Guarantee a nearby gas giant

WorldGen.gd

@@ -15,6 +15,13 @@ const ASTEROID_FIELD_THRESHOLD: float = 0.15
 const PLANET_THRESHOLD: float = 0.33
 const GAS_GIANT_THRESHOLD: float = 0.55
 
+# A predictable early gas source for play-testing. The origin chunk is
+# deterministically normal space. Its explicit in-chunk position puts it
+# roughly 1,080 world units from a fresh fleet: easy to reach, but not
+# sitting on the spawn.
+const NEARBY_GAS_GIANT_CHUNK: Vector2i = Vector2i.ZERO
+const NEARBY_GAS_GIANT_LOCAL_POS: Vector2 = Vector2(900.0, 600.0)
+
 const PLANET_NAMES: Array = [
 	"Kepler's Rest", "Ceres Minor", "Vesta's Shadow", "Ironhold",
 	"Drift Anchor", "Stonefall", "Grey Watch", "Silent Quarry",
@@ -62,6 +69,8 @@ static func biome_at_chunk(chunk: Vector2i) -> int:
 
 
 static func has_planet_at_chunk(chunk: Vector2i) -> bool:
+	if chunk == NEARBY_GAS_GIANT_CHUNK:
+		return true
 	var n: float = _get_planet_noise().get_noise_2d(float(chunk.x), float(chunk.y))
 	return (biome_at_chunk(chunk) == Biome.ASTEROID_FIELD and n > PLANET_THRESHOLD) or (biome_at_chunk(chunk) == Biome.SPACE and n > GAS_GIANT_THRESHOLD)
 
@@ -76,12 +85,14 @@ static func planet_data_at_chunk(chunk: Vector2i) -> Dictionary:
 	# can never drift out of sync with each other.
 	var rng: RandomNumberGenerator = RandomNumberGenerator.new()
 	rng.seed = hash(chunk)
-	var local_pos: Vector2 = Vector2(rng.randf() * CHUNK_SIZE, rng.randf() * CHUNK_SIZE)
+	var guaranteed_nearby_giant: bool = chunk == NEARBY_GAS_GIANT_CHUNK
+	var local_pos: Vector2 = NEARBY_GAS_GIANT_LOCAL_POS if guaranteed_nearby_giant \
+		else Vector2(rng.randf() * CHUNK_SIZE, rng.randf() * CHUNK_SIZE)
 	var planet_name: String = PLANET_NAMES[rng.randi() % PLANET_NAMES.size()]
 	var shape_seed: int = rng.randi()
 	# 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 gas_giant: bool = guaranteed_nearby_giant or biome_at_chunk(chunk) == Biome.SPACE
 	if gas_giant:
 		planet_name = GAS_GIANT_NAMES[rng.randi() % GAS_GIANT_NAMES.size()]
 	return {"local_pos": local_pos, "name": planet_name, "shape_seed": shape_seed,

tests/test_gas_system.gd

@@ -20,6 +20,19 @@ func _initialize() -> void:
 func _process(delta: float) -> bool:
 	elapsed += delta
 	if stage == 0:
+		var nearby_chunk: Vector2i = WorldGen.NEARBY_GAS_GIANT_CHUNK
+		var nearby_data: Dictionary = WorldGen.planet_data_at_chunk(nearby_chunk)
+		var nearby_position: Vector2 = WorldGen.chunk_origin(nearby_chunk) + nearby_data.local_pos
+		if not WorldGen.has_planet_at_chunk(nearby_chunk):
+			return _fail("nearby gas giant chunk does not contain a planet")
+		if WorldGen.biome_at_chunk(nearby_chunk) != WorldGen.Biome.SPACE:
+			return _fail("nearby gas giant is not in the normal space biome")
+		if String(nearby_data.get("planet_type", "")) != "gas_giant" \
+				or String(nearby_data.get("resource_type", "")) != "gas":
+			return _fail("nearby guaranteed planet is not a gas source")
+		if nearby_position.length() > WorldGen.CHUNK_SIZE * 2.0:
+			return _fail("nearby gas giant spawned too far away: %s" % nearby_position)
+
 		var found_giant: bool = false
 		for x in range(-12, 13):
 			for y in range(-12, 13):