Add ability to get underlying window handle

[notgull]

Adds the get_ref and get_mut functions, which can be used to get
references (mutable or otherwise) to the underlying window handle.

cc rust-windowing/raw-window-handle#158 (comment)

[ids1024]

For iced-rs/iced#2191, I also ended up needing Arc<Window> to create a softbuffer::Context and softbuffer::Surface from the same HasWindowHandle + HasDisplayHandle. Not sure how best to avoid that there.

Using Arc isn't really a problem even, it just seems a little odd from an API standpoint.

Having accessors like this seems reasonable, regardless.

[notgull]

For iced-rs/iced#2191, I also ended up needing Arc<Window> to create a softbuffer::Context and softbuffer::Surface from the same HasWindowHandle + HasDisplayHandle. Not sure how best to avoid that there.

Probably by using an owned display handle, tracked in rust-windowing/winit#3365

[daxpedda]

How about calling them window() and window_mut()?
See the Rust API Guidelines.

[kpreid]

In a previous much-different version of softbuffer, the window_mut() operation that existed then had to be unsafe, because mutable access is sufficient to swap it with a completely unrelated handle, thus violating the invariant that the context referred to the expected window, allowing the window in use to be dropped. Is that not still a problem here? I have not kept up with how raw-window-handle works these days.

If that invariant still applies, then window_mut() needs to be unsafe.

[notgull]

Good catch! Yes that still happens, let me fix it

[madsmtm]

LGTM after the removal of window_mut

[ids1024]

Perhaps it would also make sense to have a .context() accessor on Surface, and a .display() accessor on Context. But that is probably less often useful.