fix longer running midi-only drift with a dummy node

packages/midi/midi.mjs

@@ -22,7 +22,7 @@ import {
 import { noteToMidi, getControlName } from '@strudel/core';
 import { Note } from 'webmidi';
 import { getAudioContext } from '@strudel/webaudio';
-import { scheduleAtTime } from '../superdough/helpers.mjs';
+import { scheduleAtTime, ensureMinimalOutput } from '../superdough/helpers.mjs';
 import { getMidiDeviceNamesString, getDevice } from './util.mjs';
 import { MidiInput } from './input.mjs';
 
@@ -338,6 +338,8 @@ Pattern.prototype.midi = function (midiport, options = {}) {
       logger(`Midi device disconnected! Available: ${getMidiDeviceNamesString(outputs)}`),
   });
 
+  ensureMinimalOutput();
+
   let p; // filtered clock offset
   let lastOffset;
 

packages/superdough/helpers.mjs

@@ -12,6 +12,21 @@ export function gainNode(value) {
   return node;
 }
 
+// this helper makes sure the audio context is "used", meaning it outputs something
+// this prevents the browser from throttling timing accuracy
+// it happened when only midi was running, the clock got more drifty without this
+let constantNode, constantNodeAudioContext;
+export function ensureMinimalOutput() {
+  if (constantNode && constantNodeAudioContext === getAudioContext()) {
+    return;
+  }
+  constantNodeAudioContext = getAudioContext();
+  constantNode = new ConstantSourceNode(constantNodeAudioContext);
+  constantNode.offset.value = 1e-7;
+  constantNode.connect(constantNodeAudioContext.destination);
+  constantNode.start();
+}
+
 export function effectSend(input, effect, wet) {
   const send = gainNode(wet);
   input.connect(send);