[AS3] BimapData, Matrix translation

Code:

var tx:Number=2
var ty:Number=2

var bmp:Bitmap=new Bitmap()
var bmpData:BitmapData=new BitmapData(400,400,false,0x0000ff)
bmp.bitmapData=bmpData
addChild(bmp)
var interval:Number=setInterval(drawRect,10)
function drawRect(){
    var matrix:Matrix=new Matrix()
    matrix.translate(tx,ty)
    bmpData.fillRect(new Rectangle(150,150,100,100),0xff0000)
    bmpData.draw(bmpData,matrix)
}