add Audio struct to wrap underlying SDL AudioDevice

doesn't provide much value currently, but serves as a base for future
extension (e.g. queuing play commands, global volume changes, etc)

libretrogd/src/audio/mod.rs

@@ -1,6 +1,7 @@
 use std::ops::{Index, IndexMut};
 
-use sdl2::audio::{AudioCallback, AudioFormat};
+use sdl2::audio::{AudioCallback, AudioFormat, AudioSpecDesired};
+use sdl2::AudioSubsystem;
 use thiserror::Error;
 
 pub use self::wav::*;
@@ -283,6 +284,67 @@ impl IndexMut<usize> for AudioDevice {
 
 //////////////////////////////////////////////////////////////////////////////////////////////////
 
+#[derive(Debug, Error)]
+pub enum AudioError {
+    #[error("Failed to open audio device for playback: {0}")]
+    OpenDeviceFailed(String),
+}
+
+pub struct Audio {
+    spec: AudioSpec,
+    sdl_audio_device: sdl2::audio::AudioDevice<AudioDevice>,
+}
+
+impl Audio {
+    pub fn new(desired_spec: AudioSpecDesired, sdl_audio_subsystem: &AudioSubsystem) -> Result<Self, AudioError> {
+        let mut spec = None;
+        let sdl_audio_device = match sdl_audio_subsystem.open_playback(None, &desired_spec, |opened_spec| {
+            let our_spec = AudioSpec::new(opened_spec.freq as u32, opened_spec.channels, opened_spec.format);
+            spec = Some(our_spec);
+            AudioDevice::new(our_spec)
+        }) {
+            Ok(audio_device) => audio_device,
+            Err(error) => return Err(AudioError::OpenDeviceFailed(error)),
+        };
+
+        if let Some(spec) = spec {
+            Ok(Audio {
+                spec,
+                sdl_audio_device,
+            })
+        } else {
+            Err(AudioError::OpenDeviceFailed(String::from("Device initialization failed to set AudioSpec")))
+        }
+    }
+
+    #[inline]
+    pub fn spec(&self) -> &AudioSpec {
+        &self.spec
+    }
+
+    #[inline]
+    pub fn status(&self) -> sdl2::audio::AudioStatus {
+        self.sdl_audio_device.status()
+    }
+
+    #[inline]
+    pub fn pause(&mut self) {
+        self.sdl_audio_device.pause()
+    }
+
+    #[inline]
+    pub fn resume(&mut self) {
+        self.sdl_audio_device.resume()
+    }
+
+    #[inline]
+    pub fn lock(&mut self) -> sdl2::audio::AudioDeviceLockGuard<AudioDevice> {
+        self.sdl_audio_device.lock()
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////////////////////////
+
 #[derive(Error, Debug)]
 pub enum AudioBufferError {
     #[error("Error during format conversion: {0}")]

libretrogd/src/system/mod.rs

@@ -23,6 +23,9 @@ pub enum SystemError {
 
     #[error("System display error: {0}")]
     DisplayError(String),
+
+    #[error("System audio error: {0}")]
+    AudioError(#[from] crate::audio::AudioError),
 }
 
 /// Builder for configuring and constructing an instance of [`System`].
@@ -247,14 +250,7 @@ impl SystemBuilder {
             channels: Some(TARGET_AUDIO_SPEC.channels()),
             samples: None,
         };
-
+        let mut audio = Audio::new(audio_spec, &sdl_audio_subsystem)?;
-        let audio = match sdl_audio_subsystem.open_playback(None, &audio_spec, |spec| {
-            let our_spec = AudioSpec::new(spec.freq as u32, spec.channels, spec.format);
-            AudioDevice::new(our_spec)
-        }) {
-            Ok(audio_device) => audio_device,
-            Err(error) => return Err(SystemError::InitError(error)),
-        };
         audio.resume();
 
         // create input device objects, exposed to the application
@@ -305,7 +301,7 @@ pub struct System {
     target_framerate_delta: Option<i64>,
     next_tick: i64,
 
-    pub audio: sdl2::audio::AudioDevice<AudioDevice>,
+    pub audio: Audio,
 
     /// The primary backbuffer [`Bitmap`] that will be rendered to the screen whenever
     /// [`System::display`] is called. Regardless of the actual window size, this bitmap is always