ScreenToWorldPoint(2D上でお絵描きしたいとき)

2Dでの「Camera.main.ScreenToWorldPoint」の扱いに困った。
これは、「スクリーン座標をワールド座標に変換する関数」であるが、これを２Dで使うたいとき、カメラのプロパティ「Projection」を「Orthographic」（2D用）に設定してあげなければならない。

082 ScreenToWorldPoint関数の注意点 [stepism@Unityメモ]

docs.unity3d.com

using UnityEngine;
using System.Collections;
public class ObjectManager : MonoBehaviour {

	// 子要素
	public GameObject Child;
	// 親要素
	public GameObject Prefab;
	public GameObject NowParent;
	public Vector2 LastPos;


	void Start () {
		LastPos = transform.position;
	}

	void Update () {
		if(Input.GetMouseButtonDown(0)){
			CreatEmpty();
		}
		if(Input.GetMouseButton(0)){
			DrawLine();
		}
		if(Input.GetMouseButtonUp(0)){
			if( NowParent != null){
				NowParent.AddComponent("Rigidbody2D");
				NowParent.layer = 9;
				NowParent = null;
			}
		}

	}
	void CreatEmpty(){
		// if(PlayerPrefs.GetInt("play") == 1){
			print("マウスの位置　"+Input.mousePosition);
			Vector2 worldPoint = Camera.main.ScreenToWorldPoint(Input.mousePosition);
			RaycastHit2D hit = Physics2D.Raycast(worldPoint,Vector2.zero);
			Vector2 hitPoint;
			if(hit){
	            if( hit.transform.gameObject.layer == 8){
		            Bounds rect =  hit.collider.bounds;
		            if(rect.Contains(worldPoint)){
		            	// vector2
		            	hitPoint= hit.point;
						print ("hit!!　hitPoint = "+ hitPoint);
						Vector2 hitPointRondam = hitPoint + new Vector2(Random.Range(0f, 0.1f), Random.Range(0f, 0.1f));

						NowParent = Instantiate(Prefab, hitPointRondam, Quaternion.identity) as GameObject;
						NowParent.transform.parent = gameObject.transform;
						NowParent.name = "Parent";
					}
				}
				else{
					print ("そこは範囲外だよ");
					return;
				}
			}
		// }
	}


	void DrawLine(){
		// if(PlayerPrefs.GetInt("play") == 1){
			Vector2 Pos = Input.mousePosition;
			// if(Pos == LastPos){
			// 	return;
			// }
			Vector2 worldPoint = Camera.main.ScreenToWorldPoint(Pos);
			RaycastHit2D hit = Physics2D.Raycast(worldPoint,Vector2.zero);
			Vector2 hitPoint;

			if(hit){
	            Bounds rect =  hit.collider.bounds;
	            if(rect.Contains(worldPoint)){
	            	if( hit.transform.gameObject.layer == 8){
		            	hitPoint= hit.point;
						print ("hit.point = "+ hitPoint);
						GameObject obj = Instantiate(Child, hitPoint, transform.rotation) as GameObject;
						obj.layer = 9;
						obj.transform.parent = NowParent.transform;
						obj.name = "child";
						LastPos = Pos;
					}else{

						return;
					}
				}
			}
		// }
	}
}