12.3.10.1.23. Path editor

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

Path = mpath.Path

fig, ax = plt.subplots()

pathdata = [
    (Path.MOVETO, (1.58, -2.57)),
    (Path.CURVE4, (0.35, -1.1)),
    (Path.CURVE4, (-1.75, 2.0)),
    (Path.CURVE4, (0.375, 2.0)),
    (Path.LINETO, (0.85, 1.15)),
    (Path.CURVE4, (2.2, 3.2)),
    (Path.CURVE4, (3, 0.05)),
    (Path.CURVE4, (2.0, -0.5)),
    (Path.CLOSEPOLY, (1.58, -2.57)),
]

codes, verts = zip(*pathdata)
path = mpath.Path(verts, codes)
patch = mpatches.PathPatch(path, facecolor="green", edgecolor="yellow", alpha=0.5)
ax.add_patch(patch)


class PathInteractor:

    showverts = True
    epsilon = 5  # max pixel distance to count as a vertex hit

    def __init__(self, pathpatch: matplotlib.patches.PathPatch):
        """Path editor class. ``t`` toggle vertex markers on and off.
        When vertex markers are on, you can move them, delete them.

        Args:
            pathpatch (matplotlib.patches.PathPatch): PathPatch instance
        """

        self.ax = pathpatch.axes
        canvas = self.ax.figure.canvas
        self.pathpatch = pathpatch
        self.pathpatch.set_animated(True)

        x, y = zip(*self.pathpatch.get_path().vertices)

        (self.line,) = ax.plot(x, y, marker="o", markerfacecolor="r", animated=True)

        self._ind = None  # the active vert

        canvas.mpl_connect("draw_event", self.draw_callback)
        canvas.mpl_connect("button_press_event", self.button_press_callback)
        canvas.mpl_connect("key_press_event", self.key_press_callback)
        canvas.mpl_connect("button_release_event", self.button_release_callback)
        canvas.mpl_connect("motion_notify_event", self.motion_notify_callback)
        self.canvas = canvas

    def draw_callback(self, event: matplotlib.backend_bases.DrawEvent):
        self.background = self.canvas.copy_from_bbox(self.ax.bbox)
        self.ax.draw_artist(self.pathpatch)
        self.ax.draw_artist(self.line)
        self.canvas.blit(self.ax.bbox)

    def pathpatch_changed(self, pathpatch: matplotlib.patches.PathPatch):
        "this method is called whenever the pathpatchgon object is called"
        # only copy the artist props to the line (except visibility)
        vis = self.line.get_visible()
        plt.Artist.update_from(self.line, pathpatch)
        self.line.set_visible(vis)  # don't use the pathpatch visibility state

    def get_ind_under_point(self, event):
        "get the index of the vertex under point if within epsilon tolerance"

        # display coords
        xy = np.asarray(self.pathpatch.get_path().vertices)
        xyt = self.pathpatch.get_transform().transform(xy)
        xt, yt = xyt[:, 0], xyt[:, 1]
        d = np.sqrt((xt - event.x) ** 2 + (yt - event.y) ** 2)
        ind = d.argmin()

        if d[ind] >= self.epsilon:
            ind = None

        return ind

    def button_press_callback(self, event):
        "whenever a mouse button is pressed"
        if not self.showverts:
            return
        if event.inaxes is None:
            return
        if event.button != 1:
            return
        self._ind = self.get_ind_under_point(event)

    def button_release_callback(self, event):
        "whenever a mouse button is released"
        if not self.showverts:
            return
        if event.button != 1:
            return
        self._ind = None

    def key_press_callback(self, event):
        "whenever a key is pressed"
        if not event.inaxes:
            return
        if event.key == "t":
            self.showverts = not self.showverts
            self.line.set_visible(self.showverts)
            if not self.showverts:
                self._ind = None

        self.canvas.draw()

    def motion_notify_callback(self, event):
        "on mouse movement"
        if not self.showverts:
            return
        if self._ind is None:
            return
        if event.inaxes is None:
            return
        if event.button != 1:
            return
        x, y = event.xdata, event.ydata

        vertices = self.pathpatch.get_path().vertices

        vertices[self._ind] = x, y
        self.line.set_data(zip(*vertices))

        self.canvas.restore_region(self.background)
        self.ax.draw_artist(self.pathpatch)
        self.ax.draw_artist(self.line)
        self.canvas.blit(self.ax.bbox)


interactor = PathInteractor(patch)
ax.set_title("drag vertices to update path")
ax.set_xlim(-3, 4)
ax.set_ylim(-3, 4)

plt.show()