SOURCE

var w=20000,h=6000,size=256,l=(w>h)?w:h
console.log('l',l)
var a = Math.log(l / size) / Math.log(2)
var z = Math.ceil(a)

console.log('zoom:', z)

cut()
for (var i = z-1; i > 0; i--) {
    console.log(i)
    resize(i)
}

function cut(nw,nh) {
    console.log('cut')
    var max=Math.ceil(nw/size)
    for(var x=0;x<max;x++){
        console.log('x',x)
    }
}

function resize(i) {
    var pow=Math.pow(2,(z-i))
    console.log(pow)
    var nw=w/pow,nh=h/pow
    console.log('resize',nw,nh)
    //cut(nw,nh)
}