// create PerspectiveTransfrom
    var transform = new PerspectiveTransform(elem, width, height, useBackFacing);

    // the properties represent the 4 corners are "topLeft", "topRight", "bottomLeft" and "bottomRight"
    transform.bottomRight.x = 200;
    transform.bottomRight.y = 200;

    // check the polygon error before updating
    if(transform.checkError()==0){
        transform.update(); // update the perspective transform
        elem.style.display = "block"; // show the element
    }else{
        elem.style.display = "none"; // hide the element
    }

PerspectiveTransform.useDPRFix = true; // put true if you need to apply this fix

window.onresize = function(){
    PerspectiveTransform.dpr = window.devicePixelRatio; // update the dpr
    transform.update(); // update the PerspectiveTransform instance
}