moving_sphere.h

//==================================================================================================
// Written in 2016 by Peter Shirley <ptrshrl@gmail.com>
//
// To the extent possible under law, the author(s) have dedicated all copyright and related and
// neighboring rights to this software to the public domain worldwide. This software is distributed
// without any warranty.
//
// You should have received a copy (see file COPYING.txt) of the CC0 Public Domain Dedication along
// with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
//==================================================================================================

#ifndef MOVINGSPHEREH
#define MOVINGSPHEREH

#include "hitable.h"

class moving_sphere: public hitable  {
    public:
        moving_sphere() {}
        moving_sphere(vec3 cen0, vec3 cen1, float t0, float t1, float r, material *m) : center0(cen0), center1(cen1), time0(t0),time1(t1), 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 time) const;
        vec3 center0, center1;
        float time0, time1;
        float radius;
        material *mat_ptr;
};

vec3 moving_sphere::center(float time) const{
    return center0 + ((time - time0) / (time1 - time0))*(center1 - center0);
}


bool moving_sphere::bounding_box(float t0, float t1, aabb& box) const {
        aabb box0(center(t0) - vec3(radius, radius, radius), center(t0) + vec3(radius, radius, radius));
        aabb box1(center(t1) - vec3(radius, radius, radius), center(t1) + vec3(radius, radius, radius));
        box = surrounding_box(box0, box1);
        return true;
}



// replace "center" with "center(r.time())"
bool moving_sphere::hit(const ray& r, float t_min, float t_max, hit_record& rec) const {
    vec3 oc = r.origin() - center(r.time());
    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);
            rec.normal = (rec.p - center(r.time())) / 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);
            rec.normal = (rec.p - center(r.time())) / radius;
            rec.mat_ptr = mat_ptr;
            return true;
        }
    }
    return false;
}


#endif