var X = xcursor ; // x cursor on canvas
var Y = ycursor ; // y cursor on canvas
var Ex = W ; // (end) width canvas. Corner down-left
var Ey = H ; // (end) height canvas. Corner up-right
var zoomX = 0 ; // ? x unknown
var zoomY = 0 ; // ? y unknown
var sx = Xz ; // (start) x origin of the coord zoom.
var sy = Yz ; // (start) y origin of the coord zoom.
var Wz = Wz ; // width zoom
var Hz = Hz ; // height zoom
var ex = sx + Wz ; // (end) x width zoom. Corner down-left
var ey = sy + Hz ; // (end) y height zoom. Corner up-right
var r = X / Ex ; // 0 to 1
var s = Y / Ey ; // 0 to 1
zoomX= (1 - r) * sx + ex * r;
zoomY= (1 - s) * sy + ey * s;