Improve tree gathering and rain occlusion

tests/generated_world_runtime_validation.gd

@@ -12,6 +12,9 @@ const GeneratedLakePool: FishPool = preload(
 const GeneratedRiverPool: FishPool = preload(
 	"res://fish/pools/generated_river_pool.tres"
 )
+const PrecipitationOcclusionType = preload(
+	"res://world/environment/precipitation_occlusion.gd"
+)
 const FIRST_SEED := 13001
 const SECOND_SEED := 13002
 const RIVER_FALLBACK_SEED := 13012
@@ -502,6 +505,12 @@ func _validate_generated_region(
 		assert(PROCEDURAL_PROP_IDS.has(prop_id))
 		var definition := region.get_prop_catalog().definition_for_id(prop_id)
 		assert(definition != null)
+		if definition.procedural_group in [&"grass_tree", &"sand_tree"]:
+			assert(
+				_has_precipitation_occlusion_layer(child),
+				"Precipitation occlusion layer missing from %s (%s)."
+				% [child.name, prop_id],
+			)
 		var biome_id := StringName(
 			child.get_meta(&"terrain_biome_id", &"")
 		)
@@ -967,10 +976,12 @@ func _validate_prop_catalog(region: GeneratedWorldRegion) -> void:
 	assert(pine != null)
 	assert(pine.minimum_visual_scale < pine.maximum_visual_scale)
 	assert(pine.material_variants.is_empty())
+	assert(not pine.has_gatherable_surface())
 	var large_pine := catalog.definition_for_id(&"prop_pine_large")
 	assert(large_pine != null)
 	assert(large_pine.minimum_visual_scale < large_pine.maximum_visual_scale)
 	assert(large_pine.material_variants.is_empty())
+	assert(not large_pine.has_gatherable_surface())
 	var palm := catalog.definition_for_id(&"prop_palm")
 	assert(palm != null)
 	assert(is_equal_approx(palm.minimum_visual_scale, 0.5))
@@ -1180,6 +1191,21 @@ func _find_mesh_instance(root_node: Node) -> MeshInstance3D:
 	return null
 
 
+func _has_precipitation_occlusion_layer(root_node: Node) -> bool:
+	var mesh_instance := root_node as MeshInstance3D
+	if (
+		mesh_instance != null
+		and mesh_instance.get_layer_mask_value(
+			PrecipitationOcclusionType.RENDER_LAYER_NUMBER
+		)
+	):
+		return true
+	for child: Node in root_node.get_children():
+		if _has_precipitation_occlusion_layer(child):
+			return true
+	return false
+
+
 func _has_material_variant_override(
 	root_node: Node,
 	variants: Array[Material],

tests/world_weather_validation.gd

@@ -10,6 +10,9 @@ const WorldTimeServiceType = preload("res://world/world_time_service.gd")
 const WorldTimeVisualControllerType = preload(
 	"res://world/world_time_visual_controller.gd"
 )
+const PrecipitationOcclusionType = preload(
+	"res://world/environment/precipitation_occlusion.gd"
+)
 const FishingContextType = preload("res://fishing/fishing_context.gd")
 const FishingSpotType = preload("res://fishing/fishing_spot.gd")
 const FishAvailabilityType = preload("res://fish/fish_availability.gd")
@@ -526,6 +529,14 @@ func _validate_weather_presentation() -> void:
 	))
 	var rain_material := rain.process_material as ParticleProcessMaterial
 	assert(rain_material != null)
+	assert(
+		rain_material.collision_mode
+		== ParticleProcessMaterial.COLLISION_HIDE_ON_CONTACT
+	)
+	assert(is_equal_approx(
+		rain.collision_base_size,
+		WorldTimeVisualControllerType.RAIN_COLLISION_BASE_SIZE,
+	))
 	assert(rain_material.emission_box_extents.is_equal_approx(
 		WorldTimeVisualControllerType.RAIN_EMISSION_EXTENTS
 	))
@@ -542,6 +553,26 @@ func _validate_weather_presentation() -> void:
 	assert(rain_mesh.size.is_equal_approx(
 		WorldTimeVisualControllerType.RAIN_DROP_SIZE
 	))
+	var rain_collision := visuals.get_node(
+		"LocalRainCanopyCollision"
+	) as GPUParticlesCollisionHeightField3D
+	assert(rain_collision != null)
+	assert(rain_collision.follow_camera_enabled)
+	assert(
+		rain_collision.resolution
+		== GPUParticlesCollisionHeightField3D.RESOLUTION_256
+	)
+	assert(
+		rain_collision.update_mode
+		== GPUParticlesCollisionHeightField3D.UPDATE_MODE_WHEN_MOVED
+	)
+	assert(rain_collision.size.is_equal_approx(
+		WorldTimeVisualControllerType.RAIN_COLLISION_SIZE
+	))
+	assert(
+		rain_collision.heightfield_mask
+		== PrecipitationOcclusionType.RENDER_LAYER_MASK
+	)
 	visuals.call(
 		"_on_weather_changed",
 		WorldWeatherServiceType.Weather.SUNNY,