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//自发光材质
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class diffuse_light : public material {
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  public:
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    diffuse_light(std::shared_ptr<texture> tex) : tex(tex) {} //纹理作为发光颜色
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    diffuse_light(const color& emit) : tex(std::make_shared<solid_color>(emit)) {}  //传入颜色包装为纯色纹理
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    // 物体本身发出的光
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    color emitted(double u, double v, const point3& p) const override {
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        return tex->value(u, v, p);
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    }
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  private:
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    std::shared_ptr<texture> tex;
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};

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virtual color emitted(double u, double v, const point3& p) const {
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  return color(0,0,0);
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}

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color ray_color(const ray& r, int depth, const hittable& world) const {
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        hit_record rec;
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        // 递归深度耗尽时返回黑色，表示这条光线不再贡献能量。
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        if(depth <= 0)
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            return color(0,0,0);
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        // 如果光线没有击中物体,返回背景颜色
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        if (!world.hit(r, interval(0.001, infinity), rec))
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            return background;
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        // scattered 保存材质散射出的下一条光线，attenuation 表示本次散射后的颜色衰减。
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        ray scattered;
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        color attenuation;
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        // 先取材质自身发出的光；普通材质通常返回黑色，光源材质会返回发光颜色。
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        color color_from_emission = rec.mat->emitted(rec.u,rec.v,rec.p);
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        // 如果材质不散射光线，说明递归在这里结束，只返回自发光部分。
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        if(!rec.mat->scatter(r, rec, attenuation, scattered))
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            return color_from_emission;
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        // 递归追踪散射光线，并乘以材质衰减，得到反射/折射带来的间接光。
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        color color_from_scatter = attenuation * ray_color(scattered, depth - 1, world);
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        // 最终颜色 = 材质自身发光 + 散射光线继续追踪得到的颜色。
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        return color_from_emission + color_from_scatter;
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    }

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void simple_light() {
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    hittable_list world;
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    auto pertext = make_shared<noise_texture>(4);
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    world.add(make_shared<sphere>(point3(0,-1000,0), 1000, make_shared<lambertian>(pertext)));
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    world.add(make_shared<sphere>(point3(0,2,0), 2, make_shared<lambertian>(pertext)));
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    auto difflight = make_shared<diffuse_light>(color(4,4,4));
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    world.add(make_shared<quad>(point3(3,1,-2), vec3(2,0,0), vec3(0,2,0), difflight));
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    camera cam;
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    cam.aspect_ratio      = 16.0 / 9.0;
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    cam.image_width       = 400;
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    cam.samples_per_pixel = 100;
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    cam.max_depth         = 50;
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    cam.background        = color(0,0,0);
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    cam.vfov     = 20;
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    cam.lookfrom = point3(26,3,6);
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    cam.lookat   = point3(0,2,0);
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    cam.vup      = vec3(0,1,0);
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    cam.defocus_angle = 0;
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    cam.render(world);
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}

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void cornell_box() {
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    hittable_list world;
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    auto red   = make_shared<lambertian>(color(.65, .05, .05));
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    auto white = make_shared<lambertian>(color(.73, .73, .73));
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    auto green = make_shared<lambertian>(color(.12, .45, .15));
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    auto light = make_shared<diffuse_light>(color(15, 15, 15));
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    world.add(make_shared<quad>(point3(555,0,0), vec3(0,555,0), vec3(0,0,555), green));
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    world.add(make_shared<quad>(point3(0,0,0), vec3(0,555,0), vec3(0,0,555), red));
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    world.add(make_shared<quad>(point3(343, 554, 332), vec3(-130,0,0), vec3(0,0,-105), light));
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    world.add(make_shared<quad>(point3(0,0,0), vec3(555,0,0), vec3(0,0,555), white));
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    world.add(make_shared<quad>(point3(555,555,555), vec3(-555,0,0), vec3(0,0,-555), white));
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    world.add(make_shared<quad>(point3(0,0,555), vec3(555,0,0), vec3(0,555,0), white));
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    camera cam;
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    cam.aspect_ratio      = 1.0;
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    cam.image_width       = 600;
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    cam.samples_per_pixel = 200;
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    cam.max_depth         = 50;
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    cam.background        = color(0,0,0);
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    cam.vfov     = 40;
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    cam.lookfrom = point3(278, 278, -800);
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    cam.lookat   = point3(278, 278, 0);
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    cam.vup      = vec3(0,1,0);
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    cam.defocus_angle = 0;
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    cam.render(world);
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}