"""
.. _line_widget_example:

Line Widget
~~~~~~~~~~~

The line widget can be enabled and disabled by the
:func:`pyvista.Plotter.add_line_widget` and
:func:`pyvista.Plotter.clear_line_widgets` methods respectively.
Unfortunately, PyVista does not have any helper methods to utilize this
widget, so it is necessary to pass a custom callback method.

One particularly fun example is to use the line widget to create a source for
the :func:`pyvista.DataSetFilters.streamlines` filter. Again note the use of
the ``name`` argument in ``add_mesh``.
"""

import numpy as np

import pyvista as pv
from pyvista import examples

pv.set_plot_theme('document')

mesh = examples.download_kitchen()
furniture = examples.download_kitchen(split=True)

arr = np.linalg.norm(mesh['velocity'], axis=1)
clim = [arr.min(), arr.max()]

###############################################################################

p = pv.Plotter()
p.add_mesh(furniture, name='furniture', color=True)
p.add_mesh(mesh.outline(), color='black')
p.add_axes()


def simulate(pointa, pointb):
    streamlines = mesh.streamlines(
        n_points=10, max_steps=100, pointa=pointa, pointb=pointb, integration_direction='forward'
    )
    p.add_mesh(streamlines, name='streamlines', line_width=5, render_lines_as_tubes=True, clim=clim)


p.add_line_widget(callback=simulate, use_vertices=True)
p.show()

##############################################################################
# And here is a screen capture of a user interacting with this
#
# .. image:: ../../images/gifs/line-widget-streamlines.gif