def add_visual_sphere(client, center=(0, 0, 0), radius=0.1,
                      rgba=(0.5, 0.5, 0.5, 0.5)):
  """Add a sphere to bullet scene (visual only, no physics).

  Args:
    client: pybullet client (or pybullet library handle).
    center: Center of sphere.
    radius: Sphere radius.
    rgba: rgba color of sphere.

  Returns:
    Unique integer bullet id of constructed object.
  """
  vis_obj_id = client.createVisualShape(
      client.GEOM_SPHERE, radius=radius, rgbaColor=rgba)
  obj_id = client.createMultiBody(
      baseCollisionShapeIndex=-1, baseVisualShapeIndex=vis_obj_id,
      basePosition=center)
  return obj_id