var PngAnimator = {};
PngAnimator.DeltaX = 1;
PngAnimator.DeltaY = 1;
PngAnimator.MinX = -10;
PngAnimator.MinY = -10;
PngAnimator.MaxX = 100;
PngAnimator.MaxY = 50;
PngAnimator.Init = function(){
    var png = document.getElementById('pngDiv');
    png.style.left = PngAnimator.MinX + 'px';
    png.style.top = PngAnimator.MinY + 'px';
    };
PngAnimator.MovePng = function(){
    var png = document.getElementById('pngDiv');           
    var posX = parseInt((png.style.left.toString()).substring(0, png.style.left.length - 2));
    var posY = parseInt((png.style.top.toString()).substring(0, png.style.top.length - 2));
    if(posX > PngAnimator.MaxX)PngAnimator.DeltaX = -PngAnimator.DeltaX;
    if(posX < PngAnimator.MinX)PngAnimator.DeltaX = -PngAnimator.DeltaX;
    if(posY > PngAnimator.MaxY)PngAnimator.DeltaY = -PngAnimator.DeltaY;
    if(posY < PngAnimator.MinY)PngAnimator.DeltaY = -PngAnimator.DeltaY;
    png.style.left = posX + PngAnimator.DeltaX + 'px';
    png.style.top = posY + PngAnimator.DeltaY + 'px';
    };   
PngAnimator.Init();   
window.setInterval(PngAnimator.MovePng, 60);