Angular2 rotate using rxjs Use mouseDown+mouseMove+moseUp streams to identify a rotate by mouse

<!DOCTYPE html>
<html>

  <head>
    <base href="." />
    <title>angular2 playground</title>
    <link rel="stylesheet" href="style.css" />
    <script src="https://unpkg.com/zone.js/dist/zone.js"></script>
    <script src="https://unpkg.com/zone.js/dist/long-stack-trace-zone.js"></script>
    <script src="https://unpkg.com/reflect-metadata@0.1.3/Reflect.js"></script>
    <script src="https://unpkg.com/systemjs@0.19.31/dist/system.js"></script>
    <script src="config.js"></script>
    <script>
    System.import('app')
      .catch(console.error.bind(console));
  </script>
  </head>

  <body>
    <my-app>
    loading...
  </my-app>
  </body>

</html>

/* Styles go here */

### Angular Starter Plunker - Typescript

System.config({
  //use typescript for compilation
  transpiler: 'typescript',
  //typescript compiler options
  typescriptOptions: {
    emitDecoratorMetadata: true
  },
  paths: {
    'npm:': 'https://unpkg.com/'
  },
  //map tells the System loader where to look for things
  map: {
    
    'app': './src',
    
    '@angular/core': 'npm:@angular/core/bundles/core.umd.js',
    '@angular/common': 'npm:@angular/common/bundles/common.umd.js',
    '@angular/compiler': 'npm:@angular/compiler/bundles/compiler.umd.js',
    '@angular/platform-browser': 'npm:@angular/platform-browser/bundles/platform-browser.umd.js',
    '@angular/platform-browser-dynamic': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic.umd.js',
    '@angular/http': 'npm:@angular/http/bundles/http.umd.js',
    '@angular/router': 'npm:@angular/router/bundles/router.umd.js',
    '@angular/forms': 'npm:@angular/forms/bundles/forms.umd.js',
    
    '@angular/core/testing': 'npm:@angular/core/bundles/core-testing.umd.js',
    '@angular/common/testing': 'npm:@angular/common/bundles/common-testing.umd.js',
    '@angular/compiler/testing': 'npm:@angular/compiler/bundles/compiler-testing.umd.js',
    '@angular/platform-browser/testing': 'npm:@angular/platform-browser/bundles/platform-browser-testing.umd.js',
    '@angular/platform-browser-dynamic/testing': 'npm:@angular/platform-browser-dynamic/bundles/platform-browser-dynamic-testing.umd.js',
    '@angular/http/testing': 'npm:@angular/http/bundles/http-testing.umd.js',
    '@angular/router/testing': 'npm:@angular/router/bundles/router-testing.umd.js',
    
    'rxjs': 'npm:rxjs',
    'typescript': 'npm:typescript@2.0.2/lib/typescript.js'
  },
  //packages defines our app package
  packages: {
    app: {
      main: './main.ts',
      defaultExtension: 'ts'
    },
    rxjs: {
      defaultExtension: 'js'
    }
  }
});

//main entry point
import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
import {AppModule} from './app';

platformBrowserDynamic().bootstrapModule(AppModule)

import {Component, NgModule, OnInit, ViewChild} from '@angular/core'
import {BrowserModule, ElementRef, MouseEvent} from '@angular/platform-browser'
import {Observable} from 'rxjs/Observable';
import 'rxjs/add/observable/fromEvent';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/switchMapTo';
import 'rxjs/add/operator/takeUntil';
import 'rxjs/add/operator/combineLatest';
import 'rxjs/add/operator/startWith';


@Component({
  selector: 'my-app',
  styles: [`
  canvas{
    border: 1px solid red;
  }`],
  template: `
    <div>
      <h2>translate/Rotate by mouse</h2>
      <canvas #canvas id="3dview"></canvas>
      <p>Translate by delta: {{relativeTo$|async|json}}</p>
      <p>Rotate by angle: {{rotateToAngle$|async|json}}</p>
    </div>
  `
})
export class App extends OnInit {

    @ViewChild('canvas') 
    canvas: ElementRef;

    relativeTo$: Observable<{dx:number, dy:number, start: MouseEvent}>;
    rotateToAngle$: Observable<{angle:number, start: MouseEvent}>;
    
    ngOnInit() {
      const canvasNE = this.canvas.nativeElement;

      const mouseDown$ = Observable.fromEvent(canvasNE, 'mousedown');
      const mouseMove$ = Observable.fromEvent(canvasNE, 'mousemove');
      const mouseUp$ = Observable.fromEvent(canvasNE, 'mouseup');
      
      const moveUntilMouseUp$= mouseMove$.takeUntil(mouseUp$);
      const startRotate$ = mouseDown$.switchMapTo(moveUntilMouseUp$.startWith(null));
      
      const relativePoint = (start: MouseEvent, end: MouseEvent): 
        {x:number, y:number, start: MouseEvent} => 
        (start && end && {
          dx: start.clientX - end.clientX,
          dy: start.clientY - end.clientY,
          start: start
        } || {});
      
      this.relativeTo$ = startRotate$
        .combineLatest(mouseDown$)
        .map(arr => relativePoint(arr[0],arr[1]));
        
      this.rotateToAngle$ = this.relativeTo$
        .map((tr) => ({angle: Math.atan2(tr.dy, tr.dx), start: tr.start}));
        
//      this.relativeTo$.subscribe(console.log.bind(console,'rotate:'));
//      this.rotateToAngle$.subscribe(console.log.bind(console,'rotate 0:'));
    }
}

@NgModule({
  imports: [ BrowserModule ],
  declarations: [ App ],
  bootstrap: [ App ]
})
export class AppModule {}