spaceship/world/AsteroidField.gd

extends Node2D

# Spawns slow-drifting asteroids inside ASTEROID_FIELD biome chunks near
# the fleet, and despawns them once the fleet has moved far enough away -
# keeps the scene from accumulating unbounded nodes over a long session
# while still populating newly-entered asteroid regions on the fly.

@export var check_interval: float = 1.0
@export var spawn_radius_chunks: int = 2
# #126: no asteroid may be created anywhere the player can SEE. It used to be
# a fixed bubble around the fleet, which was smaller than the screen - so a
# rock could and did materialise in plain view, several hundred pixels from
# the fleet but well inside the window. The real rule is the visible rect,
# and this radius is now only the floor under it: what to use when the
# viewport cannot be measured (no camera yet on the very first frame of a
# scene, or a headless run with no window at all).
@export var safe_spawn_radius: float = 420.0
# Pushed this far past the edge of the visible rect, so a rock placed just
# outside does not drift into view on the same frame it was created.
@export var offscreen_margin: float = 140.0
@export var despawn_radius_chunks: int = 4
@export var asteroids_per_chunk: int = 6
@export var min_speed: float = 12.0
@export var max_speed: float = 35.0

@onready var fleet: Node2D = get_node("../Fleet")

var asteroid_scene: PackedScene = preload("res://world/Asteroid.tscn")
var populated_chunks: Dictionary = {}
var timer: float = 0.0


func _ready() -> void:
	randomize()


func _process(delta: float) -> void:
	timer += delta
	if timer < check_interval:
		return
	timer = 0.0
	update_chunks()


func update_chunks() -> void:
	# Public (not just called from _process's own timer): also invoked
	# once synchronously right after the fleet is positioned on a fresh
	# Main.tscn load, so nearby asteroids exist immediately instead of
	# only appearing ~check_interval seconds later - most noticeable as a
	# jarring pop-in right after returning from a planet's surface.
	var center_chunk: Vector2i = WorldGen.chunk_coords(fleet.get_centroid())

	for dx in range(-spawn_radius_chunks, spawn_radius_chunks + 1):
		for dy in range(-spawn_radius_chunks, spawn_radius_chunks + 1):
			var chunk: Vector2i = center_chunk + Vector2i(dx, dy)
			if populated_chunks.has(chunk):
				continue
			if WorldGen.biome_at_chunk(chunk) != WorldGen.Biome.ASTEROID_FIELD:
				continue
			_spawn_chunk_asteroids(chunk)

	var to_remove: Array = []
	for chunk in populated_chunks.keys():
		if _chebyshev_chunk_distance(chunk, center_chunk) > despawn_radius_chunks:
			for asteroid in populated_chunks[chunk]:
				if is_instance_valid(asteroid):
					asteroid.queue_free()
			to_remove.append(chunk)
	for chunk in to_remove:
		populated_chunks.erase(chunk)


func _chebyshev_chunk_distance(a: Vector2i, b: Vector2i) -> int:
	return max(abs(a.x - b.x), abs(a.y - b.y))


# The area a new asteroid must stay out of: whatever is on screen, or the
# fallback bubble around the fleet when there is no screen to measure.
#
# Public since #139: the prologue lays its own debris belt (IntroDirector)
# with its own arithmetic and had the same bug this fixed - rocks appearing
# inside the view. One rule, in one place, borrowed rather than restated.
#
# Chunks are populated around wherever the fleet happens to be, including the
# chunk it is standing in, so without this a rock could appear directly on a
# ship - worst on the frame a scene loads, where arriving back from a planet
# could cost a vessel instantly. #126 widens that from "not on the fleet" to
# "not in view", which is the same rule the player actually notices.
func keep_out_rect(centre: Vector2) -> Rect2:
	var fallback := Rect2(centre - Vector2(safe_spawn_radius, safe_spawn_radius),
		Vector2(safe_spawn_radius, safe_spawn_radius) * 2.0)
	if get_viewport() == null:
		return fallback
	var visible_rect: Rect2 = ViewUtils.get_visible_world_rect(self)
	if visible_rect.size.x < 1.0 or visible_rect.size.y < 1.0:
		return fallback
	visible_rect = visible_rect.grow(offscreen_margin)
	# Never smaller than the old bubble: on a heavily zoomed-in view the
	# screen can be narrower than the distance a rock needs to be safe.
	return visible_rect.merge(fallback)


func safe_position(candidate: Vector2, keep_out: Rect2) -> Vector2:
	if not keep_out.has_point(candidate):
		return candidate
	# Pushed out through the nearest edge rather than dropped, so the field
	# keeps its density around the fleet instead of thinning out where the
	# player is looking.
	var centre: Vector2 = keep_out.get_center()
	var away: Vector2 = candidate - centre
	if absf(away.x) < 0.001 and absf(away.y) < 0.001:
		away = Vector2.RIGHT.rotated(randf() * TAU)
	var half: Vector2 = keep_out.size * 0.5
	# The smallest scaling that puts the point on the boundary along `away`:
	# whichever axis it would leave through first decides.
	var scale_x: float = half.x / absf(away.x) if absf(away.x) > 0.001 else INF
	var scale_y: float = half.y / absf(away.y) if absf(away.y) > 0.001 else INF
	var factor: float = minf(scale_x, scale_y)
	if is_inf(factor):
		return centre + Vector2(half.x + 1.0, 0.0)
	return centre + away * factor * 1.02


func _spawn_chunk_asteroids(chunk: Vector2i) -> void:
	var origin: Vector2 = WorldGen.chunk_origin(chunk)
	var spawned: Array = []
	# Measured once per chunk rather than per asteroid: it cannot change
	# between two rocks placed in the same frame, and it is a viewport
	# transform rather than a field read.
	var keep_out: Rect2 = keep_out_rect(fleet.get_centroid())

	for i in range(asteroids_per_chunk):
		var local_pos: Vector2 = Vector2(randf() * WorldGen.CHUNK_SIZE, randf() * WorldGen.CHUNK_SIZE)
		var asteroid: Node2D = asteroid_scene.instantiate()
		asteroid.position = safe_position(origin + local_pos, keep_out)
		var angle: float = randf() * TAU
		var speed: float = randf_range(min_speed, max_speed)
		asteroid.velocity = Vector2(cos(angle), sin(angle)) * speed
		asteroid.rotation_speed = randf_range(-0.4, 0.4)
		# Deferred: update_chunks() can run synchronously from inside a
		# parent's own _ready() chain (forced once right after the fleet
		# is positioned, to avoid a pop-in on scene load) - Godot refuses
		# a direct add_child() while the tree is still "busy setting up
		# children" in that situation, so this must be deferred either way.
		get_parent().add_child.call_deferred(asteroid)
		spawned.append(asteroid)

	populated_chunks[chunk] = spawned