Modify values with channel fields

Use channel fields to modify the values of voxel or particle channels in a Bifröst simulation, such as the density of liquid, foam, or aero. You can limit the effect to a specific volume using closed polygon meshes in the scene, or an implicit shape.

Note that the final values of a channel might not always correspond exactly to the settings of a channel field. For example, you might use a channel field to clamp the vorticity channel of a liquid, but then new vorticity values will be calculated after the velocities are updated by the simulation. The clamping will prevent the vorticity values from accumulating too high, but some values may nevertheless be higher than the maximum set by the channel field.

1. Select the main Bifröst container, or a Bifröst shape node.

   For liquid simulations with foam:

   • Selecting the liquid container applies the field to both liquid and foam particles.
   • Selecting the liquid shape applies the field to liquid particles only.
   • Selecting the foam shape applies the field to foam particles only.
2. If you want to use one or more polygon meshes to define the volume of effect, then add them to the selection as well. The order of selection does not matter.

3. Select Bifrost Fluids > (Add) Channel Field.

   A bifrostChannelField object is created at the world origin and automatically selected.

4. Define the volume affected by the field by doing one of the following:

   • To affect particles inside a volume, select a Boundary Shape in the field container's Boundary Controls attributes, and then scale, rotate, and translate the field. The field's wireframe representation in the viewport indicates the volume that will be affected. Note that InMesh applies only if you selected one or more meshes in step 2.
   • To affect particles outside a volume, do the same as above and also make sure to check Invert.
   • To affect all particles everywhere, uncheck Boundary in the Kill Field Properties attribute group.
5. Select the Mode (Particles or Voxels) and enter the Channel Name. For a list of channels as well as descriptions of other settings, see Bifröst Channel Field attributes.
6. Enable the desired operations (Override, Increment, Scale, or Clamp), and set the Min and Max values for each. Each operation will be performed using a uniform random distribution between these limits.
   Note: For vector-valued channels, the operations are applied to each of the XYZ components individually.

To remove a channel field, you can either disconnect it in the Node Editor or simply delete it.