Re: Plotting to a matplotlib / pyplot window does not work

On Thu, 23 Jul 2020 at 11.50, Matthias Brennwald <[email protected]> wrote:

> On Mo, Jul 20, 2020 at 23:02, Andrea Gavana <[email protected]>
> wrote:
>
> A relatively straightforward solution is to embed your plot in a wxPython
> window and update the plot from a thread when new data becomes available.
>
>
> Ok, I revised my code accordingly (see attached example), and it works a
> lot better. However, if the plot is updated every time after adding a new
> data value, the GUI locks up if the rate of incoming data becomes too high.
>
> I worked around this by setting a flag that is TRUE while the plot is
> being updated, and the code calls the updating of the plot only if this
> flag is FALSE (this is also in the attached example). This works ok, but my
> gut feeling is that there is a better / cleaner / more elegant way of
> avoiding the GUI lockup.
>
> Thoughts, ideas, suggestions?
>

I also have an application that does heavy calculations in a separate
thread and updates the main plotting window at selected timesteps.
Depending on the model, I may get between 1 and 100 results per second and
I have to update the plot with that.

One solution that I have found is to copy the background (axes, labels,
ticks and so on) and update the lines/points on the fly. something like
this:

import numpy
import matplotlib.pyplot as plt

x = numpy .arange(0,2*numpy.pi,0.01)
line, = plt.plot(x, numpy.sin(x), animated=True)

# save the clean slate background -- everything but the animated line
# is drawn and saved in the pixel buffer background
background = canvas.copy_from_bbox(ax.bbox)

for i in range(100):
    # simulate stuff coming from a separate thread with a loop
    canvas.restore_region(background)
    # update the data
    line.set_ydata(numpy.sin(x+i/10.0))
    # just draw the animated artist
    ax.draw_artist(line)
    # just redraw the axes rectangle
    canvas.blit(ax.bbox)

I just save references to my line(s) as a class attribute and update those
when new data comes in. I get decent FPS - depending on the machine and the
model, I can keep up with 100 updates per second.

Andrea.

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