arrow(
  start = c(0, 0, 0),
  end = c(0, 1, 0),
  radius_top = 0.2,
  radius_tail = 0.1,
  tail_proportion = 0.5,
  direction = NA,
  from_center = TRUE,
  material = diffuse(),
  velocity = c(0, 0, 0),
  flipped = FALSE,
  scale = c(1, 1, 1)
)

#Draw a simple arrow from x = -1 to x = 1

generate_studio() %>% 
  add_object(arrow(start = c(-1,0,0), end = c(1,0,0), material=glossy(color="red"))) %>% 
  add_object(sphere(y=5,material=light(intensity=20))) %>% 
  render_scene(clamp_value=10,  samples=400)

#Change the proportion of tail to top
generate_studio(depth=-2) %>% 
  add_object(arrow(start = c(-1,-1,0), end = c(1,-1,0), tail_proportion = 0.5,
                   material=glossy(color="red"))) %>% 
  add_object(arrow(start = c(-1,0,0), end = c(1,0,0), tail_proportion = 0.75,
                   material=glossy(color="red"))) %>% 
  add_object(arrow(start = c(-1,1,0), end = c(1,1,0), tail_proportion = 0.9,
                   material=glossy(color="red"))) %>% 
  add_object(sphere(y=5,z=5,x=2,material=light(intensity=30))) %>% 
  render_scene(clamp_value=10, fov=25,  samples=400)
  
#Change the radius of the tail/top segments
generate_studio(depth=-1.5) %>% 
  add_object(arrow(start = c(-1,-1,0), end = c(1,-1,0), tail_proportion = 0.75,
                   radius_top = 0.1, radius_tail=0.03,
                   material=glossy(color="red"))) %>% 
  add_object(arrow(start = c(-1,0,0), end = c(1,0,0), tail_proportion = 0.75,
                   radius_top = 0.2, radius_tail=0.1,
                   material=glossy(color="red"))) %>% 
  add_object(arrow(start = c(-1,1,0), end = c(1,1,0), tail_proportion = 0.75,
                   radius_top = 0.3, radius_tail=0.2,
                   material=glossy(color="red"))) %>% 
  add_object(sphere(y=5,z=5,x=2,material=light(intensity=30))) %>% 
  render_scene(clamp_value=10, samples=400)
  
  
#We can also specify arrows via a midpoint and direction:
generate_studio(depth=-1) %>% 
  add_object(arrow(start = c(-1,-0.5,0), direction = c(0,0,1),
                   material=glossy(color="green"))) %>% 
  add_object(arrow(start = c(1,-0.5,0), direction = c(0,0,-1),
                   material=glossy(color="red"))) %>% 
  add_object(arrow(start = c(0,-0.5,1), direction = c(1,0,0),
                   material=glossy(color="yellow"))) %>% 
  add_object(arrow(start = c(0,-0.5,-1), direction = c(-1,0,0),
                   material=glossy(color="purple"))) %>% 
  add_object(sphere(y=5,z=5,x=2,material=light(intensity=30))) %>% 
  render_scene(clamp_value=10, samples=400, 
               lookfrom=c(0,5,10), lookat=c(0,-0.5,0), fov=16)

#Plot a 3D vector field for a gravitational well:

r = 1.5
theta_vals = seq(0,2*pi,length.out = 16)[-16]
phi_vals = seq(0,pi,length.out = 16)[-16][-1]
arrow_list = list()
counter = 1
for(theta in theta_vals) {
  for(phi in phi_vals) {
    rval = c(r*sin(phi)*cos(theta),r*cos(phi),r*sin(phi)*sin(theta)) 
    arrow_list[[counter]] = arrow(rval, direction = -1/2*rval/sqrt(sum(rval*rval))^3,
                                  tail_proportion = 0.66, radius_top=0.03, radius_tail=0.01,
                                  material = diffuse(color="red"))
    counter = counter + 1
  }
}
vector_field = do.call(rbind,arrow_list)
sphere(material=diffuse(noise=1,color="blue",noisecolor="darkgreen")) %>% 
  add_object(vector_field) %>% 
  add_object(sphere(y=0,x=10,z=5,material=light(intensity=200))) %>% 
  render_scene(fov=20, ambient=TRUE, samples=400,
               backgroundlow="black",backgroundhigh="white")