sphere.h

// This file contains the class for the geometric object sphere
// Refer to the documentation for technical and mathematical details

#ifndef SPHERE_H
#define SPHERE_H

#include "hitable.h"

// the sphere class.
class sphere : public hitable {
public:
    sphere() {}

    // constructor
    sphere(vec3 cen, float r, material *m) : center(cen), radius(r), mat_ptr(m) {};

    virtual bool hit(const ray &r, float tmin, float tmax, hit_record &rec) const;

    virtual bool bounding_box(float t0, float t1, aabb &box) const;

    vec3 center;
    float radius;
    material *mat_ptr;
};


// compute whether a ray hit the sphere or not
// refer to documentation for mathematics details
bool sphere::hit(const ray &r, float t_min, float t_max, hit_record &rec) const {
    vec3 oc = r.origin() - center;
    float a = dot(r.direction(), r.direction());
    float b = dot(oc, r.direction());
    float c = dot(oc, oc) - radius * radius;
    float discriminant = b * b - a * c;
    if (discriminant > 0) {
        float temp = (-b - sqrt(discriminant)) / a;
        if (temp < t_max && temp > t_min) {
            rec.t = temp;
            rec.p = r.point_at_parameter(rec.t);
            get_sphere_uv((rec.p - center) / radius, rec.u, rec.v);
            rec.normal = (rec.p - center) / radius;
            rec.mat_ptr = mat_ptr;
            return true;
        }
        temp = (-b + sqrt(discriminant)) / a;
        if (temp < t_max && temp > t_min) {
            rec.t = temp;
            rec.p = r.point_at_parameter(rec.t);
            get_sphere_uv((rec.p - center) / radius, rec.u, rec.v);
            rec.normal = (rec.p - center) / radius;
            rec.mat_ptr = mat_ptr;
            return true;
        }
    }
    return false;
}

// compute the bounding box for the sphere
bool sphere::bounding_box(float t0, float t1, aabb &box) const {
    box = aabb(center - vec3(radius, radius, radius), center + vec3(radius, radius, radius));
    return true;
}


#endif //SPHERE_H