Expand generated terrain with biome-driven props

world/generation/terrain_biome_catalog.gd

@@ -0,0 +1,74 @@
+class_name TerrainBiomeCatalog
+extends Resource
+
+@export var definitions: Array[TerrainBiomeDefinition] = []
+
+
+func definition_for_id(stable_id: StringName) -> TerrainBiomeDefinition:
+	for definition: TerrainBiomeDefinition in definitions:
+		if definition != null and definition.stable_id == stable_id:
+			return definition
+	return null
+
+
+func definitions_for_tags(
+	chunk_tags: PackedStringArray,
+) -> Array[TerrainBiomeDefinition]:
+	var result: Array[TerrainBiomeDefinition] = []
+	for definition: TerrainBiomeDefinition in definitions:
+		if definition != null and definition.supports_chunk_tags(chunk_tags):
+			result.append(definition)
+	return result
+
+
+func validation_errors() -> PackedStringArray:
+	var errors := PackedStringArray()
+	var seen_ids: Dictionary[StringName, bool] = {}
+	for index: int in definitions.size():
+		var definition := definitions[index]
+		if definition == null:
+			errors.append("Biome definition %d is empty." % index)
+			continue
+		if definition.stable_id == &"":
+			errors.append("Biome definition %d has no stable ID." % index)
+		elif seen_ids.has(definition.stable_id):
+			errors.append("Biome ID %s is duplicated." % definition.stable_id)
+		else:
+			seen_ids[definition.stable_id] = true
+		if definition.required_chunk_tags.is_empty():
+			errors.append(
+				"%s has no required chunk tags." % definition.stable_id
+			)
+		for required_tag: String in definition.required_chunk_tags:
+			if required_tag in definition.forbidden_chunk_tags:
+				errors.append(
+					"%s both requires and forbids chunk tag '%s'."
+					% [definition.stable_id, required_tag]
+				)
+		var seen_groups: Dictionary[StringName, bool] = {}
+		for rule_index: int in definition.prop_rules.size():
+			var rule := definition.prop_rules[rule_index]
+			if rule == null:
+				errors.append(
+					"%s prop rule %d is empty."
+					% [definition.stable_id, rule_index]
+				)
+				continue
+			if rule.procedural_group == &"":
+				errors.append(
+					"%s prop rule %d has no group."
+					% [definition.stable_id, rule_index]
+				)
+			elif seen_groups.has(rule.procedural_group):
+				errors.append(
+					"%s duplicates prop group %s."
+					% [definition.stable_id, rule.procedural_group]
+				)
+			else:
+				seen_groups[rule.procedural_group] = true
+			if rule.minimum_placements > 0 and rule.placement_chance <= 0:
+				errors.append(
+					"%s requires %s props but gives them no placement chance."
+					% [definition.stable_id, rule.procedural_group]
+				)
+	return errors