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fix(machine): decode QR at intrinsic frame + tuned capture resolution

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The camera pairing source decoded frames at the <video> element's CSS box
size (qr's readFrame default) rather than the intrinsic frame, and let the
stream stay at the panel-bound ~720p that frontalCamera negotiates from the
screen size. On the 1280x800 kiosk with a fixed-focus 5MP scan camera that
left far too few pixels-per-module for a dense spire-seed QR, so a centered,
in-square code never decoded.

Decode the intrinsic frame (readFrame fullSize=true) and pin a deliberate
1280x960 capture via applyConstraints. lamassu-machine caps QR scanning at
640x480 for decode speed (megapixels only slow the per-frame decode); our
seed QR is denser than a lightning invoice, so 1280x960 balances
pixels-per-module against latency and keeps auto-exposure from blowing out a
frame-filling phone screen.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Padreug 2026-06-24 23:27:09 +02:00
commit fd4f69826d
1 changed files with 30 additions and 1 deletions
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31
apps/machine/src/services/pairing/qr-source.ts
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@ -32,6 +32,31 @@ export class QrPairingSource implements PairingSource {
if (!video) throw new Error('QrPairingSource requires a <video> element')
const camera = await frontalCamera(video)
// `frontalCamera` requests `ideal: screen.{width,height}`, so on the kiosk's
// 1280x800 panel it otherwise streams at ~720p — and `decodeQR` then
// center-crops to a square, leaving too few pixels-per-module for a dense
// spire-seed QR on this fixed-focus lens. Pin a deliberate 1280x960 capture
// instead: lamassu-machine caps QR scanning at 640x480 for decode speed
// (megapixels just slow the per-frame decode), but our seed QR is denser
// than a lightning invoice, so 1280x960 is the balance — ~14-18px/module at
// frame-fill, still fast, and it meters exposure better than maxing the
// sensor (a frame-filling QR keeps auto-exposure from blowing out on a
// bright phone screen). The stream lives on the <video>'s srcObject
// (QRCamera.stream is private); soft `ideal` so a camera that can't honor
// it degrades to its closest mode instead of throwing.
try {
const stream = video.srcObject
if (stream instanceof MediaStream) {
await stream.getVideoTracks()[0]?.applyConstraints({
width: { ideal: 1280 },
height: { ideal: 960 },
})
}
} catch (e) {
onError?.(e)
}
const canvas = new QRCanvas() // decode-only; no overlay canvases needed
let stopped = false
@ -46,7 +71,11 @@ export class QrPairingSource implements PairingSource {
cancel = frameLoop(() => {
if (stopped) return
try {
const result = camera.readFrame(canvas)
// `fullSize: true` decodes the camera's intrinsic frame (videoWidth ×
// videoHeight) rather than the <video> element's CSS box — the default
// (`false`) was decoding the few-hundred-px on-screen preview, which
// (compounded by `object-cover` cropping) starved the decoder.
const result = camera.readFrame(canvas, true)
if (result) {
stop()
onScan(result)