wip: refactor pt.6, fixed tek_api

crates/tek_api/src/voice.rs

@@ -8,3 +8,23 @@ pub struct Voice {
     pub position: usize,
     pub velocity: f32,
 }
+
+impl Iterator for Voice {
+    type Item = [f32;2];
+    fn next (&mut self) -> Option<Self::Item> {
+        if self.after > 0 {
+            self.after = self.after - 1;
+            return Some([0.0, 0.0])
+        }
+        let sample = self.sample.read().unwrap();
+        if self.position < sample.end {
+            let position = self.position;
+            self.position = self.position + 1;
+            return sample.channels[0].get(position).map(|_amplitude|[
+                sample.channels[0][position] * self.velocity,
+                sample.channels[0][position] * self.velocity,
+            ])
+        }
+        None
+    }
+}