From 2172d1a767fbcc819432dbb55e3aa43fba4251d4 Mon Sep 17 00:00:00 2001
From: Felix Roos <roos@entrecode.de>
Date: Sun, 21 Aug 2022 11:20:15 +0200
Subject: [PATCH] scheduler error correction via getTime

---
 packages/core/clockworker.mjs |  2 +-
 packages/core/scheduler.mjs   | 13 +++++++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/packages/core/clockworker.mjs b/packages/core/clockworker.mjs
index 07bd45d3..c56f38a4 100644
--- a/packages/core/clockworker.mjs
+++ b/packages/core/clockworker.mjs
@@ -12,7 +12,7 @@ const createWorker = (func) => new Worker(urlifyFunction(func));
 // this is just a setInterval with a counter, running in a worker
 export class ClockWorker {
   worker;
-  interval = 0.1; // query span
+  interval = 1 / 32; // query span, use powers of 2 to get better float accuracy
   tick = 0;
   constructor(callback, interval = this.interval) {
     this.interval = interval;
diff --git a/packages/core/scheduler.mjs b/packages/core/scheduler.mjs
index a8f6ff0f..8bcef060 100644
--- a/packages/core/scheduler.mjs
+++ b/packages/core/scheduler.mjs
@@ -12,9 +12,18 @@ export class Scheduler {
   started = false;
   phase = 0;
   cps = 1;
-  constructor({ interval = 0.1, onTrigger, onError, latency = 0.1 }) {
+  lastTime;
+  constructor({ interval, onTrigger, onError, latency = 0.1, getTime }) {
     this.worker = new ClockWorker((_, interval) => {
       try {
+        let error = 0;
+        // measure time between last and current callback and calculate deviation from extected interval
+        const time = getTime?.();
+        if (time && this.lastTime) {
+          error = time - this.lastTime - interval; // how off is the callback? positive = too late
+          // console.log('ms error', error * 1000);
+        }
+        this.lastTime = time;
         const begin = this.phase;
         const end = this.phase + interval * this.cps;
         this.phase = end;
@@ -26,7 +35,7 @@ export class Scheduler {
           if (!hap.part.begin.equals(hap.whole.begin)) {
             return;
           }
-          const deadline = (hap.whole.begin - begin) / this.cps + latency;
+          const deadline = (hap.whole.begin - begin) / this.cps + latency - error;
           // TODO: use legato / duration of objectified value
           const duration = hap.duration / this.cps;
           onTrigger?.(hap, deadline, duration);