Anchored Artists

This example illustrates the use of the anchored objects without the helper classes found in mpl_toolkits.axes_grid1. This version of the figure is similar to the one found in Simple Anchored Artists, but it is implemented using only the matplotlib namespace, without the help of additional toolkits.

from matplotlib import pyplot as plt
from matplotlib.lines import Line2D
from matplotlib.patches import Circle, Ellipse
from matplotlib.offsetbox import (
    AnchoredOffsetbox, AuxTransformBox, DrawingArea, TextArea, VPacker)


def draw_text(ax):
    """Draw a text-box anchored to the upper-left corner of the figure."""
    box = AnchoredOffsetbox(child=TextArea("Figure 1a"),
                            loc="upper left", frameon=True)
    box.patch.set_boxstyle("round,pad=0.,rounding_size=0.2")
    ax.add_artist(box)


def draw_circles(ax):
    """Draw circles in axes coordinates."""
    area = DrawingArea(40, 20, 0, 0)
    area.add_artist(Circle((10, 10), 10, fc="tab:blue"))
    area.add_artist(Circle((30, 10), 5, fc="tab:red"))
    box = AnchoredOffsetbox(
        child=area, loc="upper right", pad=0, frameon=False)
    ax.add_artist(box)


def draw_ellipse(ax):
    """Draw an ellipse of width=0.1, height=0.15 in data coordinates."""
    aux_tr_box = AuxTransformBox(ax.transData)
    aux_tr_box.add_artist(Ellipse((0, 0), width=0.1, height=0.15))
    box = AnchoredOffsetbox(child=aux_tr_box, loc="lower left", frameon=True)
    ax.add_artist(box)


class AnchoredSizeBar(AnchoredOffsetbox):
    def __init__(self, transform, size, label, loc,
                 pad=0.1, borderpad=0.1, sep=2, prop=None, frameon=True):
        """
        Draw a horizontal bar with the size in data coordinate of the given
        axes. A label will be drawn underneath (center-aligned).

        pad, borderpad in fraction of the legend font size (or prop)
        sep in points.
        """
        self.size_bar = AuxTransformBox(transform)
        self.size_bar.add_artist(Line2D([0, size], [0, 0], color="black"))
        self.txt_label = TextArea(label)
        self._box = VPacker(children=[self.size_bar, self.txt_label],
                            align="center",
                            pad=0, sep=sep)
        super().__init__(loc, pad=pad, borderpad=borderpad,
                         child=self._box, prop=prop, frameon=frameon)


def draw_sizebar(ax):
    """
    Draw a horizontal bar with length of 0.1 in data coordinates,
    with a fixed label underneath.
    """
    asb = AnchoredSizeBar(ax.transData,
                          0.1,
                          r"1$^{\prime}$",
                          loc='lower center',
                          pad=0.1, borderpad=0.5, sep=5,
                          frameon=False)
    ax.add_artist(asb)


fig, ax = plt.subplots()
ax.set_aspect(1)

draw_text(ax)
draw_circles(ax)
draw_ellipse(ax)
draw_sizebar(ax)

plt.show()