refraction.glsl

        // hit point
        float eta = 1.01;
        ray.origin = h.p;
        // entering or leaving
        if( dot(ray.dir, h.n) < 0 )
            // entering ray
            ray.dir = refract(ray.dir, h.n, 1.0/eta);
        else
            // leaving ray
            ray.dir = refract(ray.dir, -h.n, eta);