godot-demo-projects/2d/dynamic_tilemap_layers/level/tile_map.gd

extends TileMapLayer

# You can have multiple layers if you make this an array.
var player_in_secret: bool = false
var layer_alpha := 1.0


func _ready() -> void:
	set_process(false)


func _process(delta: float) -> void:
	if player_in_secret:
		if layer_alpha > 0.3:
			# Animate the layer transparency.
			layer_alpha = move_toward(layer_alpha, 0.3, delta)
			self_modulate = Color(1, 1, 1, layer_alpha)
		else:
			set_process(false)
	else:
		if layer_alpha < 1.0:
			layer_alpha = move_toward(layer_alpha, 1.0, delta)
			self_modulate = Color(1, 1, 1, layer_alpha)
		else:
			set_process(false)


func _use_tile_data_runtime_update(_coords: Vector2i) -> bool:
	return true


func _tile_data_runtime_update(_coords: Vector2i, tile_data: TileData) -> void:
	# Remove collision for secret layer.
	tile_data.set_collision_polygons_count(0, 0)


func _on_secret_detector_body_entered(body: Node2D) -> void:
	if body is not CharacterBody2D:
		# Detect the player only.
		return

	player_in_secret = true
	set_process(true)


func _on_secret_detector_body_exited(body: Node2D) -> void:
	if body is not CharacterBody2D:
		return

	player_in_secret = false
	set_process(true)