球体をとある範囲で操作する

SpherePlayer.cs

using UnityEngine;
using System.Collections;

public class SpherePlayer : MonoBehaviour {

	public float speed = 5f;
	public float range = 5f;

	void Update () {
		float z = Input.GetAxisRaw ("Vertical");
		float x = Input.GetAxisRaw ("Horizontal");
		Vector3 direction = new Vector3 (x, 0, z).normalized;
		transform.Translate (direction  * speed * Time.deltaTime);

		Clamp ();
	}

	void Clamp() {
		Vector3 pos = transform.position;
		pos.x = Mathf.Clamp (pos.x, -range, range);
		pos.z = Mathf.Clamp (pos.z, -range, range);
		transform.position = pos;
	}
}