Density

synopsis

The Arnold core Density shader is very similar in functionality to the Volume Collector shader. This shader has three color parameters called Scattering, Attenuation, and Emission which are simply used to set the scattering, attenuation and emission coefficients for the volume at the integration sample inside the volume. The (Henyey-Greenstein) Anisotropy parameter is an open interval (-1,+1) where negative values mean backward anisotropic scattering, positive values mean forward anisotropic scattering and zero means isotropic scattering.

Be warned that the evaluation of a shader network for volume rendering is much more expensive than for surface shading, because the shader network is called many times per ray, once per ray march sample. So, in a production environment, it's much better to have a single shader doing all the work, instead of relying on potentially expensive inputs.

 

scatter_channel

When not empty, this channel will be used to sample the scattering values for the volume instead of the Scattering parameter.

 

scatter_color

A color to tint (multiply to) the scattering.

scatter_g

...

anisotropy

Henyey-Greenstein Anisotropy coefficient between -1 (full back-scatter) and 1 (full forward-scatter). Default is 0 for an isotropic medium.

Note that values very close to 1.0 (above 0.95) or -1.0 (below -0.95) will produce scattering that is so directional that it will not be very visible from most angles, so such values are not recommended.

absorption_channel

When not empty, this channel will be used to sample the scattering values for the volume instead of the Attenuation parameter. The sampling tab has additional parameters to control how data is sampled from volume channels.
absorption_color

A color to tint (multiply to) the attenuation.

 

emission

Emission is the rate at which a volume emits light at a given point. The light emitted by a volume is visible to GI. It will also be affected by any out-scattering or absorption effects in the volume. A heat (flames) grid would be connected to this parameter. 


emission_channel

When not empty, this channel will be used to sample the emission values for the volume instead of the Emission parameter. The sampling tab has additional parameters to control how data is sampled from volume channels.
emission_color

A color to tint (multiply to) the emission.

interpolation

The voxel interpolation to use when sampling the volume data using named channels.

 

position_offset

An object space offset to apply to the volume sampling position when using named channels to fetch the volume data. This is useful to displace the volume data.

You will need to connect a noise texture to the position offset to see any result.

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