Feat: adding LPG

crates/forth/src/vm.rs

@@ -1481,6 +1481,22 @@ impl Forth {
                     stack.push(Value::Str(s.into(), None));
                 }
 
+                Op::Lpg => {
+                    let depth = pop_float(stack)?.clamp(0.0, 1.0);
+                    let max = pop_float(stack)?;
+                    let min = pop_float(stack)?;
+                    let effective_max = min + (max - min) * depth;
+                    let sd = ctx.step_duration();
+                    let a = cmd_param_float(cmd, "attack").unwrap_or(0.0) * sd;
+                    let d = cmd_param_float(cmd, "decay").unwrap_or(1.0) * sd;
+                    let s = cmd_param_float(cmd, "sustain").unwrap_or(0.0);
+                    let r = cmd_param_float(cmd, "release").unwrap_or(0.0) * sd;
+                    use std::fmt::Write;
+                    let mut mod_str = String::new();
+                    let _ = write!(&mut mod_str, "{min}^{effective_max}:{a}:{d}:{s}:{r}");
+                    cmd.set_param("lpf", Value::Str(mod_str.into(), None));
+                }
+
                 // MIDI operations
                 Op::MidiEmit => {
                     let (_, params) = cmd.snapshot().unwrap_or((None, &[]));
@@ -1726,6 +1742,14 @@ fn extract_dev_param(params: &[(&str, Value)]) -> u8 {
         .unwrap_or(0)
 }
 
+fn cmd_param_float(cmd: &CmdRegister, name: &str) -> Option<f64> {
+    cmd.params()
+        .iter()
+        .rev()
+        .find(|(k, _)| *k == name)
+        .and_then(|(_, v)| v.as_float().ok())
+}
+
 fn is_tempo_scaled_param(name: &str) -> bool {
     matches!(
         name,