|On this page|
Given a point light, this operator computes lighting values for all input volume primitives and outputs them as volume triples representing Red, Green and Blue values.
The light transfer properties of the volumes can be modified to change their appearance when lit.
The optional second input can specify the points to bake the light values onto. These points are only used in the Gather stage. The resulting point cloud can be used in a shader using the point cloud functions.
The primitive group to compute lighting values for.
The generated lightfield volumes will use this name as a prefix to .x, .y, and .z for their own names. This allows the light field to override shading attributes in Mantra.
The position in world space of the light used to compute the volume lighting values.
The intensity of the light being used to compute volume lighting values.
An RGB scale to the light intensity.
Determines how much of the light’s radiance is absorbed by the volume per unit density.
An RGB scale to the absorption coefficient.
Determines the amount of light that is scattered (redirected) per unit density of the volume.
An RGB scale to the scattering coefficient. This affects the color of the scattered light, but the actual scattering events are controlled by the average value to ensure chromacity is preserved without excessive samples.
Determines the amount of light per unit density that is released by the volume when struck by a light ray.
An RGB scale to the emission coefficient.
The proportion of light that is assumed to be isotropically scattered (redirected in all directions evenly) whenever scattering occurs within the volume.
Compute Step Size
When set, the step size will be automatically computed from the voxel size rather than using a fixed value.
Step Size Scale
The number of voxels to step when Compute Step Size is set.
The step size is used when simulating the behavior of light rays within the volume. A smaller step size will produce better results, but take longer to compute.
Scales the density of the volume being baked.
After the initial rays are sent through the field, a light field is constructed. Then it us usually gathered to get the final result. Turning this off skips the gather stage, leaving the raw light field.
Do Multiple Scattering
Whether or not multiple scattering effects will be calculated.
Multiple Scatter Boost
A constant multiple to the multiple scattering contribution to the final light levels.
Secondary Rays Only
The resulting light field will only consist of the multiple scattered components, not the direct illumination.
If set, the initial rays will adjust their color when scattering to reflect the scatter color.
Number of Rays
The number of light rays used to simulate multiple scattering effects. Using more rays can improve the appearance of rendered volumes, but at the cost of longer computation times. Insufficient rays will result in artifact streaks along the ray direction. Turn off Gather Rays to see the raw light fields and determine if this is an issue.
The number of rays that are sent out when integrating the effects of the multi-scatter. This is independent of Number of Rays as it applies to the gather step, not the Scatter Rays step.
Coefficient defining the directional tendencies of scattering within the volume. K ranges from -1, indicating perfect backward scattering, to 1, which is perfect forward scattering. A value of 0 will cause unbiased, fully random scattering.
Optimize Light Transfer
When enabled, the operation will use previously computed light values wherever possible in order to reduce computation times.
The results of an optimized pass will not be as accurate as those of a non-optimized one.
Optimized Ray Depth
How deeply into the volume an optimized pass will cast its light rays before using previously computed values.
Lower values result in faster, less accurate calculations, while higher values cause longer computation times with more accurate results.
Values less than 2 are not recommended, because the validity of previously computed values cannot be guaranteed with rays that short.
Conversely, values greater than the voxel resolution of the volume being baked have no advantage over a non-optimized pass. The Optimize Light Transfer option should be disabled instead.
At what level of transmission the gather rays should be terminated.
This example shows how to setup the Bake Volume SOP to compute the lightfield created by the shadowing of a fog volume. It then exports the fields properly to be rendered in Mantra by a constant volume shader.
The following examples include this node.