Renderer/src/hittable.rs

use super::Point3;
use super::Ray;
use super::Vec3;

pub struct HitRecord {
    p: Point3,
    pub normal: Vec3,
    pub t: f64,
    front_face: bool,
}

pub struct Sphere {
    center: Point3,
    radius: f64,
}

pub trait Hittable {
    fn hit(&self, r: &Ray, t_min: f64, t_max: f64, rec: &mut HitRecord) -> bool;
}

impl HitRecord {
    fn set_face_normal(&mut self, r: &Ray, outward_normal: Vec3) {
        self.front_face = Vec3::dot(r.direction(), outward_normal) < 0.0;
        if self.front_face {
            self.normal = outward_normal;
        } else {
            self.normal = (-1.0) * outward_normal;
        }
    }

    pub fn new(p: Point3, normal: Vec3, t: f64, front_face: bool) -> Self {
        HitRecord {
            p: p,
            normal: normal,
            t: t,
            front_face: front_face,
        }
    }

    pub fn empty() -> Self {
        Self::new(
            Point3::new(0.0, 0.0, 0.0),
            Vec3::new(0.0, 0.0, 0.0),
            0.0,
            false,
        )
    }
}

impl Sphere {
    pub fn new(cen: Point3, r: f64) -> Self {
        Sphere {
            center: cen,
            radius: r,
        }
    }
}

impl Hittable for Sphere {
    fn hit(&self, r: &Ray, t_min: f64, t_max: f64, rec: &mut HitRecord) -> bool {
        let oc = r.origin() - self.center;
        let a = r.direction().length_squared(); // gleiches Ergebnis wie Skalarprodukt
        let half_b = Vec3::dot(oc, r.direction());
        let c = oc.length_squared() - self.radius * self.radius;

        let discriminant = half_b * half_b - a * c;
        if discriminant < 0.0 {
            return false;
        }

        let sqrtd = discriminant.sqrt();

        let root = (-half_b - sqrtd) / a;
        if root < t_min || t_max < root {
            let root2 = (-half_b + sqrtd) / a;
            if root2 < t_min || t_max < root {
                return false;
            }
        }

        rec.t = root;
        rec.p = r.at(rec.t);
        let outward_normal = (rec.p - self.center) / self.radius;
        rec.set_face_normal(r, outward_normal);

        return true;
    }
}