TouhouGD/script/effect/particle_decal.gd

extends Decal
class_name ParticleDecal

@export var lifetime: float = 1
@export var gradient: Gradient
@export var scale_curve: Curve
@export var particle_rotate: int
@export var size_random: float #0-1 0为不随机 1为随机0~2倍

var lifetime_now: float
var size_scale: float
var random_rotate: float


func on_ready() -> void:
	var scale_sample: float = scale_curve.sample(0)
	size_random = clamp(size_random, 0, 1)
	size_scale = randf_range(1-size_random, 1+size_random)
	scale = Vector3(scale_sample, 1, scale_sample) * size_scale
	random_rotate = randf_range(0, 360)


func on_process(delta: float) -> void:
	lifetime_now += delta
	var rate: float = lifetime_now / lifetime
	if rate > 1:
		return

	#色带
	if gradient:
		modulate = gradient.sample(rate)
	else:
		modulate.a = 1 - rate

	#缩放曲线
	if scale_curve:
		var scale_sample: float = scale_curve.sample(rate)
		scale = Vector3(scale_sample, 1, scale_sample) * size_scale

	#旋转
	#    rotation_degrees.y = particle_rotate * rate + random_rotate
	rotation_degrees.y = particle_rotate * rate
	return