>>> """
====================
Trifinder Event Demo
====================

Example showing the use of a TriFinder object.  As the mouse is moved over the
triangulation, the triangle under the cursor is highlighted and the index of
the triangle is displayed in the plot title.
"""
... import matplotlib.pyplot as plt
... from matplotlib.tri import Triangulation
... from matplotlib.patches import Polygon
... import numpy as np
... 
... 
... def update_polygon(tri):
...     if tri == -1:
...         points = [0, 0, 0]
...     else:
...         points = triang.triangles[tri]
...     xs = triang.x[points]
...     ys = triang.y[points]
...     polygon.set_xy(np.column_stack([xs, ys]))
... 
... 
... def on_mouse_move(event):
...     if event.inaxes is None:
...         tri = -1
...     else:
...         tri = trifinder(event.xdata, event.ydata)
...     update_polygon(tri)
...     ax.set_title(f'In triangle {tri}')
...     event.canvas.draw()
... 
... 
... # Create a Triangulation.
... n_angles = 16
... n_radii = 5
... min_radius = 0.25
... radii = np.linspace(min_radius, 0.95, n_radii)
... angles = np.linspace(0, 2 * np.pi, n_angles, endpoint=False)
... angles = np.repeat(angles[..., np.newaxis], n_radii, axis=1)
... angles[:, 1::2] += np.pi / n_angles
... x = (radii*np.cos(angles)).flatten()
... y = (radii*np.sin(angles)).flatten()
... triang = Triangulation(x, y)
... triang.set_mask(np.hypot(x[triang.triangles].mean(axis=1),
...                          y[triang.triangles].mean(axis=1))
...                 < min_radius)
... 
... # Use the triangulation's default TriFinder object.
... trifinder = triang.get_trifinder()
... 
... # Setup plot and callbacks.
... fig, ax = plt.subplots(subplot_kw={'aspect': 'equal'})
... ax.triplot(triang, 'bo-')
... polygon = Polygon([[0, 0], [0, 0]], facecolor='y')  # dummy data for (xs, ys)
... update_polygon(-1)
... ax.add_patch(polygon)
... fig.canvas.mpl_connect('motion_notify_event', on_mouse_move)
... plt.show()
...