Fix: do not upmix inputs to the AudioNode channelCount beforehand

The upmixing will happen when the inputs are mixed together, and only
when needed. This prevent unnecessary upmixes to stereo for many nodes
with channelCountMode Max and ClampedMax.

Author: orottier

src/node/biquad_filter.rs

@@ -649,7 +649,11 @@ impl AudioProcessor for BiquadFilterRenderer {
         };
 
         for (channel_number, output_channel) in output.channels_mut().iter_mut().enumerate() {
-            let input_channel = input.channel_data(channel_number);
+            let input_channel = if input.is_silent() {
+                input.channel_data(0)
+            } else {
+                input.channel_data(channel_number)
+            };
             // retrieve state from previous block
             let mut x1 = self.x1[channel_number];
             let mut x2 = self.x2[channel_number];

src/node/panner.rs

@@ -1142,7 +1142,6 @@ mod tests {
         let panner = PannerNode::new(&context, options);
         assert_eq!(panner.panning_model(), PanningModelType::EqualPower);
         panner.position_y().set_value(1.); // sound comes from above
-        panner.set_channel_count(1);
 
         src.connect(&panner);
         panner.connect(&context.destination());
@@ -1181,8 +1180,11 @@ mod tests {
         listener.up_y().set_value(0.);
         listener.up_z().set_value(1.);
 
-        // 128 input samples of value 1.
-        let input = AudioBuffer::from(vec![vec![1.; RENDER_QUANTUM_SIZE]], sample_rate);
+        // 128 input samples of value 1, stereo
+        let input = AudioBuffer::from(
+            vec![vec![1.; RENDER_QUANTUM_SIZE], vec![1.; RENDER_QUANTUM_SIZE]],
+            sample_rate,
+        );
         let mut src = AudioBufferSourceNode::new(&context, AudioBufferSourceOptions::default());
         src.set_buffer(input);
         src.start();

src/render/graph.rs

@@ -417,14 +417,6 @@ impl Graph {
             // acquire a mutable borrow of the current processing node
             let mut node = nodes[*index].borrow_mut();
 
-            // make sure all input buffers have the correct number of channels, this might not be
-            // the case if the node has no inputs connected or the channel count has just changed
-            let interpretation = node.channel_config.interpretation();
-            let count = node.channel_config.count();
-            node.inputs
-                .iter_mut()
-                .for_each(|i| i.mix(count, interpretation));
-
             // let the current node process (catch any panics that may occur)
             let params = AudioParamValues::from(nodes);
             scope.node_id.set(*index);

tests/mixing.rs

@@ -93,7 +93,7 @@ fn test_stereo_to_discrete_stereo() {
 
     assert_eq!(output.number_of_channels(), 2);
     assert_float_eq!(output.get_channel_data(0), ONES, abs_all <= 0.);
-    assert_float_eq!(output.get_channel_data(1), ONES, abs_all <= 0.);
+    assert_float_eq!(output.get_channel_data(1), ZEROES, abs_all <= 0.);
 }
 
 #[test]