untoldentertainment.com » AS3 Helper Class

Home > Blog > AS3 Helper Class – Fence()

AS3 Helper Class – Fence()

by Ryan Henson Creighton, November 11, 2008

We are building an AS3 Helper class to speed up development on Actionscript 3 projects. Feel free to use these methods in your own Helper class, or to share your own methods that you find useful.

Fence()

public class Helper
{
	import flash.geom.Point;
	import flash.geom.Rectangle;
 
	/**
	 * This method confines a Point
	 * within a Rectangle.  Useful for
	 * games where the player and
	 * enemy characters have to stay
	 * within a boundary (ie the screen!).
	 */
	public static function Fence(point:Point,
				theRect:Rectangle):Point
	{
		// Make sure the point
		// is horizontally within limits
		if (point.x &gt; theRect.right)
		{
			point.x = theRect.right;
		} else if (point.x &lt; theRect.left) {
			point.x = theRect.left;
		}
 
		// Make sure the point
		// is vertically within limits
		if (point.y &lt; theRect.top)
		{
			point.y = theRect.top;
		} else if (point.y &gt; theRect.bottom) {
			point.y = theRect.bottom;
		}
		return point;
	}
}

Usage

/* Imagine an Asteroids-style game
where you need to confine your spaceship
within the boundaries of a movieClip
instance called "spaceClip"
*/
var spaceBoundaries:Rectangle = new Rectangle(spaceClip.x,
					  spaceClip.y,
					  spaceClip.width,
					  spaceClip.height);
	// Store the outer space boundaries
var pos:Point = new Point(spaceship.x, spaceship.y);
	// Store the ship's co-ordinates
var xSpeed:Number = 30;
var ySpeed:Number = 50;
	// Set thrusters to "go!"
pos.offset(xSpeed, ySpeed);
	// add the xSpeed/ySpeed to the ship's current position
pos = Helper.Fence(pos, spaceBoundaries);
	// make sure the ship doesn't escape outer space!
spaceship.x = pos.x;
spaceship.y = pos.y;
	// position the ship on the screen

Comments

Keeping game characters and objects from leaving the play field is one of those stock-standard things you do in many, many different games – from keeping the pigs inside the sty, to keeping the ball inside the tennis court, to keeping the whatever inside the viewable screen limits. We’re sure to get a lot of mileage from the Fence() method in our future projects.

For more AS3 Helper Classses and a pile of other useful stuff, check out our Flash and Actionscript 911 feature.

Ryan Henson Creighton is a Toronto-based game developer, and founder of Untold Entertainment Inc., specializing in online games for kids, teens, tweens and preschoolers.