MacOSX does not render frames in which new artists are added when blitting

Bug report

Bug summary

Using FuncAnimation with the MacOSX backend and blitting turned on, every frame in which a new artist or patch is added to the axes is blank, while all other frames render normally. This does not happen with the TkAgg backend, and presumable MacOSX is the only affected backend.

Code for reproduction

from random import random

import matplotlib
matplotlib.use('MacOSX')
import matplotlib.pyplot as plt
from matplotlib.animation import FuncAnimation

fig = plt.figure()
axe = fig.add_axes([0, 0, 1, 1], frameon=False)
circles = []

def update(i):
    if not i % 10:
        new_circle = plt.Circle((random(), random()), 0.05, color='black')
        axe.add_patch(new_circle)
        circles.append(new_circle)

    for circle in circles:
        circle.center = (random(), random())

    return circles

animation = FuncAnimation(fig, update, frames=60, interval=1000/2, repeat=False, blit=True)
plt.show()

Actual outcome

Every 10th frame, when a new circle is added to the axes, the figure is blank; every other frame outputs normally.

Expected outcome

Every frame should render.

Matplotlib version

Operating system: macOS Mojave 10.14.6
Matplotlib version: 3.2.1
Matplotlib backend (print(matplotlib.get_backend())): MacOSX
Python version: 3.8.2

Installed using Conda from conda-forge.

I run into a similar bug with macOS Catalina as well as with Big Sur and matplotlib 3.3.2.
I try to set the positions of a PathCollection (scatter) for every frame. Furthermore, I create new quiver for every frame.
The corresponding code can be found here.

With this setup I experience the same issue as described above. Only in my case none of the mentioned artists is rendered at all. Probably because I update them for every frame.

@mfosterw

@mfosterw Does it work if you do fig.stale_callback = None before starting the animation does it solve the problem?

@HaaLeo Can you reduce your problem to a minimal reproducible example?

@tacaswell

@tacaswell sure thing.
The example should show a marker moving smoothly from [0, 0] to [1, 1] along an arrow.
It works with the TkAgg backend but not with MacOSX. With the latter one neither a marker nor arrow is shown.

Details

import matplotlib.pyplot as plt
from matplotlib import animation
import numpy as np

class BaseVisualizer():
    def __init__(self, **kwargs):
        self.__iteration_number = kwargs.get('iteration_number', 1)
        self.__intervals = 1
        self.__interval_ms = kwargs.get('interval', 2000)


        self._marker_size = 4
        self._index = 0

        self._positions = np.zeros(2)
        self._velocities = np.ones(2)
        self.__frame_interval = 50  # ms

    def replay(self):
        self._fig = plt.figure()

        ax = self._fig.add_subplot(1, 1, 1, label='BaseAxis')

        # Plot all particle pos
        self.__particles = ax.scatter([], [], marker='o', zorder=2, color='red')

        # Plot all velocities
        self.__particle_vel = ax.quiver([], [], [], [], angles='xy', scale_units='xy', scale=1)

        self.__rectangle = plt.Rectangle([0,0], 1, 1, ec='none', lw=2, fc='none')
        ax.add_patch(self.__rectangle)

        # Amount of frames to play considering one interval should last __interval ms.
        frames = int(self.__intervals*self.__interval_ms/self.__frame_interval)

        # iteration_number+1 for initialization frame
        _ = animation.FuncAnimation(self._fig, self._animate, frames=frames, interval=self.__frame_interval,
                                    blit=True, repeat=False, fargs=[frames])

        plt.show()

    def _animate(self, i: int, frames: int):
        """
        Animation function for animations. Only used for FuncAnimation
        """

        self._marker_size = int(50 * self._fig.get_figwidth()/self._fig.dpi)

        # Calculate the scale to apply to the data in order to generate a more dynamic visualization
        scale = i / (frames/self.__intervals)

        # Calculate scaled position and velocity

        pos_scaled = self._positions + scale * self._velocities
        vel_scaled = (1-scale)*self._velocities

        # Update the particle position
        self.__particles.set_offsets(pos_scaled)
        self.__particles.set_sizes([self._marker_size**2])

        # Update the velocities
        ax = self._fig.gca(label='BaseAxis')
        self.__particle_vel = ax.quiver(pos_scaled[0], pos_scaled[1], vel_scaled[0], vel_scaled[1], angles='xy', scale_units='xy', scale=1, color='#CFCFCF', width=self._marker_size*0.001)

        return self.__particles, self.__particle_vel


if __name__ == '__main__':
    vis = BaseVisualizer()
    vis.replay()

@tacaswell

@tacaswell can you reproduce the error with the sample code above?

@HaaLeo

Thank you for re-upping this, I missed your initial reply.

@HaaLeo I can not reproduce the issue (but I do not have a mac). Can you try the fig.stale_callback = None?

If you add

self._fig.canvas.mpl_connect('draw_event', lambda ev: print('Drawing!'))

to the top of replay how many times does it print 'Drawing'? My guess is that something about the osx backend is triggering an extra full-draw when an artist is added. However, when you are using blitting the animated artists are excluded from that draw pass (so that we can get a "clean" background image to animate on top of). If the order is "add artists, updating via blitting, re-draw!", then you will see blank frames when new artists are added.

attn @dopplershift

ps, that is a very cool example.

@tacaswell

@tacaswell thx for your fast reply (and the feedback on the example 😉)
I updated the example above with the following lines:

# ... other code
    def replay(self):
        self._fig = plt.figure()
        self._fig.canvas.mpl_connect('draw_event', lambda ev: print('Drawing!'))
        self._fig.stale_callback = None

# ... other code

With the MacOSX backend it prints 41 times Drawing!. With the TkAgg backend only three times.

Adding self._fig.stale_callback = None does not change that behavior.

Ok, so that confirms my guess as to why we get a blank screen and changes the question to "Why is OSX drawing 41 times?!".

Navigation Menu

Repository navigation

MacOSX does not render frames in which new artists are added when blitting #17445

Bug report

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

MacOSX does not render frames in which new artists are added when blitting #17445

Description

Bug report

Activity

HaaLeo commented on Nov 16, 2020

tacaswell commented on Nov 16, 2020

HaaLeo commented on Nov 16, 2020

HaaLeo commented on Nov 25, 2020

tacaswell commented on Nov 25, 2020

HaaLeo commented on Nov 25, 2020

tacaswell commented on Nov 25, 2020

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions