Expand generated terrain with biome-driven props

world/generation/terrain_chunk_definition.gd

@@ -11,6 +11,38 @@ var allowed_rotation_mask := 15
 ## Negative values allow unlimited placements; zero disables random placement.
 @export_range(-1, 1024, 1) var maximum_placements := -1
 @export var tags := PackedStringArray()
+## Empty permits any non-water neighbor. Otherwise at least one listed tag
+## must be present on the neighboring chunk. Water connectors are governed by
+## their inlet/outlet topology instead.
+@export var allowed_neighbor_tags := PackedStringArray()
+## These tags always reject a non-water neighbor, even when it also carries an
+## allowed tag.
+@export var forbidden_neighbor_tags := PackedStringArray()
+## Optional canonical per-edge overrides for allowed_neighbor_tags. Empty means
+## the edge inherits the chunk-wide list. These describe the visible surface at
+## a seam, such as a grass-backed coastline transition that must not meet sand.
+@export_group("Directional Neighbor Rules")
+@export var north_allowed_neighbor_tags := PackedStringArray()
+@export var east_allowed_neighbor_tags := PackedStringArray()
+@export var south_allowed_neighbor_tags := PackedStringArray()
+@export var west_allowed_neighbor_tags := PackedStringArray()
+@export_group("")
+## When non-empty, at least this many in-grid cardinal neighbors must carry one
+## of the listed tags. This supports statements such as "three sides around the
+## spawn must be safe grass" without hard-coding a particular chunk ID.
+@export var required_neighbor_tags := PackedStringArray()
+@export_range(0, 4, 1) var minimum_required_neighbors := 0
+## Matching already-placed neighbors increase this definition's selection
+## weight. This shapes regions without turning a visual preference into a hard
+## generation constraint.
+@export var preferred_neighbor_tags := PackedStringArray()
+## Coastal transition pieces should normally migrate toward the generated
+## region's perimeter while remaining legal in the interior.
+@export var prefers_map_boundary := false
+## Edges that descend from land into the surrounding ocean. Every rotated edge
+## in this mask must face outside the generated grid; it may never meet another
+## terrain chunk.
+@export_flags("North", "East", "South", "West") var ocean_facing_edges := 0
 @export_flags("North", "East", "South", "West") var water_inlet_edges := 0
 @export_flags("North", "East", "South", "West") var water_outlet_edges := 0
 ## Optional generated water footprint in the chunk's unrotated local X/Z plane.
@@ -22,3 +54,70 @@ var allowed_rotation_mask := 15
 func allows_quarter_turn(quarter_turns: int) -> bool:
 	var normalized_turns := posmod(quarter_turns, 4)
 	return (allowed_rotation_mask & (1 << normalized_turns)) != 0
+
+
+func allows_non_water_neighbor(neighbor: TerrainChunkDefinition) -> bool:
+	return _allows_neighbor_with_tags(neighbor, allowed_neighbor_tags)
+
+
+func allows_non_water_neighbor_on_edge(
+	neighbor: TerrainChunkDefinition,
+	edge: TerrainChunkTopology.Edge,
+) -> bool:
+	return _allows_neighbor_with_tags(
+		neighbor,
+		allowed_neighbor_tags_for_edge(edge),
+	)
+
+
+func allowed_neighbor_tags_for_edge(
+	edge: TerrainChunkTopology.Edge,
+) -> PackedStringArray:
+	var edge_tags := directional_allowed_neighbor_tags(edge)
+	return allowed_neighbor_tags if edge_tags.is_empty() else edge_tags
+
+
+func directional_allowed_neighbor_tags(
+	edge: TerrainChunkTopology.Edge,
+) -> PackedStringArray:
+	match edge:
+		TerrainChunkTopology.Edge.NORTH:
+			return north_allowed_neighbor_tags
+		TerrainChunkTopology.Edge.EAST:
+			return east_allowed_neighbor_tags
+		TerrainChunkTopology.Edge.SOUTH:
+			return south_allowed_neighbor_tags
+		TerrainChunkTopology.Edge.WEST:
+			return west_allowed_neighbor_tags
+	return PackedStringArray()
+
+
+func _allows_neighbor_with_tags(
+	neighbor: TerrainChunkDefinition,
+	allowed_tags: PackedStringArray,
+) -> bool:
+	if neighbor == null:
+		return false
+	for forbidden_tag: String in forbidden_neighbor_tags:
+		if forbidden_tag in neighbor.tags:
+			return false
+	if allowed_tags.is_empty():
+		return true
+	return has_any_tag(neighbor.tags, allowed_tags)
+
+
+func prefers_neighbor(neighbor: TerrainChunkDefinition) -> bool:
+	return (
+		neighbor != null
+		and has_any_tag(neighbor.tags, preferred_neighbor_tags)
+	)
+
+
+static func has_any_tag(
+	available_tags: PackedStringArray,
+	requested_tags: PackedStringArray,
+) -> bool:
+	for requested_tag: String in requested_tags:
+		if requested_tag in available_tags:
+			return true
+	return false