spaceship/ExplosionVFXBase.gd

class_name ExplosionVFXBase
extends Node2D

# Shared particle motion/fade/lifetime logic for all explosion VFX types.
# Subclasses fix their own visual style and color as facts about
# themselves (see LightBurstVFX/AsteroidExplosionVFX), not as parameters
# passed in by whatever destroyed the object - so "ships always explode
# blue" is guaranteed by the class hierarchy, not by remembering to pass
# the right Color() at each call site.

@export var particle_count: int = 12
@export var lifetime: float = 0.5
@export var min_speed: float = 60.0
@export var max_speed: float = 220.0

var age: float = 0.0
var particles: Array = []


func _ready() -> void:
	randomize()
	for i in range(particle_count):
		var angle: float = randf() * TAU
		var speed: float = randf_range(min_speed, max_speed)
		var p: Dictionary = {
			"pos": Vector2.ZERO,
			"vel": Vector2(cos(angle), sin(angle)) * speed,
			"rot": randf() * TAU,
			"rot_speed": randf_range(-6.0, 6.0),
			"size": _random_particle_size(),
		}
		# Each particle is its own child CanvasItem, drawn once at its own
		# fixed local shape (subclass decides the shape via
		# _configure_particle). From here on the "animation" is just this
		# child's position/rotation, exactly like Ship.gd/Asteroid.gd - no
		# redraw, no re-tessellating four polylines per particle per frame.
		var visual: ExplosionParticle = ExplosionParticle.new()
		_configure_particle(visual, p)
		if _particle_spins():
			visual.rotation = p["rot"]
		add_child(visual)
		p["visual"] = visual
		particles.append(p)


func _process(delta: float) -> void:
	age += delta
	if age >= lifetime:
		queue_free()
		return
	# CanvasItem modulate is inherited down the tree, so setting it once
	# here fades every particle's already-drawn shape for free - no need
	# to recompute or re-draw a single one of them.
	modulate.a = clamp(1.0 - (age / lifetime), 0.0, 1.0)
	for p in particles:
		p["pos"] += p["vel"] * delta
		p["vel"] *= 0.9
		p["rot"] += p["rot_speed"] * delta
		var visual: ExplosionParticle = p["visual"]
		visual.position = p["pos"]
		if _particle_spins():
			visual.rotation = p["rot"]


func _random_particle_size() -> float:
	return randf_range(10.0, 20.0)


# Called once per particle at spawn time. Subclasses set visual.draw_callable
# to a closure that draws their own fixed local shape (a streak, a rock
# chunk, ...) - it must not depend on `p` beyond values fixed at spawn (size,
# initial velocity direction), since it never runs again.
func _configure_particle(_visual: ExplosionParticle, _p: Dictionary) -> void:
	pass


# True for particle styles whose shape itself spins independently of its
# direction of travel (tumbling debris). Energy streaks are drawn already
# aligned to their (fixed) velocity direction, so giving them this unrelated
# per-particle spin as well would visibly rotate them off their travel line.
func _particle_spins() -> bool:
	return false