Points to note when creating animations using `ultraplot`

[munechika-koyo]

Hello,

I really enjoy using ultraplot to create publication-quality plots with simple and straightforward settings.
Likewise, when I applied it to animation creation, I ran into a couple of weird problems.
So, I would like to keep them as notes here.

1. Need to set matplotlib.use("Agg")

When creating an animation with Python scripts, it is necessary to set the backend to Agg; otherwise, the resulting video contains totally horizontal noise.

2. Set tight=False

Set tight=False to avoid changing layout during animation. This change might be triggered when using the format method in the update function used for FuncAnimation.

3. Axis labels (toplabels, leftlabels) are outside the area

Labels like toplabels and leftlabels seem to be placed outside the figure rendering area.
This might be due to the tight layout, but I haven't found a solution yet.

This issue may be irrelevant to those who only want to create static images, but I would be happy if it is useful to someone.

[cvanelteren]

Hi there,

Do you have any code that I can try. This works fine:

import numpy as np
import ultraplot as uplt

xy = np.zeros((100, 2))
fig, ax = uplt.subplots()
(line,) = ax.plot(*xy.T)


def update(t):
    x, y = t, np.sin(t * np.pi * 2)
    xy = line.get_data()
    xy = np.roll(xy, -1, axis=1)
    xy[:, -1] = (x, y)
    line.set_data(xy)
    ax.autoscale()
    ax.set_xlim(0, t * 1.2)
    ax.set_ylim(-1.2, 1.2)
    fig.canvas.draw()
    fig.canvas.flush_events()


uplt.show(block=0)
t = 0
while True:
    update(t)
    uplt.pyplot.pause(1e-3)
    t += 0.01


uplt.show(block=1)

[cvanelteren]

Ah I see indeed the func animation is showing a lot of noise.

[cvanelteren]

hmm not sure where this would be coming from. The tightcommand is probably not necessary as it is turned off at the GridSpec level so it cannot do anything.

[cvanelteren]

I think the issue is partly caused by how the layouts are determined #479 should partially address is as the redraws are replaced by a (very) fast constraint based solver. However, on the default backend I still see this issue.

You can fix the outside labels showing by fixing the figure size (e.g. width = "3cm").

[cvanelteren]

Ah I found a clue! When you overwrite partial redraws it works with the default backend
fig.canvas.draw_idle = fig.canvas.draw will force a redraw every frame.

[cvanelteren]

So the issue is caused by the layout changing too much between draws. In matplotlib the layout is drawn once and not touched. The layout algorithm present in ultraplot keeps running excessive draws causing the issue we see when animating.

One way around this issue is by overwriting the idle draw as indicated above.

Since the plan is to replace the Algorithm, I will have to bank this until that has stabilized before fixing this.

[munechika-koyo]

hmm not sure where this would be coming from. The tightcommand is probably not necessary as it is turned off at the GridSpec level so it cannot do anything.

I tried to check the animation with/without the "tight" flag.

1. In case of tight=True (default)

test_animation.mp4

2. In case of tight=False

test_animation.mp4

Demo scripts

import matplotlib
import numpy as np
import ultraplot as uplt
from matplotlib.animation import FuncAnimation

matplotlib.use("Agg")
state = np.random.RandomState(51423)

fig, axs = uplt.subplots(
    nrows=1,
    ncols=2,
    tight=True,
    width="8cm",
)

mappables = []
for ax in axs:
    data = state.rand(10, 10)
    m = ax.heatmap(data, cmap="dusk")
    ax.colorbar(m, loc="t", tickdir="out", label="Axes Colorbars")
    mappables.append(m)

axs.format(
    abc="(a)",
    abcloc="ul",
    xlabel="xlabel",
    ylabel="ylabel",
    toplabels=("Left Axes", "Right Axes"),
    urtitle="1",
    suptitle="Test Animation",
)


def update(frame):
    global axs, mappables

    for m in mappables:
        data = state.rand(10, 10)
        m.set_array(data)

    axs.format(
        urtitle=f"{frame + 1}",
    )
    return mappables


ani = FuncAnimation(
    fig,
    update,
    frames=10,
    interval=500,
    blit=False,
)

ani.save("test_animation.mp4", writer="ffmpeg")

If tight=False, colorbar's width is properly fixed, but the outside text is cropped out.

[cvanelteren]

Did you try with the monkey patch I pitched above?

[munechika-koyo]

There appears to be no change if I set fig.canvas.draw_idle = fig.canvas.draw in the update function.
Neither outside update.

[munechika-koyo]

Thank you for fixing this issue previously.
Unfortunately, the layout seems to change during the animation when I use almost the same script as above, except that I set interval=100.

test_animation.mp4

[cvanelteren]

I think I fixed it on a pr so the monkey patch is not necessary anymore.