用swift填充动画+永久面具?

如果我理解正确,可以在遮罩下添加子视图并更改其宽度,如下所示:

let fillingStartFrame = CGRect.init(x: 0, y: 0, width: 0, height: view.frame.height)
let fillingEndFrame = CGRect.init(x: 0, y: 0, width: view.frame.width, height: view.frame.width)
let fillingView = UIView(frame: fillingStartFrame)
view.insertSubview(fillingView, belowSubview: YOUR_MASK)
UIView.animate(withDuration: 0.3) {
    fillingView.frame = fillingEndFrame
}