Provide SignalProcessing methods to the Lua script

This is accomplished by providing a wrapped reference to the
SignalProcessing instance of the Rust program as a global Lua variable.
The wrapper class implements mlua::UserData, wraps the relevant
SignalProcessing methods and provides them as Lua methods.

So far, this is implemented for get_energy_in_band() only.

src/main.rs

@@ -12,25 +12,29 @@ mod userscript;
 use crate::signal_processing::SignalProcessing;
 use crate::userscript::UserScript;
 
+use std::rc::Rc;
+use std::cell::RefCell;
+
 fn main()
 {
 	let mut stdin = std::io::stdin();
 
-	// set up Lua environment
-
-	println!("Loading user script...");
-
-	let script = UserScript::new("test.lua").unwrap();
-
-	println!("Calling init()...");
-
-	script.init().unwrap();
-
 	// set up signal processing
 
 	println!("Initializing signal processing...");
 
-	let mut sigproc = SignalProcessing::new(config::BLOCK_LEN, config::SAMP_RATE).unwrap();
+	let sigproc = Rc::new(RefCell::new(
+	                  SignalProcessing::new(config::BLOCK_LEN, config::SAMP_RATE).unwrap()));
+
+	// set up Lua environment
+
+	println!("Loading user script...");
+
+	let script = UserScript::new(sigproc.clone(), "test.lua").unwrap();
+
+	println!("Calling init()...");
+
+	script.init().unwrap();
 
 	println!("Done! Starting main loop…");
 
@@ -67,12 +71,15 @@ fn main()
 		}
 
 
-		sigproc.import_i16_mono_from_iter(samples.iter()).unwrap();
-		sigproc.update_fft().unwrap();
+		{
+			let mut s = sigproc.borrow_mut();
+			s.import_i16_mono_from_iter(samples.iter()).unwrap();
+			s.update_fft().unwrap();
+		}
 
-		let energy_bass   = sigproc.get_energy_in_band(   0.0,  400.0);
-		let energy_mid    = sigproc.get_energy_in_band( 400.0, 4000.0);
-		let energy_treble = sigproc.get_energy_in_band(4000.0, config::SAMP_RATE/2.0);
+		let energy_bass   = sigproc.borrow().get_energy_in_band(   0.0,  400.0);
+		let energy_mid    = sigproc.borrow().get_energy_in_band( 400.0, 4000.0);
+		let energy_treble = sigproc.borrow().get_energy_in_band(4000.0, config::SAMP_RATE/2.0);
 
 		// dump the output
 		println!("Bass: {:11.2} – Mid: {:11.2} – Treble: {:11.2}", energy_bass, energy_mid, energy_treble);

src/userscript.rs

@@ -21,11 +21,15 @@
 */
 
 use crate::config;
+use crate::signal_processing::SignalProcessing;
 
 use mlua::Lua;
 use mlua::FromLua;
 use mlua::Error;
 
+use std::rc::Rc;
+use std::cell::RefCell;
+
 pub struct UserScript
 {
 	lua_state: Lua,
@@ -33,12 +37,26 @@ pub struct UserScript
 
 impl UserScript
 {
-	pub fn new(user_script_path: &str) -> std::result::Result<UserScript, mlua::Error>
+	pub fn new(sigproc: Rc<RefCell<SignalProcessing>>, user_script_path: &str) -> std::result::Result<UserScript, mlua::Error>
 	{
 		let s = UserScript {
 			lua_state: Lua::new(),
 		};
 
+		// provide some configuration constants to Lua via a table
+		let config_table = s.lua_state.create_table()?;
+
+		config_table.set("sampling_rate", config::SAMP_RATE)?;
+		config_table.set("block_length", config::BLOCK_LEN)?;
+		config_table.set("samples_per_update", config::SAMPLES_PER_UPDATE)?;
+
+		s.lua_state.globals().set("CONFIG", config_table)?;
+
+		// register the signal processing reference as Lua user data
+		s.lua_state.globals().set("sigproc", SignalProcessingWrapper{
+			signal_processing: sigproc
+		})?;
+
 		// load the user script and execute it to make variables and functions available
 		let user_script = std::fs::read_to_string(user_script_path)?;
 		s.lua_state.load(&user_script).exec()?;
@@ -93,3 +111,23 @@ impl UserScript
 		Ok(())
 	}
 }
+
+
+/*
+ * Wrap a SignalProcessing instance and provide a Lua interface for some of its methods.
+ */
+struct SignalProcessingWrapper
+{
+	signal_processing: Rc<RefCell<SignalProcessing>>,
+}
+
+impl mlua::UserData for SignalProcessingWrapper
+{
+	fn add_methods<'lua, M: mlua::UserDataMethods<'lua, Self>>(methods: &mut M)
+	{
+		methods.add_method("get_energy_in_band", |_, this, (start_freq, end_freq): (f32, f32)| {
+			Ok(this.signal_processing.borrow().get_energy_in_band(start_freq, end_freq))
+		});
+	}
+}
+