Rollback caveats

As with most things, rollback has some drawbacks along with its benefits.

CharacterBody velocity

Godot's move_and_slide() uses the velocity property, which is set in meters/second. The method assumes a delta time based on what kind of frame is being run. However, it is not aware of netfox's network ticks, which means that movement speed will be off.

To counteract this, multiply velocity with NetworkTime.physics_factor, which will adjust for the difference between Godot's assumed delta time and the delta time netfox is using.

If you don't want to lose your original velocity ( e.g. because it accumulates acceleration over time ), divide by the same property after using any built-in method. For example:

# Apply movement
velocity *= NetworkTime.physics_factor
move_and_slide()
velocity /= NetworkTime.physics_factor

CharacterBody on floor

CharacterBodies only update their is_on_floor() state only after a move_and_slide() call.

This means that during rollback, the position is updated, but the is_on_floor() state is not.

As a work-around, do a zero-velocity move before checking if the node is on the floor:

extends CharacterBody3D

func _rollback_tick(delta, tick, is_fresh):
    # Add the gravity.
    _force_update_is_on_floor()
    if not is_on_floor():
        velocity.y -= gravity * delta

  # ...

func _force_update_is_on_floor():
    var old_velocity = velocity
    velocity = Vector3.ZERO
    move_and_slide()
    velocity = old_velocity

Physics updates

Godot's physics system is updated only during _physics_process, while rollback updates the game state multiple times during a single frame.

Unfortunately, Godot does not support manually updating or stepping the physics system, at least at the time of writing. This means that:

• Rollback and physics-based games don't work at the moment
• Collision detection can work, but with workarounds

If there's a way to force an update for your given node type, it should work.