dialectric.v

import math
import rand

fn refract(v Vec3, n Vec3, ni_over_nt f32, mut refracted Vec3) bool {
	uv := v.unit_vector()
	dt := uv.dot(n)
	discriminant := 1.0 - ni_over_nt*ni_over_nt*(1-dt*dt)
	if discriminant > 0 {
		refracted = uv.sub(n.scalar_mul(dt)).scalar_mul(ni_over_nt).sub(n.scalar_mul(math.sqrtf(discriminant)))
		return true
	}
	return false
}

fn schlick(cosine f32, ref_idx f32) f32 {
	mut r0 := (1-ref_idx) / (1+ref_idx)
	r0 = r0 * r0
	return r0 + (1-r0)*f32(math.pow((1 - cosine), 5))
}

struct Dialectric {
	ref_idx f32
}

fn (d Dialectric) scatter(r_in Ray, rec HitRecord, mut attenuation Vec3, mut scattered Ray) bool {
	mut outward_normal := Vec3{}
	reflected := reflect(r_in.direction(), rec.normal)
	mut ni_over_nt := f32(0.0)
	attenuation = Vec3{1.0, 1.0, 1.0}
	mut refracted := Vec3{0, 0, 0}
	mut reflect_prob := f32(0.0)
	mut cosine := f32(0.0)
	if r_in.direction().dot(rec.normal) > 0 {
		outward_normal = rec.normal.scalar_mul(-1)
		ni_over_nt = d.ref_idx
		cosine = d.ref_idx * r_in.direction().dot(rec.normal) / r_in.direction().length()
	} else {
		outward_normal = rec.normal
		ni_over_nt = 1.0 / d.ref_idx
		cosine = -r_in.direction().dot(rec.normal)/r_in.direction().length()
	}
	if refract(r_in.direction(), outward_normal, ni_over_nt, mut refracted) {
		reflect_prob = schlick(cosine, d.ref_idx)
	} else {
		scattered = Ray{rec.p, reflected}
		reflect_prob = 1.0
	}
	if rand.f32() < reflect_prob {
		scattered = Ray{rec.p, reflected}
	} else {
		scattered = Ray{rec.p, refracted}
	}
	return true
}