toytracer/sphere.h

#ifndef SPHERE_H
#define SPHERE_H

#include <cmath>
#include <memory>

#include "hittable.h"
#include "material.h"
#include "vec3.h"

class Sphere : public Hittable {
public:
  Sphere() {}
  Sphere(Point3 cen, double r, std::shared_ptr<Material> m) : center(cen), radius(r), mat_ptr(m) {}

  virtual bool hit(const Ray& r, double tmin, double tmax, hit_record& rec) const;

private:
  Point3 center;
  double radius;
  std::shared_ptr<Material> mat_ptr;
};

bool Sphere::hit(const Ray& r, double tmin, double tmax, 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 = std::sqrt(discriminant);
        auto temp = (-half_b - root) / a;
        if (temp < tmax && temp > tmin) {
            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 < tmax && temp > tmin) {
            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 // SPHERE_H