function onDocumentPointerDown(event) {
    if (event.pointerType == 'touch') {
        pointerIDs.push(event.pointerId);
        pointerCoordinates.push({clientX: event.clientX, clientY: event.clientY});
        event.targetTouches = pointerCoordinates;
        onDocumentTouchStart(event);
        event.preventDefault();
    }
}