thebookofshaders/glossary/refract/README.md

Refract

Calculate the refraction direction for an incident vector

Declaration

float refract(float I, float N, float eta)  
vec2 refract(vec2 I, vec2 N, float eta)  
vec3 refract(vec3 I, vec3 N, float eta)  
vec4 refract(vec4 I, vec4 N, float eta)

Parameters

I specifies the incident vector.

N specifies the normal vector.

eta specifies the ratio of indices of refraction.

Description

For a given incident vector I, surface normal N and ratio of indices of refraction, eta, refract returns the refraction vector, R.

R is calculated as:

k = 1.0 - eta * eta * (1.0 - dot(N, I) * dot(N, I));
if (k < 0.0)
    R = genType(0.0);       // or genDType(0.0)
else
    R = eta * I - (eta * dot(N, I) + sqrt(k)) * N;

The input parameters I and N should be normalized in order to achieve the desired result.

See Also

dot(), reflect()