.. _event_handling-viewlims:

event_handling example code: viewlims.py
========================================

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

::

    # 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 MandlebrotDisplay(object):
        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 __call__(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=np.complex)
            mask = np.ones(threshold_time.shape, dtype=np.bool)
            for i in xrange(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
            dims = ax.axesPatch.get_window_extent().bounds
            self.width = int(dims[2] + 0.5)
            self.height = int(dims[2] + 0.5)
    
            #Get the range for the new area
            xstart,ystart,xdelta,ydelta = ax.viewLim.bounds
            xend = xstart + xdelta
            yend = ystart + ydelta
    
            # Update the image object with our new data and extent
            im = ax.images[-1]
            im.set_data(self.__call__(xstart, xend, ystart, yend))
            im.set_extent((xstart, xend, ystart, yend))
            ax.figure.canvas.draw_idle()
    
    md = MandlebrotDisplay()
    Z = md(-2., 0.5, -1.25, 1.25)
    
    fig = plt.figure()
    ax1 = fig.add_subplot(1, 2, 1)
    ax1.imshow(Z, origin='lower', extent=(md.x.min(), md.x.max(), md.y.min(), md.y.max()))
    
    ax2 = fig.add_subplot(1, 2, 2)
    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')
    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)
    
    plt.show()
    

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