Contour Example

/home/docs/checkouts/readthedocs.org/user_builds/mpl-skia-pathops/envs/latest/lib/python3.10/site-packages/matplotlib/colors.py:2295: RuntimeWarning: invalid value encountered in divide
  resdat /= (vmax - vmin)

import numpy as np
import matplotlib.pyplot as plt
import mpl_visual_context.patheffects as pe
from mpl_skia_pathops import SkiaShadow # make_shadow_patheffects

def make_shadow_patheffects(
        fc_white="w",
        fc_black="0.2",
        alpha=0.5,
        offset=2.5,
        angle=135):

    patheffects = []
    if fc_black is not None:
        patheffects.append(
            SkiaShadow(offset, angle)
            | pe.FillColor(fc_black)
            | pe.GCModify(alpha=alpha)
        )
    if fc_white is not None:
        patheffects.append(
            SkiaShadow(offset, 180+angle)
            | pe.FillColor(fc_white)
            | pe.GCModify(alpha=alpha)
        )

    return patheffects


from matplotlib.contour import QuadContourSet
from matplotlib.patches import PathPatch, Polygon
from matplotlib.path import Path

# Data
X, Y = np.meshgrid(np.linspace(-5, 10, 100),
                   np.linspace(-5, 10, 100))
Z = -np.sqrt(X ** 2 + Y ** 2)

# Contour
fig, ax = plt.subplots(1, 1, num=2, clear=True)

ax.set_aspect(1)
contours = ax.contourf(X, Y, Z)

ann = ax.annotate("A", (0, 1), xycoords="axes fraction",
                  xytext=(15, -15), textcoords="offset points", va="top", ha="left", size=50)

patheffects1 = make_shadow_patheffects(fc_black="k", offset=2, angle=45, alpha=0.8)[:-1]
patheffects2 = make_shadow_patheffects(fc_black="k", offset=1, angle=45, alpha=1.)[:]
patheffects = patheffects1 + patheffects2

ann.set_path_effects(patheffects)


def add_contour_shadow(ax, contours,
                       fc_white="w",
                       fc_black="0.2",
                       alpha=0.5,
                       offset=2.5,
                       angle=135):

    # we first create patches for the shadow
    zorder = contours.zorder

    patheffects = make_shadow_patheffects(
        fc_white,
        fc_black,
        alpha,
        offset,
        angle
    )


    for level, c in zip(contours.levels, contours.get_facecolors()):

        sub_contours = QuadContourSet(ax, X, Y, Z,
                                      levels=[level, np.inf],
                                      filled=True)
        sub_contours.remove() # the contour is added to the axes by default. We do not want that.

        segs = sub_contours.allsegs[0] # Essentially there is a single level.

        paths = []
        for seg in segs:
            if len(seg):
                poly = Polygon(seg, fc=c, ec="none")
                paths.append(poly.get_path())

        if paths: # we combine the paths.
            path = Path.make_compound_path(*paths)
            p = ax.add_patch(PathPatch(path, fc="none", ec="none", zorder=zorder+1))
            p.set_path_effects(patheffects)

add_contour_shadow(ax, contours, fc_white=None, offset=3, angle=45, alpha=0.6)
add_contour_shadow(ax, contours, offset=1., angle=45, alpha=0.8)

plt.show()