This page provides information on the Interaction rollout for a Fire/Smoke Simulator.


It is strongly recommended that each geometry interacting with the fluid simulation:

  • has no open edges or holes;
  • does not self-intersect;
  • has normals pointing outwards.

Phoenix will try to handle any geometry that does not comply with these conditions, but the simulation might not behave properly - in case of fire/smoke simulations some areas of the simulation could lose velocity and freeze for no apparent reason, and in liquid simulations particle explosions could appear.

This dialog is used to enable/disable the interaction with objects in the scene. There are several different types of objects that may affect the simulation: Sources, Solid objects, Forces, etc.

By default, all these scene elements will interact with the simulator unless otherwise specified by the Include/Exclude list. If you want to disable the interaction you have to put the objects in the Exclude list. If there are more objects that don't need to interact with the simulator, you may alternatively switch to the Include list mode. In this mode you have to add to the list all the objects that you want to interact with the simulator.

Since all forces affect the simulation by default, adding a force in your scene to be used by e.g. PFlow will automatically affect your simulation and this might not be desired. In the Active Forces list you can check which 3ds Max forces interact with the simulator and you may exclude them if you wish so.

 UI Path: ||Select Fire Smoke Simulator | FireSmokeSim object|| > Modify panel > Interaction rollout



Include/Exclude list | ielist, iemode  – Determines which objects will be ignored or processed by the simulation. Use the radio buttons to switch between Include list and Exclude list. When Exclude list is active (the default), all objects in the scene will interact with the simulator unless they are added to the exclusion list. In Include list mode, no objects will interact with the simulator unless they are added to the list. Note that in Include list mode, in order for a Source to work in a simulation, you must add the Source and also all of the geometries or particles it emits from.

Exclude hidden objects | exclhidden  – When enabled, the hidden objects will be excluded regardless of the list content

Object voxels | objvox  – The Fire/Smoke simulator is a grid-based simulator, and geometry is converted into voxel form in order to interact with the fluids. The voxels overlapped by Solid geometry obstacles are frozen and processed in a different way. When a given voxel is half-way inside the geometry, this option helps you choose whether this voxel is going to be frozen or not. Even if this does not produce significant changes in the simulation, in rendering you might see a gap between the fire/smoke and obstacles in Circumscribed mode. On the other hand, very thin obstacles might be missed by the simulation if you use Inscribed mode, so it would be better to use Circumscribed for such geometries. You can also override the voxel mode per object from its right-click Phoenix FD properties. For more information, see the Object Voxels example below.

Circumscribed  – All voxels that intersect the surface are considered solid.
Center – The surface voxels are considered solid only if their bigger part lies in the object.
Inscribed – All voxels that have intersection with the surface are considered non-solid.

The Object voxels setting is a simulation option. If its value changes, the simulation must be calculated again for the changes to take effect.


Example: Object Voxels

The example below shows the difference in emission when the object uses Inscribed (voxels intersecting the surface are non-solid therefore do not emit) vs Circumscribed (voxels intersecting the surface are solid) voxelization.


Object voxels = Inscribed

Object voxels = Circumscribed


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