>>> """
========
Viewlims
========

Creates two identical panels.  Zooming in on the right panel will show
a rectangle in the first panel, denoting the zoomed region.
"""
... import numpy as np
... import matplotlib.pyplot as plt
... from matplotlib.patches import Rectangle
... 
... 
... # We just subclass Rectangle so that it can be called with an Axes
... # instance, causing the rectangle to update its shape to match the
... # bounds of the Axes
... class UpdatingRect(Rectangle):
...     def __call__(self, ax):
...         self.set_bounds(*ax.viewLim.bounds)
...         ax.figure.canvas.draw_idle()
... 
... 
... # A class that will regenerate a fractal set as we zoom in, so that you
... # can actually see the increasing detail.  A box in the left panel will show
... # the area to which we are zoomed.
... class MandelbrotDisplay:
...     def __init__(self, h=500, w=500, niter=50, radius=2., power=2):
...         self.height = h
...         self.width = w
...         self.niter = niter
...         self.radius = radius
...         self.power = power
... 
...     def compute_image(self, xstart, xend, ystart, yend):
...         self.x = np.linspace(xstart, xend, self.width)
...         self.y = np.linspace(ystart, yend, self.height).reshape(-1, 1)
...         c = self.x + 1.0j * self.y
...         threshold_time = np.zeros((self.height, self.width))
...         z = np.zeros(threshold_time.shape, dtype=complex)
...         mask = np.ones(threshold_time.shape, dtype=bool)
...         for i in range(self.niter):
...             z[mask] = z[mask]**self.power + c[mask]
...             mask = (np.abs(z) < self.radius)
...             threshold_time += mask
...         return threshold_time
... 
...     def ax_update(self, ax):
...         ax.set_autoscale_on(False)  # Otherwise, infinite loop
...         # Get the number of points from the number of pixels in the window
...         self.width, self.height = \
            np.round(ax.patch.get_window_extent().size).astype(int)
...         # Get the range for the new area
...         vl = ax.viewLim
...         extent = vl.x0, vl.x1, vl.y0, vl.y1
...         # Update the image object with our new data and extent
...         im = ax.images[-1]
...         im.set_data(self.compute_image(*extent))
...         im.set_extent(extent)
...         ax.figure.canvas.draw_idle()
... 
... 
... md = MandelbrotDisplay()
... Z = md.compute_image(-2., 0.5, -1.25, 1.25)
... 
... fig1, (ax1, ax2) = plt.subplots(1, 2)
... ax1.imshow(Z, origin='lower',
...            extent=(md.x.min(), md.x.max(), md.y.min(), md.y.max()))
... ax2.imshow(Z, origin='lower',
...            extent=(md.x.min(), md.x.max(), md.y.min(), md.y.max()))
... 
... rect = UpdatingRect(
...     [0, 0], 0, 0, facecolor='none', edgecolor='black', linewidth=1.0)
... rect.set_bounds(*ax2.viewLim.bounds)
... ax1.add_patch(rect)
... 
... # Connect for changing the view limits
... ax2.callbacks.connect('xlim_changed', rect)
... ax2.callbacks.connect('ylim_changed', rect)
... 
... ax2.callbacks.connect('xlim_changed', md.ax_update)
... ax2.callbacks.connect('ylim_changed', md.ax_update)
... ax2.set_title("Zoom here")
... 
... plt.show()
...