# 锚定艺术家对象

这个使用没有辅助类的锚定对象的示例在[Matplotlib axes_grid1 Toolkit](https://matplotlib.org/api/toolkits/axes_grid1.html#toolkit-axesgrid1-index)中找到。此版本的图与Simple [Anchored Artists](https://matplotlib.org/gallery/axes_grid1/simple_anchored_artists.html)中的版本类似，但它仅使用matplotlib命名空间实现，没有其他工具包的帮助。

![锚定艺术家对象示例](https://matplotlib.org/_images/sphx_glr_anchored_artists_001.png)

```python
from matplotlib import pyplot as plt
from matplotlib.patches import Rectangle, Ellipse
from matplotlib.offsetbox import (
    AnchoredOffsetbox, AuxTransformBox, DrawingArea, TextArea, VPacker)


class AnchoredText(AnchoredOffsetbox):
    def __init__(self, s, loc, pad=0.4, borderpad=0.5,
                 prop=None, frameon=True):
        self.txt = TextArea(s, minimumdescent=False)
        super().__init__(loc, pad=pad, borderpad=borderpad,
                         child=self.txt, prop=prop, frameon=frameon)


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


class AnchoredDrawingArea(AnchoredOffsetbox):
    def __init__(self, width, height, xdescent, ydescent,
                 loc, pad=0.4, borderpad=0.5, prop=None, frameon=True):
        self.da = DrawingArea(width, height, xdescent, ydescent)
        super().__init__(loc, pad=pad, borderpad=borderpad,
                         child=self.da, prop=None, frameon=frameon)


def draw_circle(ax):
    """
    Draw a circle in axis coordinates
    """
    from matplotlib.patches import Circle
    ada = AnchoredDrawingArea(20, 20, 0, 0,
                              loc='upper right', pad=0., frameon=False)
    p = Circle((10, 10), 10)
    ada.da.add_artist(p)
    ax.add_artist(ada)


class AnchoredEllipse(AnchoredOffsetbox):
    def __init__(self, transform, width, height, angle, loc,
                 pad=0.1, borderpad=0.1, prop=None, frameon=True):
        """
        Draw an ellipse the size in data coordinate of the give axes.

        pad, borderpad in fraction of the legend font size (or prop)
        """
        self._box = AuxTransformBox(transform)
        self.ellipse = Ellipse((0, 0), width, height, angle)
        self._box.add_artist(self.ellipse)
        super().__init__(loc, pad=pad, borderpad=borderpad,
                         child=self._box, prop=prop, frameon=frameon)


def draw_ellipse(ax):
    """
    Draw an ellipse of width=0.1, height=0.15 in data coordinates
    """
    ae = AnchoredEllipse(ax.transData, width=0.1, height=0.15, angle=0.,
                         loc='lower left', pad=0.5, borderpad=0.4,
                         frameon=True)

    ax.add_artist(ae)


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(Rectangle((0, 0), size, 0, ec="black", lw=1.0))

        self.txt_label = TextArea(label, minimumdescent=False)

        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)


ax = plt.gca()
ax.set_aspect(1.)

draw_text(ax)
draw_circle(ax)
draw_ellipse(ax)
draw_sizebar(ax)

plt.show()
```

## 下载这个示例
            
- [下载python源码: anchored_artists.py](https://matplotlib.org/_downloads/anchored_artists.py)
- [下载Jupyter notebook: anchored_artists.ipynb](https://matplotlib.org/_downloads/anchored_artists.ipynb)