add Crossfade

src/source/crossfade.rs

@@ -0,0 +1,60 @@
+use std::time::Duration;
+
+use Source;
+use Sample;
+use source::Mix;
+use source::TakeDuration;
+use source::FadeIn;
+
+/// Mixes one sound fading out with another sound fading in for the given duration.
+///
+/// Only the crossfaded portion (beginning of fadeout, beginning of fadein) is returned.
+pub fn crossfade<I1,I2>(input_fadeout: I1, input_fadein: I2, duration: Duration) -> Crossfade<I1,I2>
+where
+    I1: Source,
+    I2: Source,
+    I1::Item: Sample,
+    I2::Item: Sample,
+{
+    let mut input_fadeout = input_fadeout.take_duration(duration);
+    input_fadeout.set_filter_fadeout();
+    let input_fadein = input_fadein.take_duration(duration).fade_in(duration);
+    input_fadeout.mix(input_fadein)
+}
+
+pub type Crossfade<I1,I2> = Mix<TakeDuration<I1>,FadeIn<TakeDuration<I2>>>;
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use buffer::SamplesBuffer;
+    fn dummysource(length: u8) -> SamplesBuffer<f32> {
+        let data: Vec<f32> = (1 ..= length).map(f32::from).collect();
+        let source = SamplesBuffer::new(1, 1, data);
+        source
+    }
+
+    #[test]
+    fn test_crossfade() {
+        let source1 = dummysource(10);
+        let source2 = dummysource(10);
+        let mut mixed = crossfade(source1, source2, Duration::from_secs(5) + Duration::from_nanos(1));
+        assert_eq!(mixed.next(), Some(1.0));
+        assert_eq!(mixed.next(), Some(2.0));
+        assert_eq!(mixed.next(), Some(3.0));
+        assert_eq!(mixed.next(), Some(4.0));
+        assert_eq!(mixed.next(), Some(5.0));
+        assert_eq!(mixed.next(), None);
+
+        let source1 = dummysource(10);
+        let source2 = dummysource(10).amplify(0.0);
+        let mut mixed = crossfade(source1, source2, Duration::from_secs(5) + Duration::from_nanos(1));
+        assert_eq!(mixed.next(), Some(1.0 * 1.0));
+        assert_eq!(mixed.next(), Some(2.0 * 0.8));
+        assert_eq!(mixed.next(), Some(3.0 * 0.6));
+        assert_eq!(mixed.next(), Some(4.0 * 0.4));
+        assert_eq!(mixed.next(), Some(5.0 * 0.2));
+        assert_eq!(mixed.next(), None);
+    }
+}

src/source/mod.rs

@@ -8,6 +8,7 @@ pub use self::amplify::Amplify;
 pub use self::blt::BltFilter;
 pub use self::buffered::Buffered;
 pub use self::channel_volume::ChannelVolume;
+pub use self::crossfade::Crossfade;
 pub use self::delay::Delay;
 pub use self::done::Done;
 pub use self::empty::Empty;
@@ -31,6 +32,7 @@ mod amplify;
 mod blt;
 mod buffered;
 mod channel_volume;
+mod crossfade;
 mod delay;
 mod done;
 mod empty;
@@ -202,6 +204,18 @@ where
         amplify::amplify(self, value)
     }
 
+    /// Mixes this sound fading out with another sound fading in for the given duration.
+    ///
+    /// Only the crossfaded portion (beginning of self, beginning of other) is returned.
+    #[inline]
+    fn take_crossfade_with<S: Source>(self, other: S, duration: Duration) -> Crossfade<Self, S>
+    where
+        Self: Sized,
+        <S as Iterator>::Item: Sample,
+    {
+        crossfade::crossfade(self, other, duration)
+    }
+
     /// Fades in the sound.
     #[inline]
     fn fade_in(self, duration: Duration) -> FadeIn<Self>