ASIO: open control panel

[Sin-tel]

Just putting this here for now so people know it is at least possible.

Will have to think about a proper API if we want to include this. (extension traits?)
I would also be fine having this only exposed in asio-sys for now, but you'd need to expose driver internals if you want to use it from cpal.

Also, I had to modify the build script to get rid of linker errors, not sure what's up with that.

[roderickvd]

Hey! I think the asio-sys part is worth having regardless of the cpal API discussion. While I believe the ASIO control panels are blocking modals, it seems that PortAudio and JUCE also expose them.

For the build script changes: the linker errors make sense - ASIOControlPanel() uses Windows registry APIs (Advapi32) and UI functions (User32). Just noting that you have user32 on line 66 and User32 on line 68 - they're the same lib on Windows (case-insensitive) so it works, just redundant.

Re: the cpal API, I agree we should use extension traits rather than exposing this through as_inner() downcasting. Here's what I'm thinking:

// In src/platform/asio.rs or similar
#[cfg(all(target_os = "windows", feature = "asio"))]
pub trait AsioDeviceExt {
    fn asio_open_control_panel(&self) -> Result<(), BackendSpecificError>;
}

impl AsioDeviceExt for Device {
    fn asio_open_control_panel(&self) -> Result<(), BackendSpecificError> {
        if let DeviceInner::Asio(ref d) = self.as_inner() {
            d.open_control_panel()
        } else {
            // or maybe introduce a new error variant
            Err(BackendSpecificError {
                description: "Not an ASIO device".to_string(),
            })
        }
    }
}

Usage would be like:

use cpal::platform::asio::AsioDeviceExt;

let device = host.default_output_device()?;
device.asio_open_control_panel()?;

This keeps the main Device trait platform-agnostic while allowing opt-in access to host-specific features. We could do similar for WASAPI exclusive mode, ALSA period counts, etc.

[roderickvd]

Had the above extension traits in mind for v0.18 by the way, not v0.17.

[Sin-tel]

Cool, trying out the extension trait now. It seems pretty nice! How I did it right now still has the problem with docs not generating though.