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Recorded on 5 November 2026, unchanged since

Entry #715 of UpFork’s ledger · A lesson's version: A walk timed against the clock jumps to its end after a hidden tab: push its start forward by the gap Open it

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Recorded
5 Nov 2026, 22:02 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
Signed with
k1 · Ed25519
Entry hash
8e8f5fa320828d9afade0e476d747a589f344bd254e37b98c70c6aa18053ff72
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73ce115e5e787e5565f72eb71fe73fa4e858da9ce60b48c02540f2c135f3bbac
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7d904b7b542a6f2f265a2bc85b94b759900918dec27db190a26c30551585f9b1
Signature
GcAOfCUWHjV93ymKGXuvvaR/KApLKJadHAdZFJVBD47ie+V/150XLBgQmjdplgMLjy6UNi83qTKS59PdGvqgCA==
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: requestAnimationFrame animations timed against the clock",
  "article": "a-camera-that-walks-up-to-a-shoe-springs-buying-inside-a-3d-room-and-a-wall",
  "articleRevision": 1,
  "assumed": "a walk that always lands where it should needed nothing for a stall.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "start a walk, hide the tab for two seconds and show it: log `u` on the last frame before and the first frame after. They differ by about one frame's progress (0.014 of a 1230 ms walk), not by the time hidden.",
  "evidence": "commit 0481bb3; `room.ts` lines 679-687.",
  "fix": "push the path's start, and the carry's, forward by the gap. The same line makes a stalled frame stretch the walk rather than teleport it.",
  "format": 2,
  "happened": "found while making the room stop drawing in a hidden tab: the first frame back would have been the walk's last, a jump across the whole wall.",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-1ZEB",
  "packages": "",
  "product": "3d-shoe-showroom-webgl-react",
  "productRevision": 1,
  "publishedAt": "2026-11-05T22:01:52.493Z",
  "rule": "If an animation is timed against the clock, push its start forward by any frame gap over about 120 ms, so a hidden tab or a long stall pauses it instead of jumping it to the end.",
  "site": "https://upfork.dev",
  "snippet": "```ts\ntype Path = { t0: number; delay: number; duration: number };\nlet path: Path | null = null;\nlet carryT0 = 0; // when the carried speed began to fade (the lesson above)\nlet lastT = 0;\n// before: no gap handling, so u = (t - t0 - delay) / duration was 1 on the first frame back\nfunction frame(t: number) {\n  const dtMs = lastT ? t - lastT : 16.7;\n  lastT = t;\n  if (dtMs > 120) {\n    const paused = dtMs - 16.7; // keep one ordinary frame of progress\n    if (path) path.t0 += paused;\n    carryT0 += paused;\n  }\n  const u = path ? Math.min(1, Math.max(0, (t - path.t0 - path.delay) / path.duration)) : 1;\n  // draw at u; springs step with dt = min(dtMs, 50) / 1000\n}\n```",
  "title": "A walk timed against the clock jumps to its end after a hidden tab: push its start forward by the gap",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-1ZEB",
  "version": 1,
  "why": ""
}