rigid_body_sleeping

When a dynamic rigid-body doesn't move (or moves very slowly) during a few seconds, it will be marked as sleeping by the physics pipeline. Rigid-bodies marked as sleeping are no longer simulated by the physics engine until they are woken up. That way the physics engine doesn't waste any computational resources simulating objects that don't actually move. They are woken up automatically whenever another non-sleeping rigid-body starts interacting with them (either with a joint, or with one of its attached colliders generating contacts).

However, a sleeping rigid-body won't respond to any user action. This is why it is possible to wake-up the rigid-body manually with RigidBody.wake_up() or PhysicsWorld.wake_up(handle) (if their strong argument is True, the default, the rigid-body is guaranteed to stay awake for several timesteps, otherwise it may fall asleep again immediately). Setting the pose, the velocities, the gravity scale, the type, or the locked axes of a rigid-body through its properties always wakes it up. Some methods take an additional wake_up boolean argument that, if True (the default), ensures that the rigid-body wakes up before the action takes place. For example:

• RigidBody.add_force(force, wake_up=True) will wake-up the rigid-body before adding the force.
• ImpulseJointSet.remove(joint, wake_up=True) (resp. MultibodyJointSet.remove) will wake-up the two rigid-bodies attached by the removed joint.
• ColliderSet.remove(collider, islands, bodies, wake_up=True) will wake-up the rigid-body the removed collider is attached to (PhysicsWorld.remove_collider always does).

Unless you want to achieve special effects, it is recommended to keep the default value True of the wake_up argument. One example of case where setting the argument of wake_up to False makes sense is to simulate a custom constant gravity with RigidBody.add_force(force, wake_up=False). This will result in the force being added to the rigid-body, but will allow the rigid-body to fall asleep if it reaches a dynamic equilibrium.

Whether a rigid-body is sleeping is given by the RigidBody.is_sleeping property, and it can be put to sleep manually with RigidBody.sleep(). A rigid-body can be prevented from ever sleeping with RigidBodyBuilder.can_sleep(False), or created already asleep with RigidBodyBuilder.sleeping(True). The velocity thresholds and the delay before the rigid-body falls asleep are given by the linear_threshold, angular_threshold, and time_until_sleep attributes of the RigidBodyActivation returned by the RigidBody.activation property. Keep in mind that this property returns a copy: the modified RigidBodyActivation must be assigned back to RigidBody.activation to take effect.