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# Trifinder Event DemoΒΆ

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 motion_notify(event):
if event.inaxes is None:
tri = -1
else:
tri = trifinder(event.xdata, event.ydata)
update_polygon(tri)
plt.title('In triangle %i' % 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.
plt.subplot(111, aspect='equal')
plt.triplot(triang, 'bo-')
polygon = Polygon([[0, 0], [0, 0]], facecolor='y')  # dummy data for xs,ys
update_polygon(-1)
plt.gca().add_patch(polygon)
plt.gcf().canvas.mpl_connect('motion_notify_event', motion_notify)
plt.show()
```

Keywords: matplotlib code example, codex, python plot, pyplot Gallery generated by Sphinx-Gallery