Function refract

tutorials/common/tutorial/optics.h:34–41

======================================================= !Refracts a viewing vector V at a normal N using the relative * refraction index eta. Eta is refraction index of outside medium * (where N points into) divided by refraction index of the inside * medium. The vectors V and N have to point towards the same side * of the surface. The cosine between V and N is given as input and * the c

 *  of the surface. The cosine between V and N is given as input and
 *  the cosine of -N and transmission ray is computed as output. */
inline Sample3f refract(const Vec3fa& V, const Vec3fa& N, const float eta,
                        const float cosi, float &cost)
{
  const float k = 1.0f-eta*eta*(1.0f-cosi*cosi);
  if (k < 0.0f) { cost = 0.0f; return make_Sample3f(Vec3fa(0.f),0.0f); }
  cost = sqrt(k);
  return make_Sample3f(eta*(cosi*N-V)-cost*N, sqr(eta));
}

/*! Computes fresnel coefficient for media interface with relative
 *  refraction index eta. Eta is the outside refraction index