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float fresnel_dielectric_cos(float cosi, float eta)
{
/* compute fresnel reflectance without explicitly computing
* the refracted direction */
float c = abs(cosi);
float g = eta * eta - 1.0 + c * c;
float result;
if (g > 0.0) {
g = sqrt(g);
float A = (g - c) / (g + c);
float B = (c * (g + c) - 1.0) / (c * (g - c) + 1.0);
result = 0.5 * A * A * (1.0 + B * B);
}
else {
result = 1.0; /* TIR (no refracted component) */
}
return result;
}
float fresnel_dielectric(vec3 Incoming, vec3 Normal, float eta)
{
/* compute fresnel reflectance without explicitly computing
* the refracted direction */
return fresnel_dielectric_cos(dot(Incoming, Normal), eta);
}
void node_fresnel(float ior, vec3 N, vec3 I, out float result)
{
N = normalize(N);
/* handle perspective/orthographic */
vec3 I_view = (ProjectionMatrix[3][3] == 0.0) ? normalize(I) : vec3(0.0, 0.0, -1.0);
float eta = max(ior, 0.00001);
result = fresnel_dielectric(I_view, N, (gl_FrontFacing) ? eta : 1.0 / eta);
}
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