# Tag: Math for Games

Getting enemies to move tends to be one of the more difficult things for me to get right. It just doesn’t always seem natural. And I’m not talking about moving with any type of AI. Just moving around the screen in a pattern.

Sure, straight lines are pretty easy. But games get really boring if all the enemies just go from right to left or left to right.

For this post we’re going to explore moving an enemy through a series of waypoints using ActionScript 3. I’m going to create a movie clip symbol in Flash named Enemy_mc.

## Let’s see it

Doesn’t do much good to explain with words. This is what we’re going to create.

One minor difference. I set this demo up to loop so the enemy goes back to its starting position and sets its current waypoint back to 0 when it gets to the last one. The real deal will remove the enemy from the stage.

Creating the next great side scroller? Well, you’ll need a scrolling background. And if you’re programming in Java, here’s an easy way to do it.

## Quick Demo

Here’s a little demo of what we’re going to create. What’s happening is that there are two copies of the same image scrolling from the right to left. As one copy gets all the way off the left edge it leapfrogs back over to the right side. Normally they’d be the same, but it makes more sense on the demo for the two copies to be different colors.

The black box is the screen. Everything to the right or left of the box is happening off screen.

Click to start and click to stop.

Take a look at your favorite game. Odds are good that there is a scrolling background of some type. Think Super Mario Brothers.

Mario is a bit different than what we’re after though. The background in Mario is a single graphic that scrolls as Mario moves through the world. What we want is a scrolling background that loops forever. We’re going to scroll horizontally like a platform jumping game, but the same concept works vertically.

Some games, I’m thinking tower defense, need to give the player the ability to drag symbols around. But you don’t always want to give the player free reign to drag it anywhere. Maybe you want them to only be able to position symbols in a grid. That’s what we’ll create here using ActionScript 3.

## Demo

This is what we’re going to be creating.  Try dragging the green square. It will snap so that it’s always in one of the grid squares.