.. _event_handling-looking_glass:

event_handling example code: looking_glass.py
=============================================

[`source code <looking_glass.py>`_]

::

    import numpy as np
    import matplotlib.pyplot as plt
    import matplotlib.patches as patches
    x, y = np.random.rand(2, 200)
    
    fig = plt.figure()
    ax = fig.add_subplot(111)
    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)
    
    class EventHandler:
       def __init__(self):
           fig.canvas.mpl_connect('button_press_event', self.onpress)
           fig.canvas.mpl_connect('button_release_event', self.onrelease)
           fig.canvas.mpl_connect('motion_notify_event', self.onmove)
           self.x0, self.y0 = circ.center
           self.pressevent = None
    
       def onpress(self, event):
          if event.inaxes!=ax:
             return
    
          if not circ.contains(event)[0]:
             return
    
          self.pressevent = event
    
       def onrelease(self, event):
          self.pressevent = None
          self.x0, self.y0 = circ.center
    
       def onmove(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()
    

Keywords: python, matplotlib, pylab, example, codex (see :ref:`how-to-search-examples`)