/**
* Ported from paper "Reflections and Refractions in Ray Tracing" by Bram de Greve (2006)
*
* @param incident
* @param normal
* @param n1
* @param n2
* @return
*/
private Refraction getRefraction(Vector incident, Vector normal, float n1, float n2) {
float n = n1 / n2;
float cosI = -normal.dot(incident);
float sinT2 = n * n * (1.0f - cosI * cosI);
if (sinT2 > 1.0) { // TIR
return null;
}
float cosT = (float) Math.sqrt(1.0f - sinT2);
Refraction res = new Refraction();
res.direction = incident.mult(n).add(normal.mult(n * cosI - cosT));
// Schlick approximation
float r0 = (n1 - n2) / (n1 + n2);
r0 *= r0;
float cosX = cosI;
if (n1 > n2) {
cosX = cosT;
}
float x = 1.0f - cosX;
res.reflectionAbility = r0 + (1.0f - r0) * x * x * x * x * x;
res.transmissionAbility = 1.0f - res.reflectionAbility;
return res;
}
private Vector getReflection(Vector direction, Vector normal) {
Vector rayDirection = direction.normalize().mult(-1);
return normal.mult(normal.dot(rayDirection) * 2).sub(rayDirection);
}