.. _event_handling-trifinder_event_demo:

event_handling example code: trifinder_event_demo.py
====================================================

[`source code <trifinder_event_demo.py>`_]

::

    """
    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
    import math
    
    
    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(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)
        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()
    

Keywords: python, matplotlib, pylab, example, codex (see :ref:`how-to-search-examples`)