Map Function

joel gillman — Mon, 29 Sep 2008 22:39:41 +0000

If you’ve ever used Processing you’ve probably used the ‘map’ function. From the Processing Reference section it reads: “Re-maps a number from one range to another.”

Unfortunately the function doesn’t exist in Flash, so I rewrote it. Why is this function useful? Lets say your mouse can move within the bounds of your stage from 0 to 550 pixels along its x-axis. You want a box to move back and forth from 100 to 200 pixels according to the position of the mouse. So when your mouse is halfway across the stage your box should be halfway between 100 and 200 pixels. You would simply use:

myBox.x = map(mouseX, 0, 550, 100, 200);

Easy as that!

Usage:
map(value, low1, high1, low2, high2);
low2 and high2 default to 0 and 1, respectively so you don’t have to put them in if you just want to normalize your value.

function map(value:Number,
low1:Number,
high1:Number,
low2:Number = 0,
high2:Number = 1):Number {
//if the value and the 1st range low are equal to
// the new value must be low2
if (value == low1) {
return low2;
}

//normalize both sets to a 0-? range
var range1 = high1 - low1;
var range2 = high2 - low2;

//normalize the value to the new normalized range
var result = value - low1;

//define the range as a percentage (0.0 to 1.0)
var ratio = result / range1;

//find the value in the new normalized-range
result = ratio * range2;

//un-normalize the value in the new range
result += low2;

return result;
}

And super compressed (less readable, less space, works the same):

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;
}

lab.joelGillman.com » normalize

Map Function