spaceship/vfx/ShipWreckVFX.gd

class_name ShipWreckVFX
extends Node2D

# Forgejo #130: a vessel's death, as a short sequence rather than a moment.
#
# A ship used to vanish on the frame it was hit and leave a twelve-particle
# puff behind - lighter than the one an ENEMY gets (see EnemyExplosionVFX,
# which #87 made deliberately loud). Losing a hull is the more expensive
# event of the two and it read as the cheaper one.
#
# So the hull comes off the formation and keeps going: it breaks away from
# the fleet, tumbling and venting, for the length of DRIFT_SECONDS, and only
# then goes up - out where it has some room, rather than inside the wedge it
# was flying in.
#
# It is a separate node rather than the Ship staying alive a little longer,
# and that is the important part. A dying Ship still in the tree is still an
# Area2D in the player_ships group with live weapon components: it would keep
# shooting, keep being shot at, keep counting as a target, and keep colliding
# on its way out. Everything about the ship's own lifecycle - the `destroyed`
# signal, leaving Fleet.ships, freeing the node - happens exactly when it did
# before. What is left behind is scenery.

const DRIFT_SECONDS: float = 0.62
# How hard it is pushed out of the formation. Enough to clear the wedge in
# the time above, not so much that it reads as being thrown.
const BREAKAWAY_SPEED: float = 300.0
const DRAG: float = 0.72
const SPIN_MIN: float = 2.4
const SPIN_MAX: float = 7.0
const VENT_COUNT: int = 4
const VENT_SPEED: float = 90.0
# The hull darkens as it goes, so the drift reads as dying rather than as
# flying away.
const FADE_TO: float = 0.35

var hull: PackedVector2Array = PackedVector2Array()
var glow_color: Color = Color(0.25, 0.85, 1.0)
var core_color: Color = Color.WHITE
var velocity: Vector2 = Vector2.ZERO
var spin: float = 0.0
var age: float = 0.0
var vents: Array = []
var _blown: bool = false


# `away` is the direction out of the formation, so the wreck leaves the fleet
# rather than drifting through the middle of it.
static func spawn(parent: Node, ship: Node2D, away: Vector2) -> ShipWreckVFX:
	var wreck := ShipWreckVFX.new()
	wreck.position = ship.position
	wreck.rotation = ship.rotation
	wreck.glow_color = ship.glow_color
	wreck.core_color = ship.core_color
	if ship.definition != null:
		wreck.hull = ship.definition.hull_points
	var drift: Vector2 = away if away.length() > 0.01 else Vector2.UP.rotated(ship.rotation)
	# Its own momentum plus the push: a ship hit at speed carries on the way
	# it was already going.
	wreck.velocity = ship.velocity + drift.normalized() * BREAKAWAY_SPEED
	wreck.spin = randf_range(SPIN_MIN, SPIN_MAX) * (1.0 if randf() < 0.5 else -1.0)
	parent.add_child(wreck)
	return wreck


func _ready() -> void:
	if hull.is_empty():
		hull = PackedVector2Array([Vector2(0, -22), Vector2(-14, 16), Vector2(14, 16)])
	for i in range(VENT_COUNT):
		var angle: float = TAU * float(i) / float(VENT_COUNT) + randf() * 0.6
		vents.append({
			"pos": Vector2.ZERO,
			"vel": Vector2(cos(angle), sin(angle)) * randf_range(VENT_SPEED * 0.4, VENT_SPEED),
			"len": randf_range(9.0, 18.0),
		})


func _process(delta: float) -> void:
	age += delta
	if age >= DRIFT_SECONDS:
		_blow_up()
		return
	position += velocity * delta
	velocity = velocity.lerp(Vector2.ZERO, clampf(DRAG * delta, 0.0, 1.0))
	rotation += spin * delta
	for vent in vents:
		vent.pos += vent.vel * delta
		vent.vel *= 0.94
	queue_redraw()


func _blow_up() -> void:
	if _blown:
		return
	_blown = true
	# Where it ended up, not where it was hit - the point of the drift.
	if is_inside_tree():
		ShipExplosionVFX.spawn(get_tree().root, global_position)
	queue_free()


func _draw() -> void:
	var t: float = clampf(age / DRIFT_SECONDS, 0.0, 1.0)
	var fade: float = lerpf(1.0, FADE_TO, t)
	NeonDraw.draw_glowing_polygon(self, hull, Color(glow_color, fade), 1.0,
		Color(core_color, fade))
	# What is coming out of it. Drawn in the wreck's own local space, so the
	# vents tumble with the hull the way a breach in it would.
	var vent_colour: Color = Color(1.0, 0.72, 0.35, (1.0 - t) * 0.9)
	for vent in vents:
		var dir: Vector2 = Vector2(vent.vel).normalized()
		NeonDraw.draw_glowing_line(self, vent.pos, vent.pos + dir * float(vent.len),
			vent_colour, 0.8, 0.4)