>>> """
=============
Looking Glass
=============

Example using mouse events to simulate a looking glass for inspecting data.
"""
... import numpy as np
... import matplotlib.pyplot as plt
... import matplotlib.patches as patches
... 
... # Fixing random state for reproducibility
... np.random.seed(19680801)
... 
... x, y = np.random.rand(2, 200)
... 
... fig, ax = plt.subplots()
... circ = patches.Circle((0.5, 0.5), 0.25, alpha=0.8, fc='yellow')
... ax.add_patch(circ)
... 
... 
... ax.plot(x, y, alpha=0.2)
... line, = ax.plot(x, y, alpha=1.0, clip_path=circ)
... ax.set_title("Left click and drag to move looking glass")
... 
... 
... class EventHandler:
...     def __init__(self):
...         fig.canvas.mpl_connect('button_press_event', self.on_press)
...         fig.canvas.mpl_connect('button_release_event', self.on_release)
...         fig.canvas.mpl_connect('motion_notify_event', self.on_move)
...         self.x0, self.y0 = circ.center
...         self.pressevent = None
... 
...     def on_press(self, event):
...         if event.inaxes != ax:
...             return
... 
...         if not circ.contains(event)[0]:
...             return
... 
...         self.pressevent = event
... 
...     def on_release(self, event):
...         self.pressevent = None
...         self.x0, self.y0 = circ.center
... 
...     def on_move(self, event):
...         if self.pressevent is None or event.inaxes != self.pressevent.inaxes:
...             return
... 
...         dx = event.xdata - self.pressevent.xdata
...         dy = event.ydata - self.pressevent.ydata
...         circ.center = self.x0 + dx, self.y0 + dy
...         line.set_clip_path(circ)
...         fig.canvas.draw()
... 
... handler = EventHandler()
... plt.show()
...