Add a processing status for handling reverb tails

plugins/gain/src/lib.rs

@@ -19,7 +19,7 @@ extern crate nih_plug;
 
 use nih_plug::{
     params::{FloatParam, Params, Range},
-    plugin::{BufferConfig, BusConfig, Plugin},
+    plugin::{BufferConfig, BusConfig, Plugin, ProcessStatus},
     util,
 };
 use std::pin::Pin;
@@ -88,9 +88,9 @@ impl Plugin for Gain {
         true
     }
 
-    fn process(&mut self, samples: &mut [&mut [f32]]) {
+    fn process(&mut self, samples: &mut [&mut [f32]]) -> ProcessStatus {
         if samples.is_empty() {
-            return;
+            return ProcessStatus::Error("Empty buffers");
         }
 
         // TODO: The wrapper should set FTZ if not yet enabled, mention ths in the process fuctnion
@@ -100,7 +100,7 @@ impl Plugin for Gain {
         for channel in &samples[1..] {
             nih_debug_assert_eq!(channel.len(), num_samples);
             if channel.len() != num_samples {
-                return;
+                return ProcessStatus::Error("Mismatching channel buffer sizes");
             }
         }
 
@@ -116,6 +116,8 @@ impl Plugin for Gain {
                 *sample *= util::db_to_gain(self.params.gain.value);
             }
         }
+
+        ProcessStatus::Normal
     }
 }
 

src/plugin.rs

@@ -88,12 +88,12 @@ pub trait Plugin: Default + Sync {
     /// TODO: &mut [&mut [f32]] may not be the correct type here
     /// TODO: Provide a way to access auxiliary input channels if the IO configuration is
     ///       assymetric
-    /// TODO: Add a process result to handle tails
     /// TODO: Handle FTZ stuff on the wrapper side and mention that this has been handled
-    fn process(&mut self, samples: &mut [&mut [f32]]);
+    fn process(&mut self, samples: &mut [&mut [f32]]) -> ProcessStatus;
 }
 
 /// We only support a single main input and output bus at the moment.
+#[derive(Debug, PartialEq, Eq)]
 pub struct BusConfig {
     /// The number of input channels for the plugin.
     pub num_input_channels: u32,
@@ -102,6 +102,7 @@ pub struct BusConfig {
 }
 
 /// Configuration for (the host's) audio buffers.
+#[derive(Debug, PartialEq)]
 pub struct BufferConfig {
     /// The current sample rate.
     pub sample_rate: f32,
@@ -109,3 +110,19 @@ pub struct BufferConfig {
     /// sized buffers up to this size.
     pub max_buffer_size: u32,
 }
+
+/// Indicates the current situation after the plugin has processed audio.
+#[derive(Debug, PartialEq, Eq)]
+pub enum ProcessStatus {
+    /// Something went wrong while processing audio.
+    Error(&'static str),
+    /// The plugin has finished processing audio. When the input is silent, the most may suspend the
+    /// plugin to save resources as it sees fit.
+    Normal,
+    /// The plugin has a (reverb) tail with a specific length in samples.
+    Tail(u32),
+    /// This plugin will continue to produce sound regardless of whether or not the input is silent,
+    /// and should thus not be deactivated by the host. This is essentially the same as having an
+    /// infite tail.
+    KeepAlive,
+}