Keep rain above generated tree canopies

tests/world_weather_validation.gd

@@ -524,6 +524,15 @@ func _validate_weather_presentation() -> void:
 	assert(rain.emitting)
 	assert(rain.amount_ratio > 0.99)
 	assert(rain.amount == WorldTimeVisualControllerType.RAIN_PARTICLE_AMOUNT)
+	assert(
+		WorldTimeVisualControllerType.RAIN_EMITTER_OFFSET.y
+		>= WorldTimeVisualControllerType.RAIN_SUPPORTED_CANOPY_HEIGHT
+		+ WorldTimeVisualControllerType.RAIN_CANOPY_CLEARANCE
+	)
+	assert(is_equal_approx(
+		rain.lifetime,
+		WorldTimeVisualControllerType.RAIN_LIFETIME_SECONDS,
+	))
 	assert(rain.visibility_aabb == (
 		WorldTimeVisualControllerType.RAIN_VISIBILITY_AABB
 	))
@@ -548,6 +557,9 @@ func _validate_weather_presentation() -> void:
 		rain_material.initial_velocity_max,
 		WorldTimeVisualControllerType.RAIN_VELOCITY_MAX,
 	))
+	assert(rain_material.gravity.is_equal_approx(
+		WorldTimeVisualControllerType.RAIN_GRAVITY
+	))
 	var rain_mesh := rain.draw_pass_1 as BoxMesh
 	assert(rain_mesh != null)
 	assert(rain_mesh.size.is_equal_approx(
@@ -569,6 +581,11 @@ func _validate_weather_presentation() -> void:
 	assert(rain_collision.size.is_equal_approx(
 		WorldTimeVisualControllerType.RAIN_COLLISION_SIZE
 	))
+	assert(
+		rain_collision.size.y * 0.5
+		> WorldTimeVisualControllerType.RAIN_EMITTER_OFFSET.y
+		+ WorldTimeVisualControllerType.RAIN_EMISSION_EXTENTS.y
+	)
 	assert(
 		rain_collision.heightfield_mask
 		== PrecipitationOcclusionType.RENDER_LAYER_MASK

world/world_time_visual_controller.gd

@@ -5,20 +5,31 @@ const UPDATE_INTERVAL_SECONDS: float = 0.1
 const LIGHT_UPDATE_INTERVAL_SECONDS: float = 0.25
 const SUN_YAW_DEGREES: float = -32.0
 const WEATHER_TRANSITION_SECONDS: float = 10.0
-const RAIN_EMITTER_OFFSET := Vector3(0.0, 7.0, 0.0)
+# Large generated trees reach nearly 22 m at their maximum authored scale.
+# Keep the rain source above those canopies so drops cannot be born underneath
+# the height-field surface that is meant to hide them.
+const RAIN_SUPPORTED_CANOPY_HEIGHT: float = 22.0
+const RAIN_CANOPY_CLEARANCE: float = 4.0
+const RAIN_EMITTER_OFFSET := Vector3(
+	0.0,
+	RAIN_SUPPORTED_CANOPY_HEIGHT + RAIN_CANOPY_CLEARANCE,
+	0.0,
+)
 const RAIN_EMISSION_EXTENTS := Vector3(13.0, 1.0, 13.0)
 const RAIN_VISIBILITY_AABB := AABB(
-	Vector3(-13.5, -9.0, -13.5),
+	Vector3(-13.5, -36.0, -13.5),
-	Vector3(27.0, 12.0, 27.0),
+	Vector3(27.0, 40.0, 27.0),
 )
 const RAIN_PARTICLE_AMOUNT: int = 2240
 const LIGHT_RAIN_PARTICLE_AMOUNT: int = 48
 const LIGHT_RAIN_FIXED_FPS: int = 8
-const RAIN_VELOCITY_MIN: float = 16.0
+const RAIN_LIFETIME_SECONDS: float = 1.4
-const RAIN_VELOCITY_MAX: float = 20.0
+const RAIN_VELOCITY_MIN: float = 20.0
+const RAIN_VELOCITY_MAX: float = 24.0
+const RAIN_GRAVITY := Vector3(0.0, -2.0, 0.0)
 const RAIN_DROP_SIZE := Vector3(0.014, 0.34, 0.014)
 const RAIN_COLLISION_BASE_SIZE: float = 0.08
-const RAIN_COLLISION_SIZE := Vector3(28.0, 24.0, 28.0)
+const RAIN_COLLISION_SIZE := Vector3(28.0, 64.0, 28.0)
 const FOG_DAYLIGHT_SCENE_BRIGHTNESS: float = 0.42
 const FOG_DAYLIGHT_FOG_LIGHT_BRIGHTNESS: float = 0.42
 const FOG_DAYLIGHT_WATER_BRIGHTNESS: float = 0.42
@@ -212,7 +223,7 @@ func _prepare_rain() -> void:
 		else RAIN_PARTICLE_AMOUNT
 	)
 	_rain.amount_ratio = 0.0
-	_rain.lifetime = 1.25
+	_rain.lifetime = RAIN_LIFETIME_SECONDS
 	_rain.fixed_fps = (
 		LIGHT_RAIN_FIXED_FPS if _light_performance_profile else 30
 	)
@@ -228,7 +239,7 @@ func _prepare_rain() -> void:
 	process_material.spread = 5.0
 	process_material.initial_velocity_min = RAIN_VELOCITY_MIN
 	process_material.initial_velocity_max = RAIN_VELOCITY_MAX
-	process_material.gravity = Vector3(0.0, -2.0, 0.0)
+	process_material.gravity = RAIN_GRAVITY
 	process_material.collision_mode = (
 		ParticleProcessMaterial.COLLISION_HIDE_ON_CONTACT
 	)