user interface - Matplotlib plot zooming with scroll wheel

Question

Is it possible to bind the scroll wheel to zoom in/out when the cursor is hovering over a matplotlib plot?

Answer 1

This should work. It re-centers the graph on the location of the pointer when you scroll.

import matplotlib.pyplot as plt


def zoom_factory(ax,base_scale = 2.):
    def zoom_fun(event):
        # get the current x and y limits
        cur_xlim = ax.get_xlim()
        cur_ylim = ax.get_ylim()
        cur_xrange = (cur_xlim[1] - cur_xlim[0])*.5
        cur_yrange = (cur_ylim[1] - cur_ylim[0])*.5
        xdata = event.xdata # get event x location
        ydata = event.ydata # get event y location
        if event.button == 'up':
            # deal with zoom in
            scale_factor = 1/base_scale
        elif event.button == 'down':
            # deal with zoom out
            scale_factor = base_scale
        else:
            # deal with something that should never happen
            scale_factor = 1
            print event.button
        # set new limits
        ax.set_xlim([xdata - cur_xrange*scale_factor,
                     xdata + cur_xrange*scale_factor])
        ax.set_ylim([ydata - cur_yrange*scale_factor,
                     ydata + cur_yrange*scale_factor])
        plt.draw() # force re-draw

    fig = ax.get_figure() # get the figure of interest
    # attach the call back
    fig.canvas.mpl_connect('scroll_event',zoom_fun)

    #return the function
    return zoom_fun

Assuming you have an axis object ax

 ax.plot(range(10))
 scale = 1.5
 f = zoom_factory(ax,base_scale = scale)

The optional argument base_scale allows you to set the scale factor to be what ever you want.

make sure you keep a copy of f around. The call back uses a weak-ref so if you do not keep a copy of f it might be garbage collected.

After writing this answer I decided this actually quite useful and put it in a gist