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


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


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
    return