From eba8d8d4b8db665520e693e40f79b58b8d2d1f3a Mon Sep 17 00:00:00 2001
From: Evan Hahn <69474926+EvanHahn-Signal@users.noreply.github.com>
Date: Fri, 14 Jan 2022 10:45:05 -0600
Subject: [PATCH] Render QR code with SVG, not canvas

---
 ts/components/QrCode.stories.tsx              |  3 +-
 ts/components/QrCode.tsx                      | 62 ++++++-------------
 .../InstallScreenQrCodeNotScannedStep.tsx     |  5 +-
 ts/util/lint/exceptions.json                  |  4 +-
 4 files changed, 24 insertions(+), 50 deletions(-)

diff --git a/ts/components/QrCode.stories.tsx b/ts/components/QrCode.stories.tsx
index 118c02bb91..88ce6f458e 100644
--- a/ts/components/QrCode.stories.tsx
+++ b/ts/components/QrCode.stories.tsx
@@ -10,8 +10,7 @@ const story = storiesOf('Components/QrCode', module);
 
 story.add('Default', () => (
   <QrCode
-    aria-label="Scan this little code!"
+    alt="Scan this little code!"
     data="sgnl://linkdevice?uuid=gCkj0T2xiSUaPRhMYiF24w&pub_key=7RshtQrb3UTMowITe79uW9dgw_CLTGWenj0OT80i0HpH"
-    size={256}
   />
 ));
diff --git a/ts/components/QrCode.tsx b/ts/components/QrCode.tsx
index 173e659988..aeb7304eb0 100644
--- a/ts/components/QrCode.tsx
+++ b/ts/components/QrCode.tsx
@@ -2,53 +2,33 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import type { ReactElement } from 'react';
-import React, { useEffect, useMemo, useRef } from 'react';
+import React, { useMemo, useRef } from 'react';
 import qrcode from 'qrcode-generator';
 import { getEnvironment, Environment } from '../environment';
-import { strictAssert } from '../util/assert';
-import { useDevicePixelRatio } from '../hooks/useDevicePixelRatio';
 
 const AUTODETECT_TYPE_NUMBER = 0;
 const ERROR_CORRECTION_LEVEL = 'L';
 
 type PropsType = Readonly<{
-  'aria-label': string;
+  alt: string;
   className?: string;
   data: string;
-  size: number;
 }>;
 
 export function QrCode(props: PropsType): ReactElement {
-  // I don't think it's possible to destructure this.
-  // eslint-disable-next-line react/destructuring-assignment
-  const ariaLabel = props['aria-label'];
-  const { className, data, size } = props;
+  const { alt, className, data } = props;
 
-  const qrCode = useMemo(() => {
-    const result = qrcode(AUTODETECT_TYPE_NUMBER, ERROR_CORRECTION_LEVEL);
-    result.addData(data);
-    result.make();
-    return result;
+  const elRef = useRef<null | HTMLImageElement>(null);
+
+  const src = useMemo(() => {
+    const qrCode = qrcode(AUTODETECT_TYPE_NUMBER, ERROR_CORRECTION_LEVEL);
+    qrCode.addData(data);
+    qrCode.make();
+
+    const svgData = qrCode.createSvgTag({ cellSize: 1, margin: 0 });
+    return `data:image/svg+xml;utf8,${svgData}`;
   }, [data]);
 
-  const canvasRef = useRef<null | HTMLCanvasElement>(null);
-  const dpi = useDevicePixelRatio();
-  const canvasSize = size * dpi;
-
-  useEffect(() => {
-    const canvas = canvasRef.current;
-    if (!canvas) {
-      return;
-    }
-
-    const context = canvas.getContext('2d');
-    strictAssert(context, 'Expected a canvas context');
-
-    const cellSize = canvasSize / qrCode.getModuleCount();
-    context.clearRect(0, 0, canvasSize, canvasSize);
-    qrCode.renderTo2dContext(context, cellSize);
-  }, [canvasSize, qrCode]);
-
   // Add a development-only feature to copy a QR code to the clipboard by double-clicking.
   // This can be used to quickly inspect the code, or to link this Desktop with an iOS
   // simulator primary, which has a debug-only option to paste the linking URL instead of
@@ -60,25 +40,23 @@ export function QrCode(props: PropsType): ReactElement {
 
     navigator.clipboard.writeText(data);
 
-    const canvas = canvasRef.current;
-    if (!canvas) {
+    const el = elRef.current;
+    if (!el) {
       return;
     }
-    canvas.style.filter = 'brightness(50%)';
+    el.style.filter = 'brightness(50%)';
     window.setTimeout(() => {
-      canvas.style.filter = '';
+      el.style.filter = '';
     }, 150);
   };
 
   return (
-    <canvas
-      aria-label={ariaLabel}
+    <img
+      alt={alt}
       className={className}
-      height={canvasSize}
-      ref={canvasRef}
-      style={{ width: size, height: size }}
-      width={canvasSize}
       onDoubleClick={onDoubleClick}
+      ref={elRef}
+      src={src}
     />
   );
 }
diff --git a/ts/components/installScreen/InstallScreenQrCodeNotScannedStep.tsx b/ts/components/installScreen/InstallScreenQrCodeNotScannedStep.tsx
index 84ddd9a939..360a19e97b 100644
--- a/ts/components/installScreen/InstallScreenQrCodeNotScannedStep.tsx
+++ b/ts/components/installScreen/InstallScreenQrCodeNotScannedStep.tsx
@@ -25,8 +25,6 @@ type PropsType = {
   provisioningUrl: Loadable<string>;
 };
 
-// This should match the size in the CSS.
-const QR_CODE_SIZE = 256;
 const QR_CODE_FAILED_LINK =
   'https://support.signal.org/hc/articles/360007320451#desktop_multiple_device';
 
@@ -113,10 +111,9 @@ function InstallScreenQrCode(
     case LoadingState.Loaded:
       contents = (
         <QrCode
-          aria-label={i18n('Install__scan-this-code')}
+          alt={i18n('Install__scan-this-code')}
           className={getQrCodeClassName('__code')}
           data={props.value}
-          size={QR_CODE_SIZE}
         />
       );
       break;
diff --git a/ts/util/lint/exceptions.json b/ts/util/lint/exceptions.json
index b5bcd92745..c1a1f5cf76 100644
--- a/ts/util/lint/exceptions.json
+++ b/ts/util/lint/exceptions.json
@@ -7527,10 +7527,10 @@
   {
     "rule": "React-useRef",
     "path": "ts/components/QrCode.tsx",
-    "line": "  const canvasRef = useRef<null | HTMLCanvasElement>(null);",
+    "line": "  const elRef = useRef<null | HTMLImageElement>(null);",
     "reasonCategory": "usageTrusted",
     "updated": "2022-01-04T21:43:17.517Z",
-    "reasonDetail": "Used to draw on the canvas."
+    "reasonDetail": "Used to change the style in non-production builds."
   },
   {
     "rule": "React-createRef",