Added file constant_node.rs with gain_node code

audio/src/constant_source.rs

@@ -0,0 +1,70 @@
+use block::Chunk;
+use block::Tick;
+use node::AudioNodeEngine;
+use node::BlockInfo;
+use node::{AudioNodeType, ChannelInfo};
+use param::{Param, ParamType};
+
+#[derive(Copy, Clone, Debug)]
+pub struct GainNodeOptions {
+    pub gain: f32,
+}
+
+impl Default for GainNodeOptions {
+    fn default() -> Self {
+        GainNodeOptions { gain: 1. }
+    }
+}
+
+#[derive(AudioNodeCommon)]
+pub(crate) struct GainNode {
+    channel_info: ChannelInfo,
+    gain: Param,
+}
+
+impl GainNode {
+    pub fn new(options: GainNodeOptions, channel_info: ChannelInfo) -> Self {
+        Self {
+            channel_info,
+            gain: Param::new(options.gain),
+        }
+    }
+
+    pub fn update_parameters(&mut self, info: &BlockInfo, tick: Tick) -> bool {
+        self.gain.update(info, tick)
+    }
+}
+
+impl AudioNodeEngine for GainNode {
+    fn node_type(&self) -> AudioNodeType {
+        AudioNodeType::GainNode
+    }
+
+    fn process(&mut self, mut inputs: Chunk, info: &BlockInfo) -> Chunk {
+        debug_assert!(inputs.len() == 1);
+
+        if inputs.blocks[0].is_silence() {
+            return inputs;
+        }
+
+        {
+            let mut iter = inputs.blocks[0].iter();
+            let mut gain = self.gain.value();
+
+            while let Some(mut frame) = iter.next() {
+                if self.update_parameters(info, frame.tick()) {
+                    gain = self.gain.value();
+                }
+                frame.mutate_with(|sample, _| *sample = *sample * gain);
+            }
+        }
+        inputs
+    }
+
+    fn get_param(&mut self, id: ParamType) -> &mut Param {
+        match id {
+            ParamType::Gain => &mut self.gain,
+            _ => panic!("Unknown param {:?} for GainNode", id),
+        }
+    }
+}