There are three ways to source with Axiom, VDBs, Houdini Height Fields, and primitive shapes that come with the Axiom toolset called Source Shapes.

Settings

You will see all of the fields you can source into here.

These settings control the global sourcing independent of the type of source being used however some setting are unique to certain types such as VDBs.

For each of the fields you can choose how the sources are contributed to the field.

Mask Name is the name of the source used to mask the source operation. It is not a simulation field. For the mask to work in the example above you must have a source VDB named “density” input to the solver. This can be left blank if you do not want to mask the source operation.

Scale is a multiplier of the source’s values.

Blend Mode controls how values are contributed to the field.

• Add will add the source field to the sim field.
• Replace will replace any voxel values where the source overlaps with the source’s value.
• Maximum will choose the value of the field that has the higher value.
• Pull will increase the value toward the source value but not exceed the source value.
• Blend will do a linear interpolation between the target field and the source.

Acceleration is the speed of effect of the Blend or Pull mode.

Time Step controls the rate at which the source operation occurs.

• Time Step will add the value of the input per second.
• Frame Step will add the value of the input per frame.
• None will add the value every time the solver cooks including substeps.
• Solver Time Step is the same as time step but will also take the solver time scale into consideration.
• Solver Frame Step is the same as frame step but will also take the solver time scale into consideration.

Activation allows you to use this source to activate regions in its area of effect. This does not make the field an activation field.

VDBs

You can connect VDBs directly into the first input of the solver. You can make these sources any way you want. It can be sourced using OpenVDB or on the GPU using NanoVDB which is on by default.

Naming

The solver will only accept these names for default sourcing. It is case-sensitive.

• density - float scalar fog