Intercept window procedure

[wspl]

Related to #2120. But there may be some differences.

I am using a win32 UI component provided by a third party library which provides a method to call in window procedure and pass in hwnd/message/wparam/lparam parameters which will internally handle events such as rendering.

So it would be nice to expose a method in EventLoop, e.g. EventLoop::hook_window_procedure to register a callback with signature fn(HWND, MESSAGE, WPARAM, LPARAM) -> Option<LRESULT>. It is called first in thread_event_target_callback to determine if the event is intercept and to decide whether to continue.

[msiglreith]

Does this https://github.com/rust-windowing/winit/blob/master/src/platform/windows.rs#L60-L88 work for you? It's not yet part of an official release so would require using a git revision for now.

[wspl]

Does this https://github.com/rust-windowing/winit/blob/master/src/platform/windows.rs#L60-L88 work for you? It's not yet part of an official release so would require using a git revision for now.

This looks like what I want, thanks!