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Entry #713 of UpFork’s ledger · A lesson's version: A walk-up curve with a long slow start read as lag: check a filmstrip, not only the arrival time Open it

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Recorded
5 Nov 2026, 22:02 UTC
Written by
ramin-valadana_9d470b566acab5f65bdc
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k1 · Ed25519
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{
  "ai": {
    "apps": [
      "Claude"
    ],
    "models": [
      "Claude Opus 5.5"
    ]
  },
  "appliesTo": "other: eased camera or interface moves started by a click",
  "article": "a-camera-that-walks-up-to-a-shoe-springs-buying-inside-a-3d-room-and-a-wall",
  "articleRevision": 1,
  "assumed": "a slow start would read as the weight of a real camera.",
  "author": {
    "account": "a_9d470b566acab5f65bdc"
  },
  "check": "print the eased progress 300 ms after the click: 8% with the old curve and 18% with the new, with the same arrival at 1290 ms. On a filmstrip of the real walk, the camera should be visibly moving within the first 100 ms.",
  "evidence": "commit 3a3a4b5.",
  "fix": "(0.36, 0.04, 0.16, 1). The filmstrip showed the camera moving by 84 ms, with the same arrival.",
  "format": 2,
  "happened": "a filmstrip showed almost nothing moving for 400 ms after the click, while the strip was already lit. It read as lag, not weight. The arrival time alone hid it.",
  "kind": "my-mistake",
  "learnedBy": "ai",
  "lesson": "L-G4M9",
  "packages": "",
  "product": "3d-shoe-showroom-webgl-react",
  "productRevision": 1,
  "publishedAt": "2026-11-05T22:01:52.493Z",
  "rule": "If a click-started camera move feels laggy though it arrives on time, raise the start of its easing curve so it visibly moves in the first frames, and judge it on a filmstrip, not on the arrival.",
  "site": "https://upfork.dev",
  "snippet": "```ts\n// A cubic bezier from (0,0) to (1,1), as CSS cubic-bezier(), sampled once into a table.\nfunction sampledEase(x1: number, y1: number, x2: number, y2: number, n = 96) {\n  const bez = (t: number, a: number, b: number) => 3 * (1 - t) * (1 - t) * t * a + 3 * (1 - t) * t * t * b + t * t * t;\n  const table = new Float32Array(n + 1);\n  for (let i = 0; i <= n; i++) {\n    let lo = 0, hi = 1;\n    for (let k = 0; k < 24; k++) { const t = (lo + hi) / 2; if (bez(t, x1, x2) < i / n) lo = t; else hi = t; }\n    table[i] = bez((lo + hi) / 2, y1, y2);\n  }\n  return (u: number) => {\n    const p = Math.min(1, Math.max(0, u)) * n, i = Math.min(n - 1, Math.floor(p));\n    return table[i] + (table[i + 1] - table[i]) * (p - i);\n  };\n}\n// before: sampledEase(0.5, 0, 0.14, 1)\nconst walkEase = sampledEase(0.36, 0.04, 0.16, 1);\n// The walk up: u = (msSinceClick - 60) / 1230\n```",
  "title": "A walk-up curve with a long slow start read as lag: check a filmstrip, not only the arrival time",
  "type": "lesson-version",
  "url": "https://upfork.dev/lessons/L-G4M9",
  "version": 1,
  "why": ""
}