Stage.scaleMode = "noScale";
Stage.align = "TL";

var resizeListener:Object = new Object();
resizeListener.onResize = function():Void {
    updatePos();
};
Stage.addListener(resizeListener);

var bgWidth:Number = 600;
var bgHeight:Number = 400;

updatePos();
function updatePos():Void {
    var xScale:Number = Stage.width/bgWidth;
    var yScale:Number = Stage.height/bgHeight;
    var fixScale:Number = Math.max(xScale, yScale)*100;
    bg._xscale = bg._yscale = fixScale;
    logo_mc._x = Stage.width/2;
    logo_mc._y = Stage.height/2;
}