Use the plugin's default channels for standalones

BREAKING_CHANGES.md

@@ -12,6 +12,8 @@ code then it will not be listed here.
   renamed to `Plugin::DEFAULT_INPUT_CHANNELS` and
   `Plugin::DEFAULT_OUTPUT_CHANNELS` respectively to avoid confusion as these
   constants only affect the main input and output.
+- Standalones now use the plugin's default input and output channel counts
+  instead of always defaulting to two inputs and two outputs.
 
 ## [2022-07-18]
 

src/wrapper/standalone.rs

@@ -77,7 +77,7 @@ pub fn nih_export_standalone_with_args<P: Plugin, Args: IntoIterator<Item = Stri
             }
             Err(_) => {
                 nih_log!("Could not initialize JACK, falling back to the dummy audio backend");
-                run_wrapper::<P, _>(backend::Dummy::new(config.clone()), config)
+                run_wrapper::<P, _>(backend::Dummy::new::<P>(config.clone()), config)
             }
         },
         config::BackendType::Jack => match backend::Jack::new::<P>(config.clone()) {
@@ -88,7 +88,7 @@ pub fn nih_export_standalone_with_args<P: Plugin, Args: IntoIterator<Item = Stri
             }
         },
         config::BackendType::Dummy => {
-            run_wrapper::<P, _>(backend::Dummy::new(config.clone()), config)
+            run_wrapper::<P, _>(backend::Dummy::new::<P>(config.clone()), config)
         }
     }
 }
@@ -114,12 +114,13 @@ fn run_wrapper<P: Plugin, B: Backend>(backend: B, config: WrapperConfig) -> bool
 
 fn print_error(error: WrapperError, config: &WrapperConfig) {
     match error {
-        WrapperError::IncompatibleConfig => {
+        WrapperError::IncompatibleConfig {
+            input_channels,
+            output_channels,
+        } => {
             nih_error!(
-                "The plugin does not support the {} channel input and {} channel output \
-                 configuration",
-                config.input_channels,
-                config.output_channels
+                "The plugin does not support the {input_channels} channel input and \
+                 {output_channels} channel output configuration",
             );
         }
         WrapperError::InitializationFailed => {

src/wrapper/standalone/backend/dummy.rs

@@ -5,12 +5,14 @@ use super::Backend;
 use crate::buffer::Buffer;
 use crate::context::Transport;
 use crate::midi::NoteEvent;
+use crate::plugin::{AuxiliaryIOConfig, BusConfig, Plugin};
 
 /// This backend doesn't input or output any audio or MIDI. It only exists so the standalone
 /// application can continue to run even when there is no audio backend available. This can be
 /// useful for testing plugin GUIs.
 pub struct Dummy {
     config: WrapperConfig,
+    bus_config: BusConfig,
 }
 
 impl Backend for Dummy {
@@ -27,7 +29,7 @@ impl Backend for Dummy {
 
         let mut channels = vec![
             vec![0.0f32; self.config.period_size as usize];
-            self.config.output_channels as usize
+            self.bus_config.num_output_channels as usize
         ];
         let mut buffer = Buffer::default();
         unsafe {
@@ -71,7 +73,16 @@ impl Backend for Dummy {
 }
 
 impl Dummy {
-    pub fn new(config: WrapperConfig) -> Self {
-        Self { config }
+    pub fn new<P: Plugin>(config: WrapperConfig) -> Self {
+        Self {
+            bus_config: BusConfig {
+                num_input_channels: config.input_channels.unwrap_or(P::DEFAULT_INPUT_CHANNELS),
+                num_output_channels: config.output_channels.unwrap_or(P::DEFAULT_OUTPUT_CHANNELS),
+                // TODO: Support these in the standalone
+                aux_input_busses: AuxiliaryIOConfig::default(),
+                aux_output_busses: AuxiliaryIOConfig::default(),
+            },
+            config,
+        }
     }
 }

src/wrapper/standalone/backend/jack.rs

@@ -188,7 +188,8 @@ impl Jack {
         }
 
         let mut inputs = Vec::new();
-        for port_no in 1..config.input_channels + 1 {
+        let num_input_channels = config.input_channels.unwrap_or(P::DEFAULT_INPUT_CHANNELS);
+        for port_no in 1..num_input_channels + 1 {
             inputs.push(client.register_port(&format!("input_{port_no}"), AudioIn)?);
         }
 
@@ -196,7 +197,8 @@ impl Jack {
         // no. So the connections are made just after activating the client in the `run()` function
         // above.
         let mut outputs = Vec::new();
-        for port_no in 1..config.output_channels + 1 {
+        let num_output_channels = config.output_channels.unwrap_or(P::DEFAULT_OUTPUT_CHANNELS);
+        for port_no in 1..num_output_channels + 1 {
             outputs.push(client.register_port(&format!("output_{port_no}"), AudioOut)?);
         }
 

src/wrapper/standalone/config.rs

@@ -11,12 +11,15 @@ pub struct WrapperConfig {
     #[clap(value_parser, short = 'b', long, default_value = "auto")]
     pub backend: BackendType,
 
+    // These will default to the plugin's default input and output channel count. We could set the
+    // default value here to match those, but that would require a custom Args+FromArgMatches
+    // implementation and access to the `Plugin` type.
     /// The number of input channels.
-    #[clap(value_parser, short = 'i', long, default_value = "2")]
-    pub input_channels: u32,
+    #[clap(value_parser, short = 'i', long)]
+    pub input_channels: Option<u32>,
     /// The number of output channels.
-    #[clap(value_parser, short = 'o', long, default_value = "2")]
-    pub output_channels: u32,
+    #[clap(value_parser, short = 'o', long)]
+    pub output_channels: Option<u32>,
     /// The audio backend's sample rate.
     ///
     /// This setting is ignored when using the JACK backend.

src/wrapper/standalone/wrapper.rs

@@ -75,7 +75,10 @@ pub struct Wrapper<P: Plugin, B: Backend> {
 #[derive(Debug, Clone, Copy)]
 pub enum WrapperError {
     /// The plugin does not accept the IO configuration from the config.
-    IncompatibleConfig,
+    IncompatibleConfig {
+        input_channels: u32,
+        output_channels: u32,
+    },
     /// The plugin returned `false` during initialization.
     InitializationFailed,
 }
@@ -174,8 +177,8 @@ impl<P: Plugin, B: Backend> Wrapper<P, B> {
             editor,
 
             bus_config: BusConfig {
-                num_input_channels: config.input_channels,
-                num_output_channels: config.output_channels,
+                num_input_channels: config.input_channels.unwrap_or(P::DEFAULT_INPUT_CHANNELS),
+                num_output_channels: config.output_channels.unwrap_or(P::DEFAULT_OUTPUT_CHANNELS),
                 // TODO: Expose additional sidechain IO in the JACK backend
                 aux_input_busses: AuxiliaryIOConfig::default(),
                 aux_output_busses: AuxiliaryIOConfig::default(),
@@ -199,7 +202,10 @@ impl<P: Plugin, B: Backend> Wrapper<P, B> {
         {
             let mut plugin = wrapper.plugin.write();
             if !plugin.accepts_bus_config(&wrapper.bus_config) {
-                return Err(WrapperError::IncompatibleConfig);
+                return Err(WrapperError::IncompatibleConfig {
+                    input_channels: wrapper.bus_config.num_input_channels,
+                    output_channels: wrapper.bus_config.num_output_channels,
+                });
             }
 
             // Befure initializing the plugin, make sure all smoothers are set the the default values