.. _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, 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(object):
        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`)