sphere.h

#pragma once

#include "hittable.h"

class sphere: public hittable
{
public:
    point3 center;
    double radius;
    std::shared_ptr<material> mat_ptr;

    sphere(const point3& cen, double r, std::shared_ptr<material> m) 
    : center(cen), radius(r), mat_ptr(m) {}

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

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

    double discriminant = half_b*half_b - a*c;
    if (discriminant < 0)
        return false;
    
    double sqrtd = sqrt(discriminant);

    // Find the nearest root that lies in the acceptable range
    double root = (-half_b - sqrtd) / a;
    if (root < t_min || t_max < root) {
        root = (-half_b + sqrtd) / a;
        if (root < t_min || t_max < root)
            return false;
    }

    rec.t = root;
    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;
}