def test_ray_position():
r = Ray(Point(2, 3, 4), Vector(1, 0, 0))
assert r.position(0) == Point(2, 3, 4)
assert r.position(1) == Point(3, 3, 4)
assert r.position(-1) == Point(1, 3, 4)
assert r.position(2.5) == Point(4.5, 3, 4)
s = Sphere()
r_origin = Point(0, 0, -5)
wall_z = 10
wall_size = 7
light_position = Point(-10, 10, 10)
light_color = Color(1, 1, 1)
light = PointLight(light_position, light_color)
N = 200
c = Canvas(N, N)
pixel_size = wall_size / N
half = wall_size / 2
for y in range(c.height):
world_y = half - pixel_size * y
for x in range(c.width):
world_x = -half + pixel_size * x
position = Point(world_x, world_y, wall_z)
r = Ray(r_origin, (position - r_origin).normalize())
X = r.intersects(s)
if X.hit is not None:
point = r.position(X.hit.t)
normal = X.hit.object.normal_at(point)
eye = -r.direction
color = X.hit.object.material.lighting(light, point, eye, normal)
c.write_pixel(x, y, color)
c.to_ppm('circle_shaded.ppm')