fix(QrcodeStream): iOS 15 won't render camera

When a camera stream is loaded, we assign the stream to a `video`
element via `video.srcObject`. At this point the element is hidden with
`v-show="false"` aka. `display: none`. We do that because at this point
the videos dimensions are not known yet. We have to wait for the
`loadeddata` event first. Only after that event we display the video
element. Otherwise the elements size awkwardly flickers.

However, it appears since iOS 15 all iOS browsers won't properly render
the video element if the `video.srcObject` was assigned *while* the
element was hidden with `display: none`. Using `visibility: hidden`
instead seems to have fixed the problem though.

Issue: #264 #266

src/components/QrcodeStream.vue

@@ -7,7 +7,7 @@
     -->
     <video
       ref="video"
-      v-show="shouldScan"
+      :class="{ 'qrcode-stream-camera--hidden': !shouldScan }"
       class="qrcode-stream-camera"
       autoplay
       muted
@@ -181,19 +181,6 @@ export default {
       }
     },
 
-    onLocate(location) {
-      if (this.trackRepaintFunction === undefined || location === null) {
-        this.clearCanvas(this.$refs.trackingLayer);
-      } else {
-        const video = this.$refs.video;
-        const canvas = this.$refs.trackingLayer;
-
-        if (video !== undefined && canvas !== undefined) {
-          this.repaintTrackingLayer(video, canvas, location);
-        }
-      }
-    },
-
     onLocate(detectedCodes) {
       const canvas = this.$refs.trackingLayer;
       const video = this.$refs.video;
@@ -318,4 +305,20 @@ export default {
   display: block;
   object-fit: cover;
 }
+/* When a camera stream is loaded, we assign the stream to the `video`
+ * element via `video.srcObject`. At this point the element used to be
+ * hidden with `v-show="false"` aka. `display: none`. We do that because
+ * at this point the videos dimensions are not known yet. We have to
+ * wait for the `loadeddata` event first. Only after that event we
+ * display the video element. Otherwise the elements size awkwardly flickers.
+ *
+ * However, it appears in iOS 15 all iOS browsers won't properly render
+ * the video element if the `video.srcObject` was assigned *while* the
+ * element was hidden with `display: none`. Using `visibility: hidden`
+ * instead seems to have fixed the problem though.
+ */
+.qrcode-stream-camera--hidden {
+  visibility: hidden;
+  position: absolute;
+}
 </style>