Take photos with web camera using RxJS and Angular

Connie Leung - Dec 18 '22 - - Dev Community

Introduction

This is day 19 of Wes Bos's JavaScript 30 challenge where I am going to use RxJS operators and Angular to take photos, add them to photo section for me to download to my local hard drive.

In this blog post, I inject native Navigator to component such that I can load web camera to video element. Every 16 seconds, a callback function draws the video image to canvas with special effects. Whenever I click "Take photo" button, the canvas converts data to base64 string and add it to photo section from most recent to earliest.

Create a new Angular project in workspace 

ng generate application day19-webcam-fun
Enter fullscreen mode Exit fullscreen mode

Define Native Navigator

First, we create core module and define native navigaor to inject into the web camera component.

// core.module.ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { NAVIGATOR_PROVIDERS } from './navigator.service';

@NgModule({
  declarations: [],
  imports: [
    CommonModule
  ],
  providers: [NAVIGATOR_PROVIDERS]
})
export class CoreModule { }
Enter fullscreen mode Exit fullscreen mode

Next, I create NAVIGATOR injection token and NAVIGATOR_PROVIDERS in navigator service

// navigator.service.ts
import { isPlatformBrowser } from '@angular/common';
import { ClassProvider, FactoryProvider, InjectionToken, PLATFORM_ID } from '@angular/core';

/* Create a new injection token for injecting the navigator into a component. */
export const NAVIGATOR = new InjectionToken('NavigatorToken');

export abstract class NavigatorRef {
  get nativeNavigator(): Navigator | Object {
    throw new Error('Not implemented.');
  }
}

/* Define class that implements the abstract class and returns the native navigator object. */
export class BrowserNavigatorRef extends NavigatorRef {

  constructor() {
    super();
  }

  override get nativeNavigator(): Object | Navigator {
    return navigator;    
  }
}

/* Create a injectable provider for the NavigatorRef token that uses the BrowserNavigatorRef class. */
const browserNavigatorProvider: ClassProvider = {
  provide: NavigatorRef,
  useClass: BrowserNavigatorRef
};

/* Create an injectable provider that uses the navigatorFactory function for returning the native navigator object. */
const navigatorProvider: FactoryProvider = {
  provide: NAVIGATOR,
  useFactory: (browserWindowRef: BrowserNavigatorRef, platformId: Object) => 
    isPlatformBrowser(platformId) ? browserWindowRef.nativeNavigator : new Object(),
  deps: [ NavigatorRef, PLATFORM_ID ]
};

/* Create an array of providers. */
export const NAVIGATOR_PROVIDERS = [
  browserNavigatorProvider,
  navigatorProvider
];
Enter fullscreen mode Exit fullscreen mode

After defining the providers, I provide NAVIGATOR_PROVIDERS to the core module

// core.module.ts 

@NgModule({
  declarations: [],
  imports: [
    CommonModule
  ],
  providers: [NAVIGATOR_PROVIDERS]
})
export class CoreModule { }
Enter fullscreen mode Exit fullscreen mode

The definition of the core module is now complete and I import CoreModule to AppModule.

// app.module.ts

import { APP_BASE_HREF, PlatformLocation } from '@angular/common';
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';

import { AppComponent } from './app.component';
import { CoreModule } from './core';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    WebCamModule,
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }
Enter fullscreen mode Exit fullscreen mode

Create Web Camera feature module

The next feature module to create is Web Camera feature module and it also imports into AppModule. I declare two components in the feature module: WebCameraComponent and PhotoStripeComponent. WebCameraComponent takes photos with a web camera and lists them in PhotoStripeComponent from most recent to earliest.

Then, Import WebCamModule in AppModule

// webcam.module.ts

import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { WebCameraComponent } from './web-camera/web-camera.component';
import { PhotoStripeComponent } from './photo-stripe/photo-stripe.component';

@NgModule({
  declarations: [
    WebCameraComponent,
    PhotoStripeComponent
  ],
  imports: [
    CommonModule
  ],
  exports: [
    WebCameraComponent
  ]
})
export class WebCamModule { }
Enter fullscreen mode Exit fullscreen mode 
// app.module.ts

import { APP_BASE_HREF, PlatformLocation } from '@angular/common';
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';

import { AppComponent } from './app.component';
import { CoreModule } from './core';
import { WebCamModule } from './webcam';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    WebCamModule,
    CoreModule,
  ],
  providers: [
    {
      provide: APP_BASE_HREF,
      useFactory: (platformLocation: PlatformLocation) => platformLocation.getBaseHrefFromDOM(),
      deps: [PlatformLocation]
    }
  ],
  bootstrap: [AppComponent]
})
export class AppModule { }
Enter fullscreen mode Exit fullscreen mode

Declare components in web camera feature module

In web camera module, I declare WebCameraComponent that loads the web camera of my laptop to video element in order to take photos. PhotoStripeComponent is a presentation component that iterates an array of base64 string and display them from latest to earliest.

src/assets
└── audio
    └── snap.mp3

src/app
├── app.component.ts
├── app.module.ts
├── core
│   ├── core.module.ts
│   ├── index.ts
│   └── navigator.service.ts
└── webcam
    ├── index.ts
    ├── interfaces
    │   └── webcam.interface.ts
    ├── photo-stripe
    │   └── photo-stripe.component.ts
    ├── web-camera
    │   └── web-camera.component.ts
    └── webcam.module.ts
Enter fullscreen mode Exit fullscreen mode

I define component selector, inline template and inline CSS styles in WebCameraComponent. Later sections of the blog post will implement RxJS codes to add the functionality. For your information, <app-web-camera> is the tag of the component.

// webcam.interface.ts

export interface Photo {
    data: string;
    description: string;
    download: string;
}
Enter fullscreen mode Exit fullscreen mode 
// web-camera.component.ts

import { APP_BASE_HREF } from '@angular/common';
import { ChangeDetectionStrategy, Component, ElementRef, Inject, OnDestroy, OnInit, ViewChild } from '@angular/core';
import { Observable, of, Subject } from 'rxjs';
import { NAVIGATOR } from '../../core/navigator.service';
import { Photo } from '../interfaces/webcam.interface';

@Component({
  selector: 'app-web-camera',
  template: `
  <ng-container>
    <div class="photobooth">
      <div class="controls">
        <button #btnPhoto>Take Photo</button>
      </div>
      <canvas class="photo" #photo></canvas>
      <video class="player" #video></video>
      <ng-container *ngIf="photoStripe$ | async as photoStripe">
        <app-photo-stripe [photoStripe]="photoStripe"></app-photo-stripe>
      </ng-container>
    </div>
    <audio class="snap" [src]="soundUrl" hidden #snap></audio>
  </ng-container>
  `,
  styles: [`
    :host {
      display: block;
    }
    ...omitted for brevity...
  `],
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class WebCameraComponent implements OnInit, OnDestroy {

  @ViewChild('btnPhoto', { static: true, read: ElementRef })
  btnPhoto!: ElementRef<HTMLButtonElement>;

  @ViewChild('snap', { static: true, read: ElementRef })
  snap!: ElementRef<HTMLAudioElement>;

  @ViewChild('video', { static: true, read: ElementRef })
  video!: ElementRef<HTMLVideoElement>;

  @ViewChild('photo', { static: true, read: ElementRef })
  canvas!: ElementRef<HTMLCanvasElement>;

  destroy$ = new Subject<void>();

  photoStripe$!: Observable<Photo[]>;

  constructor(@Inject(APP_BASE_HREF) private baseHref: string, @Inject(NAVIGATOR) private navigator: Navigator) { }

  ngOnInit(): void {
    const videoNative = this.video.nativeElement;
    const canvasNative = this.canvas.nativeElement;
    const ctx = canvasNative.getContext('2d', { willReadFrequently: true });

    this.getVideo();

    this.photoStripe$ = of([]);
  }

  get soundUrl() {
    const isEndWithSlash = this.baseHref.endsWith('/');
    return `${this.baseHref}${ isEndWithSlash ? '' : '/' }assets/audio/snap.mp3`; 
  }

  private getVideo() {
    console.log('navigator', this.navigator);

    this.navigator.mediaDevices.getUserMedia({ video: true, audio: false })
      .then(localMediaStream => {
        console.log(localMediaStream);

        const nativeElement = this.video.nativeElement;         
        nativeElement.srcObject = localMediaStream;
        nativeElement.play();
      })
      .catch(err => {
        console.error(`OH NO!!!`, err);
      });
  }

  private rgbSplit(pixels: ImageData) {
    for (let i = 0; i < pixels.data.length; i += 4) {
      pixels.data[i - 150] = pixels.data[i + 0]; // RED
      pixels.data[i + 500] = pixels.data[i + 1]; // GREEN
      pixels.data[i - 550] = pixels.data[i + 2]; // Blue
    }
    return pixels;
  }

  ngOnDestroy(): void {
    this.destroy$.next();
    this.destroy$.complete();
  }
}
Enter fullscreen mode Exit fullscreen mode

photoStripe$ is an Observable and async pipe resolves the observable in inline template to render the array elements.

<ng-container *ngIf="photoStripe$ | async as photoStripe">
    <app-photo-stripe [photoStripe]="photoStripe"></app-photo-stripe>
 </ng-container>
Enter fullscreen mode Exit fullscreen mode

async resolves photoStripe$ to photoStripe variable and photoStripe is the input parameter of PhotoStripeComponent.

getVideo is a method that uses the native Navigator to load web camera and assign it to video element.

// photo-stripe.component.ts

import { Component, ChangeDetectionStrategy, Input } from '@angular/core';
import { Photo } from '../interfaces/webcam.interface';

@Component({
  selector: 'app-photo-stripe',
  template: `<div class="strip">
    <a *ngFor="let photo of photoStripe; index as i;" [href]="photo.data" download="{{photo.download}}{{i + 1}}">
      <img [src]="photo.data" [alt]="photo.description" />
    </a>
  </div>`,
  styles: [`
    :host {
      display: block;
    }
    ... omitted for brevity ...
  `],
  changeDetection: ChangeDetectionStrategy.OnPush
})
export class PhotoStripeComponent {

  @Input()
  photoStripe!: Photo[];
}
Enter fullscreen mode Exit fullscreen mode

PhotoStripeComponent is a simple presentation component that renders base64 strings to lt;agt; and lt;imggt; elements, and the hyperlinks are downloaded when clicked.

Next, I delete boilerplate codes in AppComponent and render WebCameraComponent in inline template.

import { Component } from '@angular/core';
import { Title } from '@angular/platform-browser';

@Component({
  selector: 'app-root',
  template: '<app-web-camera></app-web-camera>', 
  styles: [`
    :host {
      display: block;
    }
  `],
})
export class AppComponent {
  title = 'Day 19 Web Cam Fun';

  constructor(titleService: Title) {
    titleService.setTitle(this.title);
  }
}
Enter fullscreen mode Exit fullscreen mode

Apply RxJS operators to render video capture in canvas

In ngOnInit, I use RxJS to render video capture in 2D canvas. The event streaming starts when video is ready to play.

// web-camera.component.ts

import { concatMap, filter, fromEvent, map, Observable, scan, startWith, Subject, takeUntil, tap, timer } from 'rxjs';

const videoNative = this.video.nativeElement;
const canvasNative = this.canvas.nativeElement;
const ctx = canvasNative.getContext('2d', { willReadFrequently: true });

fromEvent(videoNative, 'canplay')
  .pipe(
      filter(() => !!ctx),
      map(() => ctx as CanvasRenderingContext2D),
      concatMap((canvasContext) => {
        const width = videoNative.videoWidth;
        const height = videoNative.videoHeight;    
        canvasNative.width = width;
        canvasNative.height = height;
        const interval = 16;   

        return timer(0, interval).pipe(
           tap(() => {
              canvasContext.drawImage(this.video.nativeElement, 0, 0, width, height);
              // take the pixels out
              const pixels = canvasContext.getImageData(0, 0, width, height);

              this.rgbSplit(pixels);
              canvasContext.globalAlpha = 0.8;  
              canvasContext.putImageData(pixels, 0, 0);
           })
         )
       }),
       takeUntil(this.destroy$)
  )
  .subscribe();
Enter fullscreen mode Exit fullscreen mode

Explanations:

  • fromEvent(videoNative, 'canplay') listens to canplay event of the video
  • filter(() => !!ctx) validates 2D canvas is defined
  • map(() => ctx as CanvasRenderingContext2D) casts 2D canvas as CanvasRenderingContext2D
  • concatMap((canvasContext) => {....}) creates a timer observable to draw the canvas every 16 seconds
  • takeUntil(this.destroy$) unsubscribes the observable

timer returns an Observable; therefore, I use concatMap instead of map to write the pixels to the canvas

concatMap((canvasContext) => {
    const width = videoNative.videoWidth;
    const height = videoNative.videoHeight;    
    canvasNative.width = width;
    canvasNative.height = height;    

    return timer(0, interval).pipe(
       tap(() => {
          canvasContext.drawImage(this.video.nativeElement, 0, 0, width, height);
          // take the pixels out
          const pixels = canvasContext.getImageData(0, 0, width, height);

          this.rgbSplit(pixels);
          canvasContext.globalAlpha = 0.8;  
          canvasContext.putImageData(pixels, 0, 0);
        })
     )
})
Enter fullscreen mode Exit fullscreen mode

Build photo list with RxJS operators 

// web-camera.component.ts

this.photoStripe$ = fromEvent(this.btnPhoto.nativeElement, 'click')
  .pipe(
      tap(() => {
         const snapElement = this.snap.nativeElement;
         snapElement.currentTime = 0;
         snapElement.play();
      }),
      map(() => ({ 
         data: this.canvas.nativeElement.toDataURL('image/jpeg'),
         description: 'My photo',
         download: 'photo',
      })),
      scan((photos, photo) => [photo, ...photos], [] as Photo[]),
      startWith([] as Photo[]),
  );
Enter fullscreen mode Exit fullscreen mode

Explanations:

  • tap(() => { ...play sound... }) plays an audio file when I click "Take photo" button
  • map(() => { ...create base64 string, description and file download name ... }) constructs base64 string, description and file name
  • scan((photos, photo) => [photo, ...photos], [] as Photo[]) accumulates photos from most recent to earliest
  • startWith([] as Photo[]) initializes an empty photo list

This is the end of the example. I built an Angular and RxJS example to take photos and prepend new photo in photo stripe component for download.

Final Thoughts

In this post, I show how to use RxJS and Angular to take fun photos with web camera and make them available for download.

This is the end of the blog post and I hope you like the content and continue to follow my learning experience in Angular and other technologies.

Resources:

Image
Observability talks sure to make waves at KubeCon

observability, kubernetes, opensource
Image
This Week's Most Popular Stories About Mesothelioma And Asbestos Lawyer
Image
Javascript Essentials 101: Higher-Order Functions, Currying, and Partial Application

javascript, webdev, interview
Image
Asbestos Compensation Lawyers's History History Of Asbestos Compensation Lawyers
Image
how to invest in real estate for passive income

real, estate, investment
Image
how to invest in real estate for passive income

real, estate, investment
Image
real estate investment strategies

real, estate, investment
Image
Advertising Perl

perl, adverts, community, marketing
Image
HOW TRUST GEEKS HACK EXPERT RECOVER MY LOST BITCOIN WITH PRECISION
Image
This Is The Average Payout For Asbestos Claims Case Study You'll Never Forget
Image
TIL: joining with LIKE

sql, rails
Image
Agen Sabung ayam Online Yang Dapat Diputuskan Buat Taruhan
Image
How to Grow as a Full-Stack Engineer: Practical Tips for Young Developers

webdev, developer, entrepreneurship, softwareengineer
Image
What's The Reason Nobody Is Interested In Accident Lawyer Fort Worth
Image
A Foam isolatieschuim: Waarvoor dient het?
Image
Ten Taboos About Bifold Door Repair Near Me You Should Not Share On Twitter
Image
PostgreSQL Query Performance Tuning Tips

database, postgres, sql
Image
M-Pesa Transaction Status API

api, mpesa, beginners, programming
Image
อัพเดทเวอร์ชั่น Container runtime Colima

colima, docker, upgrade, macos
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .