def probability(self, ray: Ray) -> float:
""" Returns the probability that the interaction will occur.
"""
context = self.context
normal = np.array(context.normal)
n1 = context.n1
n2 = context.n2
# Be flexible with how the normal is defined
ray_ = ray.representation(context.normal_node.root, context.normal_node)
if np.dot(normal, ray_.direction) < 0.0:
normal = flip(normal)
angle = angle_between(normal, np.array(ray_.direction))
logger.debug("Incident angle {:.2f}".format(np.degrees(angle)))
if angle < 0.0 or angle > 0.5 * np.pi:
raise ValueError("The incident angle must be between 0 and pi/2.")
# Catch TIR case
if n2 < n1 and angle > np.arcsin(n2/n1):
return 1.0
c = np.cos(angle)
s = np.sin(angle)
k = np.sqrt(1 - (n1/n2 * s)**2)
Rs1 = n1 * c - n2 * k
Rs2 = n1 * c + n2 * k
Rs = (Rs1/Rs2)**2
Rp1 = n1 * k - n2 * c
Rp2 = n1 * k + n2 * c
Rp = (Rp1/Rp2)**2
return 0.5 * (Rs + Rp)
def transform(self, ray: Ray) -> Ray:
""" Transform ray according to the physics of the interaction.
"""
context = self.context
normal = np.array(context.normal)
ray_ = ray.representation(context.normal_node.root, context.normal_node)
vec = np.array(ray_.direction)
d = np.dot(normal, vec)
reflected_direction = vec - 2 * d * normal
new_ray_ = replace(ray_, direction=tuple(reflected_direction.tolist()))
new_ray = new_ray_.representation(context.normal_node, context.normal_node.root)
return new_ray # back to world node
def transform(self, ray: Ray) -> Ray:
""" Transform ray according to the physics of the interaction.
"""
context = self.context
n1 = context.n1
n2 = context.n2
ray_ = ray.representation(context.normal_node.root, context.normal_node)
normal = np.array(context.normal)
vector = np.array(ray_.direction)
n = n1/n2
dot = np.dot(vector, normal)
c = np.sqrt(1 - n**2 * (1 - dot**2))
sign = 1
if dot < 0.0:
sign = -1
refracted_direction = n * vector + sign*(c - sign*n*dot) * normal
new_ray_ = replace(ray_, direction=tuple(refracted_direction.tolist()))
new_ray = new_ray_.representation(context.normal_node, context.normal_node.root)
return new_ray