One of the things that makes the Flash community so strong, is the willingness of coders to share their work. I learned actionscript from people sharing code, and that’s what’s inspired me to start sharing some of the things I’ve been working on too. So I thought a good starting point would be to draw peoples attention to a few of the great Classes and Functions that I’ve found on blogs and messageboards, which I regularly use in my projects.

One brillaint function I’ve used in practically all of my projects since finding it, is Joel Gillman’s Map Function.

Joel’s Map function “Re-maps a number from one range to another“, which might sound like quite obscure functionality, but I use it for all sorts of different things. Let’s say you want a movieclip’s alpha to vary based on the user’s X mouse position and its rotation to vary based on the Y mouse position. Instead of writing lots of math, you can wrap it up in the map function.

Let’s take a look at the code -

function map(v:Number, a:Number, b:Number, x:Number = 0, y:Number = 1):Number {
    return (v == a) ? x : (v - a) * (y - x) / (b - a) + x;
}

Now that might look pretty confusing – but it’s usage is actually really simple. The map parameters are structured like this – map(value, low1, high1, low2, high2);
So you feed in the value you’re altering (for example mouseX), the lowest that value can be, the highest that value can be, the lowest return value you want, and the highest return value.
Right, let’s take a look at this simple example –
[kml_flashembed fversion="9.0.0" movie="flash-content/MapClass/UsingMapCircleBlog.swf" targetclass="flashmovie" publishmethod="static" width="400" height="300"]

[/kml_flashembed]

And the code that made it -

var SW:Number = stage.stageWidth;
var SH:Number = stage.stageHeight;
 
var c:MovieClip = new MovieClip();
	c.graphics.beginFill(0xff0000,1);
	c.graphics.drawCircle(0,50,50);
	c.graphics.endFill();
	c.x = SW/2;
	c.y = SH/2;
	c.addEventListener(Event.ENTER_FRAME, circleEvents);
	addChild(c);	
 
function circleEvents(e:Event):void{
	trace(mouseX)
	e.currentTarget.alpha =    map(mouseX, 0, SW, 0, 1);
	e.currentTarget.rotation = map(mouseY, 0, SH, 0, 360);
}
 
function map(v:Number, a:Number, b:Number, x:Number = 0, y:Number = 1):Number {
    return (v == a) ? x : (v - a) * (y - x) / (b - a) + x;
}

So in that swf, the circle’s alpha varies between 0 and 1, based on the mouse’s X position, between 0 and the width of the stage. So, every frame I calculate the alpha using the map function. To set that up, I use the line -

	e.currentTarget.alpha =    map(mouseX, 0, SW, 0, 1);

I’m monitoring the mouse’s X position, with a minimum value of 0, a maximum value of the stage width, and I want it to return a value between 0 and 1. Simple.
Similarly, the circle’s rotation ranges from 0 to 360, based on the mouse’s Y value – which ranges from 0 to the height of the stage. So -

	e.currentTarget.rotation = map(mouseY, 0, SH, 0, 360);

I hope you find this great function as useful as I did.
Cheers.