Fix FPS-dependent movement in Navigation AStar demo (#1227)

Previously, the way in which the spaceship steered depended
on the rendered framerate.

This moves ship movement to the physics step to avoid this, and
enables physics interpolation for smooth motion.

2d/navigation_astar/character.gd

@@ -25,7 +25,7 @@ func _ready() -> void:
 	_change_state(State.IDLE)
 
 
-func _process(_delta: float) -> void:
+func _physics_process(_delta: float) -> void:
 	if _state != State.FOLLOW:
 		return
 
@@ -44,6 +44,7 @@ func _unhandled_input(event: InputEvent) -> void:
 		if event.is_action_pressed(&"teleport_to", false, true):
 			_change_state(State.IDLE)
 			global_position = _tile_map.round_local_position(_click_position)
+			reset_physics_interpolation()
 		elif event.is_action_pressed(&"move_to"):
 			_change_state(State.FOLLOW)
 
@@ -52,7 +53,7 @@ func _move_to(local_position: Vector2) -> bool:
 	var desired_velocity: Vector2 = (local_position - position).normalized() * speed
 	var steering: Vector2 = desired_velocity - _velocity
 	_velocity += steering / MASS
-	position += _velocity * get_process_delta_time()
+	position += _velocity * get_physics_process_delta_time()
 	rotation = _velocity.angle()
 	return position.distance_to(local_position) < ARRIVE_DISTANCE
 

2d/navigation_astar/game.tscn

@@ -59,3 +59,4 @@ texture = ExtResource("6_b3lcn")
 
 [node name="Camera2D" type="Camera2D" parent="."]
 offset = Vector2(576, 324)
+process_callback = 0

2d/navigation_astar/project.godot

@@ -40,6 +40,11 @@ move_to={
 ]
 }
 
+[physics]
+
+common/physics_ticks_per_second=120
+common/physics_interpolation=true
+
 [rendering]
 
 renderer/rendering_method="gl_compatibility"