Undo.CreateSnapshot 创建快照

// Editor Script Side
// Create a position Handle and make the target always look at the position handle.
// This is an editor Script, this should go inside the Editor Folder.
//创建一个手柄位置，并使目标始终看向手柄位置
@CustomEditor (LookAtPoint)
class SnapshotTargetEx extends Editor {


	function OnSceneGUI () {
		Undo.SetSnapshotTarget(target, "Moved Object Around");
		target.lookAtPoint =
		Handles.PositionHandle(target.lookAtPoint, Quaternion.identity);
		if (GUI.changed)
			EditorUtility.SetDirty (target);

		if(Input.GetMouseButtonDown(0)) {
			// Register the undos when we press the Mouse button.
			//当按下鼠标键注册undo
			Undo.CreateSnapshot();
			Undo.RegisterSnapshot();
		}
	}
}

// LookAtPoint.js

@script ExecuteInEditMode()

var lookAtPoint = Vector3.zero;

function Update () {
	transform.LookAt (lookAtPoint);
}