convenience methods for playing/stopping specific audio channels

examples/audio_playback/src/main.rs

@@ -7,6 +7,7 @@ use sdl2::keyboard::Scancode;
 use libretrogd::audio::*;
 use libretrogd::graphics::*;
 use libretrogd::system::*;
+use libretrogd::utils::rnd_value;
 
 #[derive(Debug, Copy, Clone)]
 struct AudioChannelStatus {
@@ -58,11 +59,13 @@ fn main() -> Result<()> {
 
     let mut is_running = true;
 
-    let sound1 = load_and_convert_wav(Path::new("./assets/pickup-coin.wav"), system.audio.spec())?;
+    let sounds = [
-    let sound2 = load_and_convert_wav(Path::new("./assets/powerup.wav"), system.audio.spec())?;
+        load_and_convert_wav(Path::new("./assets/pickup-coin.wav"), system.audio.spec())?,
-    let sound3 = load_and_convert_wav(Path::new("./assets/explosion.wav"), system.audio.spec())?;
+        load_and_convert_wav(Path::new("./assets/powerup.wav"), system.audio.spec())?,
-    let sound4 = load_and_convert_wav(Path::new("./assets/jump.wav"), system.audio.spec())?;
+        load_and_convert_wav(Path::new("./assets/explosion.wav"), system.audio.spec())?,
-    let sound5 = load_and_convert_wav(Path::new("./assets/laser-shoot.wav"), system.audio.spec())?;
+        load_and_convert_wav(Path::new("./assets/jump.wav"), system.audio.spec())?,
+        load_and_convert_wav(Path::new("./assets/laser-shoot.wav"), system.audio.spec())?,
+    ];
 
     let mut statuses = [AudioChannelStatus { size: 0, position: 0, playing: false }; NUM_CHANNELS];
 
@@ -80,29 +83,34 @@ fn main() -> Result<()> {
         }
 
         if system.keyboard.is_key_pressed(Scancode::Num1) {
-            audio_device.play_buffer(&sound1, false)?;
+            audio_device.play_buffer(&sounds[0], false)?;
         }
 
         if system.keyboard.is_key_pressed(Scancode::Num2) {
-            audio_device.play_buffer(&sound2, false)?;
+            audio_device.play_buffer(&sounds[1], false)?;
         }
 
         if system.keyboard.is_key_pressed(Scancode::Num3) {
-            audio_device.play_buffer(&sound3, false)?;
+            audio_device.play_buffer(&sounds[2], false)?;
         }
 
         if system.keyboard.is_key_pressed(Scancode::Num4) {
-            audio_device.play_buffer(&sound4, false)?;
+            audio_device.play_buffer(&sounds[3], false)?;
         }
 
         if system.keyboard.is_key_pressed(Scancode::Num5) {
-            audio_device.play_buffer(&sound5, false)?;
+            audio_device.play_buffer(&sounds[4], false)?;
         }
 
         if system.keyboard.is_key_pressed(Scancode::Num6) {
             audio_device.play_generator(SineWaveGenerator::new(), false);
         }
 
+        if system.keyboard.is_key_pressed(Scancode::Num7) {
+            let index = rnd_value(0, sounds.len() - 1);
+            audio_device.play_buffer_on_channel(7, &sounds[index], false)?;
+        }
+
         for index in 0..NUM_CHANNELS {
             let channel = &audio_device[index];
             let mut status = &mut statuses[index];

libretrogd/src/audio/mod.rs

@@ -188,6 +188,9 @@ impl AudioChannel {
 pub enum AudioDeviceError {
     #[error("That buffer's AudioSpec does not match the device's AudioSpec")]
     AudioSpecMismatch,
+
+    #[error("The channel index {0} is out of range")]
+    ChannelIndexOutOfRange(usize),
 }
 
 pub struct AudioDevice {
@@ -230,6 +233,15 @@ impl AudioDevice {
         self.channels.iter().any(|channel| channel.playing)
     }
 
+    pub fn stop_channel(&mut self, channel_index: usize) -> Result<(), AudioDeviceError> {
+        if channel_index >= NUM_CHANNELS {
+            Err(AudioDeviceError::ChannelIndexOutOfRange(channel_index))
+        } else {
+            self.channels[channel_index].stop();
+            Ok(())
+        }
+    }
+
     pub fn stop_all(&mut self) {
         for channel in self.channels.iter_mut() {
             channel.stop();
@@ -253,7 +265,27 @@ impl AudioDevice {
         }
     }
 
-    pub fn play_generator(&mut self, generator: impl AudioGenerator + 'static, loops: bool) -> Result<Option<&mut AudioChannel>, AudioDeviceError> {
+    pub fn play_buffer_on_channel(
+        &mut self,
+        channel_index: usize,
+        buffer: &AudioBuffer,
+        loops: bool,
+    ) -> Result<(), AudioDeviceError> {
+        if buffer.spec != self.spec {
+            Err(AudioDeviceError::AudioSpecMismatch)
+        } else if channel_index >= NUM_CHANNELS {
+            Err(AudioDeviceError::ChannelIndexOutOfRange(channel_index))
+        } else {
+            self.channels[channel_index].play_buffer(buffer, loops);
+            Ok(())
+        }
+    }
+
+    pub fn play_generator(
+        &mut self,
+        generator: impl AudioGenerator + 'static,
+        loops: bool,
+    ) -> Result<Option<&mut AudioChannel>, AudioDeviceError> {
         if let Some(channel) = self.stopped_channels_iter_mut().next() {
             channel.play_generator(generator, loops);
             Ok(Some(channel))
@@ -262,6 +294,20 @@ impl AudioDevice {
         }
     }
 
+    pub fn play_generator_on_channel(
+        &mut self,
+        channel_index: usize,
+        generator: impl AudioGenerator + 'static,
+        loops: bool,
+    ) -> Result<(), AudioDeviceError> {
+        if channel_index >= NUM_CHANNELS {
+            Err(AudioDeviceError::ChannelIndexOutOfRange(channel_index))
+        } else {
+            self.channels[channel_index].play_generator(generator, loops);
+            Ok(())
+        }
+    }
+
     #[inline]
     pub fn playing_channels_iter(&mut self) -> impl Iterator<Item = &AudioChannel> {
         self.channels.iter().filter(|channel| channel.playing)