# 1.3 List of hittable Objects as the World

The List of hittable Objects is similar to the MeshList in Semester 1.

It holds all objects your are going to traverse when doing ray tracing intersection test.

### Create class hittable\_list

Create hittable\_list.h under the src directory

```cpp
#ifndef HITTABLE_LIST_H
#define HITTABLE_LIST_H

#include "hittable.h"

#include <memory>
#include <vector>

using std::make_shared;
using std::shared_ptr;

class hittable_list : public hittable {
  public:
    std::vector<shared_ptr<hittable>> objects;

    hittable_list() {}
    hittable_list(shared_ptr<hittable> object) { add(object); }

    void clear() { objects.clear(); }

    void add(shared_ptr<hittable> object) {
        objects.push_back(object);
    }

    bool hit(const ray& r, double ray_tmin, double ray_tmax, hit_record& rec) const override {
        hit_record temp_rec;
        bool hit_anything = false;
        auto closest_so_far = ray_tmax;

        // traverse all objects to test the intersections
        for (const auto& object : objects) {
            if (object->hit(r, ray_tmin, closest_so_far, temp_rec)) {
                hit_anything = true;
                closest_so_far = temp_rec.t;
                rec = temp_rec;
            }
        }
        return hit_anything;
    }
};

#endif
```