<filename>examples/01-filter/sampling_functions_2d.py
"""
Sample Function: Perlin Noise in 2D
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Here we use :func:`pyvista.core.imaging.sample_function` to sample
perlin noise over a region to generate random terrain.

Perlin noise is atype of gradient noise often used by visual effects
artists to increase the appearance of realism in computer graphics.
Source:
https://en.wikipedia.org/wiki/Perlin_noise

The development of Perlin Noise has allowed computer graphics artists
to better represent the complexity of natural phenomena in visual
effects for the motion picture industry.

"""

import pyvista as pv

###############################################################################
# Generate Perlin Noise over a StructuredGrid
# ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Feel free to change the values of ``freq`` to change the shape of
# the "mountains".  For example, lowering the frequency will make the
# terrain seem more like hills rather than mountains.
freq = [0.689, 0.562, 0.683]
noise = pv.perlin_noise(1, freq, (0, 0, 0))
sampled = pv.sample_function(noise,
                             bounds=(-10, 10, -10, 10, -10, 10),
                             dim=(500, 500, 1))


###############################################################################
# Warp by scalar
# ~~~~~~~~~~~~~~
# Here we warp by scalar to give the terrain some height based on the
# value of the perlin noise.  This is necessary to the terrain its shape.

mesh = sampled.warp_by_scalar('scalars')
mesh = mesh.extract_surface()

# clean and smooth a little to reduce perlin noise artifacts
mesh = mesh.smooth(n_iter=100, inplace=False, relaxation_factor=1)

# This makes the "water" level look flat.
z = mesh.points[:, 2]
diff = z.max() - z.min()

# water level at 70%  (change this to change the water level)
water_percent = 0.7
water_level = z.max() - water_percent*diff
mesh.points[z < water_level, 2] = water_level


###############################################################################
# Show the terrain as a contour plot

# make the water blue
rng = z.max() - z.min()
clim = (z.max() - rng*1.65, z.max())

pl = pv.Plotter()
pl.add_mesh(mesh, scalars=z,
            cmap='gist_earth', n_colors=10, show_scalar_bar=False,
            smooth_shading=True, clim=clim)
pl.show()


###############################################################################
# Show the terrain with custom lighting and shadows

pl = pv.Plotter(lighting=None)
pl.add_light(pv.Light((3, 1, 0.5), show_actor=True, positional=True,
                      cone_angle=90, intensity=1.2))
pl.add_mesh(mesh, cmap='gist_earth', show_scalar_bar=False,
            smooth_shading=True, clim=clim)
pl.enable_shadows = True
pl.show()
