import matplotlib.pyplot as plt
from matplotlib.tri import Triangulation
from matplotlib.patches import Polygon
import numpy as np
import math
import time

def update_polygon(tri):
    if tri == -1:
        points = [0, 0, 0]
    else:
        points = triangulation.triangles[tri]
    xs = triangulation.x[points]
    ys = triangulation.y[points]
    polygon.set_xy(list(zip(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)
    print("found triangle " + str(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*math.pi, n_angles, endpoint=False)
angles = np.repeat(angles[..., np.newaxis], n_radii, axis=1)
angles[:, 1::2] += math.pi / n_angles
x = (radii*np.cos(angles)).flatten()
y = (radii*np.sin(angles)).flatten()
triangulation = Triangulation(x, y)
xmid = x[triangulation.triangles].mean(axis=1)
ymid = y[triangulation.triangles].mean(axis=1)
mask = np.where(xmid*xmid + ymid*ymid < min_radius*min_radius, 1, 0)
triangulation.set_mask(mask)

# Use the triangulation's default TriFinder object.
trifinder = triangulation.get_trifinder()

# Setup plot and callbacks.
plt.subplot(111, aspect='equal')
plt.triplot(triangulation, '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()

