"""
Depth Peeling
~~~~~~~~~~~~~

Depth peeling is a technique to correctly render translucent geometry.
This is not enabled by default in ``pyvista.global_theme`` as some
operating systems and versions of VTK have issues with this routine.

For this example, we will showcase the difference that depth peeling
provides.

"""
# sphinx_gallery_thumbnail_number = 2
import pyvista as pv
from pyvista import examples


###############################################################################
centers = [(0, 0, 0), (1, 0, 0), (-1, 0, 0),
           (0, 1, 0), (0, -1, 0)]
radii = [1, 0.5, 0.5, 0.5, 0.5]

spheres = pv.MultiBlock()
for i, c in enumerate(centers):
    spheres.append(pv.Sphere(center=c, radius=radii[i]))

###############################################################################
dargs = dict(opacity=0.5, color="red", smooth_shading=True)

p = pv.Plotter(shape=(1, 2), multi_samples=8)

p.add_mesh(spheres, **dargs)
p.enable_depth_peeling(10)
p.add_text("Depth Peeling")

p.subplot(0, 1)
p.add_text("Standard")
p.add_mesh(spheres.copy(), **dargs)

p.link_views()
p.camera_position = [(11.7, 4.7, -4.33),
                     (0.0, 0.0, 0.0),
                     (0.3, 0.07, 0.9)]
p.show()

###############################################################################
# The following room surfaces example mesh, provided courtesy of
# `Sam Potter <https://github.com/sampotter>`_ has coincident topology and
# depth rendering helps correctly render those geometries when a global
# opacity value is used.

room = examples.download_room_surface_mesh()

p = pv.Plotter(shape=(1, 2))

p.enable_depth_peeling(number_of_peels=4, occlusion_ratio=0)
p.add_mesh(room, opacity=0.5, color="tan")
p.add_text("Depth Peeling")

p.subplot(0,1)
p.add_text("Standard")
p.add_mesh(room.copy(), opacity=0.5, color="tan")

p.link_views()
p.camera_position = [(43.6, 49.5, 19.8),
                     (0.0, 2.25, 0.0),
                     (-0.57, 0.70, -0.42)]

p.show()


###############################################################################
# And here is another example wheen rendering many translucent contour
# surfaces.

mesh = examples.download_brain().contour(5)
cmap = "viridis_r"

p = pv.Plotter(shape=(1,2), multi_samples=4)

p.add_mesh(mesh, opacity=0.5, cmap=cmap)
p.enable_depth_peeling(10)
p.add_text("Depth Peeling")

p.subplot(0,1)
p.add_text("Standard")
p.add_mesh(mesh.copy(), opacity=0.5, cmap=cmap)

p.link_views()
p.camera_position = [(418.3, 659., 53.8),
                     (90.2, 111.5, 90.0),
                     (0.03, 0.05, 1.0)]
p.show()
