From 14b52bcb11daca8ea53125bba0134d574d82bf20 Mon Sep 17 00:00:00 2001
From: Christoph Reiter <reiter.christoph@gmail.com>
Date: Wed, 21 Oct 2020 11:19:53 +0200
Subject: [PATCH] Fix a race when starting the scanner multiple times
We would get two scanning loops both scanning for qr codes. This makes
sure only one loop is active at all times.
---
packages/qr-code-scanner/src/qr-code-scanner.js | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/packages/qr-code-scanner/src/qr-code-scanner.js b/packages/qr-code-scanner/src/qr-code-scanner.js
index 642fef71..d4d79d9b 100644
--- a/packages/qr-code-scanner/src/qr-code-scanner.js
+++ b/packages/qr-code-scanner/src/qr-code-scanner.js
@@ -86,6 +86,7 @@ export class QrCodeScanner extends ScopedElementsMixin(DBPLitElement) {
this.clipMask = false;
this._devices = new Map();
+ this._requestID = null;
}
static get scopedElements() {
@@ -192,13 +193,20 @@ export class QrCodeScanner extends ScopedElementsMixin(DBPLitElement) {
video.play();
that.videoRunning = true;
qrContainer.scrollIntoView({ behavior: 'smooth', block: 'start' });
- requestAnimationFrame(tick);
+ if (that._requestID !== null) {
+ cancelAnimationFrame(that._requestID);
+ that._requestID = null;
+ }
+ console.assert(that._requestID === null);
+ that._requestID = requestAnimationFrame(tick);
}).catch((e) => { console.log(e); that.askPermission = true;});
let lastVideoTime = -1;
let lastCode = null;
function tick() {
+ that._requestID = null;
+
if (that.sourceChanged) {
video.srcObject.getTracks().forEach(function(track) {
track.stop();
@@ -340,7 +348,8 @@ export class QrCodeScanner extends ScopedElementsMixin(DBPLitElement) {
qrContainer.scrollIntoView({ behavior: 'smooth', block: 'start' });
scroll = true;
}
- requestAnimationFrame(tick);
+ console.assert(that._requestID === null);
+ that._requestID = requestAnimationFrame(tick);
}
}
--
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