sphere.h

//
// Created by 13240 on 2025/10/14.
//

#ifndef SIMPLE_SOFTRT_SPHERE_H
#define SIMPLE_SOFTRT_SPHERE_H

#include "hittable.h"

class sphere : public hittable {
public:
    // Moving Sphere
    sphere(const point3 &center1, const point3 &center2, double radius,
           std::shared_ptr<material> mat)
           : center(center1, center2 - center1, 0), radius(std::fmax(radius, 0)), mat(mat){
        auto rvec = vec3(radius, radius, radius);
        aabb box1 = aabb(center.at(0) - rvec, center.at(0) + rvec);
        aabb box2 = aabb(center.at(1) - rvec, center.at(1) + rvec);
        bbox = aabb(box1, box2);
    }

    // Stationary Sphere
    sphere(const point3 &static_center, double radius, std::shared_ptr<material> mat)
    : center(static_center, vec3(0,0,0)), radius(std::fmax(0, radius)), mat(mat) {
        auto rvec = vec3(radius, radius, radius);
        bbox = aabb(static_center - rvec, static_center + rvec);
    }

    bool hit(const ray &r, interval ray_t, hit_record &rec) const override {
        point3 current_center = center.at(r.time());
        vec3 oc = current_center - r.origin();
        auto a = r.direction().length_squared();  // 光线和球体的解析解
        auto h = dot(r.direction(), oc);
        auto c = oc.length_squared() - radius * radius;
        auto discriminant = h * h - a * c;
        if (discriminant < 0)
            return false;

        auto sqrtd = std::sqrt(discriminant);
        auto root = (h - sqrtd) / a;    // 尝试 第一个解（前表面交点）
        if (!ray_t.surrounds(root)) {        // t 可能是负的，需要规定 t 的范围
            root = (h + sqrtd) / a;             // 尝试第二个解
            if (!ray_t.surrounds(root))
                return false;
        }
        rec.t = root;
        rec.p = r.at(rec.t);
        vec3 outward_normal = (rec.p - current_center) / radius;
        rec.set_face_normal(r, outward_normal);
        rec.mat = mat;

        return true;
    }

    aabb bounding_box() const override { return bbox; }

private:
    ray center; // 为了支持motion blur，位置是一个class ray
    double radius;
    std::shared_ptr<material> mat;
    aabb bbox;
};

#endif //SIMPLE_SOFTRT_SPHERE_H