javascript - Get x and y values from computed CSS matrix3d?

This example (which works only on Safari), uses the deprecated function webkitConvertPointFromPageToNode

var point = webkitConvertPointFromPageToNode (
                  fieldContainerH, 
                  new WebKitPoint (e.clientX, e.clientY)
);

This returns the transformed coordinates of the mouse position.

How can I get the same x & y values, starting from the CSS matrix3D (as shown in the console)?