sphere.hpp

#ifndef SPHERE_H
#define SPHERE_H

#include "hittable.hpp"
#include "material.hpp"
#include "vec3.hpp"

class sphere : public hittable
{
public:
  sphere() {};
  sphere(point3 cen, double r, shared_ptr<material> m) : center(cen), radius(r), mat_ptr(m) {};

  virtual bool hit(const ray &r, double t_min, double t_max, hit_record &rec) const;

  point3 center;
  double radius;
  shared_ptr<material> mat_ptr;
};

bool sphere::hit(const ray &r, double t_min, double t_max, hit_record &rec) const
{
  vec3 oc = r.origin() - center;
  auto a = r.direction().length_squared();
  auto half_b = dot(oc, r.direction());
  auto c = oc.length_squared() - radius * radius;
  auto discriminant = half_b * half_b - a * c;

  if (discriminant > 0)
  {
    auto root = sqrt(discriminant);
    auto temp = (-half_b - root) / a;
    if (temp < t_max && temp > t_min)
    {
      rec.t = temp;
      rec.p = r.at(rec.t);

      vec3 outward_normal = (rec.p - center) / radius;
      rec.set_face_normal(r, outward_normal);
      rec.mat_ptr = mat_ptr;
      return true;
    }

    temp = (-half_b + root) / a;
    if (temp < t_max && temp > t_min)
    {
      rec.t = temp;
      rec.p = r.at(rec.t);
      vec3 outward_normal = (rec.p - center) / radius;
      rec.set_face_normal(r, outward_normal);
      rec.mat_ptr = mat_ptr;
      return true;
    }
  }

  return false;
}

#endif