倒计时

Coddy Godot 游戏：霓虹赛道课程的第 17 课，共 20 课。

比赛从灯光倒计时开始：3、2、1、GO。GO 之前，没人移动。

将比赛设为第三种状态 countdown，倒计时设为 3 秒，并在 _ready 中冻结所有汽车。倒计时期间，显示剩余秒数，其他什么也不做：

if state == "countdown":
	countdown -= delta
	$HUD/Message.text = str(ceili(countdown)) if countdown > 0.0 else "GO!"
	if countdown <= 0.0:
		state = "racing"
		car.active = true
		for rival in rivals:
			rival.active = true
	return

ceili 会向上取整，所以剩余 2.4 秒时会显示 3。GO 后继续倒计时，并在时钟到达 -1 时清除消息，也就是一秒后：

if countdown > -1.0:
	countdown -= delta
	if countdown <= -1.0:
		$HUD/Message.text = ""

挑战

简单

用倒计时开始比赛。

将 state 设为 "countdown"，并添加 var countdown := 3.0。
在 _ready 中，将 car.active 和每个对手的 active 设为 false。
将倒计时代码块放在 _physics_process 的开头。
在 done 检查之后，添加上面的清除代码块。

按下“开始”：画面会显示 3、2、1、GO!，然后比赛开始。接着按“检查”。

亲手试试

extends Node2D

@export var accel := 260.0
@export var max_speed := 200.0
@export var turn_speed := 3.2
@export var drag := 0.6
@export var grip := 7.0

var velocity := Vector2.ZERO
var boost_time := 0.0
var boost_charge := 0.0
var active := true

@onready var track: Node2D = $"../Track"


func _physics_process(delta: float) -> void:
	var throttle := 0.0
	var steer := 0.0
	if active:
		throttle = Input.get_axis("move_down", "move_up")
		steer = Input.get_axis("move_left", "move_right")
		if Input.is_action_just_pressed("action") and boost_charge >= 1.0:
			boost_charge = 0.0
			boost_time = 1.0
	boost_charge = minf(1.0, boost_charge + delta / 10.0)
	$"../HUD/Boost".scale.x = boost_charge

	var forward := Vector2.RIGHT.rotated(rotation)
	var speed := velocity.dot(forward)
	var top := max_speed
	var grip_now := grip
	if boost_time > 0.0:
		boost_time -= delta
		top = max_speed * 1.3
		velocity += forward * accel * delta
	for pad in get_tree().get_nodes_in_group("boost_pads"):
		if position.distance_to(pad.position) < 22.0:
			boost_time = maxf(boost_time, 0.4)
	for oil in get_tree().get_nodes_in_group("oil"):
		if position.distance_to(oil.position) < 20.0:
			grip_now = grip * 0.12
	if not track.is_on_road(position):
		top = max_speed * 0.45
		velocity *= 1.0 - 2.5 * delta

	if throttle < 0.0 and speed > 10.0:
		velocity += forward * throttle * accel * 1.6 * delta
	else:
		velocity += forward * throttle * accel * delta
	rotation += steer * turn_speed * delta * clampf(absf(speed) / 90.0, 0.0, 1.0) * signf(speed + 0.01)

	var side := forward.orthogonal()
	velocity -= side * velocity.dot(side) * minf(1.0, grip_now * delta)
	velocity *= 1.0 - drag * delta
	if velocity.length() > top:
		velocity = velocity.move_toward(velocity.limit_length(top), accel * 2.0 * delta)
	position += velocity * delta
	$Exhaust.emitting = throttle > 0.0 or boost_time > 0.0
	$Flame.visible = boost_time > 0.0