extends CanvasLayer

@export var target: Node2D
@onready var rect = $ColorRect

var mat: ShaderMaterial
var last_pos: Vector2

func _ready():
	mat = rect.material as ShaderMaterial
	if target != null:
		last_pos = target.global_position

func _process(delta: float) -> void:
	if target == null:
		return

	if mat == null:
		return

	var vp_size: Vector2 = get_viewport().get_visible_rect().size

	# 玩家世界坐标
	var world_pos: Vector2 = target.global_position

	# ✅ 世界 -> 屏幕像素坐标（包含相机影响）
	var screen_pos: Vector2 = get_viewport().get_canvas_transform() * world_pos

	# 速度方向（世界空间）
	var vel: Vector2 = (world_pos - last_pos) / max(delta, 0.0001)
	last_pos = world_pos

	var speed: float = vel.length()
	var dir: Vector2 = Vector2.RIGHT
	if speed > 0.001:
		dir = vel / speed

	# ✅ 船头前移（拨水发生在玩家前面）
	var front_offset_px: Vector2 = dir * 30.0
	var uv_front: Vector2 = (screen_pos + front_offset_px) / vp_size
	uv_front = uv_front.clamp(Vector2(0, 0), Vector2(1, 1))


	mat.set_shader_parameter("obj_uv", uv_front)
	mat.set_shader_parameter("obj_dir", dir)
	mat.set_shader_parameter("obj_speed", clamp(speed / 600.0, 0.0, 2.0))