Improve generated river terrain

tests/generated_world_runtime_validation.gd

@@ -247,6 +247,7 @@ func _validate_generated_region(
 	assert(_placement_count(placements, "chunk_0034") == 1)
 	assert(_placement_count(placements, "chunk_0035") == 1)
 	assert(_placement_count(placements, "chunk_0036") == 1)
+	assert(_placement_count(placements, "chunk_0038") == 2)
 	assert(
 		_placement_count(placements, "chunk_0014")
 		== (2 if has_secondary_elevation else 0)
@@ -285,10 +286,31 @@ func _validate_generated_region(
 	var river_edge_count := (
 		_placement_count(placements, "chunk_0024")
 		+ _placement_count(placements, "chunk_0025")
+		+ _placement_count(placements, "chunk_0038")
 	)
 	assert(river_coordinate_count >= 12)
 	assert(generator._river_feature_placements.size() == river_coordinate_count)
 	assert(river_edge_count == river_coordinate_count - 8)
+	var stone_bridge_specs: Array[Dictionary] = []
+	for spec: Dictionary in generator._river_feature_placements:
+		if spec.get("id", &"") == &"chunk_0038":
+			stone_bridge_specs.append(spec)
+	assert(stone_bridge_specs.size() == 2)
+	var first_bridge_coordinate := stone_bridge_specs[0].get(
+		"coordinate",
+		Vector2i(-1, -1),
+	) as Vector2i
+	var second_bridge_coordinate := stone_bridge_specs[1].get(
+		"coordinate",
+		Vector2i(-1, -1),
+	) as Vector2i
+	var bridge_delta := second_bridge_coordinate - first_bridge_coordinate
+	assert(absi(bridge_delta.x) + absi(bridge_delta.y) == 1)
+	assert(posmod(
+		int(stone_bridge_specs[1].get("turns", -1))
+		- int(stone_bridge_specs[0].get("turns", -1)),
+		4,
+	) == 2)
 	var river_source_coordinates := generator._river_source_coordinates(
 		generator._river_feature_origin,
 		generator._river_feature_footprint_size,
@@ -446,6 +468,20 @@ func _validate_generated_region(
 		assert(fresh.surface_size.x <= 10.0 and fresh.surface_size.y <= 10.0)
 		assert(not fresh.visual_surface_enabled)
 		assert(not (fresh.get_node("VisualWater") as MeshInstance3D).visible)
+		var generated_bed := fresh.get_node_or_null(
+			"GeneratedBed",
+		) as MeshInstance3D
+		assert(generated_bed != null and generated_bed.mesh != null)
+		assert(
+			is_equal_approx(
+				generated_bed.global_position.y,
+				GeneratedWorldRegion.GENERATED_FRESH_WATER_BED_HEIGHT,
+			)
+		)
+		assert(
+			generated_bed.material_override != null
+			and generated_bed.material_override.resource_name == "dirt"
+		)
 		var fresh_recovery := (
 			fresh.get_node("RecoveryRegion") as PlayerWaterTrigger
 		)
@@ -486,6 +522,16 @@ func _validate_generated_region(
 	)
 
 	var decorations := region.get_node("Decorations") as Node3D
+	var grass_prop_surface_triangles := region.get_spawn_surface_triangles(
+		[&"grass_lite"],
+		-INF,
+		0.35,
+	)
+	var sand_prop_surface_triangles := region.get_spawn_surface_triangles(
+		[&"sand"],
+		-INF,
+		0.35,
+	)
 	var anchors := region.get_node(
 		"GatherableAnchors/ReachableTreeTrunks"
 	) as GatherableAnchorSet3D
@@ -540,6 +586,8 @@ func _validate_generated_region(
 			region,
 			child as Node3D,
 			definition,
+			grass_prop_surface_triangles,
+			sand_prop_surface_triangles,
 		)
 		if prop_id == &"prop_palm":
 			var cluster_id := int(
@@ -1063,6 +1111,8 @@ func _validate_decoration_transform(
 	region: GeneratedWorldRegion,
 	prop: Node3D,
 	definition: TerrainPropDefinition,
+	grass_surface_triangles: Array[PackedVector3Array],
+	sand_surface_triangles: Array[PackedVector3Array],
 ) -> void:
 	assert(prop != null)
 	assert(prop.scale.is_equal_approx(Vector3.ONE))
@@ -1142,6 +1192,43 @@ func _validate_decoration_transform(
 				],
 		],
 	)
+	var required_surface_triangles: Array[PackedVector3Array] = (
+		sand_surface_triangles
+		if definition.procedural_group == &"sand_tree"
+		else grass_surface_triangles
+	)
+	var required_surface_height := _triangle_surface_height_at(
+		prop.global_position,
+		required_surface_triangles,
+	)
+	assert(
+		required_surface_height > -INF
+		and absf(required_surface_height - prop.global_position.y) <= 0.01,
+		"%s (%s) is not rooted on its required terrain material at %s."
+		% [prop.name, definition.stable_id, prop.global_position],
+	)
+
+
+func _triangle_surface_height_at(
+	position: Vector3,
+	triangles: Array[PackedVector3Array],
+) -> float:
+	var highest := -INF
+	var segment_start := position + Vector3.UP * 100.0
+	var segment_end := position + Vector3.DOWN * 100.0
+	for triangle: PackedVector3Array in triangles:
+		if triangle.size() != 3:
+			continue
+		var hit: Variant = Geometry3D.segment_intersects_triangle(
+			segment_start,
+			segment_end,
+			triangle[0],
+			triangle[1],
+			triangle[2],
+		)
+		if hit is Vector3:
+			highest = maxf(highest, (hit as Vector3).y)
+	return highest
 
 
 func _validate_tree_gatherable_anchors(