Prevent needless clone in offline rendering + in the online happy path

Author: orottier

src/render/graph.rs

@@ -354,7 +354,7 @@ impl Graph {
     }
 
     /// Render a single audio quantum by traversing the node list
-    pub fn render(&mut self, scope: &RenderScope) -> AudioRenderQuantum {
+    pub fn render(&mut self, scope: &RenderScope) -> &AudioRenderQuantum {
         // if the audio graph was changed, determine the new ordering
         if self.ordered.is_empty() {
             self.order_nodes();
@@ -460,12 +460,12 @@ impl Graph {
         }
 
         // Return the output buffer of destination node
-        self.nodes
+        &self
+            .nodes
             .get_mut(&AudioNodeId(0))
             .unwrap()
             .get_mut()
             .outputs[0]
-            .clone()
     }
 }
 

src/render/thread.rs

@@ -1,5 +1,6 @@
 //! Communicates with the control thread and ships audio samples to the hardware
 
+use std::borrow::Cow;
 use std::cell::Cell;
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
@@ -257,12 +258,14 @@ impl RenderThread {
                 node_id: Cell::new(AudioNodeId(0)), // placeholder value
             };
 
-            // render audio graph
-            let mut rendered = self.graph.as_mut().unwrap().render(&scope);
+            // render audio graph, and use a Cow in case we need to mutate/store the value later
+            let mut rendered = Cow::Borrowed(self.graph.as_mut().unwrap().render(&scope));
 
             // online AudioContext allows channel count to be less than no of hardware channels
             if rendered.number_of_channels() != self.number_of_channels {
-                rendered.mix(self.number_of_channels, ChannelInterpretation::Discrete);
+                rendered
+                    .to_mut()
+                    .mix(self.number_of_channels, ChannelInterpretation::Discrete);
             }
 
             // copy rendered audio into output slice
@@ -279,7 +282,7 @@ impl RenderThread {
                 // this is the last chunk, and it contained less than RENDER_QUANTUM_SIZE samples
                 let channel_offset = data.len() / self.number_of_channels;
                 debug_assert!(channel_offset < RENDER_QUANTUM_SIZE);
-                self.buffer_offset = Some((channel_offset, rendered));
+                self.buffer_offset = Some((channel_offset, rendered.into_owned()));
             }
 
             // handle addition/removal of nodes/edges