Add an underflow() method to Voice

src/alsa/mod.rs

@@ -107,6 +107,10 @@ impl Voice {
     pub fn pause(&mut self) {
         unimplemented!()
     }
+
+    pub fn underflowed(&self) -> bool {
+        false       // TODO: 
+    }
 }
 
 unsafe impl Send for Voice {}

src/lib.rs

@@ -339,6 +339,12 @@ impl Voice {
     pub fn pause(&mut self) {
         self.0.pause()
     }
+
+    /// Returns true if the voice has finished reading all the data you sent to it.
+    #[inline]
+    pub fn underflowed(&self) -> bool {
+        self.0.underflowed()
+    }
 }
 
 impl<'a, T> Deref for Buffer<'a, T> where T: Sample {

src/null/mod.rs

@@ -70,6 +70,10 @@ impl Voice {
 
     pub fn pause(&mut self) {
     }
+
+    pub fn underflowed(&self) -> bool {
+        false
+    }
 }
 
 pub struct Buffer<'a, T: 'a> {

src/wasapi/voice.rs

@@ -296,6 +296,16 @@ impl Voice {
 
         self.playing = false;
     }
+
+    pub fn underflowed(&self) -> bool {
+        unsafe {
+            let mut padding = mem::uninitialized();
+            let hresult = (*self.audio_client).GetCurrentPadding(&mut padding);
+            check_result(hresult).unwrap();
+            
+            padding == 0
+        }
+    }
 }
 
 impl Drop for Voice {