How to downcast a PyAny into custom pyclass

[shenjackyuanjie]

    #[pyclass(name = "Camera_rs", subclass)]
    pub struct CameraRs {
        pub window: Py<PyAny>,
        #[pyo3(get, set)]
        pub dx: f64,
        #[pyo3(get, set)]
        pub dy: f64,
        pub zoom: f64,
        #[pyo3(get, set)]
        pub max_zoom: f64,
        #[pyo3(get, set)]
        pub min_zoom: f64,
    }

I have a pyclass here
and I wish to downcast some PyAny into it by using py.downcast::<CameraRs>()?
how can I do it?
(or say, how can I impl PyTryFrom for my pyclass