Python - Blit With Subplots Only Plotting Last Subplots

I am trying to plot multiple subplots in real-time in my python application. Ideally, I should also be able to plot multiple lines in each subplot, but for simplicity here I assume

Solution 1:

In the current implementation you set the axis limits only for the last plot, i.e. plt.axis([xmin, xmax, ymin, ymax]) works on the last active subplot.

Instead you would need to update all of the axes ax1 to ax4,

ax1.axis([xmin, xmax, ymin, ymax])
ax2.axis([xmin, xmax, ymin, ymax])
ax3.axis([xmin, xmax, ymin, ymax])
ax4.axis([xmin, xmax, ymin, ymax])

to let their limits follow the data.

Additionally it seems beneficial to update the data outside the blitting condition, such that one can compare blitting without blitting.

Complete code:

import time    
import matplotlib
matplotlib.use('TkAgg')   
import matplotlib.pylab as plt
import random

deftest_fps(use_blit=True):

    ax1.cla()
    ax1.set_title('Sensor Input vs. Time -')
    ax1.set_xlabel('Time (s)')
    ax1.set_ylabel('Sensor Input (mV)')
    ax2.cla()
    ax2.set_title('Sensor Input vs. Time -' )
    ax2.set_xlabel('Time (s)')
    ax2.set_ylabel('Sensor Input (mV)')
    ax3.cla()
    ax3.set_title('Sensor Input vs. Time -')
    ax3.set_xlabel('Time (s)')
    ax3.set_ylabel('Sensor Input (mV)')
    ax4.cla()
    ax4.set_title('Sensor Input vs. Time -')
    ax4.set_xlabel('Time (s)')
    ax4.set_ylabel('Sensor Input (mV)')

    plt.ion()  # Set interactive mode ON, so matplotlib will not be blocking the window
    plt.show(False)  # Set to false so that the code doesn't stop here

    cur_time = time.time()
    #    ax1.hold(True)#    ax2.hold(True)#    ax3.hold(True)#    ax4.hold(True)

    x, y = [], []
    times = [time.time() - cur_time]  # Create blank array to hold time values
    y.append(0)

    line1, = ax1.plot(times, y, '.-', alpha=0.8, color="gray", markerfacecolor="red")
    line2, = ax2.plot(times, y, '.-', alpha=0.8, color="gray", markerfacecolor="red")
    line3, = ax3.plot(times, y, '.-', alpha=0.8, color="gray", markerfacecolor="red")
    line4, = ax4.plot(times, y, '.-', alpha=0.8, color="gray", markerfacecolor="red")


    fig.show()
    fig.canvas.draw()

    if use_blit:
        background1 = fig.canvas.copy_from_bbox(ax1.bbox) # cache the background
        background2 = fig.canvas.copy_from_bbox(ax2.bbox) # cache the background
        background3 = fig.canvas.copy_from_bbox(ax3.bbox) # cache the background
        background4 = fig.canvas.copy_from_bbox(ax4.bbox) # cache the background

    tic = time.time()

    niter = 200
    i = 0while i < niter:

        fields = random.random() * 100

        times.append(time.time() - cur_time)
        y.append(fields)

        # this removes the tail of the data so you can run for long hours. You can cache this# and store it in a pickle variable in parallel.iflen(times) > 50:
           del y[0]
           del times[0]

        xmin, xmax, ymin, ymax = [min(times) / 1.05, max(times) * 1.1, -5,110]

        # feed the new data to the plot and set the axis limits again
        ax1.axis([xmin, xmax, ymin, ymax])
        ax2.axis([xmin, xmax, ymin, ymax])
        ax3.axis([xmin, xmax, ymin, ymax])
        ax4.axis([xmin, xmax, ymin, ymax])

        line1.set_data(times, y)
        line2.set_data(times, y)
        line3.set_data(times, y)
        line4.set_data(times, y)

        if use_blit:
            fig.canvas.restore_region(background1)    # restore background
            ax1.draw_artist(line1)                   # redraw just the points
            fig.canvas.blit(ax1.bbox)                # fill in the axes rectangle

            fig.canvas.restore_region(background2)    # restore background
            ax2.draw_artist(line2)                   # redraw just the points
            fig.canvas.blit(ax2.bbox)

            fig.canvas.restore_region(background3)    # restore background
            ax3.draw_artist(line3)                   # redraw just the points
            fig.canvas.blit(ax3.bbox)         

            fig.canvas.restore_region(background4)    # restore background
            ax4.draw_artist(line4)                   # redraw just the points
            fig.canvas.blit(ax4.bbox) 

        else:
            fig.canvas.draw()

        fig.canvas.flush_events()

        i += 1

    fps = niter / (time.time() - tic)
    return fps

fig = plt.figure()
ax1 = fig.add_subplot(4, 1, 1)
ax2 = fig.add_subplot(4, 1, 2)
ax3 = fig.add_subplot(4, 1, 3)
ax4 = fig.add_subplot(4, 1, 4)
fps1 = test_fps(use_blit=True)
print fps1

Just to note this runs without blitting at 10fps and with blitting at 16 fps on my computer.