检测鼠标悬停在图例上，并在 matplotlib 中显示工具提示（标签/注释）？

Question

我已经看到当鼠标悬停在 matplotlib 中的一个点上时可以显示标签吗？ - 但不幸的是，它对这个特定案例没有帮助。

考虑这个例子：

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import matplotlib
print("matplotlib.__version__ {}".format(matplotlib.__version__))
import matplotlib.pyplot as plt
import numpy as np


def onhover(event, fig, axes):
  print(event)

def main():
  xdata = np.arange(0, 101, 1) # 0 to 100, both included
  ydata1 = np.sin(0.01*xdata*np.pi/2)

  fig, ax1 = plt.subplots(1, 1, figsize=(9, 6), dpi=120)
  fig.subplots_adjust(hspace=0)

  pl11, = ax1.plot(xdata, ydata1, color="Red", label="My plot")

  leg = ax1.legend(ncol=1, bbox_to_anchor=(0,1.01), loc="lower left", borderaxespad=0, prop={'size': 8})

  fig.canvas.mpl_connect('motion_notify_event', lambda event: onhover(event, fig, (ax1,) ))
  plt.show()

# ENTRY POINT
if __name__ == '__main__':
  main()

结果如下图：

问题是：如果我移动鼠标指针，让它悬停在图例条目上，那么我在事件中得到的打印输出是：

....
motion_notify_event: xy=(175, 652) xydata=(None, None) button=None dblclick=False inaxes=None
motion_notify_event: xy=(174, 652) xydata=(None, None) button=None dblclick=False inaxes=None
motion_notify_event: xy=(173, 652) xydata=(None, None) button=None dblclick=False inaxes=None
motion_notify_event: xy=(172, 652) xydata=(None, None) button=None dblclick=False inaxes=None

...这是有道理的，因为我故意将图例放在情节之外。

但是，现在我不知道如何获得对图例条目的引用？ 我想要做的基本上是获取对图例条目的引用，以便我可以在“工具提示”（即，在这种情况下，Matplotlib）中编写与图例标签（此处为“我的情节”）相同的文本注释）后跟一些其他文本； 然后，一旦鼠标离开图例条目的区域，工具提示/注释就会消失。

我可以用 Matplotlib 实现这一点 - 如果可以，如何实现？

Answer 1

你可以这样做：

def onhover(event):
    if leg.get_window_extent().contains(event.x,event.y):
        print(event, "In legend! do something!")


xdata = np.arange(0, 101, 1) # 0 to 100, both included
ydata1 = np.sin(0.01*xdata*np.pi/2)

fig, ax1 = plt.subplots(1, 1, figsize=(9, 6), dpi=120)
pl11, = ax1.plot(xdata, ydata1, color="Red", label="My plot")
leg = ax1.legend(ncol=1, bbox_to_anchor=(0,1.01), loc="lower left", borderaxespad=0, prop={'size': 8})

fig.canvas.mpl_connect('motion_notify_event', onhover)
plt.show()

Answer 2

这是 OP 的完整返工，有两个绘图和两个图例条目，实际悬停 - 实现有点复杂，因为还需要考虑坐标系转换和 z 顺序：

这是代码 - 包括注释：

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import matplotlib
print("matplotlib.__version__ {}".format(matplotlib.__version__))
import matplotlib.pyplot as plt
import numpy as np


def onhover(event, fig, axes, leg, tooltip):
  if leg.get_window_extent().contains(event.x,event.y):
    print(event, "In legend! do something!")
    ax1 = axes[0]
    hand, labl = ax1.get_legend_handles_labels()
    #print(hand)
    #print(labl)
    r = plt.gcf().canvas.get_renderer()
    #for ilidx, ilabl in enumerate(labl): # labl contents are just str! so no geometry data
    #  print(ilabl.get_window_extent())
    #for ihidx, ihand in enumerate(hand):
    #  # NOTE: just ihand.get_window_extent() causes: TypeError: get_window_extent() missing 1 required positional argument: 'renderer'
    #  print(ihand.get_window_extent(r)) # apparently, this is the original line, not just the legend line, as here it prints: Bbox(x0=173.04545454545456, y0=104.10999999999999, x1=933.9545454545455, y1=606.71)
    #  if ihand.get_window_extent(r).contains(event.x,event.y):
    #    print("EEEE")
    hoveredtxt = None
    for itxt in leg.get_texts():
      #print(itxt)
      #print(itxt.get_window_extent().contains(event.x,event.y))
      if itxt.get_window_extent().contains(event.x,event.y):
        #print("Legend hover on: {}".format(itxt))
        hoveredtxt = itxt
        break
    if hoveredtxt is not None:
      tooltip.set_text("'{}' is hovered!".format(hoveredtxt.get_text()))
      tooltip.set_visible(True)
      # see: https://matplotlib.org/3.1.1/gallery/recipes/placing_text_boxes.html
      # https://matplotlib.org/3.1.1/tutorials/advanced/transforms_tutorial.html - None for "display" coord system
      tooltip.set_transform( None )
      tooltip.set_position( (event.x, event.y) ) # is by default in data coords!
    else:
      tooltip.set_visible(False)
    fig.canvas.draw_idle()


def main():
  xdata = np.arange(0, 101, 1) # 0 to 100, both included
  ydata1 = np.sin(0.01*xdata*np.pi/2)
  ydata2 = 10*np.sin(0.01*xdata*np.pi/4)

  fig, ax1 = plt.subplots(1, 1, figsize=(9, 6), dpi=120)
  fig.subplots_adjust(hspace=0)

  pl11, = ax1.plot(xdata, ydata1, color="Red", label="My plot")
  pl12, = ax1.plot(xdata, ydata2, color="Blue", label="Other stuff")

  leg = ax1.legend(ncol=2, bbox_to_anchor=(0,1.01), loc="lower left", borderaxespad=0, prop={'size': 8})

  # NOTE: ax.annotate without an arrow is basically ax.text;
  #tooltip = ax.annotate("", xy=(0, 0), xytext=(-20, 20), textcoords="offset points",
  #                    bbox=dict(boxstyle="round", fc="w"),
  #                    arrowprops=dict(arrowstyle="->"))
  # however, no `textcoords` in .text; "The default transform specifies that text is in data coords, alternatively, you can specify text in axis coords", via transform=ax.transAxes
  # must add zorder of high number too, else the tooltip comes under the legend!
  tooltip = ax1.text(0, 0, 'TEST', bbox=dict(boxstyle="round", fc="w"), zorder=10)
  tooltip.set_visible(False)

  fig.canvas.mpl_connect('motion_notify_event', lambda event: onhover(event, fig, (ax1,), leg, tooltip ))
  plt.show()

# ENTRY POINT
if __name__ == '__main__':
  main()