[Bug]: stackplot creates artifacts when height of input is zero #22393
Description
Bug summary
In some cases, when a given input for stackplot has zero value entries, thin lines are drawn.
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
np.random.seed(42)
x = np.arange(10)
y0 = np.linspace(0, 1, 10)
y1 = np.linspace(0, 1, 10)
y2 = [0, 0, 0.25, 0, 0, 0, 0.25, 0, 0, 0]
y3 = np.linspace(0, 1, 10)
colors=['grey', 'blue', 'red', 'blue']
y = np.stack([y0, y1, y2, y3])
im = plt.stackplot(x, y, colors=colors, lw=0)Actual outcome
One can see thin grey lines where the red object hast zero height.
Expected outcome
The thin lines are gone
Additional information
This only happens when the color above and below the empty data has the same color, but there are some use-cases where this is needed (see e.g. fish plots for evolutionary relationships).
Fix
The individual calls to fill_between need to have the following parameters:
where=(stack[i, :] != stack[i+1, :]), interpolate=True and edgecolor=color.
These are the changes made to matplotlib/lib/matplotlib/stackplot.py
# Color between x = 0 and the first array.
color = ax._get_lines.get_next_color()
coll = ax.fill_between(x, 0, stack[0, :],
where=(stack[0, :] != 0), interpolate=True, edgecolor=color,
facecolor=color, label=next(labels, None), **kwargs)
coll.sticky_edges.y[:] = [0]
r = [coll]
# Color between array i-1 and array i
for i in range(len(y) - 1):
color = ax._get_lines.get_next_color()
r.append(ax.fill_between(x, stack[i, :], stack[i+1, :],
where=(stack[i, :] != stack[i+1, :]), interpolate=True, edgecolor=color,
facecolor=color, label=next(labels, None), **kwargs))These changes get rid of the lines but as far as I tested it do not have side effects for other plots. Probably one should check whether edgecolor is set in **kwargs as well.
Operating system
No response
Matplotlib Version
3.4.3
Matplotlib Backend
No response
Python version
No response
Jupyter version
No response
Installation
conda