Simulate dynamic effects

Specialized solvers are available for dynamic effects such as basic particle systems, aerodynamics, combustion, cloth, and granular materials like sand or snow. All simulations can be controlled in similar ways with influences like wind, as well as with colliders.

Considerations for simulation in Bifrost

Play every frame

As for all simulations, if you do not see the proper result in the viewport during playback, make sure that the scene is set to play every frame.

Set the start frame

All the simulation systems have a parameter for the start frame, which is set to 1 by default. You must change this value if you want the simulation to start at a different frame.

Modifying the graph during playback of a simulation

When you make changes to a graph during playback, the current state of feedback ports that have been cached to memory are preserved if possible. You can resume a simulation after pausing partway through playback and changing the graph — the simulation continues based on the modified graph starting from the current frame, although properties such as point_size on particles emitted on previous frames keep their old values until you restart the simulation from the first frame.

Feedback-port caches are preserved not only when modifying values on unconnected inputs, but also when adding and deleting nodes and connections. For example, you can simulate partway, then decide to add and connect a scope node to visualize values in the viewport or connect an I/O node to save the current state of a simulation, and then continue playback.

Feedback-port caches are reset when the feedback port itself does not exist, for example, if you delete a simulate node or disconnect it from all outputs (so that it gets optimized out by the compiler). They are also reset when the graph hierarchy that contains the feedback port changes, for example, if you create or explode a compound that contains a feedback port.

Not every property can be changed in the middle of a simulation. Properties such as geo_detail_size and solver properties such as time_step_size cannot be changed during playback. To see the effect of such changes, return to the start frame and play forward.

To reset the simulation immediately and clear the feedback-port caches manually, choose Edit > Reset Feedback State.