Add tentacled boss planet encounter

world/WorldGen.gd

@@ -37,9 +37,13 @@ const BLACK_HOLE_CHANCE: float = 0.05
 # from 0.08 after playtesting found that rate too scarce for how central
 # research points had become to progression.
 const RESEARCH_LAB_CHANCE: float = 0.16
+# A boss world is rarer than every ordinary discovery. Its roll uses a
+# separately seeded generator below, so adding it cannot rename or re-roll
+# any planet in an existing world.
+const BOSS_PLANET_CHANCE: float = 0.025
 
 # DEV MODE ONLY: one of every planet type, parked in the chunks immediately
-# around the spawn so all four can be reached in seconds.
+# around the spawn so all five can be reached in seconds.
 #
 # This replaces the guaranteed gas giant that used to sit in the origin
 # chunk for every game. That was a play-testing convenience which had become
@@ -56,6 +60,7 @@ const DEV_PLANET_CHUNKS: Dictionary = {
 	Vector2i(1, 0): PLANET_DEFINITIONS.ROCKY_ID,
 	Vector2i(0, 1): PLANET_DEFINITIONS.RESEARCH_LAB_ID,
 	Vector2i(1, 1): PLANET_DEFINITIONS.BLACK_HOLE_ID,
+	Vector2i(-1, 0): PLANET_DEFINITIONS.BOSS_ID,
 }
 const DEV_PLANET_LOCAL_POS: Vector2 = Vector2(600.0, 600.0)
 
@@ -143,20 +148,26 @@ static func planet_data_at_chunk(chunk: Vector2i) -> Dictionary:
 	var black_hole_roll: float = rng.randf()
 	# Same principle, its own independent roll (#63).
 	var research_lab_roll: float = rng.randf()
+	# Independent from the established generation stream: existing chunks keep
+	# their old names and shapes when this new rare outcome is introduced.
+	var boss_rng := RandomNumberGenerator.new()
+	boss_rng.seed = hash("boss:%d:%d" % [chunk.x, chunk.y])
+	var boss_roll: float = boss_rng.randf()
 	# A stable per-chunk roll makes gas giants persistent landmarks rather
 	# than a different resource whenever the scene reloads.
 	var gas_giant: bool = biome_at_chunk(chunk) == Biome.SPACE
 	var definition_id: String = PLANET_DEFINITIONS.GAS_GIANT_ID if gas_giant else PLANET_DEFINITIONS.ROCKY_ID
-	# A rare third outcome, seeded the same deterministic way as everything
-	# else here.
-	if black_hole_roll < BLACK_HOLE_CHANCE:
+	# Rare authored outcomes, seeded deterministically like everything else.
+	if boss_roll < BOSS_PLANET_CHANCE:
+		definition_id = PLANET_DEFINITIONS.BOSS_ID
+	elif black_hole_roll < BLACK_HOLE_CHANCE:
 		definition_id = PLANET_DEFINITIONS.BLACK_HOLE_ID
 	elif research_lab_roll < RESEARCH_LAB_CHANCE:
 		definition_id = PLANET_DEFINITIONS.RESEARCH_LAB_ID
 	# Dev mode's fixed planting wins over every roll above. Applied last, and
 	# AFTER all the rng draws, so switching it on cannot shift which random
 	# values any other chunk consumes - a dev world and a normal one differ
-	# only in these four chunks.
+	# only in these five chunks.
 	if not forced_definition_id.is_empty():
 		definition_id = forced_definition_id
 	var definition: Resource = PLANET_DEFINITIONS.get_definition(definition_id)