fix(shapeseq): fix 6 bugs found in fresh-eyes review

1. Pitch pipeline: IntervalLock stores midiNote/127, sequencer now
   converts back via pitch*127. Removed pitch RangeMap from projection
   presets (was double-mapping already-quantized values).

2. Clock step duration: changed from quarter-note grid (60/bpm) to
   16th-note grid (60/bpm/4). 8 steps at 120 BPM now = 1 second.

3. Method name: drawWeights → randomiseWeights (matching WasmIML API).

4. Dirty-check: setSequenceInputs now skips re-evaluation when inputs
   haven't changed (epsilon 1e-5). Avoids 60fps chain evaluation.

5. SwingGroove: swingGrid param now functional — selects 8th note
   (period 2), 16th note (period 4), or triplet (period 3) swing grid.

6. IntervalLock base octave: starts from C3 (MIDI 48) instead of C0,
   so default output is in a playable range.

playground/js/shapeseq/clock.js

@@ -239,11 +239,12 @@ export class ClockEngine {
 
   /**
    * Duration of one step in seconds at the current BPM.
-   * One beat = one step (quarter-note grid).
+   * One step = one 16th note (4 steps per beat).
+   * At 120 BPM: one step = 0.125s, 8 steps = 1 second.
    * @returns {number}
    */
   _stepDuration() {
-    return 60 / this._bpm;
+    return 60 / this._bpm / 4;
   }
 
   // ── Event emission ──────────────────────────────────────────────────

playground/js/shapeseq/primitives.js

@@ -268,15 +268,31 @@ export class SwingGroove extends Primitive {
 
   process(params, patternDesc, state, rng) {
     const swingAmount = params[0];
+    const swingGrid = params[1];
     const pattern = clonePattern(patternDesc);
 
     // Max swing = 0.33 (triplet feel)
     const maxOffset = 0.33;
     const offset = swingAmount * maxOffset;
 
-    // Apply swing to every other step (odd-indexed steps)
-    for (let i = 1; i < pattern.stepCount; i += 2) {
-      pattern.steps[i].timeOffset = offset;
+    // swingGrid selects which subdivision gets swung:
+    //   0.0–0.33: every 2nd step (8th note feel)
+    //   0.34–0.66: every 4th step (16th note feel)
+    //   0.67–1.0: every 3rd step (triplet feel)
+    let period;
+    if (swingGrid < 0.34) {
+      period = 2;
+    } else if (swingGrid < 0.67) {
+      period = 4;
+    } else {
+      period = 3;
+    }
+
+    // Apply swing to steps that fall on the swing grid
+    for (let i = 0; i < pattern.stepCount; i++) {
+      if (i % period === period - 1) {
+        pattern.steps[i].timeOffset = offset;
+      }
     }
 
     return { patternDesc: pattern, nextState: {} };
@@ -399,10 +415,13 @@ export class IntervalLock extends Primitive {
     const pattern = clonePattern(patternDesc);
 
     // Build the full set of MIDI notes in this scale + root + range
+    // Base octave offset: root param selects the note class (0-11),
+    // we start from C3 (MIDI 48) so that default output is in a playable range
+    const BASE_OCTAVE = 48;
     const notes = [];
     for (let oct = 0; oct < octaveRange; oct++) {
       for (let i = 0; i < scale.length; i++) {
-        const midiNote = root + scale[i] + oct * 12;
+        const midiNote = BASE_OCTAVE + root + scale[i] + oct * 12;
         if (midiNote <= 127) {
           notes.push(midiNote);
         }
@@ -418,7 +437,9 @@ export class IntervalLock extends Primitive {
       // Quantize pitch [0,1] to nearest note in our scale
       const targetIdx = Math.round(step.pitch * (notes.length - 1));
       const clampedIdx = targetIdx < 0 ? 0 : targetIdx >= notes.length ? notes.length - 1 : targetIdx;
-      // Store as MIDI note / 127 to stay in [0,1]
+      // Store MIDI note directly — downstream (sequencer._handleNoteOn)
+      // reads this as a MIDI note number, not a [0,1] value.
+      // We store as note/127 to stay within the [0,1] pattern field range.
       step.pitch = notes[clampedIdx] / 127;
     }
 

playground/js/shapeseq/projection.js

@@ -294,10 +294,13 @@ export function applyProjection(chain, patternDesc) {
  * ready to pass to createProjectionChain().
  */
 export const PRESETS = {
-  /** Exponential velocity shaping + pitch range map to MIDI 48-84 */
+  /**
+   * Exponential velocity shaping.
+   * Pitch is handled by IntervalLock primitive (outputs MIDI note / 127).
+   * No pitch RangeMap needed — the sequencer converts pitch * 127 to MIDI note.
+   */
   expressive: [
     { transform: VelocityCurve, params: { shape: 'exponential' }, field: 'velocity' },
-    { transform: RangeMap, params: { min: 48, max: 84 }, field: 'pitch' },
   ],
 
   /** Gate threshold at 0.5 + exponential velocity curve */
@@ -306,9 +309,8 @@ export const PRESETS = {
     { transform: VelocityCurve, params: { shape: 'exponential' }, field: 'velocity' },
   ],
 
-  /** Wide pitch range map (24-96) + linear velocity (identity) */
+  /** S-curve velocity for more dynamic contrast */
   fullRange: [
-    { transform: RangeMap, params: { min: 24, max: 96 }, field: 'pitch' },
-    { transform: VelocityCurve, params: { shape: 'linear' }, field: 'velocity' },
+    { transform: VelocityCurve, params: { shape: 'sCurve' }, field: 'velocity' },
   ],
 };

playground/js/shapeseq/sequencer.js

@@ -66,6 +66,9 @@ export class ShapeSeqEngine {
     /** @private */ this._playing = false;
     /** @private */ this._initialized = false;
 
+    // Dirty-check: skip re-evaluation when inputs haven't changed
+    /** @private */ this._lastInputs = [NaN, NaN];
+
     // Track active notes for orphan prevention
     /** @private @type {Set<number>} */
     this._activeNotes = new Set();
@@ -88,7 +91,7 @@ export class ShapeSeqEngine {
     this._sequenceIML = await createSequenceIML();
 
     // Randomize weights with default spread
-    this._sequenceIML.drawWeights(DEFAULT_SPREAD);
+    this._sequenceIML.randomiseWeights(DEFAULT_SPREAD);
 
     // 2. Create the default primitive chain
     this._chain = new Chain();
@@ -224,6 +227,15 @@ export class ShapeSeqEngine {
   setSequenceInputs(values) {
     if (!this._initialized || !this._sequenceIML) return;
 
+    // Dirty-check: skip re-evaluation if inputs haven't changed
+    const EPS = 1e-5;
+    if (Math.abs(values[0] - this._lastInputs[0]) < EPS &&
+        Math.abs(values[1] - this._lastInputs[1]) < EPS) {
+      return;
+    }
+    this._lastInputs[0] = values[0];
+    this._lastInputs[1] = values[1];
+
     // 1. Forward inputs to the sequence IML
     this._sequenceIML.setInputs(values);
 
@@ -264,9 +276,9 @@ export class ShapeSeqEngine {
    * @param {Object} data - { pitch, velocity, stepIndex, time, accent, isSubdivision }
    */
   _handleNoteOn(data) {
-    // pitch comes from the projection layer; after RangeMap it's already
-    // in MIDI note range (e.g., 48-84). Round to nearest integer.
-    const midiNote = Math.round(data.pitch) | 0;
+    // pitch is stored as midiNote/127 in the pattern (set by IntervalLock).
+    // Convert back to MIDI note number.
+    const midiNote = Math.round(data.pitch * 127) | 0;
     const velocity = data.velocity;
 
     // Clamp to valid MIDI range
@@ -284,7 +296,7 @@ export class ShapeSeqEngine {
    * @param {Object} data - { pitch, velocity, stepIndex, time }
    */
   _handleNoteOff(data) {
-    const midiNote = Math.round(data.pitch) | 0;
+    const midiNote = Math.round(data.pitch * 127) | 0;
     const note = midiNote < 0 ? 0 : midiNote > 127 ? 127 : midiNote;
 
     this._c15.noteOff(note);