[FIXED] Create custom marker with filled square and plus inside it

Issue

I want to create a line plot with custom marker style. I specifically want a square (filled/unfilled) with a plus or product symbol in it. How to do this. The following code doesn't work

import matplotlib.pyplot as plt
import matplotlib.patches as mpatches
import numpy as np

# Sample data
x = np.linspace(0, 10, 100)
y = np.sin(x)

# Create a figure and axis
fig, ax = plt.subplots()

# Define the custom marker as a combination of a filled square and a plus symbol
def custom_marker():
    square = mpatches.Rectangle((-0.5, -0.5), 1, 1, linewidth=0, edgecolor='none', facecolor='red', zorder=2)
    plus = plt.Line2D([0, 0], [-0.4, 0.4], color='white', linewidth=2, zorder=3)
    plus2 = plt.Line2D([-0.4, 0.4], [0, 0], color='white', linewidth=2, zorder=3)
    return [square, plus, plus2]

# Create a scatter plot with the custom marker style
ax.scatter(x, y, label="Data", marker=custom_marker()[0], c='blue', s=30)

# Customize the legend with the same custom marker
legend_marker = custom_marker()
ax.legend(handles=legend_marker, labels=["Custom Marker"])

# Display the plot
plt.show()

Solution

you could use a custom marker based on a Path for this...

This way, the legend also works as expected.

import matplotlib.pyplot as plt
from matplotlib.path import Path

vertices=[[-15., -15.],
          [-15.,  15.],
          [ 15.,  15.],
          [ 15., -15.],
          [-15., -15.],
          [-13., -13.],
          [ 13., -13.],
          [ 13.,  13.],
          [-13.,  13.],
          [-13., -13.],
          [ -9.,  -1.],
          [ -1.,  -1.],
          [ -1.,  -9.],
          [  1.,  -9.],
          [  1.,  -1.],
          [  9.,  -1.],
          [  9.,   1.],
          [  1.,   1.],
          [  1.,   9.],
          [ -1.,   9.],
          [ -1.,   1.],
          [ -9.,   1.],
          [ -9.,  -1.]]

codes=[Path.MOVETO, 
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.MOVETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,]

p = Path(vertices=vertices, codes=codes)

fig, ax = plt.subplots()
ax.plot([1,2,3], [1,2,3], marker=p, ms=12, label="custom path marker")
plt.legend()

Update

It is also possible to fill the marker by drawing a rectangle with a "x" and using the edgecolor to color the "x" (this will also add a border to the rectangle... I'm not sure how to avoid this without plotting the rectangle and the x separately)

import matplotlib.pyplot as plt
from matplotlib.path import Path

vertices=[[-16, -16],
          [-16,  16],
          [ 16,  16],
          [ 16, -16],
          [-16, -16],
          [  0,  10],
          [  0, -10],
          [-10,   0],
          [ 10,   0]]

codes=[Path.MOVETO, 
       Path.LINETO,
       Path.LINETO,
       Path.LINETO,
       Path.CLOSEPOLY,
       Path.MOVETO,
       Path.LINETO,
       Path.MOVETO,
       Path.LINETO
       ]       

p = Path(vertices=vertices, codes=codes)

fig, ax = plt.subplots()
ax.plot([1,2,3], [1,2,3], marker=p, ms=12, label="custom path marker",
        markerfacecolor="r", markeredgecolor="k", markeredgewidth=1.5)
plt.legend()

Answered By - raphael