Unity3D Editor Script: Moves selected object downwards till it touches the ground

DropObject.cs

//Copyright © 2015 Manoj M J
//All Rights Reserved

//Why I do copyright the code that I provide at gist.github.com 
//( https://gist.github.com/mmj-the-fighter/bccd0a7ff57c638beee8 )

/*
 * DropObject.cs - Moves selected object downwards till it touches the ground 
 * This is useful for placing 3d models on scene.
 * TODO:Add Spherecast in addition to Raycast
 * (c)mmj 2015
 */
using UnityEngine;
using UnityEditor;
using System.Collections;
using System.Collections.Generic;


public class DropObject : ScriptableObject {

	static bool optionMoveUpToDropHeightAndThenDrop = true;
	static bool optionRayCastAgainstAllColliders = false;

	static int groundLayerNumber = 8;//CAUTION:Remember to change the value of this variable"groundLayerNumber" with your data
	static float expectedHeightOffsetAfterDrop = 0.5f;
	static float dropHeight = 1000.0f;

	internal struct UndoInfo
	{
		public Transform transform;
		public Vector3 position;
	};
		
	static List<UndoInfo> undoInfoList = new List<UndoInfo>();
	static UndoInfo undoInfo;

	public enum MethodID 
	{
		MethodNone,
		MethodDropSingleObject,
		MethodDropSelectedObjects,
		MethodDropChildObjects
	};

	static MethodID recentlyExecutedMethodsID = MethodID.MethodNone;


	static void Drop(Transform target) {
		if(optionMoveUpToDropHeightAndThenDrop) {
			target.position = target.position + new Vector3(0.0f,dropHeight,0.0f);
		}
		Vector3 origin = target.position;
		Vector3 direction = Vector3.down;
		RaycastHit hitInfo = new RaycastHit();
		int layerMask = 1 << groundLayerNumber;
		if(optionRayCastAgainstAllColliders) {
			Physics.Raycast(origin,direction,out hitInfo);
		} else {
			Physics.Raycast(origin,direction,out hitInfo,Mathf.Infinity,layerMask);
		}
		target.position = hitInfo.point + new Vector3(0.0f,expectedHeightOffsetAfterDrop,0.0f);
	}
	
	[ MenuItem( "Tools/DropObject/DropSingleObject" ) ]
	static void DropSingleObject () {
		Transform activeTransform = Selection.activeTransform;
		undoInfo.transform = activeTransform;
		undoInfo.position = activeTransform.position;
		Drop (activeTransform);
		recentlyExecutedMethodsID = MethodID.MethodDropSingleObject;
	}

	[ MenuItem( "Tools/DropObject/DropSelectedObjects" ) ]
	static void DropSelectedObjects() {
		undoInfoList.Clear();
		foreach (Transform t in Selection.transforms) {
			UndoInfo undoInformation = new UndoInfo();
			undoInformation.transform = t;
			undoInformation.position = t.position;
			undoInfoList.Add(undoInformation);
			Drop (t);
		}
		recentlyExecutedMethodsID = MethodID.MethodDropSelectedObjects;
	}

	[ MenuItem( "Tools/DropObject/DropChildObjects" ) ]
	static void DropChildObjects() {
		undoInfoList.Clear();
		Transform activeTransform = Selection.activeTransform;
		foreach (Transform child in activeTransform) {
			UndoInfo undoInformation = new UndoInfo();
			undoInformation.transform = child;
			undoInformation.position = child.position;
			undoInfoList.Add(undoInformation);
			Drop (child);
		}
		recentlyExecutedMethodsID = MethodID.MethodDropChildObjects;
	}

	[ MenuItem( "Tools/DropObject/Undo" ) ]
	static void Undo() {
		switch(recentlyExecutedMethodsID)
		{
		case MethodID.MethodDropSingleObject:
			UndoDropSingleObject();
			break;
		case MethodID.MethodDropSelectedObjects:
			UndoDropSelectedObjects();
			break;
		case MethodID.MethodDropChildObjects:
			UndoDropChildObjects();
			break;
		}
	}

	static void UndoDropSingleObject () {
		undoInfo.transform.position = undoInfo.position;
	}

	static void UndoDropSelectedObjects () {
		foreach (UndoInfo undoInformation in undoInfoList) {
			undoInformation.transform.position = undoInformation.position;
		}
	}
	
	static void UndoDropChildObjects () {
		foreach (UndoInfo undoInformation in undoInfoList) {
			undoInformation.transform.position = undoInformation.position;
		}
	}

}