str(a) for a in enter]
        #print "leaving:",[str(a) for a in leave]
        # On leave restore the captured colour
        for a in leave:
            if hasattr(a, 'get_color'):
                a.set_color(self._active[a])
            elif hasattr(a, 'get_edgecolor'):
                a.set_edgecolor(self._active[a][0])
                a.set_facecolor(self._active[a][1])
            del self._active[a]
        # On enter, capture the color and repaint the artist
        # with the highlight colour.  Capturing colour has to
        # be done first in case the parent recolouring affects
        # the child.
        for a in enter:
            if hasattr(a, 'get_color'):
                self._active[a] = a.get_color()
            elif hasattr(a, 'get_edgecolor'):
                self._active[a] = (a.get_edgecolor(), a.get_facecolor())
            else:
                self._active[a] = None
        for a in enter:
            if hasattr(a, 'get_color'):
                a.set_color('red')
            elif hasattr(a, 'get_edgecolor'):
                a.set_edgecolor('red')
                a.set_facecolor('lightblue')
            else:
                self._active[a] = None
        self.draw_idle()

    def pick(self, mouseevent):
        if not self.widgetlock.locked():
            self.figure.pick(mouseevent)

    def blit(self, bbox=None):
        """
        blit the canvas in bbox (default entire canvas)
        """
        pass

    def resize(self, w, h):
        """
        set the canvas size in pixels
        """
        pass

    def draw_event(self, renderer):
        """
        This method will be call all functions connected to the
        'draw_event' with a :class:`DrawEvent`
        """

        s = 'draw_event'
        event = DrawEvent(s, self, renderer)
        self.callbacks.process(s, event)

    def resize_event(self):
        """
        This method will be call all functions connected to the
        'resize_event' with a :class:`ResizeEvent`
        """

        s = 'resize_event'
        event = ResizeEvent(s, self)
        self.callbacks.process(s, event)

    def close_event(self, guiEvent=None):
        """
        This method will be called by all functions connected to the
        'close_event' with a :class:`CloseEvent`
        """
        s = 'close_event'
        try:
            event = CloseEvent(s, self, guiEvent=guiEvent)
            self.callbacks.process(s, event)
        except (TypeError, AttributeError):
            pass
            # Suppress the TypeError when the python session is being killed.
            # It may be that a better solution would be a mechanism to
            # disconnect all callbacks upon shutdown.
            # AttributeError occurs on OSX with qt4agg upon exiting
            # with an open window; 'callbacks' attribute no longer exists.

    def key_press_event(self, key, guiEvent=None):
        """
        This method will be call all functions connected to the
        'key_press_event' with a :class:`KeyEvent`
        """
        self._key = key
        s = 'key_press_event'
        event = KeyEvent(
            s, self, key, self._lastx, self._lasty, guiEvent=guiEvent)
        self.callbacks.process(s, event)

    def key_release_event(self, key, guiEvent=None):
        """
        This method will be call all functions connected to the
        'key_release_event' with a :class:`KeyEvent`
        """
        s = 'key_release_event'
        event = KeyEvent(
            s, self, key, self._lastx, self._lasty, guiEvent=guiEvent)
        self.callbacks.process(s, event)
        self._key = None

    def pick_event(self, mouseevent, artist, **kwargs):
        """
        This method will be called by artists who are picked and will
        fire off :class:`PickEvent` callbacks registered listeners
        """
        s = 'pick_event'
        event = PickEvent(s, self, mouseevent, artist, **kwargs)
        self.callbacks.process(s, event)

    def scroll_event(self, x, y, step, guiEvent=None):
        """
        Backend derived classes should call this function on any
        scroll wheel event.  x,y are the canvas coords: 0,0 is lower,
        left.  button and key are as defined in MouseEvent.

        This method will be call all functions connected to the
        'scroll_event' with a :class:`MouseEvent` instance.
        """
        if step >= 0:
            self._button = 'up'
        else:
            self._button = 'down'
        s = 'scroll_event'
        mouseevent = MouseEvent(s, self, x, y, self._button, self._key,
                                step=step, guiEvent=guiEvent)
        self.callbacks.process(s, mouseevent)

    def button_press_event(self, x, y, button, dblclick=False, guiEvent=None):
        """
        Backend derived classes should call this function on any mouse
        button press.  x,y are the canvas coords: 0,0 is lower, left.
        button and key are as defined in :class:`MouseEvent`.

        This method will be call all functions connected to the
        'button_press_event' with a :class:`MouseEvent` instance.

        """
        self._button = button
        s = 'button_press_event'
        mouseevent = MouseEvent(s, self, x, y, button, self._key,
                                dblclick=dblclick, guiEvent=guiEvent)
        self.callbacks.process(s, mouseevent)

    def button_release_event(self, x, y, button, guiEvent=None):
        """
        Backend derived classes should call this function on any mouse
        button release.

        *x*
            the canvas coordinates where 0=left

        *y*
            the canvas coordinates where 0=bottom

        *guiEvent*
            the native UI event that generated the mpl event


        This method will be call all functions connected to the
        'button_release_event' with a :class:`MouseEvent` instance.

        """
        s = 'button_release_event'
        event = MouseEvent(s, self, x, y, button, self._key, guiEvent=guiEvent)
        self.callbacks.process(s, event)
        self._button = None

    def motion_notify_event(self, x, y, guiEvent=None):
        """
        Backend derived classes should call this function on any
        motion-notify-event.

        *x*
            the canvas coordinates where 0=left

        *y*
            the canvas coordinates where 0=bottom

        *guiEvent*
            the native UI event that generated the mpl event


        This method will be call all functions connected to the
        'motion_notify_event' with a :class:`MouseEvent` instance.

        """
        self._lastx, self._lasty = x, y
        s = 'motion_notify_event'
        event = MouseEvent(s, self, x, y, self._button, self._key,
                           guiEvent=guiEvent)
        self.callbacks.process(s, event)

    def leave_notify_event(self, guiEvent=None):
        """
        Backend derived classes should call this function when leaving
        canvas

        *guiEvent*
            the native UI event that generated the mpl event

        """

        self.callbacks.process('figure_leave_event', LocationEvent.lastevent)
        LocationEvent.lastevent = None
        self._lastx, self._lasty = None, None

    def enter_notify_event(self, guiEvent=None, xy=None):
        """
        Backend derived classes should call this function when entering
        canvas

        *guiEvent*
            the native UI event that generated the mpl event
        *xy*
            the coordinate location of the pointer when the canvas is
            entered

        """
        if xy is not None:
            x, y = xy
            self._lastx, self._lasty = x, y

        event = Event('figure_enter_event', self, guiEvent)
        self.callbacks.process('figure_enter_event', event)

    def idle_event(self, guiEvent=None):
        """Called when GUI is idle."""
        s = 'idle_event'
        event = IdleEvent(s, self, guiEvent=guiEvent)
        self.callbacks.process(s, event)

    def grab_mouse(self, ax):
        """
        Set the child axes which are currently grabbing the mouse events.
        Usually called by the widgets themselves.
        It is an error to call this if the mouse is already grabbed by
        another axes.
        """
        if self.mouse_grabber not in (None, ax):
            raise RuntimeError('two different attempted to grab mouse input')
        self.mouse_grabber = ax

    def release_mouse(self, ax):
        """
        Release the mouse grab held by the axes, ax.
        Usually called by the widgets.
        It is ok to call this even if you ax doesn't have the mouse
        grab currently.
        """
        if self.mouse_grabber is ax:
            self.mouse_grabber = None

    def draw(self, *args, **kwargs):
        """
        Render the :class:`~matplotlib.figure.Figure`
        """
        pass

    def draw_idle(self, *args, **kwargs):
        """
        :meth:`draw` only if idle; defaults to draw but backends can overrride
        """
        self.draw(*args, **kwargs)

    def draw_cursor(self, event):
        """
        Draw a cursor in the event.axes if inaxes is not None.  Use
        native GUI drawing for efficiency if possible
        """
        pass

    def get_width_height(self):
        """
        Return the figure width and height in points or pixels
        (depending on the backend), truncated to integers
        """
        return int(self.figure.bbox.width), int(self.figure.bbox.height)

    filetypes = {
        'eps': 'Encapsulated Postscript',
        'pdf': 'Portable Document Format',
        'pgf': 'LaTeX PGF Figure',
        'png': 'Portable Network Graphics',
        'ps': 'Postscript',
        'raw': 'Raw RGBA bitmap',
        'rgba': 'Raw RGBA bitmap',
        'svg': 'Scalable Vector Graphics',
        'svgz': 'Scalable Vector Graphics'}

    # All of these print_* functions do a lazy import because
    #  a) otherwise we'd have cyclical imports, since all of these
    #     classes inherit from FigureCanvasBase
    #  b) so we don't import a bunch of stuff the user may never use

    # TODO: these print_* throw ImportErrror when called from
    # compare_images_decorator (decorators.py line 112)
    # if the backend has not already been loaded earlier on.  Simple trigger:
    # >>> import matplotlib.tests.test_spines
    # >>> list(matplotlib.tests.test_spines.test_spines_axes_positions())[0][0]()

    def print_eps(self, *args, **kwargs):
        from backends.backend_ps import FigureCanvasPS  # lazy import
        ps = self.switch_backends(FigureCanvasPS)
        return ps.print_eps(*args, **kwargs)

    def print_pdf(self, *args, **kwargs):
        from backends.backend_pdf import FigureCanvasPdf  # lazy import
        pdf = self.switch_backends(FigureCanvasPdf)
        return pdf.print_pdf(*args, **kwargs)

    def print_pgf(self, *args, **kwargs):
        from backends.backend_pgf import FigureCanvasPgf  # lazy import
        pgf = self.switch_backends(FigureCanvasPgf)
        return pgf.print_pgf(*args, **kwargs)

    def print_png(self, *args, **kwargs):
        from backends.backend_agg import FigureCanvasAgg  # lazy import
        agg = self.switch_backends(FigureCanvasAgg)
        return agg.print_png(*args, **kwargs)

    def print_ps(self, *args, **kwargs):
        from backends.backend_ps import FigureCanvasPS  # lazy import
        ps = self.switch_backends(FigureCanvasPS)
        return ps.print_ps(*args, **kwargs)

    def print_raw(self, *args, **kwargs):
        from backends.backend_agg import FigureCanvasAgg  # lazy import
        agg = self.switch_backends(FigureCanvasAgg)
        return agg.print_raw(*args, **kwargs)
    print_bmp = print_rgba = print_raw

    def print_svg(self, *args, **kwargs):
        from backends.backend_svg import FigureCanvasSVG  # lazy import
        svg = self.switch_backends(FigureCanvasSVG)
        return svg.print_svg(*args, **kwargs)

    def print_svgz(self, *args, **kwargs):
        from backends.backend_svg import FigureCanvasSVG  # lazy import
        svg = self.switch_backends(FigureCanvasSVG)
        return svg.print_svgz(*args, **kwargs)

    if _has_pil:
        filetypes['jpg'] = 'Joint Photographic Experts Group'
        filetypes['jpeg'] = filetypes['jpg']

        def print_jpg(self, filename_or_obj, *args, **kwargs):
            """
            Supported kwargs:

            *quality*: The image quality, on a scale from 1 (worst) to
                95 (best). The default is 95, if not given in the
                matplotlibrc file in the savefig.jpeg_quality parameter.
                Values above 95 should be avoided; 100 completely
                disables the JPEG quantization stage.

            *optimize*: If present, indicates that the encoder should
                make an extra pass over the image in order to select
                optimal encoder settings.

            *progressive*: If present, indicates that this image
                should be stored as a progressive JPEG file.
            """
            from backends.backend_agg import FigureCanvasAgg  # lazy import
            agg = self.switch_backends(FigureCanvasAgg)
            buf, size = agg.print_to_buffer()
            if kwargs.pop("dryrun", False):
                return
            image = Image.frombuffer('RGBA', size, buf, 'raw', 'RGBA', 0, 1)
            options = cbook.restrict_dict(kwargs, ['quality', 'optimize',
                                                   'progressive'])

            if 'quality' not in options:
                options['quality'] = rcParams['savefig.jpeg_quality']

            return image.save(filename_or_obj, format='jpeg', **options)
        print_jpeg = print_jpg

        filetypes['tif'] = filetypes['tiff'] = 'Tagged Image File Format'

        def print_tif(self, filename_or_obj, *args, **kwargs):
            from backends.backend_agg import FigureCanvasAgg  # lazy import
            agg = self.switch_backends(FigureCanvasAgg)
            buf, size = agg.print_to_buffer()
            if kwargs.pop("dryrun", False):
                return
            image = Image.frombuffer('RGBA', size, buf, 'raw', 'RGBA', 0, 1)
            dpi = (self.figure.dpi, self.figure.dpi)
            return image.save(filename_or_obj, format='tiff',
                              dpi=dpi)
        print_tiff = print_tif

    def get_supported_filetypes(self):
        """Return dict of savefig file formats supported by this backend"""
        return self.filetypes

    def get_supported_filetypes_grouped(self):
        """Return a dict of savefig file formats supported by this backend,
        where the keys are a file type name, such as 'Joint Photographic
        Experts Group', and the values are a list of filename extensions used
        for that filetype, such as ['jpg', 'jpeg']."""
        groupings = {}
        for ext, name in self.filetypes.iteritems():
            groupings.setdefault(name, []).append(ext)
            groupings[name].sort()
        return groupings

    def _get_print_method(self, format):
        method_name = 'print_%s' % format

        # check for registered backends
        if format in _backend_d:
            backend_class = _backend_d[format]

            def _print_method(*args, **kwargs):
                backend = self.switch_backends(backend_class)
                print_method = getattr(backend, method_name)
                return print_method(*args, **kwargs)

            return _print_method

        formats = self.get_supported_filetypes()
        if (format not in formats or not hasattr(self, method_name)):
            formats = sorted(formats)
            raise ValueError(
                'Format "%s" is not supported.\n'
                'Supported formats: '
                '%s.' % (format, ', '.join(formats)))

        return getattr(self, method_name)

    def print_figure(self, filename, dpi=None, facecolor='w', edgecolor='w',
                     orientation='portrait', format=None, **kwargs):
        """
        Render the figure to hardcopy. Set the figure patch face and edge
        colors.  This is useful because some of the GUIs have a gray figure
        face color background and you'll probably want to override this on
        hardcopy.

        Arguments are:

        *filename*
            can also be a file object on image backends

        *orientation*
            only currently applies to PostScript printing.

        *dpi*
            the dots per inch to save the figure in; if None, use savefig.dpi

        *facecolor*
            the facecolor of the figure

        *edgecolor*
            the edgecolor of the figure

        *orientation*
            landscape' | 'portrait' (not supported on all backends)

        *format*
            when set, forcibly set the file format to save to

        *bbox_inches*
            Bbox in inches. Only the given portion of the figure is
            saved. If 'tight', try to figure out the tight bbox of
            the figure. If None, use savefig.bbox

        *pad_inches*
            Amount of padding around the figure when bbox_inches is
            'tight'. If None, use savefig.pad_inches

        *bbox_extra_artists*
            A list of extra artists that will be considered when the
            tight bbox is calculated.

        """
        if format is None:
            # get format from filename, or from backend's default filetype
            if cbook.is_string_like(filename):
                format = os.path.splitext(filename)[1][1:]
            if format is None or format == '':
                format = self.get_default_filetype()
                if cbook.is_string_like(filename):
                    filename = filename.rstrip('.') + '.' + format
        format = format.lower()

        print_method = self._get_print_method(format)

        if dpi is None:
            dpi = rcParams['savefig.dpi']

        origDPI = self.figure.dpi
        origfacecolor = self.figure.get_facecolor()
        origedgecolor = self.figure.get_edgecolor()

        self.figure.dpi = dpi
        self.figure.set_facecolor(facecolor)
        self.figure.set_edgecolor(edgecolor)

        bbox_inches = kwargs.pop("bbox_inches", None)
        if bbox_inches is None:
            bbox_inches = rcParams['savefig.bbox']

        if bbox_inches:
            # call adjust_bbox to save only the given area
            if bbox_inches == "tight":
                # when bbox_inches == "tight", it saves the figure
                # twice. The first save command is just to estimate
                # the bounding box of the figure. A stringIO object is
                # used as a temporary file object, but it causes a
                # problem for some backends (ps backend with
                # usetex=True) if they expect a filename, not a
                # file-like object. As I think it is best to change
                # the backend to support file-like object, i'm going
                # to leave it as it is. However, a better solution
                # than stringIO seems to be needed. -JJL
                #result = getattr(self, method_name)
                result = print_method(
                    io.BytesIO(),
                    dpi=dpi,
                    facecolor=facecolor,
                    edgecolor=edgecolor,
                    orientation=orientation,
                    dryrun=True,
                    **kwargs)
                renderer = self.figure._cachedRenderer
                bbox_inches = self.figure.get_tightbbox(renderer)

                bbox_artists = kwargs.pop("bbox_extra_artists", None)
                if bbox_artists is None:
                    bbox_artists = self.figure.get_default_bbox_extra_artists()

                bbox_filtered = []
                for a in bbox_artists:
                    bbox = a.get_window_extent(renderer)
                    if a.get_clip_on():
                        clip_box = a.get_clip_box()
                        if clip_box is not None:
                            bbox = Bbox.intersection(bbox, clip_box)
                        clip_path = a.get_clip_path()
                        if clip_path is not None and bbox is not None:
                            clip_path = clip_path.get_fully_transformed_path()
                            bbox = Bbox.intersection(bbox,
                                                     clip_path.get_extents())
                    if bbox is not None and (bbox.width != 0 or
                                             bbox.height != 0):
                        bbox_filtered.append(bbox)

                if bbox_filtered:
                    _bbox = Bbox.union(bbox_filtered)
                    trans = Affine2D().scale(1.0 / self.figure.dpi)
                    bbox_extra = TransformedBbox(_bbox, trans)
                    bbox_inches = Bbox.union([bbox_inches, bbox_extra])

                pad = kwargs.pop("pad_inches", None)
                if pad is None:
                    pad = rcParams['savefig.pad_inches']

                bbox_inches = bbox_inches.padded(pad)

            restore_bbox = tight_bbox.adjust_bbox(self.figure, format,
                                                  bbox_inches)

            _bbox_inches_restore = (bbox_inches, restore_bbox)
        else:
            _bbox_inches_restore = None

        self._is_saving = True
        try:
            #result = getattr(self, method_name)(
            result = print_method(
                filename,
                dpi=dpi,
                facecolor=facecolor,
                edgecolor=edgecolor,
                orientation=orientation,
                bbox_inches_restore=_bbox_inches_restore,
                **kwargs)
        finally:
            if bbox_inches and restore_bbox:
                restore_bbox()

            self.figure.dpi = origDPI
            self.figure.set_facecolor(origfacecolor)
            self.figure.set_edgecolor(origedgecolor)
            self.figure.set_canvas(self)
            self._is_saving = False
            #self.figure.canvas.draw() ## seems superfluous
        return result

    def get_default_filetype(self):
        """
        Get the default savefig file format as specified in rcParam
        ``savefig.format``. Returned string excludes period. Overridden
        in backends that only support a single file type.
        """
        return rcParams['savefig.format']

    def get_window_title(self):
        """
        Get the title text of the window containing the figure.
        Return None if there is no window (eg, a PS backend).
        """
        if hasattr(self, "manager"):
            return self.manager.get_window_title()

    def set_window_title(self, title):
        """
        Set the title text of the window containing the figure.  Note that
        this has no effect if there is no window (eg, a PS backend).
        """
        if hasattr(self, "manager"):
            self.manager.set_window_title(title)

    def get_default_filename(self):
        """
        Return a string, which includes extension, suitable for use as
        a default filename.
        """
        default_filename = self.get_window_title() or 'image'
        default_filename = default_filename.lower().replace(' ', '_')
        return default_filename + '.' + self.get_default_filetype()

    def switch_backends(self, FigureCanvasClass):
        """
        Instantiate an instance of FigureCanvasClass

        This is used for backend switching, eg, to instantiate a
        FigureCanvasPS from a FigureCanvasGTK.  Note, deep copying is
        not done, so any changes to one of the instances (eg, setting
        figure size or line props), will be reflected in the other
        """
        newCanvas = FigureCanvasClass(self.figure)
        newCanvas._is_saving = self._is_saving
        return newCanvas

    def mpl_connect(self, s, func):
        """
        Connect event with string *s* to *func*.  The signature of *func* is::

          def func(event)

        where event is a :class:`matplotlib.backend_bases.Event`.  The
        following events are recognized

        - 'button_press_event'
        - 'button_release_event'
        - 'draw_event'
        - 'key_press_event'
        - 'key_release_event'
        - 'motion_notify_event'
        - 'pick_event'
        - 'resize_event'
        - 'scroll_event'
        - 'figure_enter_event',
        - 'figure_leave_event',
        - 'axes_enter_event',
        - 'axes_leave_event'
        - 'close_event'

        For the location events (button and key press/release), if the
        mouse is over the axes, the variable ``event.inaxes`` will be
        set to the :class:`~matplotlib.axes.Axes` the event occurs is
        over, and additionally, the variables ``event.xdata`` and
        ``event.ydata`` will be defined.  This is the mouse location
        in data coords.  See
        :class:`~matplotlib.backend_bases.KeyEvent` and
        :class:`~matplotlib.backend_bases.MouseEvent` for more info.

        Return value is a connection id that can be used with
        :meth:`~matplotlib.backend_bases.Event.mpl_disconnect`.

        Example usage::

            def on_press(event):
                print('you pressed', event.button, event.xdata, event.ydata)

            cid = canvas.mpl_connect('button_press_event', on_press)

        """

        return self.callbacks.connect(s, func)

    def mpl_disconnect(self, cid):
        """
        Disconnect callback id cid

        Example usage::

            cid = canvas.mpl_connect('button_press_event', on_press)
            #...later
            canvas.mpl_disconnect(cid)
        """
        return self.callbacks.disconnect(cid)

    def new_timer(self, *args, **kwargs):
        """
        Creates a new backend-specific subclass of
        :class:`backend_bases.Timer`. This is useful for getting periodic
        events through the backend's native event loop. Implemented only for
        backends with GUIs.

        optional arguments:

        *interval*
          Timer interval in milliseconds
        *callbacks*
          Sequence of (func, args, kwargs) where func(*args, **kwargs) will
          be executed by the timer every *interval*.
        """
        return TimerBase(*args, **kwargs)

    def flush_events(self):
        """
        Flush the GUI events for the figure. Implemented only for
        backends with GUIs.
        """
        raise NotImplementedError

    def start_event_loop(self, timeout):
        """
        Start an event loop.  This is used to start a blocking event
        loop so that interactive functions, such as ginput and
        waitforbuttonpress, can wait for events.  This should not be
        confused with the main GUI event loop, which is always running
        and has nothing to do with this.

        This is implemented only for backends with GUIs.
        """
        raise NotImplementedError

    def stop_event_loop(self):
        """
        Stop an event loop.  This is used to stop a blocking event
        loop so that interactive functions, such as ginput and
        waitforbuttonpress, can wait for events.

        This is implemented only for backends with GUIs.
        """
        raise NotImplementedError

    def start_event_loop_default(self, timeout=0):
        """
        Start an event loop.  This is used to start a blocking event
        loop so that interactive functions, such as ginput and
        waitforbuttonpress, can wait for events.  This should not be
        confused with the main GUI event loop, which is always running
        and has nothing to do with this.

        This function provides default event loop functionality based
        on time.sleep that is meant to be used until event loop
        functions for each of the GUI backends can be written.  As
        such, it throws a deprecated warning.

        Call signature::

            start_event_loop_default(self,timeout=0)

        This call blocks until a callback function triggers
        stop_event_loop() or *timeout* is reached.  If *timeout* is
        <=0, never timeout.
        """
        str = "Using default event loop until function specific"
        str += " to this GUI is implemented"
        warnings.warn(str, mplDeprecation)

        if timeout <= 0:
            timeout = np.inf
        timestep = 0.01
        counter = 0
        self._looping = True
        while self._looping and counter * timestep < timeout:
            self.flush_events()
            time.sleep(timestep)
            counter += 1

    def stop_event_loop_default(self):
        """
        Stop an event loop.  This is used to stop a blocking event
        loop so that interactive functions, such as ginput and
        waitforbuttonpress, can wait for events.

        Call signature::

          stop_event_loop_default(self)
        """
        self._looping = False


def key_press_handler(event, canvas, toolbar=None):
    """
    Implement the default mpl key bindings for the canvas and toolbar
    described at :ref:`key-event-handling`

    *event*
      a :class:`KeyEvent` instance
    *canvas*
      a :class:`FigureCanvasBase` instance
    *toolbar*
      a :class:`NavigationToolbar2` instance

    """
    # these bindings happen whether you are over an axes or not

    if event.key is None:
        return

    # Load key-mappings from your matplotlibrc file.
    fullscreen_keys = rcParams['keymap.fullscreen']
    home_keys = rcParams['keymap.home']
    back_keys = rcParams['keymap.back']
    forward_keys = rcParams['keymap.forward']
    pan_keys = rcParams['keymap.pan']
    zoom_keys = rcParams['keymap.zoom']
    save_keys = rcParams['keymap.save']
    quit_keys = rcParams['keymap.quit']
    grid_keys = rcParams['keymap.grid']
    toggle_yscale_keys = rcParams['keymap.yscale']
    toggle_xscale_keys = rcParams['keymap.xscale']
    all = rcParams['keymap.all_axes']

    # toggle fullscreen mode (default key 'f')
    if event.key in fullscreen_keys:
        canvas.manager.full_screen_toggle()

    # quit the figure (defaut key 'ctrl+w')
    if event.key in quit_keys:
        Gcf.destroy_fig(canvas.figure)

    if toolbar is not None:
        # home or reset mnemonic  (default key 'h', 'home' and 'r')
        if event.key in home_keys:
            toolbar.home()
        # forward / backward keys to enable left handed quick navigation
        # (default key for backward: 'left', 'backspace' and 'c')
        elif event.key in back_keys:
            toolbar.back()
        # (default key for forward: 'right' and 'v')
        elif event.key in forward_keys:
            toolbar.forward()
        # pan mnemonic (default key 'p')
        elif event.key in pan_keys:
            toolbar.pan()
        # zoom mnemonic (default key 'o')
        elif event.key in zoom_keys:
            toolbar.zoom()
        # saving current figure (default key 's')
        elif event.key in save_keys:
            toolbar.save_figure()

    if event.inaxes is None:
        return

    # these bindings require the mouse to be over an axes to trigger

    # switching on/off a grid in current axes (default key 'g')
    if event.key in grid_keys:
        event.inaxes.grid()
        canvas.draw()
    # toggle scaling of y-axes between 'log and 'linear' (default key 'l')
    elif event.key in toggle_yscale_keys:
        ax = event.inaxes
        scale = ax.get_yscale()
        if scale == 'log':
            ax.set_yscale('linear')
            ax.figure.canvas.draw()
        elif scale == 'linear':
            ax.set_yscale('log')
            ax.figure.canvas.draw()
    # toggle scaling of x-axes between 'log and 'linear' (default key 'k')
    elif event.key in toggle_xscale_keys:
        ax = event.inaxes
        scalex = ax.get_xscale()
        if scalex == 'log':
            ax.set_xscale('linear')
            ax.figure.canvas.draw()
        elif scalex == 'linear':
            ax.set_xscale('log')
            ax.figure.canvas.draw()

    elif (event.key.isdigit() and event.key != '0') or event.key in all:
        # keys in list 'all' enables all axes (default key 'a'),
        # otherwise if key is a number only enable this particular axes
        # if it was the axes, where the event was raised
        if not (event.key in all):
            n = int(event.key) - 1
        for i, a in enumerate(canvas.figure.get_axes()):
            # consider axes, in which the event was raised
            # FIXME: Why only this axes?
            if event.x is not None and event.y is not None \
                    and a.in_axes(event):
                if event.key in all:
                    a.set_navigate(True)
                else:
                    a.set_navigate(i == n)


class NonGuiException(Exception):
    pass


class FigureManagerBase:
    """
    Helper class for pyplot mode, wraps everything up into a neat bundle

    Public attibutes:

    *canvas*
        A :class:`FigureCanvasBase` instance

    *num*
        The figure number
    """
    def __init__(self, canvas, num):
        self.canvas = canvas
        canvas.manager = self  # store a pointer to parent
        self.num = num

        self.key_press_handler_id = self.canvas.mpl_connect('key_press_event',
                                                            self.key_press)
        """
        The returned id from connecting the default key handler via
        :meth:`FigureCanvasBase.mpl_connnect`.

        To disable default key press handling::

            manager, canvas = figure.canvas.manager, figure.canvas
            canvas.mpl_disconnect(manager.key_press_handler_id)

        """

    def show(self):
        """
        For GUI backends, show the figure window and redraw.
        For non-GUI backends, raise an exception to be caught
        by :meth:`~matplotlib.figure.Figure.show`, for an
        optional warning.
        """
        raise NonGuiException()

    def destroy(self):
        pass

    def full_screen_toggle(self):
        pass

    def resize(self, w, h):
        """"For gui backends, resize the window (in pixels)."""
        pass

    def key_press(self, event):
        """
        Implement the default mpl key bindings defined at
        :ref:`key-event-handling`
        """
        key_press_handler(event, self.canvas, self.canvas.toolbar)

    def show_popup(self, msg):
        """
        Display message in a popup -- GUI only
        """
        pass

    def get_window_title(self):
        """
        Get the title text of the window containing the figure.
        Return None for non-GUI backends (eg, a PS backend).
        """
        return 'image'

    def set_window_title(self, title):
        """
        Set the title text of the window containing the figure.  Note that
        this has no effect for non-GUI backends (eg, a PS backend).
        """
        pass


class Cursors:
    # this class is only used as a simple namespace
    HAND, POINTER, SELECT_REGION, MOVE = range(4)
cursors = Cursors()


class NavigationToolbar2(object):
    """
    Base class for the navigation cursor, version 2

    backends must implement a canvas that handles connections for
    'button_press_event' and 'button_release_event'.  See
    :meth:`FigureCanvasBase.mpl_connect` for more information


    They must also define

      :meth:`save_figure`
         save the current figure

      :meth:`set_cursor`
         if you want the pointer icon to change

      :meth:`_init_toolbar`
         create your toolbar widget

      :meth:`draw_rubberband` (optional)
         draw the zoom to rect "rubberband" rectangle

      :meth:`press`  (optional)
         whenever a mouse button is pressed, you'll be notified with
         the event

      :meth:`release` (optional)
         whenever a mouse button is released, you'll be notified with
         the event

      :meth:`dynamic_update` (optional)
         dynamically update the window while navigating

      :meth:`set_message` (optional)
         display message

      :meth:`set_history_buttons` (optional)
         you can change the history back / forward buttons to
         indicate disabled / enabled state.

    That's it, we'll do the rest!
    """

    # list of toolitems to add to the toolbar, format is:
    # (
    #   text, # the text of the button (often not visible to users)
    #   tooltip_text, # the tooltip shown on hover (where possible)
    #   image_file, # name of the image for the button (without the extension)
    #   name_of_method, # name of the method in NavigationToolbar2 to call
    # )
    toolitems = (
        ('Home', 'Reset original view', 'home', 'home'),
        ('Back', 'Back to  previous view', 'back', 'back'),
        ('Forward', 'Forward to next view', 'forward', 'forward'),
        (None, None, None, None),
        ('Pan', 'Pan axes with left mouse, zoom with right', 'move', 'pan'),
        ('Zoom', 'Zoom to rectangle', 'zoom_to_rect', 'zoom'),
        (None, None, None, None),
        ('Subplots', 'Configure subplots', 'subplots', 'configure_subplots'),
        ('Save', 'Save the figure', 'filesave', 'save_figure'),
      )

    def __init__(self, canvas):
        self.canvas = canvas
        canvas.toolbar = self
        # a dict from axes index to a list of view limits
        self._views = cbook.Stack()
        self._positions = cbook.Stack()  # stack of subplot positions
        self._xypress = None  # the location and axis info at the time
                              # of the press
        self._idPress = None
        self._idRelease = None
        self._active = None
        self._lastCursor = None
        self._init_toolbar()
        self._idDrag = self.canvas.mpl_connect(
            'motion_notify_event', self.mouse_move)

        self._ids_zoom = []
        self._zoom_mode = None

        self._button_pressed = None  # determined by the button pressed
                                     # at start

        self.mode = ''  # a mode string for the status bar
        self.set_history_buttons()

    def set_message(self, s):
        """Display a message on toolbar or in status bar"""
        pass

    def back(self, *args):
        """move back up the view lim stack"""
        self._views.back()
        self._positions.back()
        self.set_history_buttons()
        self._update_view()

    def dynamic_update(self):
        pass

    def draw_rubberband(self, event, x0, y0, x1, y1):
        """Draw a rectangle rubberband to indicate zoom limits"""
        pass

    def forward(self, *args):
        """Move forward in the view lim stack"""
        self._views.forward()
        self._positions.forward()
        self.set_history_buttons()
        self._update_view()

    def home(self, *args):
        """Restore the original view"""
        self._views.home()
        self._positions.home()
        self.set_history_buttons()
        self._update_view()

    def _init_toolbar(self):
        """
        This is where you actually build the GUI widgets (called by
        __init__).  The icons ``home.xpm``, ``back.xpm``, ``forward.xpm``,
        ``hand.xpm``, ``zoom_to_rect.xpm`` and ``filesave.xpm`` are standard
        across backends (there are ppm versions in CVS also).

        You just need to set the callbacks

        home         : self.home
        back         : self.back
        forward      : self.forward
        hand         : self.pan
        zoom_to_rect : self.zoom
        filesave     : self.save_figure

        You only need to define the last one - the others are in the base
        class implementation.

        """
        raise NotImplementedError

    def mouse_move(self, event):
        if not event.inaxes or not self._active:
            if self._lastCursor != cursors.POINTER:
                self.set_cursor(cursors.POINTER)
                self._lastCursor = cursors.POINTER
        else:
            if self._active == 'ZOOM':
                if self._lastCursor != cursors.SELECT_REGION:
                    self.set_cursor(cursors.SELECT_REGION)
                    self._lastCursor = cursors.SELECT_REGION
            elif (self._active == 'PAN' and
                  self._lastCursor != cursors.MOVE):
                self.set_cursor(cursors.MOVE)

                self._lastCursor = cursors.MOVE

        if event.inaxes and event.inaxes.get_navigate():

            try:
                s = event.inaxes.format_coord(event.xdata, event.ydata)
            except (ValueError, OverflowError):
                pass
            else:
                if len(self.mode):
                    self.set_message('%s, %s' % (self.mode, s))
                else:
                    self.set_message(s)
        else:
            self.set_message(self.mode)

    def pan(self, *args):
        """Activate the pan/zoom tool. pan with left button, zoom with right"""
        # set the pointer icon and button press funcs to the
        # appropriate callbacks

        if self._active == 'PAN':
            self._active = None
        else:
            self._active = 'PAN'
        if self._idPress is not None:
            self._idPress = self.canvas.mpl_disconnect(self._idPress)
            self.mode = ''

        if self._idRelease is not None:
            self._idRelease = self.canvas.mpl_disconnect(self._idRelease)
            self.mode = ''

        if self._active:
            self._idPress = self.canvas.mpl_connect(
                'button_press_event', self.press_pan)
            self._idRelease = self.canvas.mpl_connect(
                'button_release_event', self.release_pan)
            self.mode = 'pan/zoom'
            self.canvas.widgetlock(self)
        else:
            self.canvas.widgetlock.release(self)

        for a in self.canvas.figure.get_axes():
            a.set_navigate_mode(self._active)

        self.set_message(self.mode)

    def press(self, event):
        """Called whenver a mouse button is pressed."""
        pass

    def press_pan(self, event):
        """the press mouse button in pan/zoom mode callback"""

        if event.button == 1:
            self._button_pressed = 1
        elif event.button == 3:
            self._button_pressed = 3
        else:
            self._button_pressed = None
            return

        x, y = event.x, event.y

        # push the current view to define home if stack is empty
        if self._views.empty():
            self.push_current()

        self._xypress = []
        for i, a in enumerate(self.canvas.figure.get_axes()):
            if (x is not None and y is not None and a.in_axes(event) and
                    a.get_navigate() and a.can_pan()):
                a.start_pan(x, y, event.button)
                self._xypress.append((a, i))
                self.canvas.mpl_disconnect(self._idDrag)
                self._idDrag = self.canvas.mpl_connect('motion_notify_event',
                                                       self.drag_pan)

        self.press(event)

    def press_zoom(self, event):
        """the press mouse button in zoom to rect mode callback"""
        # If we're already in the middle of a zoom, pressing another
        # button works to "cancel"
        if self._ids_zoom != []:
            for zoom_id in self._ids_zoom:
                self.canvas.mpl_disconnect(zoom_id)
            self.release(event)
            self.draw()
            self._xypress = None
            self._button_pressed = None
            self._ids_zoom = []
            return

        if event.button == 1:
            self._button_pressed = 1
        elif event.button == 3:
            self._button_pressed = 3
        else:
            self._button_pressed = None
            return

        x, y = event.x, event.y

        # push the current view to define home if stack is empty
        if self._views.empty():
            self.push_current()

        self._xypress = []
        for i, a in enumerate(self.canvas.figure.get_axes()):
            if (x is not None and y is not None and a.in_axes(event) and
                    a.get_navigate() and a.can_zoom()):
                self._xypress.append((x, y, a, i, a.viewLim.frozen(),
                                      a.transData.frozen()))

        id1 = self.canvas.mpl_connect('motion_notify_event', self.drag_zoom)
        id2 = self.canvas.mpl_connect('key_press_event',
                                      self._switch_on_zoom_mode)
        id3 = self.canvas.mpl_connect('key_release_event',
                                      self._switch_off_zoom_mode)

        self._ids_zoom = id1, id2, id3
        self._zoom_mode = event.key

        self.press(event)

    def _switch_on_zoom_mode(self, event):
        self._zoom_mode = event.key
        self.mouse_move(event)

    def _switch_off_zoom_mode(self, event):
        self._zoom_mode = None
        self.mouse_move(event)

    def push_current(self):
        """push the current view limits and position onto the stack"""
        lims = []
        pos = []
        for a in self.canvas.figure.get_axes():
            xmin, xmax = a.get_xlim()
            ymin, ymax = a.get_ylim()
            lims.append((xmin, xmax, ymin, ymax))
            # Store both the original and modified positions
            pos.append((
                a.get_position(True).frozen(),
                a.get_position().frozen()))
        self._views.push(lims)
        self._positions.push(pos)
        self.set_history_buttons()

    def release(self, event):
        """this will be called whenever mouse button is released"""
        pass

    def release_pan(self, event):
        """the release mouse button callback in pan/zoom mode"""

        if self._button_pressed is None:
            return
        self.canvas.mpl_disconnect(self._idDrag)
        self._idDrag = self.canvas.mpl_connect(
            'motion_notify_event', self.mouse_move)
        for a, ind in self._xypress:
            a.end_pan()
        if not self._xypress:
            return
        self._xypress = []
        self._button_pressed = None
        self.push_current()
        self.release(event)
        self.draw()

    def drag_pan(self, event):
        """the drag callback in pan/zoom mode"""

        for a, ind in self._xypress:
            #safer to use the recorded button at the press than current button:
            #multiple button can get pressed during motion...
            a.drag_pan(self._button_pressed, event.key, event.x, event.y)
        self.dynamic_update()

    def drag_zoom(self, event):
        """the drag callback in zoom mode"""

        if self._xypress:
            x, y = event.x, event.y
            lastx, lasty, a, ind, lim, trans = self._xypress[0]

            # adjust x, last, y, last
            x1, y1, x2, y2 = a.bbox.extents
            x, lastx = max(min(x, lastx), x1), min(max(x, lastx), x2)
            y, lasty = max(min(y, lasty), y1), min(max(y, lasty), y2)

            if self._zoom_mode == "x":
                x1, y1, x2, y2 = a.bbox.extents
                y, lasty = y1, y2
            elif self._zoom_mode == "y":
                x1, y1, x2, y2 = a.bbox.extents
                x, lastx = x1, x2

            self.draw_rubberband(event, x, y, lastx, lasty)

    def release_zoom(self, event):
        """the release mouse button callback in zoom to rect mode"""
        for zoom_id in self._ids_zoom:
            self.canvas.mpl_disconnect(zoom_id)
        self._ids_zoom = []

        if not self._xypress:
            return

        last_a = []

        for cur_xypress in self._xypress:
            x, y = event.x, event.y
            lastx, lasty, a, ind, lim, trans = cur_xypress
            # ignore singular clicks - 5 pixels is a threshold
            if abs(x - lastx) < 5 or abs(y - lasty) < 5:
                self._xypress = None
                self.release(event)
                self.draw()
                return

            x0, y0, x1, y1 = lim.extents

            # zoom to rect
            inverse = a.transData.inverted()
            lastx, lasty = inverse.transform_point((lastx, lasty))
            x, y = inverse.transform_point((x, y))
            Xmin, Xmax = a.get_xlim()
            Ymin, Ymax = a.get_ylim()

            # detect twinx,y axes and avoid double zooming
            twinx, twiny = False, False
            if last_a:
                for la in last_a:
                    if a.get_shared_x_axes().joined(a, la):
                        twinx = True
                    if a.get_shared_y_axes().joined(a, la):
                        twiny = True
            last_a.append(a)

            if twinx:
                x0, x1 = Xmin, Xmax
            else:
                if Xmin < Xmax:
                    if x < lastx:
                        x0, x1 = x, lastx
                    else:
                        x0, x1 = lastx, x
                    if x0 < Xmin:
                        x0 = Xmin
                    if x1 > Xmax:
                        x1 = Xmax
                else:
                    if x > lastx:
                        x0, x1 = x, lastx
                    else:
                        x0, x1 = lastx, x
                    if x0 > Xmin:
                        x0 = Xmin
                    if x1 < Xmax:
                        x1 = Xmax

            if twiny:
                y0, y1 = Ymin, Ymax
            else:
                if Ymin < Ymax:
                    if y < lasty:
                        y0, y1 = y, lasty
                    else:
                        y0, y1 = lasty, y
                    if y0 < Ymin:
                        y0 = Ymin
                    if y1 > Ymax:
                        y1 = Ymax
                else:
                    if y > lasty:
                        y0, y1 = y, lasty
                    else:
                        y0, y1 = lasty, y
                    if y0 > Ymin:
                        y0 = Ymin
                    if y1 < Ymax:
                        y1 = Ymax

            if self._button_pressed == 1:
                if self._zoom_mode == "x":
                    a.set_xlim((x0, x1))
                elif self._zoom_mode == "y":
                    a.set_ylim((y0, y1))
                else:
                    a.set_xlim((x0, x1))
                    a.set_ylim((y0, y1))
            elif self._button_pressed == 3:
                if a.get_xscale() == 'log':
                    alpha = np.log(Xmax / Xmin) / np.log(x1 / x0)
                    rx1 = pow(Xmin / x0, alpha) * Xmin
                    rx2 = pow(Xmax / x0, alpha) * Xmin
                else:
                    alpha = (Xmax - Xmin) / (x1 - x0)
                    rx1 = alpha * (Xmin - x0) + Xmin
                    rx2 = alpha * (Xmax - x0) + Xmin
                if a.get_yscale() == 'log':
                    alpha = np.log(Ymax / Ymin) / np.log(y1 / y0)
                    ry1 = pow(Ymin / y0, alpha) * Ymin
                    ry2 = pow(Ymax / y0, alpha) * Ymin
                else:
                    alpha = (Ymax - Ymin) / (y1 - y0)
                    ry1 = alpha * (Ymin - y0) + Ymin
                    ry2 = alpha * (Ymax - y0) + Ymin

                if self._zoom_mode == "x":
                    a.set_xlim((rx1, rx2))
                elif self._zoom_mode == "y":
                    a.set_ylim((ry1, ry2))
                else:
                    a.set_xlim((rx1, rx2))
                    a.set_ylim((ry1, ry2))

        self.draw()
        self._xypress = None
        self._button_pressed = None

        self._zoom_mode = None

        self.push_current()
        self.release(event)

    def draw(self):
        """Redraw the canvases, update the locators"""
        for a in self.canvas.figure.get_axes():
            xaxis = getattr(a, 'xaxis', None)
            yaxis = getattr(a, 'yaxis', None)
            locators = []
            if xaxis is not None:
                locators.append(xaxis.get_major_locator())
                locators.append(xaxis.get_minor_locator())
            if yaxis is not None:
                locators.append(yaxis.get_major_locator())
                locators.append(yaxis.get_minor_locator())

            for loc in locators:
                loc.refresh()
        self.canvas.draw_idle()

    def _update_view(self):
        """Update the viewlim and position from the view and
        position stack for each axes
        """

        lims = self._views()
        if lims is None:
            return
        pos = self._positions()
        if pos is None:
            return
        for i, a in enumerate(self.canvas.figure.get_axes()):
            xmin, xmax, ymin, ymax = lims[i]
            a.set_xlim((xmin, xmax))
            a.set_ylim((ymin, ymax))
            # Restore both the original and modified positions
            a.set_position(pos[i][0], 'original')
            a.set_position(pos[i][1], 'active')

        self.canvas.draw_idle()

    def save_figure(self, *args):
        """Save the current figure"""
        raise NotImplementedError

    def set_cursor(self, cursor):
        """
        Set the current cursor to one of the :class:`Cursors`
        enums values
        """
        pass

    def update(self):
        """Reset the axes stack"""
        self._views.clear()
        self._positions.clear()
        self.set_history_buttons()

    def zoom(self, *args):
        """Activate zoom to rect mode"""
        if self._active == 'ZOOM':
            self._active = None
        else:
            self._active = 'ZOOM'

        if self._idPress is not None:
            self._idPress = self.canvas.mpl_disconnect(self._idPress)
            self.mode = ''

        if self._idRelease is not None:
            self._idRelease = self.canvas.mpl_disconnect(self._idRelease)
            self.mode = ''

        if self._active:
            self._idPress = self.canvas.mpl_connect('button_press_event',
                                                    self.press_zoom)
            self._idRelease = self.canvas.mpl_connect('button_release_event',
                                                      self.release_zoom)
            self.mode = 'zoom rect'
            self.canvas.widgetlock(self)
        else:
            self.canvas.widgetlock.release(self)

        for a in self.canvas.figure.get_axes():
            a.set_navigate_mode(self._active)

        self.set_message(self.mode)

    def set_history_buttons(self):
        """Enable or disable back/forward button"""
        pass