default Rect calculateChildrenFrame() {
        Rect childrenFrame = getOurChildren().stream()
                .filter(n -> !n.isHidden())
                .map(RedUINode::calculateAccumulatedFrame)
                .reduce(Rect.ZERO, Rect::union);
        return convertRectToParent(childrenFrame);
    }
Calculate a frame encompassing all visible children and their subtrees.

@return Rect in the coordinate system of this node's parent
core/src/main/java/mrtjp/projectred/redui/RedUINode.java