Fast update of single points in a plot

Question

I have a matplotlib figure in which I have several plots. One has an image with a large number of points in it. The second has an axis in which I want to update a point loc

Answer 1

You are essentially ignoring most of what is needed for blitting. See e.g.

• why is plotting with Matplotlib so slow?
• Fast Live Plotting in Matplotlib / PyPlot

As usual you need to

• Draw the canvas, fig.canvas.draw()
• Store the background for later, fig.canvas.copy_from_bbox()
• Update the point, point.set_data
• Restore the background, fig.canvas.restore_region
• draw the point, ax.draw_artist
• blit the axes, fig.canvas.blit

Hence

import matplotlib.pyplot as plt
import numpy as np

class Test:
    def __init__(self):
        self.fig = plt.figure(1)
        # Axis with large plot
        self.ax_large = plt.subplot(121)
        self.ax_large.imshow(np.random.random((5000,5000)))
        # Follow the point
        self.ax = plt.subplot(122)
        self.ax.grid(True)

        # set some limits to the axes
        self.ax.set_xlim(-5,5)
        self.ax.set_ylim(-5,5)
        # Draw the canvas once
        self.fig.canvas.draw()
        # Store the background for later
        self.background = self.fig.canvas.copy_from_bbox(self.ax.bbox)
        # Now create some point
        self.point, = self.ax.plot(0,0, 'go')
        # Create callback to mouse movement
        self.cid = self.fig.canvas.callbacks.connect('motion_notify_event', 
                                                     self.callback)
        plt.show()

    def callback(self, event):
        if event.inaxes == self.ax:
            # Update point's location            
            self.point.set_data(event.xdata, event.ydata)
            # Restore the background
            self.fig.canvas.restore_region(self.background)
            # draw the point on the screen
            self.ax.draw_artist(self.point)
            # blit the axes
            self.fig.canvas.blit(self.ax.bbox)


tt = Test()