ENH: Use layout='constrained' for raw.plot in matplotlib

[larsoner]

There is a lot of subplot / margin / zen mode stuff in the raw.plot matplotlib backend, too much to change safely in #12050. We should see if using layout='constrained' can get us similar (or better) results as it would probably simplify a lot of code, including a lot of subplots_adjust calls in tutorials and examples to make room for fig.suptitle calls that wouldn't otherwise be required.

[larsoner]

It doesn't seem doable using 'constrained', but here is a proof of concept that it's doable using Divider to conrol the sizes rather than doing subplots_adjust gymnastics:

Code

import matplotlib.pyplot as plt
from mpl_toolkits.axes_grid1 import Divider, Size

h_normal = [Size.Fixed(0.25), Size.Scaled(1.), Size.Fixed(0.25)]
v_normal = [Size.Fixed(0.25), Size.Scaled(1.)]
h_zen = [Size.Fixed(0.25), Size.Scaled(1.), Size.Fixed(0)]
v_zen = [Size.Fixed(0), Size.Scaled(1.)]
zen = False

fig = plt.figure(layout=None)
div = Divider(fig, (0, 0, 1, 1), h_normal, v_normal)
ax_main = fig.add_axes(div.get_position(), axes_locator=div.new_locator(nx=1, ny=1))
ax_main.plot([1, 2, 3])
ax_help = fig.add_axes(div.get_position(), axes_locator=div.new_locator(nx=0, ny=0))
ax_help.text(0, 0, 'help')
ax_hscroll = fig.add_axes(div.get_position(), axes_locator=div.new_locator(nx=1, ny=0))
ax_hscroll.text(0, 0, "hscroll")
ax_vscroll = fig.add_axes(div.get_position(), axes_locator=div.new_locator(nx=2, ny=1))
ax_vscroll.text(0, 0, "vscroll", rotation=90)

def on_press(event):
    global zen
    zen = not zen
    if zen:
        h, v = h_zen, v_zen
        visible = False
    else:
        h, v = h_normal, v_normal
        visible = True
    for ax in (ax_help, ax_hscroll, ax_vscroll):
        ax.set_visible(visible)
    div.set_vertical(v)
    div.set_horizontal(h)
    fig.canvas.draw_idle()

fig.canvas.mpl_connect('key_press_event', on_press)

I'll wait until #12050 is merged then work on this.

[larsoner]

Going to see how hard this is now...

[larsoner]

Looks like in the end it's quite buggy. You can get there, but there's no way to set padding in some cases. Then the clicks go through to the wrong axes (always to horizontal). So maybe we should try this someday... but the current solution is not so bad in the end!