Simulation Zones

Using a Simulation Input and Simulation Output node, you can create effects that change over time.

The @simulation_zone decorator creates these linked nodes. Like a repeat zone, its parameters are the simulation’s state items, and the function returns their new values in the same order.

@simulation_zone
def fall(geometry: Geometry, speed: float, delta_time: float):
    moved = set_position(geometry=geometry, offset=(0.0, 0.0, -speed * delta_time)).geometry
    return moved, speed + 9.8 * delta_time

@tree("Falling")
def falling(geometry: Geometry):
    return fall(geometry, 0.0).geometry

A parameter named delta_time is not a state item. It receives the time since the previous frame, in seconds.

Each frame, the result from the previous frame is passed into the zone’s inputs. The initial call to fall in falling provides the initial values for the simulation.

Skipping Steps

Pass skip= to set the Skip input of the Simulation Output node. When it is true, the simulation keeps its previous state for that frame.

paused = scene_time().frame > 50.0
fall(geometry, 0.0, skip=paused)

Animation without a Simulation

If a value only depends on the current frame, not on the previous state, you don’t need a simulation zone. Use the Scene Time node:

frame = scene_time().frame
seconds = scene_time().seconds