legend.py

"""
The legend module defines the Legend class, which is responsible for
drawing legends associated with axes and/or figures.

The Legend class can be considered as a container of legend handles
and legend texts. Creation of corresponding legend handles from the
plot elements in the axes or figures (e.g., lines, patches, etc.) are
specified by the handler map, which defines the mapping between the
plot elements and the legend handlers to be used (the default legend
handlers are defined in the :mod:`~matplotlib.legend_handler` module). Note
that not all kinds of artist are supported by the legend yet (See
:ref:`plotting-guide-legend` for more information).
"""
from __future__ import division, print_function
import warnings

import numpy as np

from matplotlib import rcParams
from matplotlib.artist import Artist, allow_rasterization
from matplotlib.cbook import is_string_like, iterable, silent_list, safezip
from matplotlib.font_manager import FontProperties
from matplotlib.lines import Line2D
from matplotlib.patches import Patch, Rectangle, Shadow, FancyBboxPatch
from matplotlib.collections import LineCollection, RegularPolyCollection, \
     CircleCollection, PathCollection
from matplotlib.transforms import Bbox, BboxBase, TransformedBbox, BboxTransformTo, BboxTransformFrom

from matplotlib.offsetbox import HPacker, VPacker, TextArea, DrawingArea, DraggableOffsetBox

from matplotlib.container import ErrorbarContainer, BarContainer, StemContainer
import legend_handler


class DraggableLegend(DraggableOffsetBox):
    def __init__(self, legend, use_blit=False, update="loc"):
        """
        update : If "loc", update *loc* parameter of
                 legend upon finalizing. If "bbox", update
                 *bbox_to_anchor* parameter.
        """
        self.legend=legend

        if update in ["loc", "bbox"]:
            self._update = update
        else:
            raise ValueError("update parameter '%s' is not supported." % update)

        DraggableOffsetBox.__init__(self, legend, legend._legend_box,
                                    use_blit=use_blit)

    def artist_picker(self, legend, evt):
        return self.legend.contains(evt)

    def finalize_offset(self):
        loc_in_canvas = self.get_loc_in_canvas()

        if self._update == "loc":
            self._update_loc(loc_in_canvas)
        elif self._update == "bbox":
            self._update_bbox_to_anchor(loc_in_canvas)
        else:
            raise RuntimeError("update parameter '%s' is not supported." % self.update)

    def _update_loc(self, loc_in_canvas):
        bbox = self.legend.get_bbox_to_anchor()

        # if bbox has zero width or height, the transformation is
        # ill-defined. Fall back to the defaul bbox_to_anchor.
        if bbox.width ==0 or bbox.height ==0:
            self.legend.set_bbox_to_anchor(None)
            bbox = self.legend.get_bbox_to_anchor()

        _bbox_transform = BboxTransformFrom(bbox)
        self.legend._loc = tuple(_bbox_transform.transform_point(loc_in_canvas))


    def _update_bbox_to_anchor(self, loc_in_canvas):

        tr = self.legend.axes.transAxes
        loc_in_bbox = tr.transform_point(loc_in_canvas)

        self.legend.set_bbox_to_anchor(loc_in_bbox)


class Legend(Artist):
    """
    Place a legend on the axes at location loc.  Labels are a
    sequence of strings and loc can be a string or an integer
    specifying the legend location

    The location codes are::

      'best'         : 0, (only implemented for axis legends)
      'upper right'  : 1,
      'upper left'   : 2,
      'lower left'   : 3,
      'lower right'  : 4,
      'right'        : 5,
      'center left'  : 6,
      'center right' : 7,
      'lower center' : 8,
      'upper center' : 9,
      'center'       : 10,

    loc can be a tuple of the noramilzed coordinate values with
    respect its parent.

    """


    codes = {'best'         : 0, # only implemented for axis legends
             'upper right'  : 1,
             'upper left'   : 2,
             'lower left'   : 3,
             'lower right'  : 4,
             'right'        : 5,
             'center left'  : 6,
             'center right' : 7,
             'lower center' : 8,
             'upper center' : 9,
             'center'       : 10,
             }


    zorder = 5
    def __str__(self):
        return "Legend"

    def __init__(self, parent, handles, labels,
                 loc = None,
                 numpoints = None,     # the number of points in the legend line
                 markerscale = None,   # the relative size of legend markers vs. original
                 scatterpoints = 3,    # TODO: may be an rcParam
                 scatteryoffsets=None,
                 prop = None,          # properties for the legend texts

                 # the following dimensions are in axes coords
                 pad = None,           # deprecated; use borderpad
                 labelsep = None,      # deprecated; use labelspacing
                 handlelen = None,     # deprecated; use handlelength
                 handletextsep = None, # deprecated; use handletextpad
                 axespad = None,       # deprecated; use borderaxespad

                 # spacing & pad defined as a fraction of the font-size
                 borderpad = None,     # the whitespace inside the legend border
                 labelspacing=None, #the vertical space between the legend entries
                 handlelength=None, # the length of the legend handles
                 handleheight=None, # the height of the legend handles
                 handletextpad=None, # the pad between the legend handle and text
                 borderaxespad=None, # the pad between the axes and legend border
                 columnspacing=None, # spacing between columns

                 ncol=1, # number of columns
                 mode=None, # mode for horizontal distribution of columns. None, "expand"

                 fancybox=None, # True use a fancy box, false use a rounded box, none use rc
                 shadow = None,
                 title = None, # set a title for the legend
                 bbox_to_anchor = None, # bbox that the legend will be anchored.
                 bbox_transform = None, # transform for the bbox
                 frameon = None, # draw frame
                 handler_map = None,
                 ):
        """
        - *parent* : the artist that contains the legend
        - *handles* : a list of artists (lines, patches) to be added to the legend
        - *labels* : a list of strings to label the legend

        Optional keyword arguments:

        ================   ==================================================================
        Keyword            Description
        ================   ==================================================================
        loc                a location code
        prop               the font property
        markerscale        the relative size of legend markers vs. original
        numpoints          the number of points in the legend for line
        scatterpoints      the number of points in the legend for scatter plot
        scatteryoffsets    a list of yoffsets for scatter symbols in legend
        frameon            if True, draw a frame around the legend. If None, use rc
        fancybox           if True, draw a frame with a round fancybox.  If None, use rc
        shadow             if True, draw a shadow behind legend
        ncol               number of columns
        borderpad          the fractional whitespace inside the legend border
        labelspacing       the vertical space between the legend entries
        handlelength       the length of the legend handles
        handleheight       the length of the legend handles
        handletextpad      the pad between the legend handle and text
        borderaxespad      the pad between the axes and legend border
        columnspacing      the spacing between columns
        title              the legend title
        bbox_to_anchor     the bbox that the legend will be anchored.
        bbox_transform     the transform for the bbox. transAxes if None.
        ================   ==================================================================


The pad and spacing parameters are measured in font-size units.  E.g.,
a fontsize of 10 points and a handlelength=5 implies a handlelength of
50 points.  Values from rcParams will be used if None.

Users can specify any arbitrary location for the legend using the
*bbox_to_anchor* keyword argument. bbox_to_anchor can be an instance
of BboxBase(or its derivatives) or a tuple of 2 or 4 floats.
See :meth:`set_bbox_to_anchor` for more detail.

The legend location can be specified by setting *loc* with a tuple of
2 floats, which is interpreted as the lower-left corner of the legend
in the normalized axes coordinate.
        """
        from matplotlib.axes import Axes     # local import only to avoid circularity
        from matplotlib.figure import Figure # local import only to avoid circularity

        Artist.__init__(self)

        if prop is None:
            self.prop=FontProperties(size=rcParams["legend.fontsize"])
        elif isinstance(prop, dict):
            self.prop=FontProperties(**prop)
            if "size" not in prop:
                self.prop.set_size(rcParams["legend.fontsize"])
        else:
            self.prop=prop

        self._fontsize = self.prop.get_size_in_points()

        propnames=['numpoints', 'markerscale', 'shadow', "columnspacing",
                   "scatterpoints", "handleheight"]

        self.texts = []
        self.legendHandles = []
        self._legend_title_box = None


        self._handler_map = handler_map

        localdict = locals()

        for name in propnames:
            if localdict[name] is None:
                value = rcParams["legend."+name]
            else:
                value = localdict[name]
            setattr(self, name, value)

        # Take care the deprecated keywords
        deprecated_kwds = {"pad":"borderpad",
                           "labelsep":"labelspacing",
                           "handlelen":"handlelength",
                           "handletextsep":"handletextpad",
                           "axespad":"borderaxespad"}

        # convert values of deprecated keywords (ginve in axes coords)
        # to new vaules in a fraction of the font size

        # conversion factor
        bbox = parent.bbox
        axessize_fontsize = min(bbox.width, bbox.height)/self._fontsize

        for k, v in deprecated_kwds.iteritems():
            # use deprecated value if not None and if their newer
            # counter part is None.
            if localdict[k] is not None and localdict[v] is None:
                warnings.warn("Use '%s' instead of '%s'." % (v, k),
                              DeprecationWarning)
                setattr(self, v, localdict[k]*axessize_fontsize)
                continue

            # Otherwise, use new keywords
            if localdict[v] is None:
                setattr(self, v, rcParams["legend."+v])
            else:
                setattr(self, v, localdict[v])

        del localdict

        handles = list(handles)
        if len(handles)<2:
            ncol = 1
        self._ncol = ncol

        if self.numpoints <= 0:
            raise ValueError("numpoints must be > 0; it was %d"% numpoints)

        # introduce y-offset for handles of the scatter plot
        if scatteryoffsets is None:
            self._scatteryoffsets = np.array([3./8., 4./8., 2.5/8.])
        else:
            self._scatteryoffsets = np.asarray(scatteryoffsets)
        reps =  int(self.scatterpoints / len(self._scatteryoffsets)) + 1
        self._scatteryoffsets = np.tile(self._scatteryoffsets, reps)[:self.scatterpoints]

        # _legend_box is an OffsetBox instance that contains all
        # legend items and will be initialized from _init_legend_box()
        # method.
        self._legend_box = None

        if isinstance(parent,Axes):
            self.isaxes = True
            self.set_axes(parent)
            self.set_figure(parent.figure)
        elif isinstance(parent,Figure):
            self.isaxes = False
            self.set_figure(parent)
        else:
            raise TypeError("Legend needs either Axes or Figure as parent")
        self.parent = parent

        if loc is None:
            loc = rcParams["legend.loc"]
            if not self.isaxes and loc in [0,'best']:
                loc = 'upper right'
        if is_string_like(loc):
            if loc not in self.codes:
                if self.isaxes:
                    warnings.warn('Unrecognized location "%s". Falling back on "best"; '
                                  'valid locations are\n\t%s\n'
                                  % (loc, '\n\t'.join(self.codes.iterkeys())))
                    loc = 0
                else:
                    warnings.warn('Unrecognized location "%s". Falling back on "upper right"; '
                                  'valid locations are\n\t%s\n'
                                   % (loc, '\n\t'.join(self.codes.iterkeys())))
                    loc = 1
            else:
                loc = self.codes[loc]
        if not self.isaxes and loc == 0:
            warnings.warn('Automatic legend placement (loc="best") not implemented for figure legend. '
                          'Falling back on "upper right".')
            loc = 1

        self._mode = mode
        self.set_bbox_to_anchor(bbox_to_anchor, bbox_transform)

        # We use FancyBboxPatch to draw a legend frame. The location
        # and size of the box will be updated during the drawing time.

        self.legendPatch = FancyBboxPatch(
            xy=(0.0, 0.0), width=1., height=1.,
            facecolor=rcParams["axes.facecolor"],
            edgecolor=rcParams["axes.edgecolor"],
            mutation_scale=self._fontsize,
            snap=True
            )

        # The width and height of the legendPatch will be set (in the
        # draw()) to the length that includes the padding. Thus we set
        # pad=0 here.
        if fancybox is None:
            fancybox = rcParams["legend.fancybox"]

        if fancybox == True:
            self.legendPatch.set_boxstyle("round",pad=0,
                                          rounding_size=0.2)
        else:
            self.legendPatch.set_boxstyle("square",pad=0)

        self._set_artist_props(self.legendPatch)

        self._drawFrame = frameon
        if frameon is None:
            self._drawFrame = rcParams["legend.frameon"]

        # init with null renderer
        self._init_legend_box(handles, labels)

        self._loc = loc

        self.set_title(title)

        self._last_fontsize_points = self._fontsize

        self._draggable = None

    def _set_artist_props(self, a):
        """
        set the boilerplate props for artists added to axes
        """
        a.set_figure(self.figure)
        if self.isaxes:
            a.set_axes(self.axes)
        a.set_transform(self.get_transform())


    def _set_loc(self, loc):
        # find_offset function will be provided to _legend_box and
        # _legend_box will draw itself at the location of the return
        # value of the find_offset.
        self._loc_real = loc
        if loc == 0:
            _findoffset = self._findoffset_best
        else:
            _findoffset = self._findoffset_loc

        #def findoffset(width, height, xdescent, ydescent):
        #    return _findoffset(width, height, xdescent, ydescent, renderer)

        self._legend_box.set_offset(_findoffset)

        self._loc_real = loc

    def _get_loc(self):
        return self._loc_real

    _loc = property(_get_loc, _set_loc)

    def _findoffset_best(self, width, height, xdescent, ydescent, renderer):
        "Helper function to locate the legend at its best position"
        ox, oy = self._find_best_position(width, height, renderer)
        return ox+xdescent, oy+ydescent

    def _findoffset_loc(self, width, height, xdescent, ydescent, renderer):
        "Heper function to locate the legend using the location code"

        if iterable(self._loc) and len(self._loc)==2:
            # when loc is a tuple of axes(or figure) coordinates.
            fx, fy = self._loc
            bbox = self.get_bbox_to_anchor()
            x, y = bbox.x0 + bbox.width * fx, bbox.y0 + bbox.height * fy
        else:
            bbox = Bbox.from_bounds(0, 0, width, height)
            x, y = self._get_anchored_bbox(self._loc, bbox, self.get_bbox_to_anchor(), renderer)

        return x+xdescent, y+ydescent

    @allow_rasterization
    def draw(self, renderer):
        "Draw everything that belongs to the legend"
        if not self.get_visible(): return


        renderer.open_group('legend')


        fontsize = renderer.points_to_pixels(self._fontsize)

        # if mode == fill, set the width of the legend_box to the
        # width of the paret (minus pads)
        if self._mode in ["expand"]:
            pad = 2*(self.borderaxespad+self.borderpad)*fontsize
            self._legend_box.set_width(self.get_bbox_to_anchor().width-pad)

        if self._drawFrame:
            # update the location and size of the legend
            bbox = self._legend_box.get_window_extent(renderer)
            self.legendPatch.set_bounds(bbox.x0, bbox.y0,
                                        bbox.width, bbox.height)

            self.legendPatch.set_mutation_scale(fontsize)

            if self.shadow:
                shadow = Shadow(self.legendPatch, 2, -2)
                shadow.draw(renderer)

            self.legendPatch.draw(renderer)

        self._legend_box.draw(renderer)

        renderer.close_group('legend')


    def _approx_text_height(self, renderer=None):
        """
        Return the approximate height of the text. This is used to place
        the legend handle.
        """
        if renderer is None:
            return self._fontsize
        else:
            return renderer.points_to_pixels(self._fontsize)


    # _default_handler_map defines the default mapping between plot
    # elements and the legend handlers.

    _default_handler_map = {
        StemContainer:legend_handler.HandlerStem(),
        ErrorbarContainer:legend_handler.HandlerErrorbar(),
        Line2D:legend_handler.HandlerLine2D(),
        Patch:legend_handler.HandlerPatch(),
        LineCollection:legend_handler.HandlerLineCollection(),
        RegularPolyCollection:legend_handler.HandlerRegularPolyCollection(),
        CircleCollection:legend_handler.HandlerCircleCollection(),
        BarContainer:legend_handler.HandlerPatch(update_func=legend_handler.update_from_first_child),
        tuple:legend_handler.HandlerTuple(),
        PathCollection:legend_handler.HandlerPathCollection()
        }

    # (get|set|update)_default_handler_maps are public interfaces to
    # modify the defalut handler map.

    @classmethod
    def get_default_handler_map(cls):
        """
        A class method that returns the default handler map.
        """
        return cls._default_handler_map

    @classmethod
    def set_default_handler_map(cls, handler_map):
        """
        A class method to set the default handler map.
        """
        cls._default_handler_map = handler_map

    @classmethod
    def update_default_handler_map(cls, handler_map):
        """
        A class method to update the default handler map.
        """
        cls._default_handler_map.update(handler_map)

    def get_legend_handler_map(self):
        """
        return the handler map.
        """

        default_handler_map = self.get_default_handler_map()

        if self._handler_map:
            hm = default_handler_map.copy()
            hm.update(self._handler_map)
            return hm
        else:
            return default_handler_map

    @staticmethod
    def get_legend_handler(legend_handler_map, orig_handle):
        """
        return a legend handler from *legend_handler_map* that
        corresponds to *orig_handler*.

        *legend_handler_map* should be a dictionary object (that is
        returned by the get_legend_handler_map method).

        It first checks if the *orig_handle* itself is a key in the
        *legend_hanler_map* and return the associated value.
        Otherwised, it checks for each of the classes in its
        method-resolution-order. If no matching key is found, it
        returns None.
        """
        legend_handler_keys = legend_handler_map.keys()
        if orig_handle in legend_handler_keys:
            handler = legend_handler_map[orig_handle]
        else:

            for handle_type in type(orig_handle).mro():
                if handle_type in legend_handler_map:
                    handler = legend_handler_map[handle_type]
                    break
            else:
                handler = None

        return handler


    def _init_legend_box(self, handles, labels):
        """
        Initiallize the legend_box. The legend_box is an instance of
        the OffsetBox, which is packed with legend handles and
        texts. Once packed, their location is calculated during the
        drawing time.
        """

        fontsize = self._fontsize

        # legend_box is a HPacker, horizontally packed with
        # columns. Each column is a VPacker, vertically packed with
        # legend items. Each legend item is HPacker packed with
        # legend handleBox and labelBox. handleBox is an instance of
        # offsetbox.DrawingArea which contains legend handle. labelBox
        # is an instance of offsetbox.TextArea which contains legend
        # text.


        text_list = []  # the list of text instances
        handle_list = []  # the list of text instances

        label_prop = dict(verticalalignment='baseline',
                          horizontalalignment='left',
                          fontproperties=self.prop,
                          )

        labelboxes = []
        handleboxes = []


        # The approximate height and descent of text. These values are
        # only used for plotting the legend handle.
        descent = 0.35*self._approx_text_height()*(self.handleheight - 0.7)
        # 0.35 and 0.7 are just heuristic numbers. this may need to be improbed
        height = self._approx_text_height() * self.handleheight - descent
        # each handle needs to be drawn inside a box of (x, y, w, h) =
        # (0, -descent, width, height).  And their corrdinates should
        # be given in the display coordinates.

        # The transformation of each handle will be automatically set
        # to self.get_trasnform(). If the artist does not uses its
        # default trasnform (eg, Collections), you need to
        # manually set their transform to the self.get_transform().


        legend_handler_map = self.get_legend_handler_map()

        for orig_handle, lab in zip(handles, labels):

            handler = self.get_legend_handler(legend_handler_map, orig_handle)

            if handler is None:
                warnings.warn("Legend does not support %s\nUse proxy artist instead.\n\nhttp://matplotlib.sourceforge.net/users/legend_guide.html#using-proxy-artist\n" % (str(orig_handle),))
                handle_list.append(None)
                continue

            textbox = TextArea(lab, textprops=label_prop,
                               multilinebaseline=True, minimumdescent=True)
            text_list.append(textbox._text)

            labelboxes.append(textbox)

            handlebox = DrawingArea(width=self.handlelength*fontsize,
                                    height=height,
                                    xdescent=0., ydescent=descent)

            handle = handler(self, orig_handle, \
                             #xdescent, ydescent, width, height,
                             fontsize,
                             handlebox)
            handle_list.append(handle)




            handleboxes.append(handlebox)


        if len(handleboxes) > 0:

            # We calculate number of rows in each column. The first
            # (num_largecol) columns will have (nrows+1) rows, and remaing
            # (num_smallcol) columns will have (nrows) rows.
            ncol = min(self._ncol, len(handleboxes))
            nrows, num_largecol = divmod(len(handleboxes), ncol)
            num_smallcol = ncol-num_largecol

            # starting index of each column and number of rows in it.
            largecol = safezip(range(0, num_largecol*(nrows+1), (nrows+1)),
                               [nrows+1] * num_largecol)
            smallcol = safezip(range(num_largecol*(nrows+1), len(handleboxes), nrows),
                               [nrows] * num_smallcol)
        else:
            largecol, smallcol = [], []

        handle_label = safezip(handleboxes, labelboxes)
        columnbox = []
        for i0, di in largecol+smallcol:
            # pack handleBox and labelBox into itemBox
            itemBoxes = [HPacker(pad=0,
                                 sep=self.handletextpad*fontsize,
                                 children=[h, t], align="baseline")
                         for h, t in handle_label[i0:i0+di]]
            # minimumdescent=False for the text of the last row of the column
            itemBoxes[-1].get_children()[1].set_minimumdescent(False)

            # pack columnBox
            columnbox.append(VPacker(pad=0,
                                        sep=self.labelspacing*fontsize,
                                        align="baseline",
                                        children=itemBoxes))

        if self._mode == "expand":
            mode = "expand"
        else:
            mode = "fixed"

        sep = self.columnspacing*fontsize

        self._legend_handle_box = HPacker(pad=0,
                                          sep=sep, align="baseline",
                                          mode=mode,
                                          children=columnbox)

        self._legend_title_box = TextArea("")

        self._legend_box = VPacker(pad=self.borderpad*fontsize,
                                   sep=self.labelspacing*fontsize,
                                   align="center",
                                   children=[self._legend_title_box,
                                             self._legend_handle_box])

        self._legend_box.set_figure(self.figure)

        self.texts = text_list
        self.legendHandles = handle_list


    def _auto_legend_data(self):
        """
        Returns list of vertices and extents covered by the plot.

        Returns a two long list.

        First element is a list of (x, y) vertices (in
        display-coordinates) covered by all the lines and line
        collections, in the legend's handles.

        Second element is a list of bounding boxes for all the patches in
        the legend's handles.
        """

        assert self.isaxes # should always hold because function is only called internally

        ax = self.parent
        vertices = []
        bboxes = []
        lines = []

        for handle in ax.lines:
            assert isinstance(handle, Line2D)
            path = handle.get_path()
            trans = handle.get_transform()
            tpath = trans.transform_path(path)
            lines.append(tpath)

        for handle in ax.patches:
            assert isinstance(handle, Patch)

            if isinstance(handle, Rectangle):
                transform = handle.get_data_transform()
                bboxes.append(handle.get_bbox().transformed(transform))
            else:
                transform = handle.get_transform()
                bboxes.append(handle.get_path().get_extents(transform))

        return [vertices, bboxes, lines]

    def draw_frame(self, b):
        'b is a boolean.  Set draw frame to b'
        self.set_frame_on(b)

    def get_children(self):
        'return a list of child artists'
        children = []
        if self._legend_box:
            children.append(self._legend_box)
        children.extend(self.get_lines())
        children.extend(self.get_patches())
        children.extend(self.get_texts())
        children.append(self.get_frame())

        if self._legend_title_box:
            children.append(self.get_title())
        return children

    def get_frame(self):
        'return the Rectangle instance used to frame the legend'
        return self.legendPatch

    def get_lines(self):
        'return a list of lines.Line2D instances in the legend'
        return [h for h in self.legendHandles if isinstance(h, Line2D)]

    def get_patches(self):
        'return a list of patch instances in the legend'
        return silent_list('Patch', [h for h in self.legendHandles if isinstance(h, Patch)])

    def get_texts(self):
        'return a list of text.Text instance in the legend'
        return silent_list('Text', self.texts)

    def set_title(self, title, prop=None):
        """
        set the legend title. Fontproperties can be optionally set
        with *prop* parameter.
        """
        self._legend_title_box._text.set_text(title)

        if prop is not None:
            if isinstance(prop, dict):
                prop = FontProperties(**prop)
            self._legend_title_box._text.set_fontproperties(prop)

        if title:
            self._legend_title_box.set_visible(True)
        else:
            self._legend_title_box.set_visible(False)

    def get_title(self):
        'return Text instance for the legend title'
        return self._legend_title_box._text

    def get_window_extent(self, *args, **kwargs) :
        'return a extent of the the legend'
        return self.legendPatch.get_window_extent(*args, **kwargs)


    def get_frame_on(self):
        """
        Get whether the legend box patch is drawn
        """
        return self._drawFrame

    def set_frame_on(self, b):
        """
        Set whether the legend box patch is drawn

        ACCEPTS: [ *True* | *False* ]
        """
        self._drawFrame = b

    def get_bbox_to_anchor(self):
        """
        return the bbox that the legend will be anchored
        """
        if self._bbox_to_anchor is None:
            return self.parent.bbox
        else:
            return self._bbox_to_anchor


    def set_bbox_to_anchor(self, bbox, transform=None):
        """
        set the bbox that the legend will be anchored.

        *bbox* can be a BboxBase instance, a tuple of [left, bottom,
        width, height] in the given transform (normalized axes
        coordinate if None), or a tuple of [left, bottom] where the
        width and height will be assumed to be zero.
        """
        if bbox is None:
            self._bbox_to_anchor = None
            return
        elif isinstance(bbox, BboxBase):
            self._bbox_to_anchor = bbox
        else:
            try:
                l = len(bbox)
            except TypeError:
                raise ValueError("Invalid argument for bbox : %s" % str(bbox))

            if l == 2:
                bbox = [bbox[0], bbox[1], 0, 0]

            self._bbox_to_anchor = Bbox.from_bounds(*bbox)

        if transform is None:
            transform = BboxTransformTo(self.parent.bbox)

        self._bbox_to_anchor = TransformedBbox(self._bbox_to_anchor,
                                               transform)



    def _get_anchored_bbox(self, loc, bbox, parentbbox, renderer):
        """
        Place the *bbox* inside the *parentbbox* according to a given
        location code. Return the (x,y) coordinate of the bbox.

        - loc: a location code in range(1, 11).
          This corresponds to the possible values for self._loc, excluding "best".

        - bbox: bbox to be placed, display coodinate units.
        - parentbbox: a parent box which will contain the bbox. In
            display coordinates.
        """
        assert loc in range(1,11) # called only internally

        BEST, UR, UL, LL, LR, R, CL, CR, LC, UC, C = range(11)

        anchor_coefs={UR:"NE",
                      UL:"NW",
                      LL:"SW",
                      LR:"SE",
                      R:"E",
                      CL:"W",
                      CR:"E",
                      LC:"S",
                      UC:"N",
                      C:"C"}

        c = anchor_coefs[loc]

        fontsize = renderer.points_to_pixels(self._fontsize)
        container = parentbbox.padded(-(self.borderaxespad) * fontsize)
        anchored_box = bbox.anchored(c, container=container)
        return anchored_box.x0, anchored_box.y0


    def _find_best_position(self, width, height, renderer, consider=None):
        """
        Determine the best location to place the legend.

        `consider` is a list of (x, y) pairs to consider as a potential
        lower-left corner of the legend. All are display coords.
        """

        assert self.isaxes # should always hold because function is only called internally

        verts, bboxes, lines = self._auto_legend_data()

        bbox = Bbox.from_bounds(0, 0, width, height)
        consider = [self._get_anchored_bbox(x, bbox, self.get_bbox_to_anchor(),
                                            renderer) for x in range(1, len(self.codes))]

        #tx, ty = self.legendPatch.get_x(), self.legendPatch.get_y()

        candidates = []
        for l, b in consider:
            legendBox = Bbox.from_bounds(l, b, width, height)
            badness = 0
            badness = legendBox.count_contains(verts)
            badness += legendBox.count_overlaps(bboxes)
            for line in lines:
                if line.intersects_bbox(legendBox):
                    badness += 1

            ox, oy = l, b
            if badness == 0:
                return ox, oy

            candidates.append((badness, (l, b)))

        # rather than use min() or list.sort(), do this so that we are assured
        # that in the case of two equal badnesses, the one first considered is
        # returned.
        # NOTE: list.sort() is stable.But leave as it is for now. -JJL
        minCandidate = candidates[0]
        for candidate in candidates:
            if candidate[0] < minCandidate[0]:
                minCandidate = candidate

        ox, oy = minCandidate[1]

        return ox, oy

    def contains(self, event):
        return self.legendPatch.contains(event)

    def draggable(self, state=None, use_blit=False, update="loc"):
        """
        Set the draggable state -- if state is

          * None : toggle the current state

          * True : turn draggable on

          * False : turn draggable off

        If draggable is on, you can drag the legend on the canvas with
        the mouse.  The DraggableLegend helper instance is returned if
        draggable is on.

        The update parameter control which parameter of the legend changes
        when dragged. If update is "loc", the *loc* paramter of the legend
        is changed. If "bbox", the *bbox_to_anchor* parameter is changed.
        """
        is_draggable = self._draggable is not None

        # if state is None we'll toggle
        if state is None:
            state = not is_draggable

        if state:
            if self._draggable is None:
                self._draggable = DraggableLegend(self, use_blit, update=update)
        else:
            if self._draggable is not None:
                self._draggable.disconnect()
            self._draggable = None

        return self._draggable