Tutorial: Create a Tower Defense Game in AS2

Written By MrSun at 8:01 am - Saturday, April 25th, 2009
Categories: Flash

Step 1: Setting Up a Level

The tower defense genre is one that has become extremely popular over the years. Although they can become quite complicated to develop, they are almost always very fun to play. I am here to walk you through the creation of one of these games. Let us begin, shall we?

In this section of the tutorial, we’re going to set up the roads and stuff onto the stage. However, the first thing we need to do is create a blank flash document with a black background with the frames per second set at 24.

Now, we can dive into some code. Let’s first create some code that will lay down the track for the enemies to go through. Create a new layer called “actions” and add the following code to it:


//setting vars to step in for turns and special blocks
var S:String = 'START';
var F:String = 'FINISH';
var U:String = 'UP';
var R:String = 'RIGHT';
var D:String = 'DOWN';
var L:String = 'LEFT';

var startDir:String;//the direction the enemies go when they enter
var finDir:String;//the direction the enemies go when they exit
var startCoord:Number;//the coordinates of the beginning of the road
var lvlArray:Array = new Array();//this array will hold the formatting of the roads

lvlArray = [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,

//the names of these variables explain what they do
var currentLvl:Number = 1;
var gameOver:Boolean = false;

function startGame():Void{//we'll run this function every time a new level begins
	//right now we don't have any code

_root.createEmptyMovieClip('roadHolder',_root.getNextHighestDepth());//add a MovieClip to hold the road
function makeRoad():Void{
	var row:Number = 0;//the current row we're working on
	var block;//this will act as the block that we're placing down

That's a lot of code, ain't it? Hopefully, I've given you enough instructions in the comments. If you test out our game, a nice little path should be shown which the enemies will travel through, along with some blank gray boxes where we'll be able to place some turrets.

Before I end this part of the tutorial, I want to give these empty boxes some rollOver and rollOut effects. Find where I added the comment saying /////*****EMPTY BLOCK*****///// (lines 44-54). Add this code to the bottom of that section of the if statement:

_root['block'+i].onRollOver = function(){
	//Change the color to green
	var newColor = new Color(this);
_root['block'+i].onRollOut = function(){
	//Change this color back to gray
	var newColor = new Color(this);

Final Product

Source Files (Zipped)



Hello, I’ve been following this tutorial exactly how it is written and everything and when I go to test my game the level will not show up. All I see is the black background and the script has no errors. I’m using this tutorial with Macromedia Flash MX Professional 2004, is this the problem?


what’s AS2 im a noob but im here to learn :O


wow me too im using mx what a coincidence! i see just black stuff and nothing


Hey. I’m having problems with the onRollOver mouse square color change. I keep getting 3 errors.

} else if(lvlArray[i] == 1){//if there is supposed to be a row
function makeRoad():Void{

I’ve been adding the scrip into line 45 of the code, just after your comment about Empty Blocks, and the errors come as i press CTRL+Enter to see the Movie.

Thanks 😀


I don’t program in Flash but just looking over the code i think you need another For loop after
you seem to be only rendering i row and not going through the entire array


hi the piece of code for the rollover didnt work
can i ask what flash you are using?


Awesome ty


A good tip to check your code is to use /* */ between blocks of the code and copy the above code into your own actionscript – sometimes it’s just something simple like typing 1 for l or vise versa


I can’t see the rollOver and rollOut stuff on my SWF file, please help


I do believe this code is set for the adobe cs3 version of flash, I followed the tutorial and see the end result so far. That may be the problem.


These errors come in AS:
Clipboard Actions: Line 34: ‘{‘ expected
function startGame():Void{//we’ll run this function every time a new level begins

Clipboard Actions: Line 39: ‘{‘ expected
function makeRoad():Void{

Clipboard Actions: Line 86: Unexpected ‘}’ encountered


Im using macromedia flash 8 and this 1st part has worked fine on my version


Hi I am making a game for a class and want to alterter this game i was wondering how I would go about instead of having a grey box having a white one

help please:

i dont get where it says “Before I end this part of the tutorial, I want to give these empty boxes some rollOver and rollOut effects. Find where I added the comment saying /////*****EMPTY BLOCK*****///// (lines 44-54). Add this code to the bottom of that section of the if statement”


i have the same problem as micheal but i am useing flash CS4


doesn’t work on mine either…I used flash mx…