Rounded Rectangle Mask via Scripting

Hey Guys,

I am creating a script that applies a round rectangle mask to any layer that is selected. I have written the following code.

My question is, how do I make the vertices scale correctly to the size of any given comp? For example the code below has the vertices hard coded for a compostion of 1920x1080. How can I make this dynamic so it would work the same on an 8k comp for example.

Thanks,

Liam

btnMaskRoudRect.onClick = function() {
    if(app.project.activeItem == undefined || app.project.activeItem == null) {
        alert("Please Select a Composition.");
        return false;
     }
     if(app.project.activeItem.selectedLayers.length < 1) {
         alert("Please Select a Layer.");
     }
 else {
    maskRoudRect(app.project.activeItem.selectedLayers);
     }
     function maskRoudRect() {
        for(var i = 0; i < app.project.activeItem.selectedLayers.length; i++) {
        app.beginUndoGroup("Undo Rounded Rectangle Mask");
        myLayer = app.project.activeItem.selectedLayers[i];
        comp = app.project.activeItem;
        newMask = myLayer.Masks.addProperty("ADBE Mask Atom");
        newMask.maskMode = MaskMode.ADD;
        myProperty = newMask.property("ADBE Mask Shape");
        myShape = myProperty.value;
        myShape.vertices = [[1900, 0],[20, 0],[0, 20],[0, 1060],[20, 1080],[1900, 1080],[1920, 1060],[1920, 20]];
        myShape.inTangents = [[11.045654296875,0],[0,0],[0,-11.457153320312],[0,0],[-11.457153320312,0],[0,0],[0,11.045654296875],[0,0]];
        myShape.outTangents = [[0,0],[-11.457153320312,0],[0,0],[0,11.045654296875],[0,0],[11.045654296875,0],[0,0],[0,-11.457153320312]];
        myShape.closed = true;
        myProperty.setValue(myShape);
        app.endUndoGroup();
    } 
}