How to fill a polygon with a custom hatch in matplotlib?

Question

I'm using python and matplotlib to create several closed polygons. I then need to fill them with a hatch, which can be done through set_hatch.

http://matplotlib.org/api/artist_api.html#matplotlib.patches.Patch.set_hatch

http://matplotlib.org/examples/pylab_examples/hatch_demo.html

Unfortunately I am working with greyscale images, and I need more hatches than provided by default - I would prefer to provide a bitmap (or some similar image) which could be tiled instead of using these hatches with varying densities.

I am open to other python libraries (pyglet, pygame, PIL, etc) however I would prefer the solution to be in python.

Augustineaugustinian

There's an example of custom hatches here, but the author says it's brittle. – Hornsby

The standard set_hatch has eight distinct hatches, each of which can operate in at least two densities, and which can be combined. I would think a plot would be too confusing long before you ran out of combinations of hatches. Do you have an example of greyscale hatching with dozens of usable fills? – Hornsby

Answer 1

You can subclass matplotlib.hatch.Shapes and define a custom hatch based on any reference path drawn inside unit square [[-0.5, 0.5] x [-0.5, 0.5]].

Tentative:

import numpy as np
import matplotlib.hatch
import matplotlib.pyplot as plt
from matplotlib.patches import Ellipse, Polygon


house_path = Polygon(
    [[-0.3, -0.4], [0.3, -0.4], [0.3, 0.1], [0., 0.4], [-0.3, 0.1]],
    closed=True, fill=False).get_path()

class CustomHatch(matplotlib.hatch.Shapes):
    """
    Custom hatches defined by a path drawn inside [-0.5, 0.5] square.
    Identifier 'c'.
    """
    filled = True
    size = 1.0
    path = house_path

    def __init__(self, hatch, density):
        self.num_rows = (hatch.count('c')) * density
        self.shape_vertices = self.path.vertices
        self.shape_codes = self.path.codes
        matplotlib.hatch.Shapes.__init__(self, hatch, density)

matplotlib.hatch._hatch_types.append(CustomHatch)

fig = plt.figure()
ax = fig.add_subplot(111)

ellipse = ax.add_patch(Ellipse((0.5, 0.5), 0.3, 0.5, fill=False))
ellipse.set_hatch('c')
ellipse.set_color('red')
plt.show()

Giving:

Ungrounded