feat(QrcodeStream): add torch prop

Adds `torch` prop for turning a devices flashlight on/off.

Initially suggested by @magyarb

Author: gruhn

src/components/QrcodeStream.vue

@@ -47,6 +47,11 @@ export default {
       }
     },
 
+    torch: {
+      type: Boolean,
+      default: false
+    },
+
     track: {
       type: [Function, Boolean],
       default: true
@@ -146,6 +151,10 @@ export default {
       }
     },
 
+    torch() {
+      this.$emit("init", this.init());
+    },
+
     constraints() {
       this.$emit("init", this.init());
     }
@@ -168,7 +177,9 @@ export default {
       if (this.constraints === undefined) {
         this.cameraInstance = null;
       } else {
-        this.cameraInstance = await Camera(this.constraints, this.$refs.video);
+        this.cameraInstance = await Camera(this.constraints, this.$refs.video, {
+          torch: this.torch
+        });
 
         // if the component is destroyed before `cameraInstance` resolves a
         // `beforeDestroy` hook has no chance to clear the remaining camera

src/misc/camera.js

@@ -28,7 +28,7 @@ const STREAM_API_NOT_SUPPORTED = !(
 
 let streamApiShimApplied = false;
 
-export default async function(constraints, videoEl) {
+export default async function(constraints, videoEl, advancedConstraints) {
   // At least in Chrome `navigator.mediaDevices` is undefined when the page is
   // loaded using HTTP rather than HTTPS. Thus `STREAM_API_NOT_SUPPORTED` is
   // initialized with `false` although the API might actually be supported.
@@ -64,5 +64,15 @@ export default async function(constraints, videoEl) {
 
   await eventOn(videoEl, "loadeddata");
 
+  if (advancedConstraints.torch) {
+    const [track] = stream.getVideoTracks();
+
+    try {
+      await track.applyConstraints({ advanced: [{ torch: true }] });
+    } catch (error) {
+      console.warn("device does not support torch capability");
+    }
+  }
+
   return new Camera(videoEl, stream);
 }