matplotlib绘制多子图共享鼠标光标的方法示例

matplotlib官方除了提供了鼠标十字光标的示例，还提供了同一图像内多子图共享光标的示例，其功能主要由widgets模块中的MultiCursor类提供支持。

MultiCursor类与Cursor类参数类似，差异主要在：

• Cursor类参数只有一个ax，即需要显示光标的子图；MultiCursor类参数为canvas和axes，其中axes为需要共享光标的子图列表。
• Cursor类中，光标默认是十字线；MultiCursor类中，光标默认为竖线。

官方示例

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.widgets import MultiCursor

t = np.arange(0.0, 2.0, 0.01)
s1 = np.sin(2*np.pi*t)
s2 = np.sin(4*np.pi*t)

fig, (ax1, ax2) = plt.subplots(2, sharex=True)
ax1.plot(t, s1)
ax2.plot(t, s2)

multi = MultiCursor(fig.canvas, (ax1, ax2), color='r', lw=1)
plt.show()

简易修改版

multi = MultiCursor(fig.canvas, (ax1, ax2), color='r', lw=1, horizOn=True, vertOn=True)

MultiCursor类源码

class MultiCursor(Widget):
  """
  Provide a vertical (default) and/or horizontal line cursor shared between
  multiple axes.

  For the cursor to remain responsive you must keep a reference to it.

  Example usage::

    from matplotlib.widgets import MultiCursor
    import matplotlib.pyplot as plt
    import numpy as np

    fig, (ax1, ax2) = plt.subplots(nrows=2, sharex=True)
    t = np.arange(0.0, 2.0, 0.01)
    ax1.plot(t, np.sin(2*np.pi*t))
    ax2.plot(t, np.sin(4*np.pi*t))

    multi = MultiCursor(fig.canvas, (ax1, ax2), color='r', lw=1,
              horizOn=False, vertOn=True)
    plt.show()

  """
  def __init__(self, canvas, axes, useblit=True, horizOn=False, vertOn=True,
         **lineprops):

    self.canvas = canvas
    self.axes = axes
    self.horizOn = horizOn
    self.vertOn = vertOn

    xmin, xmax = axes[-1].get_xlim()
    ymin, ymax = axes[-1].get_ylim()
    xmid = 0.5 * (xmin + xmax)
    ymid = 0.5 * (ymin + ymax)

    self.visible = True
    self.useblit = useblit and self.canvas.supports_blit
    self.background = None
    self.needclear = False

    if self.useblit:
      lineprops['animated'] = True

    if vertOn:
      self.vlines = [ax.axvline(xmid, visible=False, **lineprops)
              for ax in axes]
    else:
      self.vlines = []

    if horizOn:
      self.hlines = [ax.axhline(ymid, visible=False, **lineprops)
              for ax in axes]
    else:
      self.hlines = []

    self.connect()
    
  def connect(self):
    """Connect events."""
    self._cidmotion = self.canvas.mpl_connect('motion_notify_event',
                         self.onmove)
    self._ciddraw = self.canvas.mpl_connect('draw_event', self.clear)

  def disconnect(self):
    """Disconnect events."""
    self.canvas.mpl_disconnect(self._cidmotion)
    self.canvas.mpl_disconnect(self._ciddraw)

  def clear(self, event):
    """Clear the cursor."""
    if self.ignore(event):
      return
    if self.useblit:
      self.background = (
        self.canvas.copy_from_bbox(self.canvas.figure.bbox))
    for line in self.vlines + self.hlines:
      line.set_visible(False)

  def onmove(self, event):
    if self.ignore(event):
      return
    if event.inaxes is None:
      return
    if not self.canvas.widgetlock.available(self):
      return
    self.needclear = True
    if not self.visible:
      return
    if self.vertOn:
      for line in self.vlines:
        line.set_xdata((event.xdata, event.xdata))
        line.set_visible(self.visible)
    if self.horizOn:
      for line in self.hlines:
        line.set_ydata((event.ydata, event.ydata))
        line.set_visible(self.visible)
    self._update()


  def _update(self):
    if self.useblit:
      if self.background is not None:
        self.canvas.restore_region(self.background)
      if self.vertOn:
        for ax, line in zip(self.axes, self.vlines):
          ax.draw_artist(line)
      if self.horizOn:
        for ax, line in zip(self.axes, self.hlines):
          ax.draw_artist(line)
      self.canvas.blit()
    else:
      self.canvas.draw_idle()

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