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.. _bpy.types.ShaderNodeVolumeScatter:
**************
Volume Scatter
**************
.. figure:: /images/node-types_ShaderNodeVolumeScatter.png
:align: right
:alt: Volume Scatter node.
The *Volume Scatter* node allows light to be scattered as it passes through the volume.
Typical usage would be to add fog to a scene. It can also be used with
the :doc:`Volume Absorption </render/shader_nodes/shader/volume_absorption>` node to create smoke.
Inputs
======
Color
Scattering coefficients per color channel.
Density
The density of the scatter effect.
Anisotropy :guilabel:`Henyey-Greenstein` :guilabel:`Draine`
Controls the relative amount of backward and forward scattering.
IOR :guilabel:`Fournier-Forand`
Refractive index of the scattering particles relative to water. Common ocean waters range between
1.0 and 1.2, while turbid waters with higher density of particles have higher IORs.
Backscatter :guilabel:`Fournier-Forand`
Fraction of light that is scattered backwards. Most oceanic particles have backscatter
values between 0.001 (e.g., very large phytoplankton) and 0.1 (e.g., very small mineral particles),
pure water has a backscatter of 0.5. Values taken from
`Ocean Optics Web Book <https://www.oceanopticsbook.info/view/scattering/the-fournier-forand-phase-function>`__.
Alpha :guilabel:`Draine`
Blending factor between Henyey-Greenstein (:math:`\alpha = 0`)
and Cornette & Shanks (:math:`\alpha = 1`) phase functions.
Diameter :guilabel:`Mie`
Diameter of the scattering particles in µm.
Properties
==========
Phase
Volume scattering phase function.
:Henyey-Greenstein:
Simple and widely used phase function, useful for approximating scattering in biological tissues.
:Fournier-Forand:
:guilabel:`Cycles Only`
Suitable for modeling the scattering of light in underwater environments.
:Draine:
:guilabel:`Cycles Only`
Suitable for modeling the scattering of interstellar dust.
:Rayleigh:
:guilabel:`Cycles Only`
Describes the scattering by particles with a size smaller than the wavelength of light,
such as the scattering of sunlight in earth's atmosphere.
:Mie:
:guilabel:`Cycles Only`
Describes the scattering by particles with a size larger than the wavelength of light, such as cloud and fog.
.. tip::
These phase functions can be combined using a :doc:`/render/shader_nodes/shader/mix`.
.. figure:: /images/render_shader-nodes_shader_volume-scatter_phase.svg
:align: center
:alt: Volume Scattering Function in logarithmic scale.
Volume scattering phase as a function of angles between the incoming and the outgoing direction,
in logarithmic scale. Light comes from the left side.
Outputs
=======
Volume
The Volume Shader output must be plugged into the *Volume Input*
of the :doc:`Material </render/shader_nodes/output/material>`
or :doc:`World </render/shader_nodes/output/world>` Output node.
Examples
========
.. figure:: /images/render_shader-nodes_shader_volume-scatter_example.png
Example of Volume Scatter.
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