The combine volume compound serves the purpose of merging volumes while providing options for how the information is combined for level sets, fog density, and other data present in the objects.

volumes

Input objects fan-in port. Objects may contain only fog, or only level set or both. If there is a mix of objects with fogs/levelsets, then this logic is applied: If volA = level set + fog and volB = level set and volC = fog, then combining the three would mean that the output is a new volume with a level set which is the combination of the level sets in volA and volB, and similarly a fog which combines the fogs of volA and volC.

General

enable

If false, outputs the first volume in volumes or an empty object if none exists.

invert_order

The order of operations is inverted.

Level Set

level_set_mode

Modes:

• Union: Generate the union of level sets A and B and C and so on (default).
• Difference: Level set A minus level set B, then result minus level set C and so on.
• Intersection: Generate the intersection of level sets A and B and C and so on.

Fog Density

fog_density_mode

Modes:

• Add: A + B (default)
• Subtract: A - B
• Divide: A / B
• Multiply: A x B
• Min: use the minimum of each corresponding value from A and B.
• Max: use the maximum of each corresponding value from A and B.
• Average: (A + B) / 2
• SoftCut: (1 - A) x B
• SoftCombine: A + (1 - A) x B
• AlphaBlend: (1 - alpha) x A + alpha x B

alpha

The alpha value used in the alpha blend mode.

Properties

properties_mode

Properties support the modes also available for fog density, and in addition supports an Automatic mode (default). In Automatic mode, the properties are merged based on the level set and fog density operations. This means when you combine fog densities, whichever operation you choose for the fog density, is also done for the other properties. The same thing applies when you combine level sets, where: When combining level sets using CSG operations Union, Difference, Intersection, one can combine properties based on from which volume the level set voxel is chosen. In particular a CSG operation is a min or max operation that picks a voxel from either input level set A or input level set B based on the min and max. For properties this means that if the level set voxel from volume A is chosen in the output level set, then for all properties we similarly pick the property value from volume A in that particular voxel to be the output and vice versa if volume B is chosen. If there is no fog density or level set in the volume, or if there is both, Automatic defaults to Add.

Currently only types with float components (scalars, vectors, matrices) are supported.

Resolution

optimized_adaptivity

If enabled and the input volumes contain a level set then the output will only be refined where the sampling error introduced by not refining is greater than 0.1 times the detail size.

adaptive_voxel_scale

Scales the detail size of the output volume when optimized_adaptivity is enabled.

volume_subdivision_structure

The subdivision structure of the Bifrost volume.

• In Automatic mode this will use Power2 if eitheradaptivity is enabled or any of the input volumes is `Power2.
• In Power2 mode the resolution doubles with each level in volume.
• In Power5 mode the resolution quintuples with each level in volume.