Hi all.

I'm trying to create a weighted random distribution, and can't figure out how to go about it. basically I want to create a starry sky, where most of the stars are in the middle of the screen. by making the y random, like:

star.y =Math.random()*_mc.stage.stageHeight;

I just get an even distribution on the Y axis. What I really want is to have most of the stars near _mc.stage.stageHeight/2.

Anyone has a good idea of how to accomplish?

thanks!

::| ITAI |::

[pixelbath]

function weightMiddle(input:Number, strength:int = 2):Number {
	if (input < 0.5) return 1 - Math.pow(1 - input, strength) / 2;
	return 0.5 + Math.pow((input - 0.5) * 2, strength) / 2;
}

You may (or not) recognize this as the exploded version of the easeOutIn function from Flash's own easing equations. I only marginally tested it, but it seems to work.

Use the "strength" parameter to force it closer to middle distribution. Default value is 2, which still preserves some randomness.

You would use this function like this:

star.y = weightMiddle(Math.random()) * _mc.stage.stageHeight;

[iasseo]

thanks! I'll give it a shot.

here's what I ended up with:

function triRand(a : Number, b : Number, u : Number):Number
{			
	var result : Number;
	var c : Number = b - ((b-a)/2);
			
	if (u <= 1){
		result = a + Math.sqrt(u * (b-a) * (c-a));
	}else{
		result = b - Math.sqrt((u-1) * (b-a) * (b-c));
	}

	return result;	
}

var a: Number = 0;
var b: Number = _mc.stage.stageHeight;
var RAN : Number = (Math.random()* 2);
var result : Number = Distribute.triRand(a, b, RAN);