Expand generated terrain with biome-driven props

world/generation/terrain_prop_definition.gd

@@ -0,0 +1,53 @@
+class_name TerrainPropDefinition
+extends Resource
+
+@export var stable_id: StringName
+@export var label := ""
+@export var packed_scene: PackedScene
+## Empty means the prop is available for deliberate placement only.
+@export var procedural_group: StringName
+@export var required_chunk_tags := PackedStringArray()
+@export_range(0.01, 100.0, 0.01) var selection_weight := 1.0
+## Manhattan distance in chunks from the forced center spawn. Two keeps the
+## spawn chunk and its four immediate neighbors clear of this prop.
+@export_range(0, 16, 1) var minimum_spawn_chunk_distance := 0
+## These groups influence placement selection but are not a hard requirement.
+## A nearby match multiplies this prop's weight; an absent match divides it by
+## the same amount.
+@export var preferred_nearby_prop_groups := PackedStringArray()
+@export_range(0.0, 100.0, 0.5) var preferred_nearby_radius := 0.0
+@export_range(1.0, 10.0, 0.1) var nearby_preference_weight_multiplier := 1.0
+@export_range(0.0, 10.0, 0.05) var clearance_radius := 0.5
+@export_range(0.0, 5.0, 0.05) var collision_radius := 0.0
+@export_range(0.0, 20.0, 0.05) var collision_height := 0.0
+@export var collision_box_size := Vector3.ZERO
+@export var collision_offset := Vector3.ZERO
+## Values above zero add this prop to the tree-gathering anchor set.
+@export_range(0.0, 20.0, 0.05) var gatherable_anchor_height := 0.0
+
+
+func supports_chunk_tags(chunk_tags: PackedStringArray) -> bool:
+	for required_tag: String in required_chunk_tags:
+		if required_tag not in chunk_tags:
+			return false
+	return true
+
+
+func has_collision() -> bool:
+	return has_cylinder_collision() or has_box_collision()
+
+
+func has_cylinder_collision() -> bool:
+	return collision_radius > 0.0 and collision_height > 0.0
+
+
+func has_box_collision() -> bool:
+	return (
+		collision_box_size.x > 0.0
+		and collision_box_size.y > 0.0
+		and collision_box_size.z > 0.0
+	)
+
+
+func is_procedural() -> bool:
+	return procedural_group != &""