Platform Game, Part 1, Movement - Page 3

The Code

Place this code in the first frame of the movie, preferably in a different layer.

	sprite.speed = 5;
	sprite.onEnterFrame = function() {
	if (Key.isDown(Key.RIGHT)) {
		this._x += this.speed;
	}
	if (Key.isDown(Key.LEFT)) {
		this._x -= this.speed;
	}
	if (Key.isDown(Key.DOWN)) {
		this._y += this.speed;
	}
	if (Key.isDown(Key.UP)) {
		this._y -= this.speed;
	}
};

I guess I have to do some explanation or this wouldn't be a tutorial, damn. Okay, well here it goes.
Lets look at the first line.

	sprite.speed = 5;
	

Here you define a variable inside the sprite movie clip called 'speed' and assign a value of 5 to it.

	sprite.onEnterFrame = function() {
	if (Key.isDown(Key.RIGHT)) {
		this._x += this.speed;
	}
	if (Key.isDown(Key.LEFT)) {
		this._x -= this.speed;
	}
	if (Key.isDown(Key.DOWN)) {
		this._y += this.speed;
	}  
	if (Key.isDown(Key.UP)) {
		this._y -= this.speed;
	}

Here you define a function that will execute whenever the sprite movie clip enters a frame. Depending on your movie's frame speed, a movie clip would go through a frame 30 times per second if your movie's frame speed were 30 frames/sec. Lets say your frame speed was 30, then this function would be executing 30 times per second, pretty fast huh?

	if (Key.isDown(Key.RIGHT)) {
		this._x += this.speed;
	}

The translation of this code to english would be something like this:
"If " the RIGHT ARROW key is "pressed down" than move "this" movie clip in the "positive x" direction by increments of 5 pixels.
The rest is basically the same thing except that the last two are in the y direction.