feat(vfx): animate movement and scoring effects

Game/scripts/ball.gd

@@ -17,10 +17,54 @@ extends RigidBody3D
 const MAX_SPEED := 32.0
 
 var _boundary: ArenaBoundary
+var _trail: GPUParticles3D
 
 
 func _ready() -> void:
 	_boundary = get_tree().get_first_node_in_group("arena_boundary")
+	if DisplayServer.get_name() == "headless":
+		# _integrate_forces remains active; only the render-side trail updater is
+		# disabled across the many parallel RL environments.
+		set_physics_process(false)
+	else:
+		_build_trail()
+
+
+func _physics_process(_delta: float) -> void:
+	if _trail:
+		var speed_ratio := clampf(linear_velocity.length() / MAX_SPEED, 0.0, 1.0)
+		_trail.emitting = speed_ratio > 0.12
+		_trail.amount_ratio = smoothstep(0.12, 1.0, speed_ratio)
+
+
+func _build_trail() -> void:
+	var mat := StandardMaterial3D.new()
+	mat.transparency = BaseMaterial3D.TRANSPARENCY_ALPHA
+	mat.shading_mode = BaseMaterial3D.SHADING_MODE_UNSHADED
+	mat.billboard_mode = BaseMaterial3D.BILLBOARD_ENABLED
+	mat.albedo_color = Color(0.55, 0.85, 1.0, 0.42)
+	mat.emission_enabled = true
+	mat.emission = Color(0.35, 0.72, 1.0)
+	mat.emission_energy_multiplier = 1.8
+	var quad := QuadMesh.new()
+	quad.size = Vector2(0.22, 0.22)
+	quad.material = mat
+	var process := ParticleProcessMaterial.new()
+	process.emission_shape = ParticleProcessMaterial.EMISSION_SHAPE_SPHERE
+	process.emission_sphere_radius = 0.35
+	process.gravity = Vector3.ZERO
+	process.scale_min = 0.35
+	process.scale_max = 1.0
+	_trail = GPUParticles3D.new()
+	_trail.name = "BallTrail"
+	_trail.amount = 48
+	_trail.lifetime = 0.48
+	_trail.local_coords = false
+	_trail.process_material = process
+	_trail.draw_pass_1 = quad
+	_trail.visibility_aabb = AABB(Vector3(-18, -18, -18), Vector3(36, 36, 36))
+	_trail.emitting = false
+	add_child(_trail)
 
 
 func _integrate_forces(state: PhysicsDirectBodyState3D) -> void: