Add play() and pause() functions

examples/beep.rs

@@ -18,11 +18,15 @@ fn main() {
             });
 
     loop {
-        let mut buffer = channel.append_data(1, cpal::SamplesRate(44100), 32768);
+        {
+            let mut buffer = channel.append_data(1, cpal::SamplesRate(44100), 32768);
 
-        for sample in buffer.iter_mut() {
-            let value = data_source.next().unwrap();
-            *sample = value;
+            for sample in buffer.iter_mut() {
+                let value = data_source.next().unwrap();
+                *sample = value;
+            }
         }
+
+        channel.play();
     }
 }

examples/music.rs

@@ -5,6 +5,7 @@ use std::io::BufReader;
 
 fn main() {
     let mut channel = cpal::Voice::new();
+    channel.play();
 
     let mut decoder = vorbis::Decoder::new(BufReader::new(include_bin!("music.ogg")))
         .unwrap();
@@ -20,22 +21,27 @@ fn main() {
                 continue 'main;
             }
 
-            let mut buffer = channel.append_data(channels, cpal::SamplesRate(rate as u32), data.len());
-            let mut buffer = buffer.iter_mut();
-
-            loop {
-                let next_sample = match data.get(0) {
-                    Some(s) => *s,
-                    None => continue 'main
-                };
-
-                if let Some(output) = buffer.next() {
-                    *output = next_sample as u16;
-                    data = data.slice_from(1);
-                } else {
-                    break;
+            {
+                let mut buffer = channel.append_data(channels, cpal::SamplesRate(rate as u32), 
+                                                     data.len());
+                let mut buffer = buffer.iter_mut();
+
+                loop {
+                    let next_sample = match data.get(0) {
+                        Some(s) => *s,
+                        None => continue 'main
+                    };
+
+                    if let Some(output) = buffer.next() {
+                        *output = next_sample as u16;
+                        data = data.slice_from(1);
+                    } else {
+                        break;
+                    }
                 }
             }
+
+            channel.play();
         }
     }
 }

src/alsa/mod.rs

@@ -63,6 +63,15 @@ impl Voice {
             buffer: Vec::from_elem(elements, unsafe { mem::uninitialized() })
         }
     }
+
+    pub fn play(&mut self) {
+        // already playing
+        //unimplemented!()
+    }
+
+    pub fn pause(&mut self) {
+        unimplemented!()
+    }
 }
 
 impl Drop for Voice {

src/lib.rs

@@ -27,8 +27,15 @@ for e in buffer.iter_mut() {
 This is the case if the device doesn't have enough space available. **It happens very often**,
 this is not some obscure situation that can be ignored.
 
+After you have submitted data for the first time, call `play`:
+
+```no_run
+# let mut voice = cpal::Voice::new();
+voice.play();
+```
+
 The audio device of the user will read the buffer that you sent, and play it. If the audio device
-reaches the end of the data, it will stop playing. You **must** continuously fill the buffer by
+reaches the end of the data, it will stop playing. You must continuously fill the buffer by
 calling `append_data` repeatedly if you don't want the audio to stop playing.
 
 # Native format
@@ -212,6 +219,25 @@ impl Voice {
             }
         }
     }
+
+    /// Sends a command to the audio device that it should start playing.
+    ///
+    /// Has no effect is the voice was already playing.
+    ///
+    /// Only call this after you have submitted some data, otherwise you may hear
+    /// some glitches.
+    pub fn play(&mut self) {
+        self.0.play()
+    }
+
+    /// Sends a command to the audio device that it should stop playing.
+    ///
+    /// Has no effect is the voice was already paused.
+    ///
+    /// If you call `play` afterwards, the playback will resume exactly where it was.
+    pub fn pause(&mut self) {
+        self.0.pause()
+    }
 }
 
 impl<'a, T> Deref<[T]> for Buffer<'a, T> {

src/wasapi/mod.rs

@@ -13,15 +13,13 @@ pub struct Voice {
     bytes_per_frame: winapi::WORD,
     samples_per_second: winapi::DWORD,
     bits_per_sample: winapi::WORD,
-    started: bool,
+    playing: bool,
 }
 
 pub struct Buffer<'a, T> {
-    audio_client: *mut winapi::IAudioClient,
     render_client: *mut winapi::IAudioRenderClient,
     buffer: CVec<T>,
     frames: winapi::UINT32,
-    start_on_drop: bool,
 }
 
 impl Voice {
@@ -83,18 +81,39 @@ impl Voice {
                 };
 
                 let buffer = Buffer {
-                    audio_client: self.audio_client,
                     render_client: self.render_client,
                     buffer: buffer,
                     frames: frames_available,
-                    start_on_drop: !self.started,
                 };
 
-                self.started = true;
                 return buffer;
             }
         }
     }
+
+    pub fn play(&mut self) {
+        if !self.playing {
+            unsafe {
+                let f = self.audio_client.as_mut().unwrap().lpVtbl.as_ref().unwrap().Start;
+                let hresult = f(self.audio_client);
+                check_result(hresult).unwrap();
+            }
+        }
+
+        self.playing = true;
+    }
+
+    pub fn pause(&mut self) {
+        if self.playing {
+            unsafe {
+                let f = self.audio_client.as_mut().unwrap().lpVtbl.as_ref().unwrap().Stop;
+                let hresult = f(self.audio_client);
+                check_result(hresult).unwrap();
+            }
+        }
+
+        self.playing = false;
+    }
 }
 
 impl Drop for Voice {
@@ -124,12 +143,6 @@ impl<'a, T> Buffer<'a, T> {
             let f = self.render_client.as_mut().unwrap().lpVtbl.as_ref().unwrap().ReleaseBuffer;
             let hresult = f(self.render_client, self.frames as u32, 0);
             check_result(hresult).unwrap();
-
-            if self.start_on_drop {
-                let f = self.audio_client.as_mut().unwrap().lpVtbl.as_ref().unwrap().Start;
-                let hresult = f(self.audio_client);
-                check_result(hresult).unwrap();
-            }
         };
     }
 }
@@ -237,7 +250,7 @@ fn init() -> Result<Voice, String> {
             bytes_per_frame: format.nBlockAlign,
             samples_per_second: format.nSamplesPerSec,
             bits_per_sample: format.wBitsPerSample,
-            started: false,
+            playing: false,
         })
     }
 }