Initial non-zero global beat counter start support

 * Revamp + modernize MIDI editor scheduling
   * Delete local tempo scheduling mode.  Always start global beat counter when play button is pressed.
   * Add support for non-zero start time
 * Event scheduler/global beat counter changes to support non-zero start time
   * Update cbs to take start time
   * Update internal state to keep track of global beat counter position even when playback isn't active
   * Sync cursor position with global beat counter position, main thread -> audio thread
 * Existing MIDI editor scheduling seems to be working in both loop and oneshot mode

public/EventSchedulerWorkletProcessor.js

@@ -88,7 +88,7 @@ class EventSchedulerWorkletProcessor extends AudioWorkletProcessor {
     globalThis.curBeat = 0;
     if (typeof SharedArrayBuffer !== 'undefined') {
       this.beatManagerSABInner = new SharedArrayBuffer(1024);
-      this.beatManagerSAB = new Float32Array(this.beatManagerSABInner);
+      this.beatManagerSAB = new Float64Array(this.beatManagerSABInner);
     }
     this.port.postMessage({ type: 'beatManagerSAB', beatManagerSAB: this.beatManagerSAB });
 
@@ -108,7 +108,7 @@ class EventSchedulerWorkletProcessor extends AudioWorkletProcessor {
             break;
           }
 
-          globalThis.curBeat = 0;
+          globalThis.curBeat = event.data.startBeat;
           this.lastRecordedTime = currentTime;
           globalThis.globalBeatCounterStarted = true;
           this.isStarted = true;
@@ -120,7 +120,6 @@ class EventSchedulerWorkletProcessor extends AudioWorkletProcessor {
             break;
           }
 
-          globalThis.curBeat = 0;
           globalThis.globalBeatCounterStarted = false;
           this.wasmInstance.exports.stop();
           this.isStarted = false;
@@ -281,6 +280,9 @@ class EventSchedulerWorkletProcessor extends AudioWorkletProcessor {
 
   updateGlobalBeats(globalTempoBPM) {
     globalThis.globalTempoBPM = globalTempoBPM;
+    if (this.beatManagerSAB) {
+      globalThis.curBeat = this.beatManagerSAB[0];
+    }
 
     if (this.isStarted) {
       const passedTime = currentTime - this.lastRecordedTime;

src/eventScheduler/eventScheduler.ts

@@ -55,7 +55,7 @@ const registerCb = (cb: () => void): number => {
 
 export const cancelCb = (cbId: number) => RegisteredCbs.delete(cbId);
 
-let StartCBs: (() => void)[] = [];
+let StartCBs: ((startBeat: number) => void)[] = [];
 let StopCBs: (() => void)[] = [];
 let isStarted = false;
 let lastStartTime = 0;
@@ -65,14 +65,14 @@ export const getIsGlobalBeatCounterStarted = (): boolean => isStarted;
 /**
  * Registers a callback to be called when the global beat counter is started
  */
-export const registerGlobalStartCB = (cb: () => void) => StartCBs.push(cb);
+export const registerGlobalStartCB = (cb: (startBeat: number) => void) => StartCBs.push(cb);
 
 /**
  * Registers a callback to be called when the global beat counter is stopped
  */
 export const registerGlobalStopCB = (cb: () => void) => StopCBs.push(cb);
 
-export const unregisterStartCB = (cb: () => void) => {
+export const unregisterStartCB = (cb: (startBeat: number) => void) => {
   StartCBs = StartCBs.filter(ocb => ocb !== cb);
 };
 
@@ -99,12 +99,15 @@ export const useIsGlobalBeatCounterStarted = () => {
 };
 
 /**
- * Starts the global beat counter loop, resetting the current beat to zero.  Until this is called, no
- * events will be processed and the global current beat will remain at zero.
+ * Starts the global beat counter loop, resetting the current beat to the specified beat or
+ * zero if not provided.
+ *
+ * Until this is called, no events will be processed and the global current beat will remain
+ * at zero (or the last beat it reached before being stopped).
  *
  * Triggers all callbacks registered with `addStartCB` to be called.
  */
-export const startAll = () => {
+export const startAll = (startBeat = 0) => {
   if (isStarted) {
     console.warn("Tried to start global beat counter, but it's already started");
     return;
@@ -115,8 +118,8 @@ export const startAll = () => {
 
   isStarted = true;
   lastStartTime = ctx.currentTime;
-  SchedulerHandle.port.postMessage({ type: 'start' });
-  scheduleEventBeats(0, () => StartCBs.forEach(cb => cb()));
+  SchedulerHandle.port.postMessage({ type: 'start', startBeat });
+  scheduleEventBeats(0, () => StartCBs.forEach(cb => cb(startBeat)));
 };
 
 /**
@@ -152,7 +155,7 @@ const callCb = (cbId: number) => {
   cb();
 };
 
-let beatManagerSAB: Float32Array | null = null;
+let beatManagerSAB: Float64Array | null = null;
 
 /**
  * Returns the current beat of the global beat counter.  This value is updated directly from the web audio rendering thread
@@ -165,6 +168,24 @@ export const getCurBeat = (): number => {
   return beatManagerSAB[0];
 };
 
+/**
+ * Sets the current beat of the global beat counter.  This is used to sync the global beat counter with the UI when the user
+ * drags the playhead around.
+ */
+export const setCurBeat = (beat: number) => {
+  if (!beatManagerSAB) {
+    console.error('Tried to set beat before beat manager initialized');
+    return;
+  }
+
+  if (getIsGlobalBeatCounterStarted()) {
+    console.warn('Tried to set beat while beat counter was running');
+    return;
+  }
+
+  beatManagerSAB[0] = beat;
+};
+
 export const getCurGlobalBPM = () => {
   if (!beatManagerSAB) {
     return 0;
@@ -173,7 +194,7 @@ export const getCurGlobalBPM = () => {
 };
 
 // Init the scheduler AWP instance
-export const EventScheduleInitialized = Promise.all([
+export const EventSchedulerInitialized = Promise.all([
   retryAsync(() =>
     fetch(
       process.env.ASSET_PATH +

src/graphEditor/nodes/CustomAudio/FMSynth/FMSynth.tsx

@@ -39,7 +39,7 @@ import { mkContainerCleanupHelper, mkContainerRenderHelper } from 'src/reactUtil
 import { getSample, hashSampleDescriptor, type SampleDescriptor } from 'src/sampleLibrary';
 import { getSentry } from 'src/sentry';
 import { AsyncOnce, normalizeEnvelope } from 'src/util';
-import { EventScheduleInitialized } from 'src/eventScheduler';
+import { EventSchedulerInitialized } from 'src/eventScheduler';
 import type { FilterParams } from 'src/redux/modules/synthDesigner';
 import { buildDefaultFilter } from 'src/synthDesigner/filterHelpersLight';
 import { FilterType } from 'src/synthDesigner/FilterType';
@@ -366,7 +366,7 @@ export default class FMSynth implements ForeignNode {
     const [wasmBytes] = await Promise.all([
       WavetableWasmBytes.get(),
       RegisterFMSynthAWP.get(),
-      EventScheduleInitialized,
+      EventSchedulerInitialized,
     ] as const);
     this.awpHandle = new AudioWorkletNode(this.ctx, 'fm-synth-audio-worklet-processor', {
       numberOfInputs: 0,

src/midiEditor/MIDIEditor.tsx

@@ -10,7 +10,7 @@ import FileUploader, { type FileUploaderValue } from 'src/controls/FileUploader'
 import { renderGenericPresetSaverWithModal } from 'src/controls/GenericPresetPicker/GenericPresetSaver';
 import { getMidiImportSettings, type MidiFileInfo } from 'src/controls/MidiImportDialog';
 import { renderModalWithControls, type ModalCompProps } from 'src/controls/Modal';
-import { useIsGlobalBeatCounterStarted } from 'src/eventScheduler';
+import { getCurBeat, startAll } from 'src/eventScheduler';
 import type { MIDIEditorInstance, SerializedMIDIEditorState } from 'src/midiEditor';
 import { CVOutputTopControls } from 'src/midiEditor/CVOutput/CVOutputTopControls';
 import { mkLoadMIDICompositionModal } from 'src/midiEditor/LoadMIDICompositionModal';
@@ -28,8 +28,6 @@ import type { ManagedInstance, MIDIEditorUIManager } from 'src/midiEditor/MIDIEd
 import type MIDIEditorPlaybackHandler from 'src/midiEditor/PlaybackHandler';
 import EditableInstanceName from './EditableInstanceName.svelte';
 
-const ctx = new AudioContext();
-
 const MIDIWasmModule = new AsyncOnce(() => import('src/midi'));
 
 interface MIDIEditorControlsState {
@@ -227,7 +225,6 @@ const MIDIEditorControlsInner: React.FC<MIDIEditorControlsProps> = ({
   initialState,
   onChange: onChangeInner,
 }) => {
-  const isGlobalBeatCounterStarted = useIsGlobalBeatCounterStarted();
   const [state, setState] = useState(initialState);
   const [isRecording, setIsRecording] = useState(false);
   const [metronomeEnabled, setMetronomeEnabled] = useState(initialState.metronomeEnabled);
@@ -239,17 +236,12 @@ const MIDIEditorControlsInner: React.FC<MIDIEditorControlsProps> = ({
   return (
     <div className='midi-editor-controls'>
       <MIDIEditorControlButton
-        disabled={isGlobalBeatCounterStarted}
         title='Start/Stop Playback'
         onClick={() => {
           if (playbackHandler.isPlaying) {
             playbackHandler.stopPlayback();
           } else {
-            playbackHandler.startPlayback({
-              type: 'localTempo',
-              bpm: state.bpm,
-              startTime: ctx.currentTime,
-            });
+            startAll(getCurBeat());
           }
         }}
         label='⏯'