feat(rivet): storyboard composition with flexible lengths and meters

Rivet 0.4.0 tells a motif as a story. A timeline of blocks with roles
(statement, answer, departure, return, rest) replaces tasks, pins and
branches. Rivet writes each block from a motif and joins the seams with
a cut, breath, pickup or approach.

- Motifs of 1-8 bars in a bin of 16; storyboards up to 32 bars.
- Meters 2/4, 3/4, 4/4, 5/4, 6/8, 7/8 and 12/8 for import, writing,
  audition and export. Phrygian, harmonic minor and Mixolydian scales.
- Per-block options, Another take and Keep; templates for new boards.
- Editor rebuilt: motif bin, timeline, large piano roll, inspector,
  tabs for generation, harmony and sound roles, 32-step undo/redo.
- Sessions from 0.1-0.3 open as a storyboard from their source motif.

plugins/rivet/preview/src/main.rs

@@ -1,5 +1,5 @@
 //! Headless end-to-end development harness; uses exactly the plugin's composition and voice.
-use rivet_core::{demo_motif, Harmony, Performance, PerformancePlayer, Session};
+use rivet_core::{Harmony, Performance, PerformancePlayer, Session, Template};
 use std::{env, fs, io::Write, path::PathBuf};
 
 fn main() {
@@ -11,13 +11,13 @@ fn main() {
 fn run() -> Result<(), Box<dyn std::error::Error>> {
     let args: Vec<_> = env::args().skip(1).collect();
     if args.is_empty() || args[0] == "--help" {
-        println!("Rivet preview\n  rivet-preview demo <output-directory>\n  rivet-preview develop <input.mid> <track-index> <output-directory> [harmony.mid harmony-track-index]\n  rivet-preview session <session.json> <output-directory>\nWrites source.mid, up to three distinct candidates, session.json, and selected.wav. Track indices start at 0.");
+        println!("Rivet preview\n  rivet-preview demo <output-directory>\n  rivet-preview develop <input.mid> <track-index> <output-directory> [harmony.mid harmony-track-index]\n  rivet-preview session <session.json> <output-directory>\nBuilds an arc storyboard from the motif (or uses the saved one) and writes motif.mid, storyboard.mid, session.json, and storyboard.wav. Track indices start at 0.");
         return Ok(());
     }
     let mut session = Session::default();
     let output = match args[0].as_str() {
         "demo" if args.len() == 2 => {
-            session.source = Some(demo_motif());
+            session = Session::demo();
             PathBuf::from(&args[1])
         }
         "session" if args.len() == 3 => {
@@ -25,62 +25,65 @@ fn run() -> Result<(), Box<dyn std::error::Error>> {
             PathBuf::from(&args[2])
         }
         "develop" if args.len() == 4 || args.len() == 6 => {
-            let bytes = fs::read(&args[1])?;
-            let file = rivet_midi::read(&bytes)?;
+            let file = rivet_midi::read(&fs::read(&args[1])?)?;
             let index: usize = args[2].parse()?;
             let track = file.tracks.get(index).ok_or("Track index out of range")?;
-            track.phrase.validate_source()?;
             for w in &track.warnings {
                 eprintln!("{w}");
             }
-            session.source = Some(track.phrase.clone());
+            session.settings.meter = file.meter.unwrap_or_default();
+            if args.len() == 6 {
+                let file = rivet_midi::read(&fs::read(&args[4])?)?;
+                let index: usize = args[5].parse()?;
+                let track = file
+                    .tracks
+                    .get(index)
+                    .ok_or("Harmony track index out of range")?;
+                session.harmony = Harmony::from_midi(&track.phrase.notes, track.phrase.length)?;
+            }
+            let id = session.add_motif(&track.name, track.phrase.clone())?;
+            session.apply_template(Template::Arc, id)?;
             PathBuf::from(&args[3])
         }
         _ => return Err("Use --help for usage.".into()),
     };
-    if args.len() == 6 {
-        let file = rivet_midi::read(&fs::read(&args[4])?)?;
-        let index: usize = args[5].parse()?;
-        let track = file
-            .tracks
-            .get(index)
-            .ok_or("Harmony track index out of range")?;
-        session.harmony = Harmony::from_midi(&track.phrase.notes, track.phrase.length)?;
-    }
-    if args[0] != "session" {
-        session.regenerate()?;
-        session.accept();
-    }
-    let selected = session.composed_phrase()?;
+    let meter = session.settings.meter;
+    let selected = session.compose()?;
     fs::create_dir_all(&output)?;
-    if let Some(source) = &session.source {
+    if let Some(motif) = session.motifs.first() {
         fs::write(
-            output.join("source.mid"),
-            rivet_midi::write(source, session.tempo)?,
+            output.join("motif.mid"),
+            rivet_midi::write(&motif.phrase, session.tempo, meter)?,
         )?;
     }
-    for (i, c) in session.candidates.iter().enumerate() {
-        fs::write(
-            output.join(format!("candidate-{}.mid", i + 1)),
-            rivet_midi::write_performance(&c.phrase, &session.performance, session.tempo)?,
-        )?;
-        println!("{}: {}", c.strategy.name(), c.explanation);
+    for (i, block) in session.blocks.iter().enumerate() {
+        let option = block.options.get(block.choice);
+        println!(
+            "{:>2}. {:<9} {} bars  {:<22} → {}",
+            i + 1,
+            block.role.name(),
+            block.bars,
+            option.map_or("(empty)", |c| c.strategy.name()),
+            block.join.name()
+        );
     }
     fs::write(output.join("session.json"), session.to_json()?)?;
     fs::write(
-        output.join("selected.mid"),
-        rivet_midi::write_performance(&selected, &session.performance, session.tempo)?,
+        output.join("storyboard.mid"),
+        rivet_midi::write_performance(&selected, &session.performance, session.tempo, meter)?,
     )?;
     let mut player = PerformancePlayer::default();
     player.set_sample_rate(44100.)?;
-    player
-        .play(Performance::compile(&selected, &session.performance, session.tempo, false)?.clip()?);
+    player.play(
+        Performance::compile(&selected, &session.performance, session.tempo, false, meter)?
+            .clip()?,
+    );
     let mut samples = Vec::new();
     while player.is_playing() {
         samples.push((player.next_frame(session.tempo).0 * i16::MAX as f32) as i16);
     }
     let len = (samples.len() * 2) as u32;
-    let mut wav = fs::File::create(output.join("selected.wav"))?;
+    let mut wav = fs::File::create(output.join("storyboard.wav"))?;
     wav.write_all(b"RIFF")?;
     wav.write_all(&(36 + len).to_le_bytes())?;
     wav.write_all(b"WAVEfmt ")?;