public class GroundMakeCube : MonoBehaviour{

    private void Update() {
        if (Input.GetKeyDown(KeyCode.Space)) {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            if (Physics.Raycast(ray, out hit)) {
                Vector3 pos = hit.point;
                pos.y = 0f;
                GameObject pref = Resources.Load("Prefabs/Cube") as GameObject;
                GameObject cubeNew=Instantiate(pref);
                cubeNew.GetComponent<Renderer>().material.color =
                    UnityEngine.Random.ColorHSV(0f, 1f, 1f, 1f, 0.5f, 1f);
                cubeNew.transform.position = pos;
            }
        }
    }
}





public class GroundMoveCube : MonoBehaviour {
    private Vector3 clickPos;
    public GameObject obj;

    private void Update() {
        if (Input.GetMouseButton(0)) {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            int layerMask = LayerMask.GetMask("Ground");
            if (obj!=null) {
                if (Physics.Raycast(ray, out hit, Mathf.Infinity, layerMask)) {
                    clickPos = hit.point;
                }

                clickPos.y = 0f;
                obj.transform.position = clickPos;

                Debug.Log("MOVE"+clickPos);
            }
        }

        if (Input.GetMouseButtonUp(0)) {
            obj = null;
        }
    }
}






public class SelectCube : MonoBehaviour {
    private void Update() {
        if (Input.GetMouseButtonDown(0)) {
            Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
            RaycastHit hit;
            int layerMask = LayerMask.GetMask("Object");
            if (Physics.Raycast(ray, out hit, Mathf.Infinity, layerMask)) {
                Debug.Log("Select"+hit.transform.name+" "+hit.transform.GetInstanceID());
                GameObject.Find("Main Camera").GetComponent<GroundMoveCube>().obj =
                    hit.transform.gameObject;
            }
        }
    }
}