Implement AudioWorkletNode message passing from render to control

Author: orottier

examples/worklet_message_port.rs

@@ -75,7 +75,7 @@ impl AudioWorkletProcessor for WhiteNoiseProcessor {
         _inputs: &'b [&'a [&'a [f32]]],
         outputs: &'b mut [&'a mut [&'a mut [f32]]],
         _params: AudioParamValues<'_>,
-        _scope: &RenderScope,
+        scope: &RenderScope,
     ) -> bool {
         // edit the output buffer in place
         outputs[0].iter_mut().for_each(|buf| {
@@ -93,6 +93,10 @@ impl AudioWorkletProcessor for WhiteNoiseProcessor {
             })
         });
 
+        if scope.current_frame % 12800 == 0 {
+            scope.post_message(Box::new(scope.current_frame));
+        }
+
         true // tail time, source node will always be active
     }
 
@@ -125,6 +129,12 @@ fn main() {
     // connect to speakers
     noise.node().connect(&context.destination());
 
+    // add event handling for the heartbeat events from the render thread
+    noise.node().port().set_onmessage(|m| {
+        let frame = m.downcast::<u64>().unwrap();
+        println!("rendered frame {frame}");
+    });
+
     // enjoy listening
     println!("White noise");
     std::thread::sleep(std::time::Duration::from_secs(2));

src/render/processor.rs

@@ -38,6 +38,18 @@ impl std::fmt::Debug for RenderScope {
 }
 
 impl RenderScope {
+    /// Send a message to the corresponding AudioWorkletNode of this processor
+    ///
+    /// This method is just a shim of the full
+    /// [`MessagePort`](https://webaudio.github.io/web-audio-api/#dom-audioworkletprocessor-port)
+    /// `onmessage` functionality of the AudioWorkletProcessor.
+    pub fn post_message(&self, msg: Box<dyn Any + Send + 'static>) {
+        if let Some(sender) = self.event_sender.as_ref() {
+            // sending could fail if the channel is saturated or the main thread is shutting down
+            let _ = sender.try_send(EventDispatch::message(self.node_id.get(), msg));
+        }
+    }
+
     pub(crate) fn send_ended_event(&self) {
         if let Some(sender) = self.event_sender.as_ref() {
             // sending could fail if the channel is saturated or the main thread is shutting down